Anal Bioanal Chem (2014) 406:2651–2658 DOI 10.1007/s00216-014-7680-4

RESEARCH PAPER

Quinolinium ionic liquid-modified silica as a novel stationary phase for high-performance liquid chromatography Min Sun & Juanjuan Feng & Chuannan Luo & Xia Liu & Shengxiang Jiang

Received: 19 November 2013 / Revised: 6 January 2014 / Accepted: 5 February 2014 / Published online: 16 March 2014 # Springer-Verlag Berlin Heidelberg 2014

Abstract A novel stationary phase based on quinolinium ionic liquid-modified silica was prepared and evaluated for high-performance liquid chromatography. The stationary phase was investigated via normal-phase (NP), reversedphase (RP), and anion-exchange (AE) chromatographic modes, respectively. Polycyclic aromatic hydrocarbons, phthalates, parabens, phenols, anilines, and inorganic anions were used as model analytes in chromatographic separation. Using the newly established column, organic compounds were separated successfully by both NP and RP modes, and inorganic anions were also separated completely by AE mode. The obtained results indicated that the stationary phase could be applied in different chromatographic modes, with multipleinteraction mechanism including van der Waals forces (dipole–dipole, dipole–induced dipole interactions), hydrophobic, π–π stacking, electrostatic forces, hydrogen bonding, anion-exchange interactions, and so on. The column packed with the stationary phase was applied to analyze phthalates and parabens in hexane extracts of plastics. Tap water and bottled water were also analyzed by the column, and nitrate was detected as 20.1 and 13.8 mg L−1, respectively. The results illustrated that the stationary phase was potential in practical applications. Electronic supplementary material The online version of this article (doi:10.1007/s00216-014-7680-4) contains supplementary material, which is available to authorized users. M. Sun : J. Feng : C. Luo (*) Key Laboratory of Chemical Sensing & Analysis in Universities of Shandong (University of Jinan), School of Chemistry and Chemical Engineering, University of Jinan, Jinan 250022, China e-mail: [email protected] X. Liu : S. Jiang Key Laboratory of Chemistry of Northwest Plant Resources/Key Laboratory for Natural Medicine of Gansu Province, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, China

Keywords Quinolinium ionic liquid . Stationary phase . Normal-phase chromatography . Reversed-phase chromatography . Anion-exchange chromatography

Introduction Ionic liquids (ILs) have got considerable considerations as green solvents or novel materials in organic synthesis [1], catalysis [2], separation science [3], and so on, due to their excellent properties such as wide liquid ranges, good thermal stabilities, wide range of viscosities, adjustable miscibility, good solvation characteristic, and reusability [4]. Recently, they were applied to almost all areas of the separation science [5] such as extraction [6, 7], gas chromatography [8–10], liquid chromatography [11–24], capillary electrophoresis [25–27], mass spectrometry [28, 29], and electrochemistry [30, 31]. In high-performance liquid chromatography (HPLC), ILs were firstly studied as the additives in mobile phase. For the separation of ephedrines [11], catecholamines [12], and nucleotides [13], peak shape, resolution, and column efficiency were dramatically improved. The silanol effect for the separation of basic drug molecules [14, 15] was also effectively suppressed. On the basis of the advantages of IL additives in mobile phase, the IL-functionalized stationary phases attracted great attentions. Liu et al. firstly prepared an ILmodified silica stationary phase by functionalizing silica with 1-allyl-3-hexyl imidazolium tetrafluoroborate and obtained the effective separation of alkaloids through both hydrophobicity and ionic property of the phase [16]. Qiu et al. prepared imidazolium IL-based anion-exchange (AE) stationary phases by immobilizing N-methylimidazolium and imidazolium groups to silica [17, 18] for the separation of inorganic and organic anions. Furthermore, two zwitterionic stationary phases based on sulfonated imidazolium IL-functionalized

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silica separated anions and cations [19, 20, 32] simultaneously and some bases and vitamins [19]. Stalcup and co-workers attached N-butylimidazolium IL to silica and evaluated it with the linear solvation energy relationship method [21–23]. The column retained aromatic compounds with a similar way to the phenyl column. Colón et al. synthesized two alkylimidazolium IL (1-methyl-3-propylimidazolium bromide and 1-n-butyl-3-propylimidazolium bromide)-modified silicas using trimethoxysilane derivatives of ILs for separating aromatic carboxylic acids [24]. Ihara’s group researched 1-allyl-3-octadecylimidazolium bromide-modified silica (SiImC18) and the polymer of 1-(2-acryloyloxyundecyl)3-methylimidazolium bromide-grafted silica (Sil-pC11C1Im), which exhibited high selectivity for polycyclic aromatic hydrocarbons (PAHs) and polar compounds based on the multiple interactions and retention mechanisms such as π–π, ion-dipole, and electrostatic interactions [33]. The multi-mode chromatographic performances were represented for the effective separation of anions, hydrophobic compounds, and small polar molecules, respectively [34]. Recently, they investigated the effect of anions of ILs on the separation performance of stationary phases [35–38]. After the change of the IL anions from Br− to methyl orange, the enhanced selectivity toward shape-constrained PAH isomers was exhibited [35, 37, 38]. Imidazolium IL-functionalized silica stationary phases have been researched more, but the quinolinium IL-based stationary phase was less reported. Quinolinium ILs have a larger cation than imidazolium ILs, and the quinolinium cation can provide different properties than the imidazolium cation, such as stronger π–π stacking, weaker electrostatic, and anion-exchange interactions. IL-modified silica stationary phases have been used in anion-exchange and reversed-phase (RP) liquid chromatography [24, 34]. However, there are very few reports that describe IL-modified silica stationary phases used in normal-phase (NP) liquid chromatography [22]. In addition, the existing columns are rarely suitable for application in three modes. In this work, a quinolinium IL-modified silica stationary phase was prepared and investigated by NP, RP, and AE modes. Using the newly established column, organic compounds (PAHs, phthalates, parabens, phenols, and anilines) were successfully separated by both NP and RP modes. Inorganic anions were also separated completely by AE mode.

(BET), which were made according to [39] in our laboratory, were used as the support. 3-Chlorpropyltrimethoxysilane (98 %) was obtained from Qufu Chenguang Fine Chemical Co. (Shandong, China). Quinoline (98 %) was purchased from Shanghai Jingchun Industry Co. (Shanghai, China). 3-Chlorpropyltrimethoxysilane and quinoline were purified by vacuum distillation before use. Toluene was bought from Sinopharm Chemical Reagent Co. (Shanghai, China). Toluene was dried by refluxing with sodium for 24 h and then distilled before use. Organics including PAHs, phthalates, parabens, phenols, anilines, hexane, ethanol, and methanol and inorganic salts including potassium chloride, potassium iodate, potassium bromate, potassium bromide, and potassium nitrate were purchased from Shanghai Jingchun Industry Co. (Shanghai, China). These chemicals were of analytical grade quality. A Kromasil C18 column was obtained from Hanbon Science & Technology Co. (Jiangsu, China). Silica column and Sil-NH2 column were as described in our previous report [40].

Experimental

Chromatographic conditions

Reagents and materials

All chromatographic tests were performed on an Agilent 1260 Infinity series (Santa Clara, CA, USA) with a 20-μL sample loop and a UV–VIS detector. SilprQui column (150×4.6 mm I.D.) was packed by the slurry-packed method, and it was

Spherical and porous silica particles of 5 μm, with 8 nm average pore diameter and 390 m2 g−1 specific surface area

Preparation of stationary phase Quinolinium ionic liquid-modified silica stationary phase (SilprQui) was prepared by treatment of the chloropropyl group-modified silica (SilprCl) with a large excess of quinoline in N, N-dimethylformamide as described in our previous report [41] (shown in Fig. 1). Characterizations Fourier transform infrared (FTIR) spectra of the samples in the range of 4,000–400 cm−1 were obtained on a Thermo Nicolet 5700 FTIR spectrophotometer (Madison, WI, USA). The carbon, hydrogen, and nitrogen contents of SilprCl and SilprQui were determined by the elemental analysis, performed on an Elementar Vario EL cube (Hanau, Germany). The coverage of quinolinium groups on silica was calculated based on the nitrogen content of SilprQui. X-ray photoelectron spectroscopy (XPS) was used to characterize SilprCl and SilprQui. The XPS spectra were recorded on an Escalab 210 Axis Ultra photoelectron spectrometer (VG Scientific, UK) using an Mg K alpha excitation source. The specific surface area (BET) of silica, SilprCl, and SilprQui was determined on an ASAP 2010 Accelerated Surface Area and Porosimetry System (Micromeritics, USA).

Quinolinium ionic liquid-modified silica as a novel stationary

compared with Kromasil C18, silica, and Sil-NH2 columns (150×4.6 mm I.D.), respectively. Mobile phases were filtered with a 0.45-μm nylon membrane filter. All tests in NP mode used hexane–ethanol as the mobile phase, and all tests in RP chromatographic mode used methanol–water as the mobile phase. The separation of inorganic anions used 50–200 mmol L−1 KCl solution as the mobile phase. All tests were performed at 25 °C and 1 mL min−1. The column dead time was determined from the mobile phase signal in the UV detection.

Results and discussion Preparation of stationary phase The preparation process of the SilprQui stationary phase is schematically described in Fig. 1. Silica was modified by 3-chloropropyltrimethoxysilane to obtain SilprCl. Then SilprQui was prepared through the reaction between quinoline and the chloropropyl groups of SilprCl. Characterizations In FTIR spectra of SilprCl and SilprQui (see Electronic Supplementary Material Fig. S1), the bands around 1,110 cm−1 and broad bands around 3,450 cm−1 are attributed to the stretching vibrations of Si–O and O–H groups, respectively, and sourced from the matrix of silica. Bands appeared at 2,920 cm−1 are attributed to aliphatic C–H stretching in the spectrum of SilprCl and are attributed to aliphatic C–H stretching in the spectrum of SilprQui. In the spectrum of SilprQui, two new bands appeared at 1,630 and 1,530 cm−1 are attributed to the aromatic C=C or C=N stretching vibration, resulting from the presence of the quinolinium groups on SilprQui. In XPS spectra of SilprCl and SilprQui (see Electronic Supplementary Material Fig. S2), except for the peaks at Fig. 1 The preparation process of the SilprQui stationary phase

2653 Table 1 The elemental analysis results, the specific surface area (S), and the coverage of SilprCl and SilprQui Stationary phases

C%

H%

N%

S (m2 g−1)

Coverage (μmol m−2)

SilprCl SilprQui

4.62 8.08

1.18 1.29

0 0.54

340 335

3.77 1.15

C% percentage of carbon, H% percentage of hydrogen, N% percentage of nitrogen, S specific surface area of stationary phases

532.7 eV (O 1s) and 103.3 eV (Si 2p) sourced from the matrix of silica, the peaks at 285.0 eV are sourced from C 1s. The peak at 200.3 eV is from Cl 2p in the spectrum of SilprCl, and it decreases significantly in the spectrum of SilprQui. In the spectrum of SilprQui, the new peak at 401.2 eV is from the nitrogen (N 1s) of the quinolinium groups. The presence of N 1s peak indicated that quinolinium ionic liquid was attached onto the silica. The contents of carbon, nitrogen, and hydrogen of SilprCl and SilprQui were determined by the elemental analysis. As shown in Table 1, the contents of carbon and nitrogen of SilprQui are higher than that of SilprCl. According to the content of carbon and the specific surface area (S1) of SilprCl, the coverage of silica by the chloropropyl groups was calculated as 3.77 μmol m−2. From the nitrogen content, the average concentration of the quinolinium ionic liquid groups on silica surface was calculated as 1.15 μmol m−2 for SilprQui. The calculating formulas are as follows:
C%  106 Chloropropyl groups on SilprCl Hmol m−2 ¼ ¼ 3:77 36  S 1

Quinolinium ionic liquid groups on SilprBim Hmol m−2 N%  106 ¼ 1:15 ¼ 14  S 2




ð1Þ ð2Þ

where C% and N% represent the percentage of carbon and nitrogen, respectively. S1 and S2 are the specific surface area of SilprCl and SilprQui, respectively.

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Fig. 2 Effect of hexane content on retention (log k) of PAHs by normalphase chromatography (a); effect of methanol content on retention (log k) of PAHs by reversed-phase chromatography (b). PAHs included benzene (1), naphthalene (2), fluorene (3), anthracene (4), fluoranthene (5), and

chrysene (6). Chromatographic conditions: SilprQui column (150× 4.6 mm I.D.), mobile phase: hexane–ethanol as normal-phase eluent and methanol–water as reversed-phase eluent, flow-rate: 1 mL min −1, injection volume 20 μL, and detection: UV at 254 nm

Chromatographic separations

As shown in Fig. 2b, the retention of PAHs on SilprQui decreases with the increase of methanol in methanol–water eluent. It was indicated that the hydrophobic interaction was involved in RP chromatographic separation of PAHs. With the increase of the π-electron in PAH molecules, their retention increases, which illustrates the π–π stacking mechanism in separation process. Compared with a C18 stationary phase, SilprQui provided a stronger retention for analytes with larger π-electron system by π–π interaction. As shown in Fig. 3, the first four compounds including benzene, naphthalene, fluorene, and anthracene were weakly retained on SilprQui than that on Kromasil C18 for weak hydrophobicity of SilprQui, but it is opposite for fluoranthene and chrysene. Compared to a classical old Kromasil column, SilprQui column has lower column efficiency for PAHs.

Separation of PAHs The test mixture of PAHs containing benzene, naphthalene, fluorene, anthracene, fluoranthene, and chrysene was used to evaluate SilprQui column by NP and RP chromatographic modes. SilprQui column could separate these PAHs by two chromatographic modes, respectively. As shown in Fig. 2a, with the increase of hexane in hexane–ethanol mobile phase, the retention of PAHs increases. Under the same conditions, the larger π-electron-conjugated PAH molecules were more retained. Although PAHs are a class of nonpolar compounds, they had a strong retention on SilprQui with a high content of polar eluent in NP chromatography. It indicated that SilprQui was strong polar for quinolinium chloride ionic liquid groups. According to above results, the retention mechanism of PAHs on SilprQui was mainly dipole–induced dipole, π–π interactions in NP chromatography.

Fig. 3 Comparison of separation performance for PAHs between SilprQui and C18 stationary phases by reversed-phase chromatography. The test mixture included benzene (1), naphthalene (2), fluorene (3), anthracene (4), fluoranthene (5), and chrysene (6). Chromatographic conditions: mobile phase: methanol–water (95:5, v/v); other conditions are the same as in Fig. 2

Separation of phthalates and parabens Four phthalates and three parabens containing di-n-octyl phthalate, di-n-butyl phthalate, diallyl phthalate, dimethyl

Fig. 4 Effect of hexane content on retention (log k) of di-n-octyl phthalate (1), di-n-butyl phthalate (2), diallyl phthalate (3), dimethyl phthalate (4), p-hydroxybenzoic n-butyl ester (5), p-hydroxybenzoic ethyl ester (6), and p-hydroxybenzoic methyl ester (7) on SilprQui column by normalphase chromatography. Chromatographic conditions: mobile phase: hexane–ethanol; other conditions are the same as in Fig. 2

Quinolinium ionic liquid-modified silica as a novel stationary

Fig. 5 Comparison of separation performance for four phthalates and three parabens among SilprQui, silica, and Sil-NH2 columns by normalphase chromatography. The test mixture contained di-n-octyl phthalate (1), di-n-butyl phthalate (2), diallyl phthalate (3), dimethyl phthalate (4), p-hydroxybenzoic n-butyl ester (5), p-hydroxybenzoic ethyl ester (6), and p-hydroxybenzoic methyl ester (7). Chromatographic conditions: mobile phase: hexane–ethanol (80:20, v/v) for SilprQui and Sil-NH2 columns, hexane–ethanol (90:10, v/v) for silica column; other conditions are the same as in Fig. 2

phthalate, p-hydroxybenzoic n-butyl ester, p-hydroxybenzoic ethyl ester, and p-hydroxybenzoic methyl ester were used to evaluate SilprQui by NP chromatography. As shown in Fig. 4, the retention of these compounds increases with increasing hexane in hexane–ethanol eluent. The retention of parabens is stronger than that of phthalates on SilprQui. Furthermore, more polar compounds in four phthalates or three parabens had the larger retention time. These indicated that the polar interaction was the main retention mechanism of phthalates and parabens on SilprQui by NP chromatography. SilprQui was compared with common NP stationary phases including silica and Sil-NH2 phases. The results indicated that SilprQui was superior to silica and Sil-NH2 for separating phthalates and parabens. As shown in Fig. 5, a baseline separation of these compounds on SilprQui is accomplished within 8.5 min with hexane–ethanol (80:20, v/v) as mobile phase. Under the

Fig. 6 Separation of test mixture of dimethyl phthalate (1), diallyl phthalate (2), di-n-butyl phthalate (3), p-hydroxybenzoic methyl ester (4), and p-hydroxybenzoic n-butyl ester (5) by reversed-phase chromatography. Chromatographic conditions: mobile phase: methanol–water (50:50, v/v); other conditions are the same as in Fig. 4

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Fig. 7 Separation of test mixture of 2, 4-ditertbutyl phenol (1), 2-methylphenol (2), phenol (3), 1-naphthol (4), m-nitrophenol (5), and p-nitrophenol (6) by normal-phase chromatography. Chromatographic conditions: mobile phase: hexane–ethanol (75:25, v/v); other conditions are the same as in Fig. 2

same condition, the retention time of three parabens on Sil-NH2 is too large, and four phthalates cannot be separated well. Silica cannot separate these compounds successfully even using hexane–ethanol (90:10, v/v) as mobile phase. Comparing the retention of weak polar phthalates on three stationary phases, the polarity of SilprQui was larger than silica and Sil-NH2. However, the retention of parabens on Sil-NH2 was stronger than that on SilprQui. It may attribute to hydrogen bonding and stronger electrostatic interactions between parabens and Sil-NH2. SilprQui can separate dimethyl phthalate, diallyl phthalate, di-n-butyl phthalate, p-hydroxybenzoic methyl ester, and p-hydroxybenzoic n-butyl ester by RP chromatography. As shown in Fig. 6, the retention of two parabens is stronger than that of three phthalates for possible electrostatic interaction between parabens and SilprQui. The retention order of analytes in phthalates or parabens in RP mode was

Fig. 8 Separation of test mixture of N, N-dimethylaniline (1), Nethylaniline (2), N-phenylaniline (3), p-methylaniline (4), aniline (5), onitroaniline (6), m-nitroaniline (7), and p-nitroaniline (8) by normal-phase chromatography. Chromatographic conditions: mobile phase: hexane– ethanol (80:20, v/v); other conditions are the same as in Fig. 2

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Fig. 9 Effect of KCl concentration (50–200 mol L−1) on the retention (1/k) of inorganic anions including iodate (1), bromate (2), bromide (3), and nitrate (4). Chromatographic conditions: mobile phase: the solution of KCl, detection: UV at 210 nm; other conditions are the same as in Fig. 2

contrary with that in NP mode. The more hydrophobic compounds in either three phthalates or two parabens were more retained. The results indicated that hydrophobic and electrostatic interactions may be involved in RP separation of phthalates and parabens. In addition, five phthalates containing dimethyl, diallyl, di-n-butyl, di-n-pentyl, and dicyclohexyl phthalates were separated well on SilprQui column with methanol–water (50:50, v/v) mobile phase (see Electronic Supplementary Material Fig. S3). There is larger retention time for more hydrophobic analytes on SilprQui based on hydrophobic mechanism. The hydrophobic mechanism of SilprQui was further exhibited in the separation of five phthalates. So, the separation mechanism of SilprQui mainly included hydrophobic, electrostatic, and π–π interactions in RP chromatographic mode. Separation of phenols The separation of phenols containing 2, 4-ditertbutyl phenol (pKa, 12.15; log P, 4.61), 2-methylphenol (pKa, 10.29; log

Fig. 10 The analysis of water samples (a) and the hexane extracts of plastics (b) by SilprQui column. a The peaks of stand sample included iodate (40 mg L−1) (1), bromate (40 mg L−1) (2), bromide (35 mg L−1) (3), and nitrate (30 mg L−1) (4); mobile phase: the solution of 150 mmol L−1 KCl, detection: UVat 210 nm. b The peaks of stand sample included di-noctyl phthalate (25 mg L−1) (1), di-n-butyl phthalate (25 mg L−1) (2),

M. Sun et al.

P, 1.94), phenol (pKa, 10.00; log P, 1.54), 1-naphthol (pKa, 9.45; log P, 2.71), m-nitrophenol (pKa, 8.39; log P, 1.93), and p-nitrophenol (pKa, 7.25; log P, 1.67) on SilprQui column was investigated. As shown in Fig. 7, the good separation of six phenols is achieved by NP chromatography using hexane– ethanol (75:25, v/v) as mobile phase. Compared with NP mode, RP mode provided poor separation and lower column efficiency for phenols owing to stronger electronic interaction (see Electronic Supplementary Material Fig. S4). The resolution and the peak shape were poor, and the retention time was large in RP mode. The elution order of phenols was different in two modes. The elution order of six phenols depended on their polarity, and polar compounds had large retention time in NP chromatography. However, the elution order depended on their hydrophobicity and electronegativity in RP chromatography. m-Nitrophenol and p-nitrophenol are higher electronegative than other phenols, so they had too large retention time in RP mode. 1-Naphthol was retained strong on SilprQui in two chromatographic modes for its large π-electron system. SilprQui was potential to separate phenols by NP and RP chromatography, based on the different retention mechanisms including polar, hydrophobic, electrostatic, and π–π interactions. Separation of anilines Some anilines including N, N-dimethylaniline, N-ethylaniline, N-phenylaniline, p-methylaniline, aniline, o-nitroaniline, m-nitroaniline, and p-nitroaniline were also used to investigate SilprQui column by NP and RP modes. As shown in Fig. 8, the separation of anilines was obtained by NP chromatography with hexane–ethanol (80:20, v/v) mobile phase. In NP mode, o-, m-, p-nitroaniline had larger retention time for their strong polarity. The separation of anilines by RP chromatography is poor and has low column efficiency (see

diallyl phthalate (20 mg L−1) (3), dimethyl phthalate (20 mg L−1) (4), p-hydroxybenzoic n-butyl ester (20 mg L−1) (5), p-hydroxybenzoic ethyl ester (35 mg L−1) (6), and p-hydroxybenzoic methyl ester (40 mg L−1) (7); mobile phase: hexane–ethanol (80:20, v/v), detection: UV at 254 nm. Other conditions are the same as in Fig. 2

Quinolinium ionic liquid-modified silica as a novel stationary

Electronic Supplementary Material Fig. S5). In RP mode, Nphenylaniline had the largest retention time for its strong hydrophobicity and two phenyls in molecule. The elution order of aniline, p-methylaniline, and N-ethylaniline in two modes was opposite. It was ascribed to the different retention mechanisms of SilprQui in two modes. Dipole–dipole, π–π, and H–π interactions may be involved in the separation of anilines on SilprQui in NP mode [42]. Electrostatic repulsion, π–π, and hydrophobic interactions may be included in the separation mechanism of anilines on SilprQui in RP mode [43]. Separation of inorganic anions SilprQui can separate inorganic anions by anion-exchange chromatography. The test mixture of inorganic anions including iodate, bromate, bromide, and nitrate was used to investigate the anion-exchange characteristic of SilprBim column using the KCl solution as mobile phase. The effect of KCl concentration on the retention of inorganic anions was investigated from 50 to 200 mmol L−1. As shown in Fig. 9, anion-exchange mechanism of SilprBim column is demonstrated by a linear 1/k versus KCl concentration of mobile phase relationship. The separation of inorganic anions with high resolution (R s ≥ 4.51) and column efficiency (31,400–40,600 platesm−1) was achieved (see Electronic Supplementary Material Fig. S6). Chromatographic application The SilprQui column was applied to analyze samples. Tap water and bottled water were analyzed using SilprQui column by AE mode. As shown in Fig. 10a, nitrate was detected as 20.1 mg L−1 in tap water and 13.8 mg L−1 in bottled water, and iodate, bromate, and bromide were not detected. The SilprQui column was also used to analyze the hexane extracts of plastics by NR mode. As shown in Fig. 10b, four phthalates and three parabens were not detected or not quantified for too little. The obtained results illustrated that the SilprQui was a potential stationary phase in the practical application.

Conclusions A novel stationary phase based on quinolinium ionic liquidmodified silica was prepared and characterized by FTIR, XPS spectra, and the elemental analysis. The stationary phase was investigated with PAHs, phthalates, parabens, phenols, anilines, and inorganic anions, by NP, RP, and AE chromatographic modes, respectively. The results illustrated that SilprQui was an excellent NP/RP/AE mixed-mode HPLC stationary phase. Using SilprQui column, organic compounds were separated successfully by NP and RP chromatographic

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modes, and inorganic anions were also separated well by AE chromatographic mode. SilprQui provided multiple interactions including van der Waals forces (dipole–dipole, dipole– induced dipole interactions), hydrophobic, π–π stacking, electrostatic forces, hydrogen bonding, anion-exchange interactions, and so on during the separation process. The SilprQui column was applied to analyze real samples, and the obtained results were satisfactory. The SilprQui was a potential stationary phase in the practical application. Acknowledgments This work was supported by the National Natural Science Foundation of China (NSFC; No. 21205048), the Shandong Provincial Natural Science Foundation of China (Nos. ZR2012BQ018 and ZR2012BM020), and the Doctoral Foundation of University of Jinan (No. XBS1207).

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