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Forensic analysis of ballpoint pen inks using paper spray mass spectrometry† Priscila da Silva Ferreira, De´bora Fernandes de Abreu e Silva, Rodinei Augusti and Evandro Piccin* A novel analytical approach based on paper spray mass spectrometry (PS-MS) is developed for a fast and effective forensic analysis of inks in documents. Ink writings made in ordinary paper with blue ballpoint pens were directly analyzed under ambient conditions without any prior sample preparation. Firstly, the method was explored on a set of distinct pens and the results obtained in the positive ion mode, PS(+)MS, demonstrated that pens from different brands provide typical profiles. Simple visual inspection of the PS(+)-MS led to the distinction of four different combinations of dyes and additives in the inks. Further discrimination was performed by using the concept of relative ion intensity (RII), owing to the large variability of dyes BV3 and BB26 regarding their demethylated homologues. Following screening and differentiation studies, the composition changes of ink entries subjected to light exposure were also monitored by PS-MS. The results of these tests revealed distinct degradation behaviors which were
Received 1st September 2014 Accepted 9th November 2014
reflected on the typical chemical profiles of the studied inks, attesting that PS-MS may be also useful to verify the fading of dyes thus allowing the discrimination of entries on a document. As proof of concept
DOI: 10.1039/c4an01617c
experiments, PS-MS was successfully utilized for the analysis of archived documents and
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characterization of overlapped ink lines made on simulated forged documents.
Introduction The investigation of questionable documents is an important research topic in forensic science. Along with handwriting examination and physical analysis (e.g. microscopic examination under different light sources), chemical screening of writing inks is used to identify possible insertions to original writings, such as modications of dates, values, or signatures. Chemical analysis can also be used to establish whether entries on a document were made with a single pen or at the same time. Ballpoint pens are the most common writing instruments used in the majority of insertions, especially for dating and signing documents.1–5 Many methods have been reported for performing chemical analysis and degradation studies of writing inks. Methods that involve UV-vis spectrometry,6,7 direct infusion electrospray ionization mass spectrometry (ESI-MS),8 and separation techniques, such as thin layer chromatography (TLC),9–11 high performance liquid chromatography (HPLC),12–15 capillary electrophoresis (CE),16,17 and gas chromatography-mass spectrometry,18 commonly require prior sample extraction using organic solvents, which is a laborious and time-consuming Departamento de Qu´ımica, Instituto de Ciˆencias Exatas, Universidade Federal de Minas Gerais, Belo Horizonte 31270-901, Brazil. E-mail: [email protected]; Tel: +55 31 3409 6389 † Electronic supplementary information (ESI) available: Further examples of applications of PS-MS to detect forgeries in documents. See DOI: 10.1039/c4an01617c
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procedure. Moreover, the ink extraction procedure leads to the sample destruction, which is undesirable in forensic science where the preservation of proofs is an important issue. Recently, Williams and collaborators19 proposed a method for ink analysis based on ESI-MS where the samples were prepared from ink-coated paper bers pulled from the paper using a forceps. Although the method allowed minimal sample destruction, the multiple step procedure (pulling paper bers and solvent extraction) is undesirably too laborious. Raman spectroscopy20–22 and ambient ionization mass spectrometry1–3,23–31 techniques are more appropriate for forensic analysis on document inks since they guarantee minimal sample destruction. In particular, the main advantage of ambient ionization MS techniques is the possibility for direct analysis of samples in their native form and in the open environment without prior preparation. Thus, this family of techniques, in which the analyte desorption accompanies the ionization step, provide the preservation of spatial chemistry information of the sample, maximize the sensitivity, and afford high throughput analysis.28–33 The characteristics of ambient ionization together with the sensitivity and resolution power of MS make them very attractive for the eld of forensic sciences, where the results must ensure the specicity of analysis and the sample traceability and integrity are important issues.34,35 Paper spray (PS) was rst proposed by Wang et al.36 in 2009 as a new ambient ionization technique for fast, qualitative, and quantitative analysis of complex mixtures by MS. In this recently
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developed technique, the analyte ions are generated by applying a high voltage and a small volume (10 mL) of spray solvent onto a triangular shape paper (usually 10 mm in height and 5 mm of base) positioned at the MS inlet. The sample may be preloaded onto the paper or mixed in the spray solution.36,37 In PS, pneumatic assistance is not required to transport the analyte. Thus, its instrumentation/operation is simpler and more compatible with miniature mass spectrometers, when compared to other ambient ionization techniques, such as, for example, desorption electrospray ionization (DESI),3,23,31 direct analysis in real time (DART),38,39 extractive electrospray ionization (EESI),40,41 and easy ambient sonic ionization (EASI).42,43 PS-MS has been used for the analysis of several compounds in different matrices, including pharmaceuticals in whole blood,44 therapeutic drugs in biological tissues,45 acylcarnitines in blood and urine,46,47 food additives and contaminants,48,49 protein complexes in blood,50 corrosion inhibitors in oil,51 coffee origin discrimination,52 discriminant analysis of teas,53 differentiation of bacteria,54 and analysis of inorganic ions.55 Recently, PS-MS was explored as a platform to conduct organic reactions allowing rate acceleration and prompt characterization of products.56 In forensic sciences, PS-MS has been investigated in the direct analysis of drugs of abuse in blood spots57,58 and raw urine,59 and cocaine residues in various material surfaces.60 Herein we take advantage of PS-MS, with its appealing features, to verify whether this technique can be employed to furnish typical proles aiming at distinguishing among several inks of assorted ballpoint pens. Furthermore, the viability of using PS-MS to track changes in the composition of ink entries subjected to light exposure is also assessed. Finally, analyses of naturally aged archived documents are also conducted aiming at verifying whether overlapped ink lines that simulate counterfeit documents would be detected by PS-MS.
Experimental Materials and instrumentation HPLC grade methanol was purchased from J.T. Baker Chemicals (Center Valley, PA, USA). Ultrapure water puried with a Milli-Q system (Millipore, Milford, MA) was used in all studies. Nine brands/models of blue ballpoint pens (Compactor 07, Compactor Economic, Faber Castel, Paper Mate, Pentel Star V, Pilot, Cis Silver Stick, Bic, and Bic Diamante) were purchased at local stores. Three no brand blue ballpoint pens (from three different origins) were also evaluated and were a courtesy of companies and conferences. All PS-MS experiments were carried out using a Thermo LCQ Fleet mass spectrometer (Thermo Scientic, San Jose, CA, USA) operating in the positive ion mode. Instrumental conditions were as follows: paper spray voltage, 4.5 kV; capillary temperature, 275 C; capillary voltage, 35 V; tube lens voltage, 65 V. Full scan mass spectra were acquired over a 100–1000 m/z range. Paper spray For the PS-MS experiments, ordinary white office paper was cut into small pieces with triangular shape (10 mm height and 5
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mm base width). Each one of the ballpoint pens was used to draw straight lines on the paper triangles, which were positioned 10 mm away from the MS inlet using a copper clip xed on a three-dimensional moving stage. An optimized high voltage (4.5 kV) was applied to the paper through the copper clip. Subsequently, 7 mL of the spray solvent (9 : 1 v/v of methanol–water) was added to the paper triangle to generate the MS. For the accelerated degradation studies, ink lines drawn on paper triangles were exposed to a 23 W uorescent lamp for 72 h. For the experiments involving the analysis of naturally aged inks from archived documents and detection of superimposition of ink lines, the portions of paper containing the assayed ink lines were cut into triangles using a paper punch.
Results and discussion Ink analysis PS(+)-MS were obtained for different ballpoint pen inks aiming at distinguishing among these types of samples. The choice for the positive ion mode was based on the basic and cationic characteristics of most dyes and additives commonly present in blue ballpoint pen inks. Positive ion mode was successfully utilized in previous studies of mass spectrometry analysis of these inks with different ambient ion sources such as EASI,1 DESI,23 and DART.24 The following PS parameters were optimized to generate MS with a minimal background noise level and signals with an adequate stability/intensity: solvent system (9 : 1 v/v of methanol–water); high voltage applied at the base of the triangular paper (4.5 kV); distance between the tip of the triangular paper and the MS inlet (10 mm); and the solvent volume (7 mL). A qualitative comparison among the PS(+)-MS of all samples allowed the classication of the pens into four distinct groups (1 to 4). The pens within each group are characterized to possess identical composition of dyes and additives, as indicated in Table 1. The following groups (and the pen brands in each one) were therefore delineated: group 1 (pen A),
Table 1 Dyes and additives distinguished in inks of several ballpoint pens detected upon PS(+)-MS analysis
Componentsb Pen
Group
Descriptiona
AG
BV3
BB26
A B C D E F G H I J K L
1 2 3 4 4 4 4 4 4 4 4 3
Pentel Star V Pilot Bic No brand 1 No brand 2 Compactor 07 Compactor Economic No brand 3 Faber Castel Paper Mate Cis Silver Stick Bic Diamante
a
BB7
NP
b
Three samples of each pen brand were analyzed. AG, Aryl Guanidines (m/z 212, 268); BV3, Basic Violet 3 (m/z 372); BB26, Basic Blue 26 (m/z 470); BB7, Basic Blue 7 (m/z 478); NP, Nickel Phthalocyanine (m/z 571).
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Representative PS(+)-MS of blue ballpoint pens (A–D) that belong to distinct groups (1–4): A (group 1), B (group 2), C (group 3), and D (group 4). These groups are constituted by pens that possess characteristic combinations of dyes in their composition.
Fig. 1
group 2 (pen B), group 3 (pens C and L) and group 4 (pens D to K). PS(+)-MS recorded for a typical sample of each group is displayed in Fig. 1 (the structures of dyes and additives are shown in Fig. 2). As observed, all analyzed inks contained Basic Violet 3 (m/z 372) and its demethylated homologues (m/z 358 and m/z 344). Other three constituent dyes frequently used in
Fig. 2
the composition of blue ballpoint pen inks were also detected: Basic Blue 26 (m/z 470), Basic Blue 7 (m/z 478), and nickel phthalocyanine (m/z 571). The ions of m/z 268 and 212 were ascribed to 1,3-dimethyl-1,3-ditolylguanidine and diphenylguanidine, respectively. These aryl guanidines are additives
Chemical structures of the dyes and aryl guanidines detected by PS(+)-MS in the inks of the blue ballpoint pens studied in this work.
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commonly used to form salts with acid dyes or to raise the ink pH.8 As observed in Table 1 and Fig. 1, a simple visual inspection on the PS(+)-MS (presence/absence of dyes and guanidines) only allows a prompt distinction of pens allocated into different groups. That is not the case, for instance, for pens D to K that belong to group 4. The exclusive presence of BV3 and BB26 dyes in the inks precludes their discrimination on the basis of a simple qualitative evaluation. Thus, the concept of relative ion intensity (RII) was utilized for further discrimination of these pens. In MS, RII describes the proportion of a given ion in regard to correlated compounds. Thus, this parameter has been used to characterize the extension of demethylation of the
Fig. 3
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amine groups present in BV3 and BB26.11,25,27 It is dened as RIIi ¼ Ii/Itot, where Ii is the intensity of the ion i and Itot is the sum of the intensities of all related ions. Therefore, the RII values for BV3 (m/z 372) and BB26 (m/z 470) were calculated as RII372 ¼ I372/(I372 + I358 + I344) and RII470 ¼ I470/(I470 + I456), respectively. One sample of each pen brand (D to K) was selected and analyzed in triplicate (n ¼ 3) and the values of RII372 and RII470 were calculated. Fig. 3 shows the PS(+)-MS recorded for pens D to K and the respective values of RII372 and RII470. Relative standard deviations (RSDs) were below 4.0% and 2.0% for RII372 and RII470, respectively. As observed, RII372 values allow discrimination of pens D and E (RII372) of 0.54 and 0.44, respectively) from pens F and G (RII372 of 0.75 and 0.73,
PS(+)-MS recorded for pens D to K belonging to group 4 (Table 1) and the respective values of RII372 and RII470.
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respectively) and pens H, I, J, and K (RII372 of 0.65, 0.65, 0.68, and 0.64, respectively). On the other hand, pens F and G can be differentiated by the RII470 values (0.90 for F and 0.73 for G). Moreover, the proportion of dyes BV3 and BB26 in these pens, reected by the relative intensities between the mass signals of m/z 372 and 470, is clearly different. In sequence, pens H and J can be differentiated from pens I and K by the RII470 values (0.94 and 0.91 for H and J, respectively, against 0.76 for both I and K). Finally, the relative intensities between the ions of m/z 372 and 470 can be used to discriminate among pens H from J and I from K. Fading and degradation patterns of dyes Following the screening and differentiation studies between fresh blue ballpoint pen inks, PS-MS was tested on the analysis of inks exposed to light for 72 h. This study was carried out in order to verify the effectiveness of PS-MS to assess the degradation patterns of the ink components. Fig. 4 shows the PS(+)MS of inks of pens A, B, C, and F aer 72 h of light exposure. When compared with the fresh inks (see Fig. 1), it clearly appears that the chemical proles have changed aer light exposure. For all pen inks, the intensity of ions of m/z 358 and m/z 344 increased relative to their methylated precursor Basic Violet 3 (m/z 372). The ions of m/z 330 and 344, detected in the light-exposed inks of pens A, C, and F, were assigned to further degradation products resulting from the demethylation of ion m/z 372. A similar degradation behavior was observed for Basic Blue 26 (m/z 470) detected in pens A and F. Its decomposition is a result of the replacement of methyl groups by hydrogen atoms at the amine functions to yield the ions of m/z 456 and 442. Note that the ion of m/z 456 increased relative to its precursor Basic Violet 3 (m/z 470). The degradation prole of Basic Blue
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7 (m/z 478) present in pen B was characterized by a sequential substitution of ethyl groups by hydrogen at its amine functions yielding MS signals of m/z 450 and 422 (Fig. 4, pen B). Similar degradation proles were observed by others using mass spectrometry with different ionization modes.1,8,25–27 For the aryl guanidines noticed in pens A and C (m/z 212 and 268, respectively) and the dye nickel phthalocyanine (m/z 571) detected in pen C, no evident degradation products could be observed. Detection of forgeries in old documents: case examples The suitability of PS-MS for analysis of old inks and detection of superimposition ink lines was tested. For this, archived documents were analyzed in their original form and aer being altered (“counterfeited”) using some of the pens studied in this work. Fig. 5 shows the analysis of a document from 2009 that was dated and signed by the human resource secretary of our department. First, some entries of the original version (Fig. 5A) were modied or overlapped by pens with known composition yielding the altered version (Fig. 5B). Then, the portions marked in red in Fig. 5B were cut into triangles and analyzed by PS-MS. Fig. 5a shows the PS(+)-MS obtained for the original ink. The ink composition was similar to that observed for pens of group 3 (pens C and L), with the presence of 1,3-dimethyl-1,3-ditolylguanidine (m/z 268), Basic Violet 3 (m/z 372), and nickel phthalocyanine (m/z 571) (see Fig. 1C and Table 1). Note that the intensities of MS signals of m/z 268 and 571 are increased relative to m/z 372, when compared with the fresh ink of pen C. This is probably due to a more accentuated process of degradation experienced by Basic Violet 3, when compared with the aryl guanidine and nickel phthalocyanine. Fig. 5b displays the PS(+)-MS of region (b) of the document (number 0 of the month date) aer being overlaid with pen C and subjected to light
Fig. 4 PS(+)-MS of inks of pens A, B, C, and F after 72 h of light exposure to simulate ageing.
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Fig. 5 Optical images of an original document (A) and its forged version (B) modified by inserting writings using pens of known composition (portions marked in red). The PS(+)-MS were recorded for the original (a) and adulterated (b–d) regions of the document. The insets in each MS are the optical images of the paper triangles taken from the document after PS-MS analysis.
exposure for 72 h. The insertion of the “counterfeiting” ink to the original writing can be readily detected by comparing the MS proles (Fig. 5a versus b). Note that two main differences can be observed: (i) the intensity of MS signals of m/z 372, 358, and 344 increased relative to those of m/z 268 and 571, and (ii) the proportion of dye Basic Violet 3 (m/z 372) in regard to its degradation products (m/z 358 and 344) changed (RII372 of 0.58 and 0.62 for Fig. 5a and b, respectively). Fig. 5c shows the PS(+)MS of region (c) of the document (number 7 from the month date) aer being overlaid with pen I and exposed to light for 72 h. As observed, the alteration in the document is easily identied by the presence of Basic Blue 26 (m/z 470) and its demethylated homologues (m/z 456, 442, and 428), which were not detected in the original document and are characteristics of pen I ink composition. Moreover, the intensity of the MS signal of m/z 372 increased relative to those of m/z 268 and 571. Owing to the light exposure, note that Basic Violet 3 (m/z 372) and Basic Blue 26 (m/z 470) displayed the characteristic serial cascade of demethylated degradation products. On the other hand, the same pen I was utilized to convert number 9 from the original document to number 8 in the “counterfeited” document (region d of the “counterfeited” document), with no light exposure.
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Again, as can be observed in the PS(+)-MS of Fig. 5d, the falsication can be detected by the presence of Basic Blue 26 (m/z 470) and its demethylated homologue of m/z 456. Nevertheless, owing to the absence of light exposure, the cascades of demethylation displayed by Basic Violet 3 (m/z 372) and Basic Blue 26 (m/z 470) were not signicant as in the MS of Fig. 5c. The insets of MS in Fig. 5(a)–(d) present the optical images of the paper triangles cut from the document aer being analyzed by PS-MS. As observed, although the document must be perforated in order to perform the analysis, the PS-MS technique causes a minimal destruction to the ink writings. Thus, the ink le in the paper triangles may be saved and used for further analysis, even using other analytical techniques, which is very important in forensic investigations. Another case example of ink analysis on an archived document and detection of overlapping ink lines using PS-MS is shown in Fig. 6. The document is a hotel receipt originally dated and signed in 2005. Again, several modications were made in the original document yielding the “counterfeited” version shown in Fig. 6. The red triangles designed on the scanned document represent the portions analyzed by PS-MS, which yielded the MS from (a) to (e). Fig. 6a shows the MS of the
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PS(+)-MS for the original (a) and adulterated (b–e) regions of hotel receipt dated from 2005. The insets in each MS are the optical images of the paper triangles taken from the document after PS-MS analysis.
Fig. 6
original ink without any insertion. As observed, the original entries were made using a pen with a similar composition to those of pens D–K, i.e., the presence of dyes Basic Violet 3 (m/z 372) and Basic Blue 26 (m/z 470) (Table 1, Fig. 1D and 3). Note that when compared with the analogous inks subjected to the light exposure experiments (Fig. 3, pens D–K), a higher number of degradation products with more intense MS signals were observed for the naturally aged ink (Fig. 6a). Actually the MS signal of m/z 358 ascribed for the BV3 demethylated homologue is even higher than the MS signal of its precursor BV3. These ndings indicate therefore that even when the document is stored in the absence of light, the degradation processes of BV3 (m/z 372) and BB26 (m/z 470) are signicant and useful for discriminating the ink entries. Fig. 6(b)–(e) show the PS(+)-MS of the document writings where the following insertions/modications were made: (b) number 3 from the original document was converted to 8 using pen J, (c) number 5 from the original document was converted to 6 using pen F, (d) number 3 from the original document was converted to 8 using
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pen I, and (e) number 5 from the original document was converted to 6 using pen C. Note that the writing insertions represented by b, c, and d were made with pens having identical ink compositions: dyes BV3 (m/z 372) and BB26 (m/z 470) (Table 1). In all cases, RII372 and RII470 clearly increased in comparison to those values obtained for the original ink. The forgery displayed in Fig. 6e can be easily veried as the ion of m/z 372 (dye BV3) and its demethylation products (m/z 358, 344, 330), typical of pen C ink, became predominant in the PS(+)-MS. Moreover, the ion of m/z 268 ascribed for 1,3-dimethyl-1,3ditolylguanidine and diagnostic for pen C clearly emerges in the PS(+)-MS of the forged portion of the document. A further example of application of PS-MS to detect forgeries in writing documents is displayed in the ESI (Fig. S1†). The PS(+)-MS of the original ink (Fig. S1a†) from a document dated from 2009 is clearly distinguishable in relation to other regions of the document where several inserts were made with other pens, as clearly visualized in the PS(+)-MS displayed in Fig. S1b– d.† Finally, it is important to emphasize that although optical
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methods can also be employed to discriminate among entries from distinct pens, the results displayed herein demonstrate that PS-MS can furnish a complementary but crucial piece of data that can assist one to take a balanced decision.
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Conclusions In this paper, the ability of PS-MS to distinguish among several blue ballpoint pen brands by assessing the dye and additive composition of each ink was demonstrated. This was done by an ample visual inspection of the PS(+)-MS or by comparing the relative intensities of the major components. This approach was also useful to assess the fading of writing ink entries by evaluating the changes in the chemical proles as reected in the increasing presence of degradation products as a function of time. PS-MS was also successfully utilized to typify forged documents by the comparison of the original and overlapped ink lines. A minimal sample preparation is required. Most importantly, once the PS-MS analysis causes no total destruction of a given sample, it can be stored and analyzed several times upon request using the proposed method or even other approaches that require sample extraction, such as chromatography and capillary electrophoresis. As previously stated, other ambient ionization MS methods allow characterization of ink entries with less sample destruction and better chances to continue the analytical sequence by using other methods. On the other hand, PS-MS does not require any special assembly to implementation, being therefore very simple in terms of instrumentation/operation and can be coupled to any mass spectrometer (including the miniature ones). Finally, it has been demonstrated that PS-MS is a fast, reliable and inexpensive approach with remarkable application potential in other unexplored forensic issues.
Acknowledgements D.F.A.S. acknowledges a fellowship from CNPq. Grants from FAPEMIG (Proc. APQ-02162-12) and CNPq (Proc. 479574/2012-0) are gratefully acknowledged.
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Forensic analysis of ballpoint pen inks using paper spray mass spectrometry† Priscila da Silva Ferreira, De´bora Fernandes de Abreu e Silva, Rodinei Augusti and Evandro Piccin* A novel analytical approach based on paper spray mass spectrometry (PS-MS) is developed for a fast and effective forensic analysis of inks in documents. Ink writings made in ordinary paper with blue ballpoint pens were directly analyzed under ambient conditions without any prior sample preparation. Firstly, the method was explored on a set of distinct pens and the results obtained in the positive ion mode, PS(+)MS, demonstrated that pens from different brands provide typical profiles. Simple visual inspection of the PS(+)-MS led to the distinction of four different combinations of dyes and additives in the inks. Further discrimination was performed by using the concept of relative ion intensity (RII), owing to the large variability of dyes BV3 and BB26 regarding their demethylated homologues. Following screening and differentiation studies, the composition changes of ink entries subjected to light exposure were also monitored by PS-MS. The results of these tests revealed distinct degradation behaviors which were
Received 1st September 2014 Accepted 9th November 2014
reflected on the typical chemical profiles of the studied inks, attesting that PS-MS may be also useful to verify the fading of dyes thus allowing the discrimination of entries on a document. As proof of concept
DOI: 10.1039/c4an01617c
experiments, PS-MS was successfully utilized for the analysis of archived documents and
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characterization of overlapped ink lines made on simulated forged documents.
Introduction The investigation of questionable documents is an important research topic in forensic science. Along with handwriting examination and physical analysis (e.g. microscopic examination under different light sources), chemical screening of writing inks is used to identify possible insertions to original writings, such as modications of dates, values, or signatures. Chemical analysis can also be used to establish whether entries on a document were made with a single pen or at the same time. Ballpoint pens are the most common writing instruments used in the majority of insertions, especially for dating and signing documents.1–5 Many methods have been reported for performing chemical analysis and degradation studies of writing inks. Methods that involve UV-vis spectrometry,6,7 direct infusion electrospray ionization mass spectrometry (ESI-MS),8 and separation techniques, such as thin layer chromatography (TLC),9–11 high performance liquid chromatography (HPLC),12–15 capillary electrophoresis (CE),16,17 and gas chromatography-mass spectrometry,18 commonly require prior sample extraction using organic solvents, which is a laborious and time-consuming Departamento de Qu´ımica, Instituto de Ciˆencias Exatas, Universidade Federal de Minas Gerais, Belo Horizonte 31270-901, Brazil. E-mail: [email protected]; Tel: +55 31 3409 6389 † Electronic supplementary information (ESI) available: Further examples of applications of PS-MS to detect forgeries in documents. See DOI: 10.1039/c4an01617c
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procedure. Moreover, the ink extraction procedure leads to the sample destruction, which is undesirable in forensic science where the preservation of proofs is an important issue. Recently, Williams and collaborators19 proposed a method for ink analysis based on ESI-MS where the samples were prepared from ink-coated paper bers pulled from the paper using a forceps. Although the method allowed minimal sample destruction, the multiple step procedure (pulling paper bers and solvent extraction) is undesirably too laborious. Raman spectroscopy20–22 and ambient ionization mass spectrometry1–3,23–31 techniques are more appropriate for forensic analysis on document inks since they guarantee minimal sample destruction. In particular, the main advantage of ambient ionization MS techniques is the possibility for direct analysis of samples in their native form and in the open environment without prior preparation. Thus, this family of techniques, in which the analyte desorption accompanies the ionization step, provide the preservation of spatial chemistry information of the sample, maximize the sensitivity, and afford high throughput analysis.28–33 The characteristics of ambient ionization together with the sensitivity and resolution power of MS make them very attractive for the eld of forensic sciences, where the results must ensure the specicity of analysis and the sample traceability and integrity are important issues.34,35 Paper spray (PS) was rst proposed by Wang et al.36 in 2009 as a new ambient ionization technique for fast, qualitative, and quantitative analysis of complex mixtures by MS. In this recently
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developed technique, the analyte ions are generated by applying a high voltage and a small volume (10 mL) of spray solvent onto a triangular shape paper (usually 10 mm in height and 5 mm of base) positioned at the MS inlet. The sample may be preloaded onto the paper or mixed in the spray solution.36,37 In PS, pneumatic assistance is not required to transport the analyte. Thus, its instrumentation/operation is simpler and more compatible with miniature mass spectrometers, when compared to other ambient ionization techniques, such as, for example, desorption electrospray ionization (DESI),3,23,31 direct analysis in real time (DART),38,39 extractive electrospray ionization (EESI),40,41 and easy ambient sonic ionization (EASI).42,43 PS-MS has been used for the analysis of several compounds in different matrices, including pharmaceuticals in whole blood,44 therapeutic drugs in biological tissues,45 acylcarnitines in blood and urine,46,47 food additives and contaminants,48,49 protein complexes in blood,50 corrosion inhibitors in oil,51 coffee origin discrimination,52 discriminant analysis of teas,53 differentiation of bacteria,54 and analysis of inorganic ions.55 Recently, PS-MS was explored as a platform to conduct organic reactions allowing rate acceleration and prompt characterization of products.56 In forensic sciences, PS-MS has been investigated in the direct analysis of drugs of abuse in blood spots57,58 and raw urine,59 and cocaine residues in various material surfaces.60 Herein we take advantage of PS-MS, with its appealing features, to verify whether this technique can be employed to furnish typical proles aiming at distinguishing among several inks of assorted ballpoint pens. Furthermore, the viability of using PS-MS to track changes in the composition of ink entries subjected to light exposure is also assessed. Finally, analyses of naturally aged archived documents are also conducted aiming at verifying whether overlapped ink lines that simulate counterfeit documents would be detected by PS-MS.
Experimental Materials and instrumentation HPLC grade methanol was purchased from J.T. Baker Chemicals (Center Valley, PA, USA). Ultrapure water puried with a Milli-Q system (Millipore, Milford, MA) was used in all studies. Nine brands/models of blue ballpoint pens (Compactor 07, Compactor Economic, Faber Castel, Paper Mate, Pentel Star V, Pilot, Cis Silver Stick, Bic, and Bic Diamante) were purchased at local stores. Three no brand blue ballpoint pens (from three different origins) were also evaluated and were a courtesy of companies and conferences. All PS-MS experiments were carried out using a Thermo LCQ Fleet mass spectrometer (Thermo Scientic, San Jose, CA, USA) operating in the positive ion mode. Instrumental conditions were as follows: paper spray voltage, 4.5 kV; capillary temperature, 275 C; capillary voltage, 35 V; tube lens voltage, 65 V. Full scan mass spectra were acquired over a 100–1000 m/z range. Paper spray For the PS-MS experiments, ordinary white office paper was cut into small pieces with triangular shape (10 mm height and 5
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mm base width). Each one of the ballpoint pens was used to draw straight lines on the paper triangles, which were positioned 10 mm away from the MS inlet using a copper clip xed on a three-dimensional moving stage. An optimized high voltage (4.5 kV) was applied to the paper through the copper clip. Subsequently, 7 mL of the spray solvent (9 : 1 v/v of methanol–water) was added to the paper triangle to generate the MS. For the accelerated degradation studies, ink lines drawn on paper triangles were exposed to a 23 W uorescent lamp for 72 h. For the experiments involving the analysis of naturally aged inks from archived documents and detection of superimposition of ink lines, the portions of paper containing the assayed ink lines were cut into triangles using a paper punch.
Results and discussion Ink analysis PS(+)-MS were obtained for different ballpoint pen inks aiming at distinguishing among these types of samples. The choice for the positive ion mode was based on the basic and cationic characteristics of most dyes and additives commonly present in blue ballpoint pen inks. Positive ion mode was successfully utilized in previous studies of mass spectrometry analysis of these inks with different ambient ion sources such as EASI,1 DESI,23 and DART.24 The following PS parameters were optimized to generate MS with a minimal background noise level and signals with an adequate stability/intensity: solvent system (9 : 1 v/v of methanol–water); high voltage applied at the base of the triangular paper (4.5 kV); distance between the tip of the triangular paper and the MS inlet (10 mm); and the solvent volume (7 mL). A qualitative comparison among the PS(+)-MS of all samples allowed the classication of the pens into four distinct groups (1 to 4). The pens within each group are characterized to possess identical composition of dyes and additives, as indicated in Table 1. The following groups (and the pen brands in each one) were therefore delineated: group 1 (pen A),
Table 1 Dyes and additives distinguished in inks of several ballpoint pens detected upon PS(+)-MS analysis
Componentsb Pen
Group
Descriptiona
AG
BV3
BB26
A B C D E F G H I J K L
1 2 3 4 4 4 4 4 4 4 4 3
Pentel Star V Pilot Bic No brand 1 No brand 2 Compactor 07 Compactor Economic No brand 3 Faber Castel Paper Mate Cis Silver Stick Bic Diamante
a
BB7
NP
b
Three samples of each pen brand were analyzed. AG, Aryl Guanidines (m/z 212, 268); BV3, Basic Violet 3 (m/z 372); BB26, Basic Blue 26 (m/z 470); BB7, Basic Blue 7 (m/z 478); NP, Nickel Phthalocyanine (m/z 571).
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Representative PS(+)-MS of blue ballpoint pens (A–D) that belong to distinct groups (1–4): A (group 1), B (group 2), C (group 3), and D (group 4). These groups are constituted by pens that possess characteristic combinations of dyes in their composition.
Fig. 1
group 2 (pen B), group 3 (pens C and L) and group 4 (pens D to K). PS(+)-MS recorded for a typical sample of each group is displayed in Fig. 1 (the structures of dyes and additives are shown in Fig. 2). As observed, all analyzed inks contained Basic Violet 3 (m/z 372) and its demethylated homologues (m/z 358 and m/z 344). Other three constituent dyes frequently used in
Fig. 2
the composition of blue ballpoint pen inks were also detected: Basic Blue 26 (m/z 470), Basic Blue 7 (m/z 478), and nickel phthalocyanine (m/z 571). The ions of m/z 268 and 212 were ascribed to 1,3-dimethyl-1,3-ditolylguanidine and diphenylguanidine, respectively. These aryl guanidines are additives
Chemical structures of the dyes and aryl guanidines detected by PS(+)-MS in the inks of the blue ballpoint pens studied in this work.
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commonly used to form salts with acid dyes or to raise the ink pH.8 As observed in Table 1 and Fig. 1, a simple visual inspection on the PS(+)-MS (presence/absence of dyes and guanidines) only allows a prompt distinction of pens allocated into different groups. That is not the case, for instance, for pens D to K that belong to group 4. The exclusive presence of BV3 and BB26 dyes in the inks precludes their discrimination on the basis of a simple qualitative evaluation. Thus, the concept of relative ion intensity (RII) was utilized for further discrimination of these pens. In MS, RII describes the proportion of a given ion in regard to correlated compounds. Thus, this parameter has been used to characterize the extension of demethylation of the
Fig. 3
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amine groups present in BV3 and BB26.11,25,27 It is dened as RIIi ¼ Ii/Itot, where Ii is the intensity of the ion i and Itot is the sum of the intensities of all related ions. Therefore, the RII values for BV3 (m/z 372) and BB26 (m/z 470) were calculated as RII372 ¼ I372/(I372 + I358 + I344) and RII470 ¼ I470/(I470 + I456), respectively. One sample of each pen brand (D to K) was selected and analyzed in triplicate (n ¼ 3) and the values of RII372 and RII470 were calculated. Fig. 3 shows the PS(+)-MS recorded for pens D to K and the respective values of RII372 and RII470. Relative standard deviations (RSDs) were below 4.0% and 2.0% for RII372 and RII470, respectively. As observed, RII372 values allow discrimination of pens D and E (RII372) of 0.54 and 0.44, respectively) from pens F and G (RII372 of 0.75 and 0.73,
PS(+)-MS recorded for pens D to K belonging to group 4 (Table 1) and the respective values of RII372 and RII470.
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respectively) and pens H, I, J, and K (RII372 of 0.65, 0.65, 0.68, and 0.64, respectively). On the other hand, pens F and G can be differentiated by the RII470 values (0.90 for F and 0.73 for G). Moreover, the proportion of dyes BV3 and BB26 in these pens, reected by the relative intensities between the mass signals of m/z 372 and 470, is clearly different. In sequence, pens H and J can be differentiated from pens I and K by the RII470 values (0.94 and 0.91 for H and J, respectively, against 0.76 for both I and K). Finally, the relative intensities between the ions of m/z 372 and 470 can be used to discriminate among pens H from J and I from K. Fading and degradation patterns of dyes Following the screening and differentiation studies between fresh blue ballpoint pen inks, PS-MS was tested on the analysis of inks exposed to light for 72 h. This study was carried out in order to verify the effectiveness of PS-MS to assess the degradation patterns of the ink components. Fig. 4 shows the PS(+)MS of inks of pens A, B, C, and F aer 72 h of light exposure. When compared with the fresh inks (see Fig. 1), it clearly appears that the chemical proles have changed aer light exposure. For all pen inks, the intensity of ions of m/z 358 and m/z 344 increased relative to their methylated precursor Basic Violet 3 (m/z 372). The ions of m/z 330 and 344, detected in the light-exposed inks of pens A, C, and F, were assigned to further degradation products resulting from the demethylation of ion m/z 372. A similar degradation behavior was observed for Basic Blue 26 (m/z 470) detected in pens A and F. Its decomposition is a result of the replacement of methyl groups by hydrogen atoms at the amine functions to yield the ions of m/z 456 and 442. Note that the ion of m/z 456 increased relative to its precursor Basic Violet 3 (m/z 470). The degradation prole of Basic Blue
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7 (m/z 478) present in pen B was characterized by a sequential substitution of ethyl groups by hydrogen at its amine functions yielding MS signals of m/z 450 and 422 (Fig. 4, pen B). Similar degradation proles were observed by others using mass spectrometry with different ionization modes.1,8,25–27 For the aryl guanidines noticed in pens A and C (m/z 212 and 268, respectively) and the dye nickel phthalocyanine (m/z 571) detected in pen C, no evident degradation products could be observed. Detection of forgeries in old documents: case examples The suitability of PS-MS for analysis of old inks and detection of superimposition ink lines was tested. For this, archived documents were analyzed in their original form and aer being altered (“counterfeited”) using some of the pens studied in this work. Fig. 5 shows the analysis of a document from 2009 that was dated and signed by the human resource secretary of our department. First, some entries of the original version (Fig. 5A) were modied or overlapped by pens with known composition yielding the altered version (Fig. 5B). Then, the portions marked in red in Fig. 5B were cut into triangles and analyzed by PS-MS. Fig. 5a shows the PS(+)-MS obtained for the original ink. The ink composition was similar to that observed for pens of group 3 (pens C and L), with the presence of 1,3-dimethyl-1,3-ditolylguanidine (m/z 268), Basic Violet 3 (m/z 372), and nickel phthalocyanine (m/z 571) (see Fig. 1C and Table 1). Note that the intensities of MS signals of m/z 268 and 571 are increased relative to m/z 372, when compared with the fresh ink of pen C. This is probably due to a more accentuated process of degradation experienced by Basic Violet 3, when compared with the aryl guanidine and nickel phthalocyanine. Fig. 5b displays the PS(+)-MS of region (b) of the document (number 0 of the month date) aer being overlaid with pen C and subjected to light
Fig. 4 PS(+)-MS of inks of pens A, B, C, and F after 72 h of light exposure to simulate ageing.
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Fig. 5 Optical images of an original document (A) and its forged version (B) modified by inserting writings using pens of known composition (portions marked in red). The PS(+)-MS were recorded for the original (a) and adulterated (b–d) regions of the document. The insets in each MS are the optical images of the paper triangles taken from the document after PS-MS analysis.
exposure for 72 h. The insertion of the “counterfeiting” ink to the original writing can be readily detected by comparing the MS proles (Fig. 5a versus b). Note that two main differences can be observed: (i) the intensity of MS signals of m/z 372, 358, and 344 increased relative to those of m/z 268 and 571, and (ii) the proportion of dye Basic Violet 3 (m/z 372) in regard to its degradation products (m/z 358 and 344) changed (RII372 of 0.58 and 0.62 for Fig. 5a and b, respectively). Fig. 5c shows the PS(+)MS of region (c) of the document (number 7 from the month date) aer being overlaid with pen I and exposed to light for 72 h. As observed, the alteration in the document is easily identied by the presence of Basic Blue 26 (m/z 470) and its demethylated homologues (m/z 456, 442, and 428), which were not detected in the original document and are characteristics of pen I ink composition. Moreover, the intensity of the MS signal of m/z 372 increased relative to those of m/z 268 and 571. Owing to the light exposure, note that Basic Violet 3 (m/z 372) and Basic Blue 26 (m/z 470) displayed the characteristic serial cascade of demethylated degradation products. On the other hand, the same pen I was utilized to convert number 9 from the original document to number 8 in the “counterfeited” document (region d of the “counterfeited” document), with no light exposure.
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Again, as can be observed in the PS(+)-MS of Fig. 5d, the falsication can be detected by the presence of Basic Blue 26 (m/z 470) and its demethylated homologue of m/z 456. Nevertheless, owing to the absence of light exposure, the cascades of demethylation displayed by Basic Violet 3 (m/z 372) and Basic Blue 26 (m/z 470) were not signicant as in the MS of Fig. 5c. The insets of MS in Fig. 5(a)–(d) present the optical images of the paper triangles cut from the document aer being analyzed by PS-MS. As observed, although the document must be perforated in order to perform the analysis, the PS-MS technique causes a minimal destruction to the ink writings. Thus, the ink le in the paper triangles may be saved and used for further analysis, even using other analytical techniques, which is very important in forensic investigations. Another case example of ink analysis on an archived document and detection of overlapping ink lines using PS-MS is shown in Fig. 6. The document is a hotel receipt originally dated and signed in 2005. Again, several modications were made in the original document yielding the “counterfeited” version shown in Fig. 6. The red triangles designed on the scanned document represent the portions analyzed by PS-MS, which yielded the MS from (a) to (e). Fig. 6a shows the MS of the
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PS(+)-MS for the original (a) and adulterated (b–e) regions of hotel receipt dated from 2005. The insets in each MS are the optical images of the paper triangles taken from the document after PS-MS analysis.
Fig. 6
original ink without any insertion. As observed, the original entries were made using a pen with a similar composition to those of pens D–K, i.e., the presence of dyes Basic Violet 3 (m/z 372) and Basic Blue 26 (m/z 470) (Table 1, Fig. 1D and 3). Note that when compared with the analogous inks subjected to the light exposure experiments (Fig. 3, pens D–K), a higher number of degradation products with more intense MS signals were observed for the naturally aged ink (Fig. 6a). Actually the MS signal of m/z 358 ascribed for the BV3 demethylated homologue is even higher than the MS signal of its precursor BV3. These ndings indicate therefore that even when the document is stored in the absence of light, the degradation processes of BV3 (m/z 372) and BB26 (m/z 470) are signicant and useful for discriminating the ink entries. Fig. 6(b)–(e) show the PS(+)-MS of the document writings where the following insertions/modications were made: (b) number 3 from the original document was converted to 8 using pen J, (c) number 5 from the original document was converted to 6 using pen F, (d) number 3 from the original document was converted to 8 using
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pen I, and (e) number 5 from the original document was converted to 6 using pen C. Note that the writing insertions represented by b, c, and d were made with pens having identical ink compositions: dyes BV3 (m/z 372) and BB26 (m/z 470) (Table 1). In all cases, RII372 and RII470 clearly increased in comparison to those values obtained for the original ink. The forgery displayed in Fig. 6e can be easily veried as the ion of m/z 372 (dye BV3) and its demethylation products (m/z 358, 344, 330), typical of pen C ink, became predominant in the PS(+)-MS. Moreover, the ion of m/z 268 ascribed for 1,3-dimethyl-1,3ditolylguanidine and diagnostic for pen C clearly emerges in the PS(+)-MS of the forged portion of the document. A further example of application of PS-MS to detect forgeries in writing documents is displayed in the ESI (Fig. S1†). The PS(+)-MS of the original ink (Fig. S1a†) from a document dated from 2009 is clearly distinguishable in relation to other regions of the document where several inserts were made with other pens, as clearly visualized in the PS(+)-MS displayed in Fig. S1b– d.† Finally, it is important to emphasize that although optical
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methods can also be employed to discriminate among entries from distinct pens, the results displayed herein demonstrate that PS-MS can furnish a complementary but crucial piece of data that can assist one to take a balanced decision.
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Conclusions In this paper, the ability of PS-MS to distinguish among several blue ballpoint pen brands by assessing the dye and additive composition of each ink was demonstrated. This was done by an ample visual inspection of the PS(+)-MS or by comparing the relative intensities of the major components. This approach was also useful to assess the fading of writing ink entries by evaluating the changes in the chemical proles as reected in the increasing presence of degradation products as a function of time. PS-MS was also successfully utilized to typify forged documents by the comparison of the original and overlapped ink lines. A minimal sample preparation is required. Most importantly, once the PS-MS analysis causes no total destruction of a given sample, it can be stored and analyzed several times upon request using the proposed method or even other approaches that require sample extraction, such as chromatography and capillary electrophoresis. As previously stated, other ambient ionization MS methods allow characterization of ink entries with less sample destruction and better chances to continue the analytical sequence by using other methods. On the other hand, PS-MS does not require any special assembly to implementation, being therefore very simple in terms of instrumentation/operation and can be coupled to any mass spectrometer (including the miniature ones). Finally, it has been demonstrated that PS-MS is a fast, reliable and inexpensive approach with remarkable application potential in other unexplored forensic issues.
Acknowledgements D.F.A.S. acknowledges a fellowship from CNPq. Grants from FAPEMIG (Proc. APQ-02162-12) and CNPq (Proc. 479574/2012-0) are gratefully acknowledged.
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