Identification of colorants in pigmented pen inks by laser desorption mass spectrometry

Pigments are rapidly replacing dyes as colorants in pen and printer inks, due to their superior colors and stability. Unfortunately, tools commonly used in questioned document examination for analyzing pen inks, such as TLC, cannot be used for the analysis of insoluble pigments on paper. Laser desorption mass spectrometry is demonstrated here as a tool for analyzing pigment-based pen inks. A pulsed nitrogen laser can be focused onto a pen stroke from a pigmented ink pen on paper, and positive and negative ions representative of the pigment can be generated for subsequent mass spectrometric analysis. Targeted pens for this work were a set of Uni-ball 207 pigmented ink pens containing blue, light blue, orange, green, violet, red, pink, and black inks. Copper phthalocyanine was identified as the pigment used to make both blue inks. A mixture of halogenated copper phthalocyanines were identified in the green ink. Unexpectedly, the pink ink was found to contain a red pigment, Pigment Red 12, treated with a mixture of water-soluble dyes. Each sample yielded ions representative of the pigments present.     

Age determination of ballpoint pen ink by thermal desorption and gas chromatography-mass spectrometry

Two main approaches can be used for determining the age of an ink: indirect dating and direct dating. Indirect dating is based on the chemical analysis of an ink followed by comparison with known samples in a reference collection. The collection should contain information about the inks including the market introduction dates. This approach may allow for an anachronism to be detected. The second concept is based on measuring ink components that change with age. The analysis of solvents in ballpoint inks may be a useful parameter for determining the age of ink on paper. In a previous study, the authors demonstrated that thermal desorption of ink directly from paper, followed by chemical analysis using gas chromatography-mass spectrometry (GC-MS), is a promising procedure for characterizing ink-binder resins and solvents. Preliminary tests showed that monitoring the evaporation of ink solvent from ink on paper is not a suitable method for ink dating. Thermal analysis of ink on paper in two steps revealed that fresh ink releases a relative amount of solvent at a certain low temperature in a defined period of time, which decreases as the ink ages. As a consequence, this relative amount of solvent released at a certain low temperature, and its decrease with time, can be used to estimate ink age. This age-dependent parameter was studied in 85 different inks ranging in age from 1 week to 1.5 years. It was found that some inks showed a significant decrease of this parameter up to an age of several months, and that the aging process can be monitored within this period. For other inks, however, the age-dependent parameter decreases relatively fast, e.g., within a few days, to a constant level, which can be too fast for casework. Based on these results, a general procedure for assessing the age of ballpoint pen inks on paper was developed.     

The detection of multiply charged dyes using matrix-assisted laser desorption/ionization mass spectrometry for the forensic examination of pen ink dyes directly from paper

Abstract:  Laser desorption mass spectrometry (LDMS) is emerging as a technique for questioned document examination. Its use is limited to detecting ink dyes that are neutral or singly charged. Several inks contain dyes that are multiply charged and LDMS cannot be employed for their identification. We have successfully detected >20 polyionic dyes that can be used in the manufacture of inks using matrix-assisted laser desorption/ionization (MALDI) MS, directly from paper, with the matrix, 2-(4-hydroxyphenylazo)benzoic acid (HABA), and the additive, diammonium hydrogen citrate (DAHC). For example, Acid Violet 49, a charged dye containing one positively-charged site and two negatively charged sulfonate groups, cannot be detected by LDMS, but forms intact, singly charged ions in the MALDI MS experiment. The method described is also useful for identifying multiply charged dye mixtures that are used in modern pen inks.     

A statistical methodology for the comparison of blue gel pen inks analyzed by laser desorption/ionization mass spectrometry

A statistical methodology for the objective comparison of LDI-MS mass spectra of blue gel pen inks was evaluated. Thirty-three blue gel pen inks previously studied by RAMAN were analyzed directly on the paper using both positive and negative mode. The obtained mass spectra were first compared using relative areas of selected peaks using the Pearson correlation coefficient and the Euclidean distance. Intra-variability among results from one ink and inter-variability between results from different inks were compared in order to choose a differentiation threshold minimizing the rate of false negative (i.e. avoiding false differentiation of the inks). This yielded a discriminating power of up to 77% for analysis made in the negative mode. The whole mass spectra were then compared using the same methodology, allowing for a better DP in the negative mode of 92% using the Pearson correlation on standardized data. The positive mode results generally yielded a lower differential power (DP) than the negative mode due to a higher intra-variability compared to the inter-variability in the mass spectra of the ink samples.     

Differentiating writing inks using direct analysis in real time mass spectrometry

Writing ink analysis is used in establishing document authenticity and the sources and relative ages of written entries. Most analytical methods require removing samples or visibly altering the document. Nondestructive, in situ analysis of writing inks on paper without visible alteration is possible using mass spectrometry with a new ion source called Direct Analysis in Real Time. Forty-three different black and blue ballpoint, black fluid, and black gel inks were examined. Both dyes and persistent but thermally labile components of the inks contribute to the mass spectra, principally as protonated molecules [M+H](+). Numerous ink components were identified from the spectra. The spectra were placed in a searchable library, which was then challenged with two spectra from each of the 43 inks. The best match for each of the challenge spectra was correct for all but one ink, which matched with a very similar ink by the same manufacturer.     

Ballpoint pen inks: the quantitative analysis of ink solvents on paper by solid-phase microextraction

We wish to describe further developments to a method previously reported on the detection of 2-phenoxyethanol in ink. The solid-phase microextraction (SPME) sampling technique, together with gas chromatography-mass spectrometry (GC-MS), has been used to quantify solvents in writing ink. In conventional approaches, the analysis of ink on documents requires some degree of destructive sampling. The methods commonly used remove ink samples from paper using a scalpel or a paper punch. To avoid document destruction, a sampling cell was constructed that allows solvents to be adsorbed directly onto the SPME fiber from the headspace above the document surface. Analytes (ink volatiles) are then desorbed from the SPME fiber on a gas chromatograph equipped with a mass selective detector (GC-MSD). With this method, it was possible to detect the presence of ink solvents on documents for a period lasting up to c. 2 years.     

Validation of LAB color mode as a nondestructive method to differentiate black ballpoint pen inks

Nondestructive digital processing methods such as lab color mode (available in Adobe Photoshop) are emerging as alternative methods for forensic document examiners to use when attempting to differentiate writing instrument inks. Although these techniques appear to be viable, little data currently exists regarding the known or potential error rates associated with these techniques. Without adequate data, the validity and reliability of these techniques, including lab color, can not be established. In an attempt to begin to address these issues, 44 black ballpoint ink pens were obtained and used to create 990 pen-pair samples for analysis using established lab color mode techniques. No erroneous findings of "different" were reported following the examination of the known pen-pair combinations in which the same pen was used to create the samples (n = 44). Of the remaining 946 samples, 737 pen-pair samples were differentiated using the lab color mode method, while 209 samples were unable to be differentiated and were recorded as either being "similar" (n = 153) or "unsure" (n = 56). Comparison of the lab color mode results with the results obtained through additional testing using traditional infrared reflectance and infrared luminescence test methods showed that lab color differentiated 102 pen-pair samples (11%; 102/946) that were not differentiated using a VSC-4C.     

基体辅助激光解吸电离飞行时间质谱鉴别乌头的研究

目的建立乌头类中药鉴别的基体辅助激光解吸电离飞行时间质谱方法。方法以DHB为基体,优化飞行时间质谱分析条件,对不同种类的乌头类中药进行飞行时间质谱分析,找出乌头类的指纹峰。结果通过比较炮制乌头与生乌头质谱指纹峰的差异,可作出乌头类是否经炮制的判断。结论基体辅助激光解吸电离飞行时间质谱用于乌头类中药的定性鉴别,分析方法灵敏、准确、快速。     

Identification of organic pigments in automotive coatings using laser desorption mass spectrometry

When one looks at an automotive coating, one sees color due to pigments. Modern organic pigments, with high molar absorptivities, may be only minor components of the mixture. Laser desorption mass spectrometry (LDMS) has been shown to be a useful tool for the analysis of colorants such as pen ink dyes. Here, LDMS is used to determine its utility for the identification of pigments, in simple media and in more complex paints. Small paint chips can be introduced into the LDMS instrument, and when an ultraviolet laser is focused on a portion of a chip, ions representative of the pigment(s) are selectively formed. Some pigments such as quinacridones and copper phthalocyanine are very stable and are desorbed and ionized intact. In contrast, benzimidazolones, which contain some single-skeletal bonds, form fragment ions. This method proves to be sensitive and convenient, as no sample preparation is required. The presence of inorganic pigments in addition to modern organic pigments can be determined, and pigments can be directly identified in actual automotive paint chip samples.     

Comparison of natural and artificial aging of ballpoint inks

Abstract:  Solvent evaporation caused by aging from ballpoint inks was measured by gas chromatography/mass spectroscopy (GC/MS). The sample preparation was carried out with two different thermal desorption systems. The results are compared. Thirteen inks were classified with regard to their solvents, polymers, and additives. The variation of the aforementioned compounds caused by aging was monitored for naturally and artificially aged samples. In this paper, the results are compared and discussed with respect to forensic casework.     

Laser desorption/ionization time-of-flight mass spectrometry of triacylglycerols and other components in fingermark samples

The chemical composition of fingermarks could potentially be important for determining investigative leads, placing individuals at the time of a crime, and has applications as biomarkers of disease. Fingermark samples containing triacylglycerols (TAGs) and other components were analyzed using laser desorption/ionization (LDI) time-of-flight mass spectrometry (TOF MS). Only LDI appeared to be useful for this application while conventional matrix-assisted LDI-TOF MS was not. Tandem MS was used to identify/confirm selected TAGs. A limited gender comparison, based on a simple t-distribution and peaks intensities, indicated that two TAGs showed gender specificity at the 95% confidence level and two others at 97.5% confidence. Because gender-related TAGs differences were most often close to the standard deviation of the measurements, the majority of the TAGs showed no gender specificity. Thus, LDI-TOF MS is not a reliable indicator of gender based on fingermark analysis. Cosmetic ingredients present in some samples were identified.     

Analyzing Brazilian vehicle documents for authenticity by easy ambient sonic-spray ionization mass spectrometry

Using desorption/ionization techniques such as easy ambient sonic-spray ionization mass spectrometry (EASI-MS), it is possible to analyze documents of Brazilian vehicles for authenticity, providing a chemical profile directly from the surface of each document. A method for the detection of counterfeit documents is described, and the falsification procedure is elucidated. Forty authentic and counterfeit documents were analyzed by both positive and negative ion modes, EASI(±)-MS. EASI(+)-MS results identified the presence of (bis(2-ethylhexyl)phthalate plasticizer and of dihexadecyldimethylammonium biocide in both types of documents. For EASI(-)-MS results, the 4-octyloxybenzoic acid additive ([M + H](+): m/z 249) is present only in counterfeit documents. It was also found that counterfeit vehicle documents are produced via Laserjet printers. Desorption/ionization techniques, such as EASI-MS, offer therefore, an intelligent way to characterize the counterfeiting method.     

Direct identification of various copper phthalocyanine pigments in automotive paints and paint smears by laser desorption ionization mass spectrometry

Direct identification of copper phthalocyanine (CuPc) and chlorinated CuPcs in paints for discrimination between blue automobile paints by means of laser desorption mass spectrometry (LDMS) in the absence of a matrix is reported. The models consisted of eight commercially available CuPc pigments applied to a piece of plain white coating paper. The relationship between the peak intensity at m/z 575 of the CuPc, the number of pulsed laser shots, and laser power was compared to optimize laser abrasion. LDMS analysis of the model paints demonstrated that all characteristic components of the CuPc pigments in the paint films were in good agreement with those in the powder pigments. Further, the chlorinated CuPcs in the paint films could be distinguished. A quantity of 42 blue paint films, representing the paints used for painting Japanese domestic trucks, was examined by LDMS analysis. Results indicate that the paints can be classified into four categories based on the chlorinated CuPc components of the paints. Therefore, LDMS spectra of CuPc pigments would be useful for the identification of paints in forensic investigations. Herein, we report the successful identification of the CuPcs in a paint smear on the frame of a bicycle damaged in a hit-and-run accident, using the LDMS spectra.     

LC-MS/MS法检测圆珠笔墨迹中碱性蓝7及其去乙基产物的降解变化

目的考察圆珠笔墨迹中碱性蓝7及其去乙基产物的降解变化,为圆珠笔墨迹书写时间的研究提供基础数据。方法用氙灯老化碱性蓝7以生成其5个去乙基产物。建立LC-MS/MS检测碱性蓝7及其去乙基产物的方法。制作圆珠笔墨迹样本,在室内自然光照条件下老化3个月,同时进行控制实验条件的氙灯老化和高温老化实验。结果碱性蓝7的相对含量持续下降,其第一、第二级去乙基产物E4、E3的相对含量相继达到最大值,剩余三个去乙基产物E2、E1和E0的相对含量在三个月内持续增加。结论碱性蓝7的相对含量与光的辐照能量呈指数函数关系,其去乙基产物E4、E3的相对含量与光的辐照能量呈二次函数关系。不同油墨中碱性蓝7的老化曲线不同。温度对碱性蓝7的降解基本没有影响。     

Statistical discrimination of black gel pen inks analysed by laser desorption/ionization mass spectrometry

Pearson correlation coefficients were applied for the objective comparison of 30 black gel pen inks analysed by laser desorption ionization mass spectrometry (LDI-MS). The mass spectra were obtained for ink lines directly on paper using positive and negative ion modes at several laser intensities. This methodology has the advantage of taking into account the reproducibility of the results as well as the variability between spectra of different pens. A differentiation threshold could thus be selected in order to avoid the risk of false differentiation. Combining results from positive and negative mode yielded a discriminating power up to 85%, which was better than the one obtained previously with other optical comparison methodologies. The technique also allowed discriminating between pens from the same brand.     

Characterization and dating of blue ballpoint pen inks using principal component analysis of UV-Vis absorption spectra, IR spectroscopy, and HPTLC

The ink of pens and ink extracted from lines on white photocopier paper of 10 blue ballpoint pens were subjected to ultraviolet-visible (UV-Vis) spectroscopy, infrared (IR), and high-performance thin-layer liquid chromatography (HPTLC). The R(f) values and color tones of the bands separated by thin-layer chromatography (TLC) analysis used to classify the writing inks into three groups. The principal component analysis (PCA) investigates the pen responsible for a piece of writing, and how time affects spectroscopy of written ink. PCA can differentiate between pen ink and ink line indicates the influence of solvent extraction process on the results. The PCA loadings are useful in individualization of a questioned ink from a database. The PCA of ink lines extracted at different times can be used to estimate the time at which a questioned document was written. The results proved that the UV-Vis spectra are effective tool to separate blue ballpoint pen ink in most cases rather than IR and HPTLC.     

The discrimination potential of ultraviolet-visible spectrophotometry, thin layer chromatography, and Fourier transform infrared spectroscopy for the forensic analysis of black and blue ballpoint inks

The knowledge of the discriminating power of analytical techniques used for the differentiation of writing inks can be useful when interpreting results. Ultraviolet-visible (UV-VIS) spectrophotometry, thin layer chromatography (TLC), and diffuse reflectance Fourier transform infrared spectroscopy (FT-IR) were used to examine a population of 21 black and 12 blue ballpoint writing inks. Based on corroborative results of these methods, the discrimination power for UV-VIS, TLC, and FT-IR was determined to be 100% and 98% for the black and blue inks, respectively. Generally, TLC and UV-VIS can be used to differentiate the colorant components (i.e., dyes and some pigments) found in inks. As FT-IR can be utilized to identify some of the noncolorant components, it was determined to be an excellent complementary technique that can be implemented into an analytical scheme for ink analysis.     

The use of filtered light for the evaluation of writing inks analyzed using thin layer chromatography

Thin layer chromatography (TLC) is a scientific methodology that can be used to compare and characterize ink formulations. Occasionally, when evaluating chromatographic profiles on a TLC plate with ambient light, different ink formulations, or the same inks from different batches, may appear indistinguishable. The use of filtered light can be very effective to illuminate characteristics that are not readily apparent with ambient light. There are a diverse number of components commonly found in writing inks, and it may be that some of them respond to particular wavelengths of energy that are not visible to the unaided eye (i.e., colorless). There has been very little information published that addresses the use of filtered light for evaluating TLC plates. Twenty-nine ballpoint writing ink samples were selected for TLC analysis. Further evaluation using an alternate light source, coupled with the appropriate filter, proved to be an effective means for definitive discrimination in some cases.     

Ink Dating Using Thermal Desorption and Gas Chromatography/Mass Spectrometry: Comparison of Results Obtained in Two Laboratories

An ink dating method based on solvent analysis was recently developed using thermal desorption followed by gas chromatography/mass spectrometry (GC/MS) and is currently implemented in several forensic laboratories. The main aims of this work were to implement this method in a new laboratory to evaluate whether results were comparable at three levels: (i) validation criteria, (ii) aging curves, and (iii) results interpretation. While the results were indeed comparable in terms of validation, the method proved to be very sensitive to maintenances. Moreover, the aging curves were influenced by ink composition, as well as storage conditions (particularly when the samples were not stored in “normal” room conditions). Finally, as current interpretation models showed limitations, an alternative model based on slope calculation was proposed. However, in the future, a probabilistic approach may represent a better solution to deal with ink sample inhomogeneity.     

Analysis of Pigmented Inkjet Printer Inks and Printed Documents by Laser Desorption/Mass Spectrometry*,†

Abstract: Anyone with a computer, scanner, and color printer has the capability for creating documents such as identification cards, passports, and counterfeit currency. Laser desorption mass spectrometry (LDMS) has been demonstrated as a powerful tool for colorant analysis. Inkjet printers are now moving largely toward the use of pigments as colorants; their insolubility makes analysis by simpler methods such as thin‐layer chromatography no longer an option. Recent developments in pigmented inkjet printer inks, such as gloss optimizers that coat pigment particles, may prohibit colorant analysis by LDMS. We demonstrate here that pigments used in inks from two Epson printers can be detected and analyzed by LDMS. Also, LDMS spectra of various colors created using a 4‐cartridge (cyan/magenta/yellow/black, CMYK) inkset are evaluated, to begin to develop an approach for unraveling LDMS data from real samples, to determine the number of inks used by a printer, and the chemical composition of the colorants.