Graphene-Based Materials as Solid Phase Extraction Sorbent for Trace Metal Ions, Organic Compounds, and Biological Sample Preparation.

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Graphene-based Materials as Solid Phase Extraction Sorbent for Trace Metal Ions, Organic Compounds and Biological Sample Preparation ab

a

Wan Aini Wan Ibrahim , Hamid Rashidi Nodeh & Mohd Marsin Sanagi

bc

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Separation Science and Technology Group (SepSTec), Department of Chemistry, Faculty of Science, Universiti Teknologi Malaysia, Johor, Malaysia. b

Nanotechnology Research Alliance, Universiti Teknologi Malaysia, Johor, Malaysia.

c

Ibnu Sina Institute for Fundamental Science Studies, Universiti Teknologi Malaysia, Johor, Malaysia. Accepted author version posted online: 17 Jul 2015.

To cite this article: Wan Aini Wan Ibrahim, Hamid Rashidi Nodeh & Mohd Marsin Sanagi (2015): Graphene-based Materials as Solid Phase Extraction Sorbent for Trace Metal Ions, Organic Compounds and Biological Sample Preparation, Critical Reviews in Analytical Chemistry, DOI: 10.1080/10408347.2015.1034354 To link to this article: http://dx.doi.org/10.1080/10408347.2015.1034354

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ACCEPTED MANUSCRIPT Graphene-based Materials as Solid Phase Extraction Sorbent for Trace Metal Ions, Organic Compounds and Biological Sample Preparation Wan Aini Wan Ibrahim1, 2*, Hamid Rashidi Nodeh1, Mohd Marsin Sanagi2, 3

1

Separation Science and Technology Group (SepSTec), Department of Chemistry, Faculty of

Downloaded by [University of Otago] at 18:08 21 July 2015

Science, Universiti Teknologi Malaysia, 81310 UTM Johor Bahru, Johor, Malaysia 2

Nanotechnology Research Alliance, Universiti Teknologi Malaysia, 81310 UTM Johor Bahru,

Johor, Malaysia 3

Ibnu Sina Institute for Fundamental Science Studies, Universiti Teknologi Malaysia, 81310

UTM Johor Bahru, Johor, Malaysia

*Corresponding author: W. A. Wan Ibrahim (UTM) Tel: (+60)-7-5534002/(+60)-7-5534311) Fax: (+60)-7-5566162, e-mail: [email protected]; [email protected] (Wan Aini Wan Ibrahim)

Abstract Graphene is a new carbon-based material that is of interest in separation science. Graphene has extraordinary properties including nano-sized, high surface area, thermally and chemically stable, and provide excellent adsorption affinity to pollutants. Its adsorption mechanisms are through non-covalent interactions (π-π stacking, electrostatic interactions and H-bonding) for

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ACCEPTED MANUSCRIPT organic compounds and covalent interactions for metal ions. These properties lead to graphenebased material becoming a desirable adsorbent in a popular sample preparation technique known as solid phase extraction (SPE). Numerous publications on graphene applications are available in recent times, but few review papers focused on its applications in analytical chemistry. This article focuses on recent pre-concentration of trace elements, organic compounds and biological species using SPE-based graphene, graphene oxide and their modified forms. Solid phase


microextraction and micro SPE (µSPE) methods based on graphene are discussed. Keywords: Graphene, sample preparation, magnetic solid phase extraction, metal ions, organic pollutant, biological sample preparation. Abbreviation: GO, graphene oxide; CNTs, carbon nanotubes; MWCNTs, multi wall carbon nanotubes; MNPs, magnetic nanoparticles; SPE, solid phase extraction; MSPE, magnetic solid phase extraction; SPME, solid phase microextraction; DSPE, dispersive solid phase extraction; µSPE, micro solid phase extraction; MRLs, maximum residual level; GC, gas chromatography; GC-MS, GC with mass spectrometry detector; GC-FID, GC with flame ionization detector; HPLC, high performance liquid chromatography; ICP-MS, inductive couple plasma mass spectrometry; FAAS, flame atomic absorption spectroscopy; PAHs, polycyclic aromatic hydrocarbons; EF, enrichment factor; LOD, limit of detection; VOCs, volatile organic compounds

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ACCEPTED MANUSCRIPT Introduction In recent years, increasing chemical contamination in the environment becomes a global challenge. Chemical contaminants are highly toxic substrates and possess risk to the environment and human health. Inorganic contaminants include metal ions, heavy metal ions and inorganic metal species. Organic pollutants include volatile organic compounds (VOCs), polycyclic


aromatic hydrocarbons (PAHs), organic solvents, pesticides and others [1–3]. Due to their high toxicity in trace level, the World Health Organization and European Union have set maximum allowable existence in water and food samples. Council Directive 98/83/EC [4] decided that the maximum residual levels (MRLs) of pollutants in drinking water are 0.1 ng mL-1 for single pesticide, 0.5 ng mL-1 for total pesticides, below 10.0 ng mL-1 for arsenic species, 50.0 ng mL-1 for chromium, 1.0 ng mL-1 for mercury, 5 ng mL-1 for cadmium and 0.1 ng mL-1 for specific PAHs including (benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(ghi)perylene, indeno(1,2,3cd) pyrene). The European Commission regulation no. 396/2005 set the MRLs for pesticides in milk samples between 0.01-0.05 mg kg-1 [5]. Therefore, removing of chemical pollutants from the environment is often necessary, although it is big challenge [6]. The removal of contaminants from food and water samples has been investigated using different techniques including liquid extraction, catalytic degradation and adsorption process. Liquid extraction method is the most common until recently, but it is tedious, time-consuming and consumes high volume of environmentally unfriendly organic solvents.

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ACCEPTED MANUSCRIPT Photocatalytic degradation is a useful method for environmental decontamination. Two different methods, namely photocatalyst and photo-Fenton, have been investigated for pollutants degradation process [7]. In both methods, oxidation reagents such as titanium dioxide, , ozone, and hydrogen peroxide play a major role since they produce electrons to obtain free radicals. Figure 1 shows pesticide degradation using advanced oxidation process using photocatalyst and


photo-Fenton methods. Advantages of photocatalytic technologies include self-regeneration, avoidance of secondary method, low-cost oxidant, and recyclability [8]. In contrast, in a catalytic process, the produced free radicals attack the target molecules and produce secondary compounds thereafter. This probably increases secondary contamination and incurs extra costs for further purification. For example, when chlorpyrifos is degraded using catalytic activity, it produces a highly toxic compound, trichloropyridinol and hazardous organophosphate. In the past few decades, solid adsorbents have been developed for environmental decontamination. Adsorption method is a sufficient technique since it is easy, fast, highly efficient, low-cost and effective for decontamination [3, 6]. Nanomaterial based on carbon, alkoxides and metal nanoparticles have emerged as interesting materials for adsorption of metal ions and organic contaminants from environmental samples. Due to their high surface area, great adsorption capacity, satisfactory efficiency, chemical stability and less toxicity, they are suitable candidates for clean up, isolation, enrichment and pre-concentration of various contaminations. In addition to these tremendous advantages, the adsorption process does not produce secondary contamination [6].

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ACCEPTED MANUSCRIPT Carbon-based materials (Figure 2) include graphite (3 D), carbon nanotube (1 D), fullerene (0 D), graphene oxide (GO) (2 D) and graphene (2 D) [10]. Graphene as a new allotrope of carbon material was successfully applied as an adsorbent. Although studies on graphene has increased noticeably after the exfoliation of graphene single sheet using cellophane tape in 2004 [11], the oldest experimental observation dated back 40 years ago and its electrical application was reported since 1992 [9,10]. Graphene properties include single sheet with one


atom carbon thick, two-dimensional layer, high surface area, hybrid sp2 for carbon, thermally stable and excellent mechanical, electrical and optical properties due to long π-electron conjugation [7,11,12]. Graphene is a transparent material with 2.3% optic absorption [15]. Due to the zero band gap of a single sheet, graphene is a semiconductor since highest occupied molecular orbital and lowest occupied molecular orbital touch each other [10]. Graphene have been prepared via micro chemical, chemical vapor, electrochemical, thermal process, mechanical process, epitaxial growth using silicon carbide in high temperature and carbon nanotubes (CNTs) unzipping (efficiency 100%) [15]. Graphene growth on silicon carbide showed high surface area compared to other substrates such as Cu [16]. The chemical process of graphene preparation was first reported by Stankovich et al.,[17], graphite was oxidized into graphene oxide (GO) and then reduced to graphene using hydrazine. Different reduction agents have been used for GO reduction including thermal process, microwave radiation, hydrazine, NaBH4 [15], LiAlH4 [18] and also ascorbic acid and iron powder [19]. Among these, hydrazine shows higher product efficiency with less impurity, but hydrazine is a cancer causing agent and destroys the nervous system [15]. Advantages of

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ACCEPTED MANUSCRIPT graphene preparation from GO are low-cost, inexpensive starting material from graphite, massive scalability, large adsorption sites and micrometer-sized graphene was obtained [10]. Graphene is able to participate in covalent and non-covalent approaches. In the covalent system, graphene is bonded through three different processes including the addition of free radical in sp2 carbon atom, reduction of GO extra functional groups after target bonding and


halogens attachment. The non-covalent approaches include π-π interaction, H-π, cation-π, anionπ, non-covalent ligand interaction, metal nanoparticle deposition and substitution doping [20]. Similar to graphene, GO can also be modified through non-bonding and covalent processes since it provides large π-π stacking and various functional groups. Graphene and GO have different optical properties, surface area and crystalline structure [6]. Usually, GO is obtained from graphite through chemical oxidation with concentrated acids. GO provides separate single sheets since both sides of the plane possess oxygen functional groups including hydroxide, epoxy on the basal plane, carboxyl, carbonyl, phenol, lactol and quinone [17, 18]. X-ray photoelectron spectroscopy and Raman spectra demonstrated epoxy as a basal bridge, the hydroxyl group found on both planes and carboxyl group at the edge [20,22]. As seen in Figure 3, the 13C-NMR spectra also provides lactol and oxygen groups in GO. These functional groups can provide easy functionalization of GO with different materials. Single sheets of GO interact with each other through H-bonding. Additionally, due to the presence of oxygen group on both sides of GO plane, the distance between sheets is larger than multilayers graphene [22].

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ACCEPTED MANUSCRIPT GO also shows potential benefits for electrochemical targets since it has high surface area, direct electron transfer and excess active sites. Successful GO applications include molecular gas sensors, electrochemical protein detection, electrocatalyst, enzyme immobilizer and DNA identification [21]. Graphene has been used as a sensor for ammonia and nitrogen dioxide [7, 20]. The adsorption capacity obtained was 61 mg g-1 for ammonia [23]. GO is more effective compared to graphene in electrochemical processes since the functional groups play a


main role in target detection. For example, GO-based glucose sensor [21, 22] showed high efficiency in glucose detection because the functional groups allowed easy mass transfer of the reactant on the electro-active sites of GO electrode surface [21]. Absorption efficiency depends on high surface area, pore volume, porosity, and functional groups. Carbon-based material is porous and provides high adsorption capacity. For example, the theoretical surface area for graphene is 2630 m2 g-1 [3, 23] and the experimental area is 433.1 m2 g-1 for graphene synthesized from GO [27], while for CNTs the surface area is 1315 m2 g-1 and for graphite the surface area is 10 m2 g-1 [28]. Otherwise, GO provides both covalent and non-covalent interactions in adsorption process such as electrostatic interaction, hydrogen binding, hydrophobic interaction and π-π stacking [21]. Due to the presence of various functional groups in GO, it can form covalent bond with enzyme, bovine serum albumin, deoxyribonucleic acid [17], organic compounds and metal ions. Although, graphene possesses fewer functional groups, it shows high adsorption capacity for metal ions and organic compound due to large π-electron stacking. Protein affinity of graphene increases significantly when protein size decreases [15]. Also graphene provides extraordinary molecular interaction between protein, deoxyribonucleic acid, enzyme and drugs [20].

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ACCEPTED MANUSCRIPT Sample preparation is a critical stage in analytical chemistry because many samples cannot be analyzed directly by instruments. Therefore, interference must be eliminated from complex samples and analytes trace level must be concentrated to give excellent detection. Solid phase extraction (SPE) is convenient, fast, has short extraction time, simple, flexible, emulsionfree, easily automated and can be easily coupled with detection techniques [26, 29]. Furthermore, SPE provides high enrichment factor and extraction recovery [30]. The main core of SPE


technique is the sorbent material as they provide good extraction efficiency, sensitivity, selectivity and reusability. Various types of sorbent have been applied as an extraction adsorbent in SPE such as hybrid sol-gel material [31], alkoxides nanoparticles, carbon material, polymers and membranes [32]. Porosity and high surface area are the main factors in SPE sorbent, which confirm its extraction ability. Among the different types of sorbent, carbon nanomaterials (active carbon, CNTs, fullerene, GO and graphene) have shown above advantages [26]. Fullerene and CNTs were used as adsorbents in SPE technique in 1991 and 2003, respectively [19]. Graphene-based material has become a superior candidate as SPE sorbent [19] due to its potential benefits. The first report of graphene for sample preparation dated back in 2010 when it was used as solid phase microextraction (SPME) fiber coating [33] and in 2011 as µSPE sorbent [34]. Graphene has shown high extraction recovery compared to CNTs because both sides of graphene plane are easily available for analyte extraction. Extraction using graphene usually involves non-covalent interactions with target analytes. In extraction technique, graphene has been used in different methods including pack-in commercial tubes in conventional SPE (Figure 4A) and dispersed in samples in the dispersive solid phase extraction (DSPE) method (Figure 4B). In the dispersive process, due to significant increase of the surface impact, interaction

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ACCEPTED MANUSCRIPT occurs as fast as possible to obtain great extraction efficiency in comparison with conventional SPE. Magnetic nanoparticles (MNPs) can be fabricated on graphene by self-assembly in a suitable solvent, which can then be applied as magnetic solid phase extraction (MSPE) adsorbent for analyte isolation [30]. MSPE provides fast collection of adsorbent from large volumes of


samples using an external magnet without the need for centrifugation, filtration and avoiding column (Figure 4C). Graphene was also applied as an adsorbent in SPME fiber [33] as well as in µ-SPE method [35]. In order to improve graphene selectivity, stability, compatibility and avoid aggregation in SPE method, graphene was functionalized with different organic and inorganic materials such as amino, silica, TiO2, polymers and MNPs [16, 23]. In addition, graphene can also be functionalized simply from GO route [36]. GO-based material as SPE sorbent is called normal phase extraction method. It has been shown to have high adsorption affinity for metal ions, polar compounds including polar groups (hydroxyl, carboxyl, amines) and hetero atoms (O, N, S, P). Graphene as SPE sorbent is suitable for adsorption of metal chelates and non-polar analytes (aromatics, alkyl, alicyclic), or known as reversed phase extraction [37]. Recently, graphenebased sorbents were successfully applied as a new SPE sorbent in sample preparation process. It exhibited fast extraction, high adsorption capacity and low limit of detection (LOD) for pesticides, PAHs, phthalates, heavy metal ions, metal species, sulfonamides, proteins and deoxyribonucleic acid.

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ACCEPTED MANUSCRIPT Metal ions, heavy metal ions (Mn, Co, Ni, Zn, Cr, Cd, Cu, Ag, Pb, Hg) and toxic ions species (Cr(VI), CrO42-, Cr2O72-, As(V), H2AsO4 -, HAsO42-) can cause high risk on human health and environmental organisms [3, 6, 35]. The determination of trace level of metal ions has become a challenge due to matrix interferences. Therefore, sample preparation is often necessary for metal ion analysis. The analytical monitoring process includes sample preparation, separation, pre-concentration and detection [36]. Unique adsorbent and solution pH are


important in metal ion isolation as they directly affect sample preparation. pH is important in metal ion adsorption due to influence of the adsorbent surface charges and ions charges. Metal ions adsorption affinity also depends on metal properties such as electronegativity and constant stability of metal and hydroxide [37]. A suitable adsorbent is important and necessary in metal ion monitoring in order to obtain high recovery, good sensitivity, less interference and great enrichment factor. Recently, graphene provides great ability with regard to metal ions pre-concentration since it is suitable for adsorption of cation and anion species, while GO is more suitable for cations. GO modified successfully with different materials can be used for both cations and anions species. Due to fewer functional groups in graphene compared to GO, non-covalent interactions are involved in metal ions adsorption mechanism. The main interaction between metal ions and graphene is a cation-π interaction [20]. For example, adsorption of Pb(II) onto graphene is formed by van der Waals interaction. In metal ions pre-concentration, graphene is more suitable compared to other carbon nanomaterials such as CNTs because firstly, in the synthesis of CNTs, metal is used as a catalyst (interference) and secondly, CNTs internal plane is not responsible in the adsorption process,

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ACCEPTED MANUSCRIPT while both sides of plane in graphene are available in adsorption process [37]. GO also provides great adsorption capacity for metal ions compared to CNTs because it possesses more oxygen groups (30 wt%) than CNTs (5%) [37]. Rich oxygenate functional groups increase GO hydrophobicity, which can provide strong affinity for metal ions with coordination and also electrostatic interaction. The coordination between Cu2+ and GO functional groups causes higher adsorption capacity (46.6 mg g-1) [39] than CNTs (28.5 mg g -1) [40] and active carbon (4 mg g -1)


[41]. Sample preparation based on SPE is an efficient technique for metal ions preconcentration. Natural and unique properties of the required material as SPE sorbent are the main factors since they control the selectivity, affinity and adsorption capacity [29]. SPE based on GO-modified amino (GO-NH2) was used for isolation of two hazardous metal ions, Pb(II) and Cd(II) [38]. In this process, the prepared adsorbent was packed in cartridges as conventional SPE method. Graphene has been shown to have high affinity, but low selectivity, for metal ions. To overcome this, graphene was modified with amine. The proposed SPE based on GO-NH2 provided high enrichment factor (417 for Pb(II) and 333 for Cd(II)), lower LOD (0.005 ng mL-1) and reusability (8×). GO-NH2 showed great adsorption capacity (461 mg g-1) in comparison with prepared Fe3O4@mesoporous silica-GO for Pb(II) (333 mg g-1) and for Cd(II) (167 mg g-1) [42]. These results highlighted that GO-NH2 is more sensitive to Pb(II) and Cd(II) due to strong coordination between analytes and amine groups [38]. The study showed that SPE performance depends on amino group since GO functionalized with amino group showed high adsorption capacity (461 mg g -1) compared to GO without functionalized amino group (359 mg g-1). pH effect was studied in acidic and alkaline conditions. At lower pH, recovery was reduced

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ACCEPTED MANUSCRIPT since N atom is protonated and at high pH recovery was also reduced due to participation of metal ions as hydroxide. GO-NH2 was shown to have 700× lower LOD, 10× higher preconcentration factor [43] and 5× higher adsorption capacity [44] in comparison with MWCNT. To overcome graphene and GO limitations in conventional SPE, MNPs were applied followed by fast extraction from liquid using an external magnet through MSPE method.


Fe3O4@SiO2 @polyaniline-GO was synthesized using non-covalent method and used as MSPE adsorbent for the pre-concentration of trace rare earth elements from water prior to inductive couple plasma mass spectrometry (ICP-MS) analysis [45]. Polyaniline and GO bound together using H-binding, electrostatic interaction and π-π stacking. Polyaniline increased π-stacking length and GO-MNPs stability. These results showed that GO-based polyaniline is suitable for metal ions due to its rich functional groups in comparison with graphene, since they can bind to metal ions through electrostatic and covalent interactions. Extraction recovery decreased at pH > 8 due to metal ions precipitation into hydroxide. In acidic condition, recovery also decreased since H+ competed with metal ions. The developed MSPE based on the GO-SiO2/Polyaniline provided high sensitivity (LOD, 0.04-1.49 ng L-1), good recovery (81-119%), suitable preconcentration factor (50), short extraction time (1 min) and reusable up to 30×. The magnetic GO-SiO2/Polyaniline provided higher adsorption capacity (7.7-16.3 mg g-1) for rare earth elements compared to alkyl phosphinic acid extraction resin in (13.1-15.7 mg g−1) [46], and nanosized TiO2 (6.1-9.8 mg g-1) [47]. However, it was slightly lower than mesoporous TiO2 (13.8-21.3 mg g-1) [48] since porosity is the main factor in adsorption process. The developed MSPE-ICP-MS showed high sensitivity within range of SPE-ICP-MS (0.01-0.17 ng L-1) [49], DLLME-ICP-MS (0.05-0.55 ng L-1) [50].

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ACCEPTED MANUSCRIPT MSPE based on G-Fe3O4 was developed for cadmium pre-concentration from water samples [51] as Cd(II) allowable MRLs (5 ng mL-1) is lower than flame atomic absorption spectroscopy (FAAS) instrument LODs. At high pH, Cd ions are hydrolyzed and at lower pH the adsorbent ligands are protonated, thus MSPE recovery was decreased. Electrostatic interaction is the main key in Cd ion adsorption on graphene surface due to lack of functional groups. Graphene-based adsorbent showed great enrichment factor (200), good sensitivity (0.32 ng mL -1)


and high recovery (93.1-102.3%). The potential benefit of G-Fe3O4 is selectivity for cadmium ions since the recovery was greater than 90% in the presence of 100-1000× of interferences ions. The comparison of mentioned result shows that the proposed method was more capable for cadmium analysis in comparison with MWCNT [52] and commercial Chromosorb101 SPE [52] due to wider range of dynamic range and lower LOD. Simultaneous extraction was studied for Fe(III), Cu(II) and Pb(II) from water samples prior to FAAS detection [29]. The three metal ions were isolated using different sources of MNPs, cobalt oxide nanoparticles dispersed on graphene (Co3O4/G), with good adsorption capacity (58-78 mg g-1). GO-SPE provided great adsorption affinity, lower LOD (0.81 µg L-1), high enrichment factor (175) and good recovery (95-195%) compared to other carbon-based material because it has high surface area and more functional groups in comparison with CNTs and graphite. New Co 3O4/GO provided noticeable stability up to 130 adsorption-elution cycles without significant decrease in the recoveries (> 90%). At low pH, the adsorbent surface became positively charged and formed strong repulsion with metal ions, also H+ competitive to adsorption site occupation. In alkaline pH, hydroxide formation of metal ions is the main reason for decrease in the recovery [29].

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ACCEPTED MANUSCRIPT Removal of metal ions using in-house adsorbent based on graphene has become more interesting in the past few years. Reduced graphene oxide (rGO) was modified with cobalt ferrite (CoF2O4) for adsorption of Pb(II) and Hg(II) from water with good adsorption capacity;299.4 mg g-1 and 157.9 mg g-1 for Pb(II) and Hg(II), respectively. The experimental procedure demonstrated that metal ions adsorption using the prepared graphene-based adsorbent (CoF2O4rGO) depended completely on the sample pH. At lower pH, the net charge of the adsorbent


became positive, which caused repulsion of positive metal ions followed by reduced adsorption efficiency. At high pH, efficiency was increased due to strong affinity between the positive ions and the negative net charge of the adsorbent [53]. Reduced graphene modified polypyrrole provided extraordinary adsorption capacity for Hg2+ (980 mg g−1) [54] as compared to CoF2O4rGO. Three dimensional free-standing graphene oxide foam (GOF) was successfully synthesized and applied as a metal ion removal agent [9]. GOF has high surface area (578.4 m2 g-1), which is a main factor in adsorption process. Adsorption capacity was observed in the following order: Fe3+ (587.6 mg g-1) > Pd2+ (381.3 mg g-1) > Zn2+ (326.4 mg g-1) > Cd2+ (252.5 mg g-1). GOF adsorption capacity is higher than Chromsorb 108 as SPE sorbent i.e., Fe3+ (6.4 mg g-1), Pd2+ (6.8 mg g-1), Zn2+ (5.3 mg g-1) and Cd2+ (3.5 mg g-1) [55]. The data showed that outstanding adsorption capacity for Fe3+ might be related to strong electrostatic force between trivalent ions and GOF adsorption sites. Furthermore, GO showed lower adsorption capacity (246 mg g-1) [56] in comparison with GOF, but much higher than activated carbon (22.3 mg g-1) [57], CNTs (43.66 mg g -1) [58] and approximately 2× higher than carbon foam (130.76 mg g -1) [59].

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ACCEPTED MANUSCRIPT Recently, graphene-based adsorbent was used for simultaneous determination of metal ion species such as Cr(III) and Cr(VI) [60]. Magnetic GO was modified using cyclodextrinchitosan (CC) to produce Fe3O4@CCGO, with high surface area (445.6 m2 g-1) compared to pure GO (342.3 m2 g-1). The Fe3O4@CCGO was shown all functional groups were involved in adsorption mechanism as Cr(VI)- formed electrostatic interaction with amine groups (+NH). Simultaneous adsorption was treated with the assistance of carboxylic electron, which converted


Cr(VI) to Cr(III)+ that was then adsorbed by–COO- through electrostatic interaction. Cyclodextrin can also form coordination with both Cr(III) and Cr(VI). pH is the main factor in metal ion species due to the formation of different ion charge such as Cr(III) at low pH, CrO42- at pH > 6.8, Cr2O72- and HCrO4 - at pH < 6.8 [61]. In lower pH, CCGO showed high affinity for HCrO4- due to formation of strong electrostatic interaction with NH and COO-+OH2 groups. At higher pH, adsorption capacity was decreased due to electrostatic repulsion. The proposed Fe3O4@CCGO showed high adsorption capacity (67.66 mg g-1) in comparison with Fe2O3 nanowire (14.6 mg g-1) [62], activated carbon (20.0 mg g -1), mesoporous TiO2 (33.9 mg g-1) [63], silica matrices (2.14 - 19.31 mg g-1) [64] and amino starch (12.12 mg g-1), Chromosorb 108 (4.50 mg g-1) [65], but lower than Fe3O4-ethylendiamine (136.98 mg g-1) [66], since amine groups provide strong electrostatic interaction with chromium ions. An interesting application of GO was selective ions penetration of membranes [22]. Rich functional groups in GO facilitated strong interaction with some metal ions and organic compounds, which provide unable to pass from membrane. Figure 5 shows the schematic of GO membrane, which allows sodium to pass though the membrane, but not Cu and organic compounds. Therefore, the membrane was able to separate Mn2+, Cd2+ from Cu2+.

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ACCEPTED MANUSCRIPT As seen in Table 1, SPE based on GO@SiO2 showed lower LOD for Cu(II) and Pb(II) pre-concentrations in comparison with pure GO. It probably depended on SiO2 porosity or pure GO aggregation during the extraction. Due to amine group, SPE based on dipyridyl showed selective behavior for Cd(II). SPE based on pure GO for simultaneous metal ions isolation provided high sensitivity. Pure GO functional groups, high surface area, and graphene sheets are important reasons for great adsorption affinity and more chelating sites are also responsible for


its adsorption mechanism. Cobalt ion was removed sufficiently using Fe3O4/GO through coordination of metal ion with various functional groups on both sides of GO plane such as hydroxyl and epoxy as basal bridge as well as carboxylic group at the edge of the sheet. At high pH, adsorption capacity of Co(II) increased due to formation of Co2+ and Co(OH)+ in lower pH, which can cause repulsion with positive surface of GO. Graphene hydrogel (GH) modified polydopamine showed higher adsorption capacity for Pb(II) in comparison with Cd(II) due to stronger affinity to phenolic and carboxylic groups. GO solution exhibited great adsorption capacity for Cd(II) in comparison with dipyridyl-graphene, GO-TiO2, smart magnetic graphene and graphene hydrogel modified polydopamine due to significant adsorption sites available in GO, but the adsorption sites might be occupied with nanoparticles and dipyridyl. Also, GO showed high adsorption capacity of uranium (299 mg g-1) in comparison to Amberlite IRA-402 (213 mg g-1) [67] and Amberlite XAD-4 (17.4 mg g-1) [68]. According to data’s in text and Table 1, graphene- based material showed higher adsorption capacity towards metal ions compared to conventional material such as Amberlite XAD-4 that showed much lower capacity for metal ions i.e., Cu2+ (14.0), Cd2+ (9.5), Co2+ (6.5), Ni2+ (12.6), Pb2+ (12.6), Zn2+ (11.1), Mn2+ (10.0), Fe3+ (5.6) and UO2 2+ (7.7) [69].

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ACCEPTED MANUSCRIPT 1. Application of graphene-based SPE for isolation of organic pollutants Chlorophenol was the first organic compound isolated by SPE based on graphene [27]. Organic compounds can be adsorbed by graphene or GO through five electrostatic interactions including hydrophobic effects, covalent, hydrogen bonding and π-π stacking. The main interaction between organic ions and graphene are π-π stacking, πcation-π interaction [20], dative


bonding and hydrophobic effects. Cation polarization and electrostatic interaction between cations can cause formation of πcation interaction in the adsorption process [37]. GO can form Hbonding with organic compounds including oxygen and nitrogen groups. Meanwhile, graphene is suitable as adsorbent for extraction of aromatic compounds without polar functional group due to rich delocalized π-electron system that provides strong affinity via π-π interaction with carbonbased aromatic ring structure [36]. GO was successfully used in the stationary phase in electrophoresis capillary for dopamine enantiomer separation [91]. It was also successfully applied in high performance stationary phase in capillary column of a GC system [92]. GO provides significant high surface area and functional groups with various covalent and non-covalent interactions causing sufficient separation efficiency for various organic compounds. Chromatogram (Figure 6) confirmed the ability of GO as stationary phase at two different temperatures for the separation of VOC and aromatic compounds. The clean and high peak areas showed sensitivity and selectivity of GO for capillary coating. Also sharp peaks revealed that GO has excellent adsorption affinity for wide range of polarity (separation of high polar compound (ethanol, Log KO/W -0.3), mid-polar (mxylene, Log KO/W 2.7) and non-polar compounds (naphthalene, Log KO/W 3.3).)

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ACCEPTED MANUSCRIPT Pre-concentration of highly toxic pesticides, dyes, PAHs, phthalates and etc, using graphene-based material are discussed as follows. Pesticides were successfully isolated from water sources using graphene-based SPE because significant delocalized π-electron in graphene provides strong π-stacking interaction with benzene ring in pesticides. Due to hydrophobic properties of graphene, it is suitable for non-polar pesticides (Log KO/W > 3). Otherwise, GO is a more suitable adsorbent for polar and mid-polar compounds (Log KO/W < 3) due to the presence


of various functional groups. Graphene-based SPE was applied for clean-up and as adsorbent for 24 pesticides preconcentration process for food samples [93]. Reversed dispersive SPE showed good extraction recovery (70.1-109.7%) and LOD (0.3 µg kg-1). Chromatograms (figures not shown) for before and after the clean-up process demonstrated graphene’s ability for the process since significant interferences were eliminated from the chromatograms [93, 94]. Graphene-Fe3O4 was used as chloroacetanilide herbicides pre-concentration from water prior to GC-ECD analysis. All analytes such as benzene ring and amine group showed π-stacking and hydrophilic interactions, respectively. The developed MSPE was independent of salt effect since the recovery was unchanged up to 20% (w/v) NaCl. Chromatogram (figure not shown) showed that the adsorbent was sensitive to mid-and non-polar analytes (Log KO/W 2.65-4.51) according to sharp peaks, and provided high selectivity based on the obtained clear peaks. Other potential benefits included noticeable enrichment factor (649-1078), reusability (30×) and good recovery (80.7-105.3).

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ACCEPTED MANUSCRIPT SPME fiber based on graphene-polyaniline were used as an organochlorine pesticides (OCPs) pre-concentration from water samples [95]. The prepared adsorbent was stable at 320ºC with great reusability (70×, RSD < 11%). It possessed noticeable sensitivity (11 pg mL-1) and high extraction recovery (81-112%) due to high surface area and longer delocalized π-electron in graphene. Polyaniline benefits include polar groups, hydrophobic properties, hydrogen bonding and it increases graphene’s thermal stability. They found the ability of the hydrophobic adsorbent


to sufficiently extract all non-polar OCPs (Log KO/W > 4.8). Polyaniline fiber without graphene showed 50× extraction capability and thermal stability at 200ºC [96]. . Dye is used excessively in industry [97] and it can contaminate water sources. It is toxic to human due to its complex structure, which is easily biodegraded. Most dyes are found in anionic and cationic forms in water or is dissolved in water [6]. Graphene and GO were used successfully as dye adsorbent. GO is more suitable for removal of cationic dyes [81] due to strong electrostatic interaction. Graphene can adsorb both cationic and anionic dye due to the large distribution of π-π stacking between the dye and graphene [6]. Graphene was used as SPME fiber for methylene blue (MB) isolation from water with good extraction performance including LOD (0.89 nM), recovery (95.7-113.0%), RSD (< 5%) and 20× enrichment factor [97]. Graphene was modified using carboxylic (G-COO-) since it increases polarity and negative charges followed by simply adsorbing cationic MB. Monolithic GO gels was showed to have high adsorption capacity (833.3 mg g-1) towards MB [98]. This is possibly explained by anionic nature of GO and MB as cationic dye, high porosity of monolith GO gels, and existence of electrostatic and π-π interaction.

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ACCEPTED MANUSCRIPT Graphene is packed in columns and used for PAHs pre-concentration [99]. The obtained results showed that PAHs adsorption by graphene is independent of pH and ionic strength because the change in recovery is insignificant between pH 3 to 10 and in the presence of NaCl (0-100 mM). The graphene SPE performance was as follows: LOD was 0.84-13 ng mL-1, recovery was 72.8-106.2%, EF was 60 and reusability was 40×. For PAHs preconcentration, the developed graphene SPE revealed higher sensitivity than multi wall carbon nanotubes


(MWCNTs) SPE (2 ng mL-1) [100], membrane SPE (30 ng mL-1) [101] and Fe3O4-C18 (1.6 ng mL-1) [102]. Magnetic GO as SPE sorbent was synthesized using electrostatic interactions due to positively charged Fe3O4 in weak acid and the negative surface charge of GO. The synthesised GO- Fe3O4 was developed for PAHs pre-concentration from water [103]. Not only the sample pH can change the analytes form, but it also influences the analyte-adsorbent interaction. PAHs adsorption affinity for GO is independent of pH due to unchanged extraction recovery. GOFe3O4 showed great enrichment factor (1000), lower LOD (0.09-0.19 ng mL-1) and high recovery (76.8-103.2%) due to strong π-π interaction. Also, strong π-stacking between GO and PAHs benzene ring caused significant selectivity and sensitivity, as confirmed by the high peaks in the spiked chromatogram (Figure 7). The benzo[a]anthracene has four benzene rings that possess long stacking to provide the highest peak in the chromatogram. Finally, the chromatogram demonstrated hydrophobic selectivity of adsorbent as sharp peaks were obtained for all non-polar PAHs (Log KO/W 4.5-6.3). Also, MSPE based on GO-Fe3O4 provided excellent ability in PAHs adsorption with LOD in the range of 0.09-0.19 ng mL-1 which is (8-18)× lower LOD than C18/

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ACCEPTED MANUSCRIPT Fe3O4 [102]. However, MSPE-MWCNT provided 3-18× lower LOD than MSPE-GO-Fe3O4 [104]. Volatile aromatic carbons were isolated using in-house graphene-poly(ethylene glycol) adsorbent [105]. The synthesized adsorbent provided great stability up to 200 times elutionadsorption recycles. It also showed high extraction recovery (83.2-108.8%), durability, thermal


stability and low LOD (1-6 pg mL-1). GO was modified by porous SiO2 nanoparticles and applied as SPE sorbent for chlorophenols extraction prior to HPLC-UV [106]. The developed SiO2 @rGO resulted in higher SPE performance than CNT, graphitic carbon black and silica C18 since it possessed both porosity and polarity. Hydrophilic and π-π interactions are the main analyte-adsorbent interactions. SiO2@rGO-SPE performance was evaluated using adsorption capacity (781.5 µg g-1), LOD (1.1 ng mL-1), and recovery (81.1-104.7%). Magnetic GO (Fe3O4@GO) was used as MSPE adsorbent to extract polychlorinated biphenyls from water using an external magnet [107]. The resulting enrichment factor, LOD, recovery and adsorption capacity were 200, 0.28 ng mL -1, 97.5% and 28 mg g -1, respectively. The great performance of Fe3O4@GO MSPE can be explained by hydrophilic-hydrophobic properties of GO, which shows great affinity to analytes benzene ring. SPME based on graphene was used for the pre-concentration of phenols of various polarity (Log KO/W 3.5-9.0 for all) from water with high sensitivity (1.1-25 pg mL-1) and great recovery (86.5-105%) [108]. Due to the benzene ring in phenols, they form strong π-π interaction with graphene resulting in high performance in reusability of over 200×. Graphene SPME was

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ACCEPTED MANUSCRIPT also used in PAHs extraction with at least 120× reusability, very low LOD (2 pg L-1) and good recovery (88.9-105.3%) [109]. These provided three orders of magnitude better LOD than that of the previously published graphene-based fibers. Strong π-stacking between graphene and benzene rings of PAHs is the main key in adsorption mechanism. Magnetic Fe3O4 nanoparticles were deposited on unique sheets of graphene (Graphene-


Fe3O4) followed by pre-concentration of phthalate acid from water prior to GC-MS analysis [110]. The proposed MSPE provided high surface area, fast extraction (15 min), low LOD (0.01 ng mL-1), high recovery (88-110%) and good reusability (12×). MSPE based on graphene showed higher adsorption than liquid-liquid extraction and conventional SPE for phthalates including the benzene ring, which increases the π-π interaction. Graphene MSPE showed good enrichment factor (15) and good LOD, which was approximately 1000× lower than graphene SPE method [111] and 7× lower than graphene-SiO2-SPE method [112]. The chromatogram (Figure 8) demonstrated that non-polar analytes (Log KO/W 4.05-7.2 for all) with benzene ring was successfully extracted from river water. Graphene showed selective behavior to phthalate due to less extra peaks appearance. GrapheneFe3O4 modified with SiO2 and C18 were used as an adsorbent to extract phthalate from water [113]. The proposed adsorbent provided lower LOD (0.1-10 ng mL-1) than that of polymer-based SPE (3-10 ng mL-1) and MWCNTs and liquid-liquid extraction (6-50 ng mL-1). These results were confirmed by the high surface area and strong π-π stacking in graphene, porosity of SiO2 and hydrophobicity of C18. Pipette tip graphene adsorbent was used in sulfonamides pre-concentration method with extraordinary sensitivity (0.5-1.7 pg mL-1) and good recovery (90.4-108.2) [114]. Due to formation of strong π-π interaction between reduced graphene and benzene ring of analytes,

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ACCEPTED MANUSCRIPT reduced graphene provided both hydrophobic and hydrophilic interactions. Sulfonamides isolation depends on the sample pH due to the presence of amine group. At pH 5, there was higher recovery and at pH below 3 and more than 8, the recovery decreased due to protonation of analytes and negative charge repulsion, respectively. Table 2 shows that Fe3O4-graphene showed higher enrichment factor (2×) in comparison with


GO-SPE with electromembrane (50×), Fe3O4@SiO2-graphene (10×), Graphene-SiO2 SPE and Hemimicelle/Ad-micelle graphene SPE (45×). These results demonstrated that the adsorption sites were occupied with modifier, which decreased the enrichment factor. MSPE method based on Fe3O4@SiO2-graphene provided lower LOD for PAHs in comparison with graphene µSPE (2×), graphene-aminopropyltriethoxysilane SPE (40×), GO/ poly(3,4-ethylenedioxythiophene) SPE (100×) and graphene-SiO2 SPE (400×). These results showed that Fe3O4@SiO2-graphene was sensitive to PAHs isolation since SiO2 porosity helps the adsorption process, and also graphene high surface area was the main factor. In phthalate pre-concentration, MSPE based on Fe3O4@SiO2-graphene had lower LOD in comparison with graphene-SPE due to the aggregation of pure graphene, which decreased sensitivity. In herbicides pre-concentration, graphene-based SPME showed higher sensitivity in comparison with MSPE based on Fe3O4@graphene, and SPE based on GO. Due to solventless properties of SPME, it showed high enrichment factor, which increased the sensitivity. 2.

Applications of graphene-based SPE in biological sample analysis Recently, modified nano-graphenebased material have gained tremendous attention in the

biological purpose due to their exceptional properties i.e., biocompatibility, easily functionalize,

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ACCEPTED MANUSCRIPT chemical or thermal stability and electrical conductivity [139] and the high reproducibility of graphene encourage researchers to pay attention to biomedicine application sample preparation such as SPE. Recently too, SPE method was applied successfully for biological sample analysis where an imprinted polymer was used as the sorbent for pre-concentration of Zn(II) from milk and food


samples prior to FAAS [140] . The advantages of the proposed method were low LOD (0.15 ng mL-1), high recovery (99.8%) and good adsorption capacity (0.07 mg g-1). SPE column packed with graphene oxide-3-(1-methyl-1H-pyrrol-2-yl)-1H-pyrazole-5carboxylic acid was used for pre-concentration of Mn(II) and Fe(III) from milk and food samples [141]. In this case, GO-based adsorbent was synthesized with high surface area (398.24 m2 g-1) to provide reliable adsorption capacity of 21.6 mg g-1 for Mn(II) and 24.0 mg g -1 for Fe(III). The adsorption mechanism used the potential empirical surface theory (PES), which demonstrated that the coordination was accrued with OH and epoxy groups. The developed SPE-GO-MPPS isolated metal ions from complex matrices with less interference. Excellent sensitivity (145-162 ng L-1), great enrichment factor (325), and good recovery (99-103%) were obtained. Selectivity was considered in the presence of various coexisting ions with > 90% extraction recovery. The proposed modified GO showed 50× lower LOD and 16× higher enrichment factor in comparison with MWCNTs for Mn(II) and Fe(III) extractions [142]. This is attributed to the rich oxygen functional group present on GO surface that are available for adsorption which CNTs lacks. Graphene packed in SPE cartridge was used for extraction of neurotransmitters from rat brain [143]. The analytes included amine group, which can be adsorbed by graphene using

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ACCEPTED MANUSCRIPT electrostatic interactions. Also, its derivative was rich in benzene, which increased π-π stacking. The proposed SPE performance was evaluated using LOD (23.4 ng g -1), enrichment factor (82152) and recovery (62.3-105.1%). The high peak areas obtained and clear chromatogram (Figure 9) demonstrated the high sensitivity and low interference for graphene-based adsorbent in complex biological sample.


Column-packed SPE based on graphene was applied for simultaneous preconcentration of 30 sulfonamides from fish [144]. The performance of graphene was compared with conventional sorbents i.e., C18 and MWCNTs. Graphene provided high recovery (76.2-91.5%, 15 mg) in comparison with graphitic carbon (42-68.5%, 15 mg), MWCNT (50.5-77.9%, 15 mg) and C18 (68.4-88.5, 200 mg) due to strong π-π interaction in comparison with C18 and available adsorption sites on both sides of graphene plane, while the CNTs internal planar was inert. Hybrid metal-organic frameworks with graphene oxide was synthesized using a solvothermal process and applied as SPE sorbent for luteolin pre-concentration from tablet and tea [145]. Luteolin plays an important role in the human body. It possesses two benzene rings and various oxygen groups which is sufficient for interaction with GO-based adsorbent. The proposed method showed high recovery (97-102%) and high selectivity demonstrated by less interference in the presence of 500 times dopamine, cysteine and ascorbic acid as well as 1000× common water ions (1-205). A smart magnetic graphene was used as an antibacterial agent since it provides disinfection of E. coli (40 ng mL-1) bacteria with 100% killing efficiency [78]. MSPE based on Fe3O4@SiO2-G was used to isolate phthalate extracts from soybean milk [112]. High adsorption

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ACCEPTED MANUSCRIPT capacity (413 mg g-1) was obtained as graphene provided hydrophobicity and interaction with non-polar phthalates. Potential benefits of a in-house adsorbent are selectivity and less protein effects since it is used directly in crude milk samples. At pH 2 to 8, the recovery was unchanged and pH was decreased due to negative charge repulsion. Fe3O4 is a low toxic material and SiO2 increases its chemical stability, resulting in 30× reusability for Fe3O4@SiO2-graphene. The proposed adsorbent showed great ability for pre-concentration of analytes from complex


biological samples since the recovery and LOD ranged between (0.15-0.3 ng mL-1) and (87.2103.4), respectively. Its enrichment factor was 92. Pipette tip SPE based on graphene was used to extract lipophilic marine toxic analytes from fish tissues [146]. Graphene showed high extraction recovery due to high surface area, thermal stability and compatibility with different solvents. Experimental data showed that Pipette tip SPE based on graphene was sensitive (0.1 µg kg-1) and a repeatable method (at least 7×). SPE based on graphene oxide/ graphene nanosheet/ poly(glycidyl methacrylate-ethylene dimethacrylate)-polymer monolith microextraction was used in sarcosine pre-concentration from urine [147]. Sarcosine has polar amine and hydroxide groups that can form electrostatic interaction. High extraction recovery (93%) was obtained between pH 5 to 7 as its isoelectric pH was 6.2. The LOD and reusability were 1.0 ng mL-1 and 50×, respectively. Table 3 shows some applications of graphene as SPE sorbent for different biological samples and analytes. Malachite green has benzene ring, longer π-stacking and amide group, which provides strong π-π electron and electrostatic interactions with graphene, result in increased sensitivity. Bisphenol has two benzene rings, which increased the π-π interaction.

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ACCEPTED MANUSCRIPT Table 3 Graphene-based SPE applications in biological sample preparation. 3. Conclusions and perspectives Various applications using graphene, graphene oxide and its modified form have been reported recently. Graphene is obtained from graphene oxide through chemical reduction. Furthermore, its chemical structure, morphology and size are also considered. Graphene provides high surface


area, great hydrophobicity and long π-stacking. In contrast, graphene oxide provides high hydrophilic affinity due to rich functional groups. These advantages are the main factors in adsorption process as they contributed towards graphene-based material to become a suitable adsorbent candidate in analytical chemistry. Hydrophobicity and large π-stacking system in graphene allow non-covalent interactions (electrostatic, H-bonding and delocalized π-π electron interaction) with organic compounds and electrostatic interaction with metal ions. Graphene oxide, due to significant functional groups, allows strong coordination and electrostatic interactions with metal ions. Graphene-based material has been used successfully in multiple sample preparation techniques including SPE, µSPE, DSPE, MSPE and SPME with great ability in preconcentration of trace level metal ions, pesticides, PAHs, dye and phthalates from water samples as well as complex biological matrices such as milk, meat, fish and vegetables. Excellent analytical results (lower LOD, high enrichment factor, reusability, less interferences and high recovery) demonstrated that graphene has better analytical performance in comparison with C18, polymers, alkoxides, graphite, activated carbon and MWCNTs.

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ACCEPTED MANUSCRIPT Graphene-based sample preparation methods are relatively new in analytical chemistry, and its great analytical potential can support sample preparation in the future. Its use in MSPE, DSPE method offers green analytical chemistry process which is safe to the operator and contributes much less organic solvent usage, thus more environmentally friendly. Although graphene or graphene-based material showed potential benefits for wide range of


applications in adsorption and extraction process but there are problems that needs to be addressed for future studies such as preparation of large quantities or large scale single sheets for treatment of real industrial pollutions as the most of the studies currently concentrates on analytical scale/lab scale, challenge in 100% reduction of GO, and its safety problem waiting for efficient studies, particularly regarding the environmental and mammalian protection on the toxicity of carbon-based nanoparticles. Functionalization of graphene is a hot topic currently as it provides many possibilities of tailoring/tuning surface chemistry on demand to adapt the material to a given application. The products of functionalized graphene or hybrid graphenebased materials for pollutants applications waits to be discovered especially materials which are inexpensive, selective, and applicable directly in dirty matrix with minimum samples preparation and green to our environment. Acknowledgment The authors would like to thank the Ministry of Education Malaysia for financial support through the Research University Grant No. 10J43 and Ministry of Education Malaysia for the Fundamental Research Grant Scheme (FRGS) grant no. 4F307. H. R. Nodeh would like to thank UTM for the IDF award received.

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ACCEPTED MANUSCRIPT Table 1 Comparison of figure of merits including limit of detection (LOD), enrichment factor (EF), recovery (% R) and adsorption capacity (qm) of different adsorbent for different metal ions. LOD Adsorbent

Method

Sample

Analyte

Detector

(ng mL 1

GO@SiO2

SPE

water

Cu(II)

FAAS


Pb(II)

Ref.

qm -

EF

%R

(mg g 1

)

-

)

0.084

200 98.7

6.0

0.27

250 95.2

13.6

[70]

Graphene

SPE

water

Pb(II)

FAAS

0.61

125 96.3

16.6

[71]

Graphene

SPE

water

Co(II)

FAAS

0.36

200 102.6 20.6

[72]

DiPy-G1

SPE

water

Cd(II)

FAAS

0.19

416 99.1

392.0

[73]

GO

SPE

water

Co(II)

ED-

0.5

---

----

[74]

Ni(II)

7

XRF

94

0.7

98

Cu(II)

1.5

95

Zn(II)

1.8

102

Pb(II)

1.4

104

Fe3O4/GO

removal water

Co(II)

FAAS

----

---

---

23.75

[75]

Fe3O4/GO

removal water

Cd(II)

FAAS

----

---

---

91.29

[76]

GH-PDA2

removal water

Cd(II)

ICP-MS

----

---

---

336.32 [77]

Pb(II) SMG3

removal water

Cr(VI)

145.48 ICP-MS

----

---

---

4.86

As(V)

3.26

Pb(II)

6.0

[78]

GO-EDTA removal water

Pb(II)

FAAS

----

---

---

479.0

[79]

GO

Cu(II)

FAAS

----

---

---

294.0

[80]

removal water

Zn(II)

345.0

54

ACCEPTED MANUSCRIPT


ACCEPTED MANUSCRIPT Cd(II)

530.0

Pb(II)

1119.0

GO-CS4

removal water

Cu(II)

FAAS

----

---

---

25.4

[81]

GO

removal water

Cu(II)

FAAS

----

---

---

117.5

[82]

GO

removal water

U(VI)

UV

----

---

---

299.0

[83]

GO-Sep5

removal water

U(VI)

KPA8

----

---

---

161.29 [84]

Fe3O4/GO

removal water

U(VI)

UV

----

---

---

69.49

[85]

GO

removal water

Tl(IV)

EDX9

----

---

98.7

411.0

[86]

Fe3O4/GO

removal water

Cr(III)

AAS

----

---

---

4.7

[87]

PPy/GO6

removal water

Cr(VI)

UV

----

---

---

497.1

[88]

GO-TiO2

removal water

Zn(II)

AAS

----

---

---

88.9

[89]

GO

removal water

Cd(II)

72.8

Pb(II)

65.6

Cd(II)

AAS

----

---

---

Co(II)

106.3

[90]

68.2

1. DiPy-G, Dipyridyl-graphene 2. GH-PDA, 3. SMG, smart magnetic graphene 4. GO-CS, graphene oxide-chitosan 5. GO-Sep, graphene oxide-sepiolite 6. PPy/GO, polypyrrole/ graphene oxide 7. ED XRF, Energy dispersive X-ray fluorescence 8. KPA, kinetic phosphorescence analyzer 9. EDX, Energy dispersive X-ray spectroscopy

55

ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT Table 2 Comparison of graphene-based SPE performance including limit of detection (LOD), enrichment factor (EF), recovery (% R) and reusability.

Adsorbent


Graphene

G-SiO2

Meth od SPE

SPE

Ref.

LOD Sample

Analyte

Detector

(ng mL 1

water

water

phthalates

PAHs

GC-MS

HPLC-

-

EF

%R

---

71-

Reusabil ity

)

2-7

0.2-0.5

500

UV

---

[11

117

1]

89.0 ---

[11

-

5]

115. 4 G-

SPE

water

PAHs

APTEOS1

HPLC-

0.02-0.1 330

UV

84.6 ---

[11

-

6]

109. 5 Graphene

SPE

Cosmet

parabens

CE

100-

ic

---

150

62.6 ---

[11

-

7]

100. 4 Graphene

SPE

water

coronene

MALDI-

0.00000

TOF-

01 M

---

----

---

[11 8]

MS10 Graphene

SPE

water

chlorophe

HPLC-

nol

UV

0.1-0.4

---

77.2 ---

[27]

116. 6

Graphene

µSPE

water

PAHs

GC-MS

56

0.8-3.9

---

81.6 ---

[35]

ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT ng L-1

113. 5

GO

SPE-

water

herbicides

CE

0.3-0.5

EME

200

93.3 ---

[11

0

-

9]

103. 0


Graphene

SPE

Oil

pesticides

LC-MS

0.1-8.3

---

70.5 ---

[12

-

0]

100. 0 TiO2-G

SPE

water

nitrosothi

SF

0.08 nM ---

ols Fe3O4@Si O2-G

MSP

water

PAHs

E

HPLCFLD

0.5-5 ng L

173

-1

92-

---

[12

104

1]

83.2 ---

[12

-

2]

108. 2 Fe3O4@Si

MSP

O2-G

E

water

phthalate

HPLC-

0.07-0.1 150

UV

88.6 30

[11

-

2]

109. 0 Fe3O4@Si

MSP

cucumb carbamate

HPLC-

0.08-

O2-G

E

er

UV

0.02

s

100

pears

96.6 30

[12

-

3]

107. 2

Fe3O4@G

MSP

Juice

E

water

fungicides

GC-ECD

0.001-

184

79.2 30

[12

0.007

9

-

4]

102. 4

57

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ACCEPTED MANUSCRIPT Fe3O4@G

MSP

water

E

green

herbicides

GC-FID

0.01-

400

80.2 ---

[12

0.03

2

-

5]

tea

105. 3

Fe3O4@G

MSP

water

herbicides

E

HPLC-

0.02-

DAD

0.04

295

91.0 20

[12

-

6]


96.2 He/Ad-

MSP

MG2

E

water

PFASs6

HPLC-

0.15-

DAD

0.50

113

56.3 ---

[12

-

7]

93.9 Fe3O4@Si

MSP

O2-G

E

water

sulfonami

HPLC-

0.09-

des

UV

0.16

---

74.2 ---

[12

-

8]

104. 1 Fe3O4-G

MSP

water

E Fe3O4-G

MSP

water

carbamate

HPLC-

0.02-

s

DAD

0.04

fungicides

HPLC-

0.005-

582

86-

UV

0.01

4

102.

E

864

87-

12

[12 9]

95 15

[13 0]

0 Fe0-G

MSP

water

PAHs

GC-MS

----

---

7

E

PCBs

90-

---

[13 1]

93

phthalates GO/PEDT

SPM

3

E

Graphene

SPM

water

PAHs

GC-FID

0.05-

---

0.13 water

OCPs8

GC-MS

E

85-

70

[13

107

2]

0.19-

128

77.7 ---

[13

18.3

6

-

3]

120 Mo-G4

SPM

water

PAHs

GC-FID

58

0.004-

215

78.9 160

[13

ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT E

0.05

0

4]

115. 9

Graphene

SPM

water

OCPs8

GC-ECD

0.1-0.9

---

ng L-1

E

80.1 250

[13

-

5]

101. 1 Graphene

SPM

water

herbicides


E G/CNTs/C

SPE

HPLC-

0.05-0.2 ---

DAD water

OPPs9

S5

86-

---

6]

94.6

Voltamme 0.5

---

---

10

SPE

1. G-APTEOS,

water

parathion

graphene-amino

Hemimicelles/admicelles-magnetic

[13 7]

try

Graphene

[13

Stripping

0.6

---

96.5 ---

[13

voltammet

-

8]

ry

106

propyltrimethoxysilane graphene

2.

He/Ad-MG,

3.GO/PEDT,

poly(3,4-

ethylenedioxythiophene)/graphene oxide 4. Mo-G, monolithic graphene 5.G/CNTs/CS, graphene/carbon nanotubes/ chitosan 6. PFASs, perfluoroalkyl and polyfluoroalkyl substances 7. PCBs8, polychlorinated biphenyls 8. OCPs, organochlorine pesticides 9. OPPs, organophosphorus pesticides 10. MALDI-TOF-MS, matrix assisted laser desorption-time of flight-mass spectrometry

59

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ACCEPTED MANUSCRIPT Table 3 Some graphene-based SPE applications in biological sample preparation

Adsorbent

Method

Graphene

SPE

Graphene


Graphene

Graphene

SPE

SPE

SPE

Sample Fish

Fish

Meat

Dairy

Analyte

Detector

Malachite green

Macrolides

Sulfonamide

Bisphenol A

LOD (ng g-1)

HPLC-

0.09-

82-

MS/MS

0.12

103.4

UHPLC-

0.09-

81.7-

MS/MS

0.72

110.5

CZE

0.029-

60.9-

0.063

111.4

GC-MS

0.8 ng 95.7mL-1

Graphene

SPE

Food

Chloramphenicol

HPLC-

Graphene

PPy/G*

SPE

µSPE

SPME

Fish

Milk

Ant &

PBDEs**

Sulfonamide

PBVOC***

coriander

0.03

92.3103.4

GC-ECD 0.005-

74.2-

mg g

Ref.

[148]

[149]

[150]

[151]

90.1 -1

MS/MS Graphene

%R

0.21

109.3

HPLC-

0.004

90.1-

UV

µg g-1

113.5

GC-MS

0.05-

79-

2.1

114

[152]

[153]

[154]

[155]

*PPy/G, polypyrrole/graphene; ** PBDEs, polybrominated diphenyl ethers; ***PBVOC, polar biological volatile organic compounds

60

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ACCEPTED MANUSCRIPT

Figure 1

Schematic of pesticide degradation using photocatalyst (A) and photo-Fenton (B) Reprinted with permission from ref. [4]. Copyright 2012 American Chemical Society

61

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Figure 2

Carbon nanomaterial and the schematic for preparation of graphene from graphite

62

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63

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Figure 3

GO functional groups as shown in

13

C-NMR spectra. Reprinted with permission

from ref. [18]. Copyright 2012 American Chemical Society

64

ACCEPTED MANUSCRIPT


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Figure 4

Schematic of graphene as sorbent in three different extraction techniques (A) conventional SPE, (B) dispersive SPE (DSPE) and (C) magnetic graphene-based SPME.

65

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Figure 5

GO as a membrane for sodium separation. Reprinted with permission from ref. [19]. Copyright 2012 American Chemical Society

66

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Figure 6

GC-FID chromatograms with GO as the capillary stationary phase of (A) volatile organic compounds separation at 50ºC oven temperature, and (B) aromatic compounds separation at 90ºC oven temperature. Reprinted with permission from ref. [82]. Copyright 2012 Elsevier.

67

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Figure 7

HPLC-UV chromatogram of PAHs derivatives extraction at (A) zero and its corresponding spiked samples with (B) 1 ng mL -1 and (C) 10 ng mL-1 of each analytes. Reprinted with permission from ref. [92]. Copyright 2012 Elsevier.

68

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Figure 8

GC-MS chromatogram of extracted phthalate acids from river water. Reprinted with permission from ref. [99]. Copyright 2014 Elsevier

69

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Figure 9

HPLC-UV chromatogram for neurotransmitters (Glycine, Taurine and γ-Aminobutyric acid) isolation from rat brain. Reprinted with permission from ref. [131]. Copyright 2011 Springer-Verlag.

70

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Micro-solid-phase extraction of organochlorine pesticides using porous metal-organic framework MIL-101 as sorbent.

Impregnated multiwalled carbon nanotubes as efficient sorbent for the solid phase extraction of trace amounts of heavy metal ions in food and water samples.

Microextraction by Packed Sorbent (MEPS) and Solid-Phase Microextraction (SPME) as Sample Preparation Procedures for the Metabolomic Profiling of Urine.

Preparation of an aminopropyl imidazole-modified silica gel as a sorbent for solid-phase extraction of carboxylic acid compounds and polycyclic aromatic hydrocarbons.

Application of solid-phase extraction for trace elements in environmental and biological samples: a review.

Trace-chitosan-wrapped multi-walled carbon nanotubes as a new sorbent in dispersive micro solid-phase extraction to determine phenolic compounds.

Fabrication of a Dipole-assisted Solid Phase Extraction Microchip for Trace Metal Analysis in Water Samples.

Polypyrrole-montmorillonite nanocomposite as sorbent for solid-phase microextraction of phenolic compounds in water.

The metal-organic framework HKUST-1 as efficient sorbent in a vortex-assisted dispersive micro solid-phase extraction of parabens from environmental waters, cosmetic creams, and human urine.

Comparison of different sorbent materials for solid-phase extraction of selected drugs in human urine analyzed by UHPLC-UV.

Cotton-supported graphene functionalized with aminosilica nanoparticles as a versatile high-performance extraction sorbent for trace organic analysis.

Liquid-phase extraction coupled with metal-organic frameworks-based dispersive solid phase extraction of herbicides in peanuts.

Solid-phase extraction of prostanoids using an automatic sample preparation system.

Preparation and characterization of metal-organic framework MIL-101(Cr)-coated solid-phase microextraction fiber.

Extraction and sample preparation.

Solid-phase extraction of the alcohol abuse biomarker phosphatidylethanol using newly synthesized polymeric sorbent materials containing quaternary heterocyclic groups.

Graphene oxide as a micro-solid-phase extraction sorbent for the enrichment of parabens from water and vinegar samples.

2nd dimensional GC-MS analysis of sweat volatile organic compounds prepared by solid phase micro-extraction.

A novel hierarchical nanobiocomposite of graphene oxide-magnetic chitosan grafted with mercapto as a solid phase extraction sorbent for the determination of mercury ions in environmental water samples.

Highly selective dummy molecularly imprinted polymer as a solid-phase extraction sorbent for five bisphenols in tap and river water.

New sorbent in the dispersive solid phase extraction step of quick, easy, cheap, effective, rugged, and safe for the extraction of organic contaminants in drinking water treatment sludge.

Restricted accessed nanoparticles for direct magnetic solid phase extraction of trace metal ions from human fluids followed by inductively coupled plasma mass spectrometry detection.

Dispersive micro-solid-phase extraction of herbicides in vegetable oil with metal-organic framework MIL-101.

Graphene nanoplatelets as a highly efficient solid-phase extraction sorbent for determination of phthalate esters in aqueous solution.