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.     

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.     

高效液相色谱法鉴别蓝色签字笔墨水的种类

目的通过对签字笔字迹成分进行检验，达到对签字笔成分进行分离并对签字笔种类进行鉴定的目的。方法使用高效液相色谱法对蓝色签字笔字迹色痕中的色料成分进行分析，并依据分析结果对墨水的种类划分，同时考察了纸张的背景影响、最小用样量以及实验结果的重现性。结果22种蓝色签字笔样品均可以实现区分。结论本研究对实际应用有较大参考价值。     

Investigation of the new possibility of mathematical processing of Raman spectra for dating documents

The use of spectral analysis methods to determine the age of writing inks is an important forensic task. However, the use of spectral data for this purpose has a number of limitations and difficulties. This paper considers the application of the Raman spectroscopy method to an urgent forensic task. The known mechanisms of dye degradation are analyzed; Raman bands are identified that are related to the age of the sample. In a sample of 5 randomly selected writing inks, temporary markers were identified. Narrow sections of Raman spectra containing characteristic lines were used for analysis. It was shown that processing narrow sections of the Raman spectra using the PCA chemometric method allowed the separation of writing inks into groups (clusters) corresponding to different creation intervals.     

Evaluation of the Forensic Utility of Scanning Electron Microscopy‐Energy Dispersive Spectroscopy and Laser Ablation‐Inductively Coupled Plasma‐Mass Spectrometry for Printing Ink Examinations

Improvements in printing technology have exacerbated the problem of document counterfeiting, prompting the need for analytical techniques that better characterize inks for forensic analysis and comparisons. In this study, 319 printing inks (toner, inkjet, offset, and Intaglio) were analyzed directly on the paper substrate using scanning electron microscopy‐energy dispersive spectroscopy (SEM‐EDS) and Laser Ablation‐Inductively Coupled Plasma‐Mass Spectrometry (LA‐ICP‐MS). As anticipated, the high sensitivity of LA‐ICP‐MS pairwise comparisons resulted in excellent discrimination (average of ~ 99.6%) between different ink samples from each of the four ink types and almost 100% correct associations between ink samples known to originate from the same source. SEM‐EDS analysis also resulted in very good discrimination for different toner and intaglio inks (>97%) and 100% correct association for samples from the same source. SEM‐EDS provided complementary information to LA‐ICP‐MS for certain ink types but showed limited utility for the discrimination of inkjet and offset inks.     

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.     

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.     

Evaluation of desorption/ionization mass spectrometric methods in the forensic applications of the analysis of inks on paper.

Fast atom bombardment and laser desorption mass spectrometry (LDMS) provide molecular level information concerning an ink's composition. Two ink-jet printer inks, Ink A containing the cationic dye Methyl Violet 2B, and Ink B containing the anionic dye, Solvent Black, were studied. Both positive and negative ion detection modes of the mass spectrometer were used. LD may be used for the analysis of inks on paper. Once on paper, the ink's solvent system has evaporated, leaving mainly the dyes behind, which are detected using LDMS. An ink fades with time, indicating that the dyes are degrading. Preliminary results from an accelerated aging study of ballpoint pen ink using UV irradiation confirm that dye degradation products are formed. The degradation chemistry follows an oxidative demethylation process for which all products formed are detected using LDMS. Results suggest that LDMS may be developed to determine the relative age of inks.     

油性圆珠笔字迹书写时间鉴定的研究综述

本文追述了油性圆珠笔问世以来,字迹书写时间的检验发展过程;总结了静态法,如标准样品比对法和基准物标记法,动态法,如如溶剂萃取法、色谱法、质谱法和光谱法用于鉴定圆珠笔字迹书写时间的研究成果;展望了非破坏性方法在鉴定书写时间上的发展趋势。     

墨水书写时间测定的进展

本文追述了从20世纪20年代初到90年代末书写墨水的时间测定的进展.这包括,介绍新检验方法建立所需遵循的基本要求;推荐目前案件检验的工作程序,即墨水种类的确定,可疑文件的外观检验,同牌号、同配方、同批号比对样本的寻找;评述目前已为办案使用的各种书写年代测定的方法,如扩散法,转印法,染料比值法,气相色谱法、溶剂萃取法,差示扫描量热法等;以及讨论了有望用于年代测定的一些新技术,如用于钢笔墨水的电化学法,光谱法和用于圆珠笔墨水的显微分光光度法,付里叶变换拉曼光谱法等.     

Differentiation of blue ballpoint pen inks by laser desorption ionization mass spectrometry and high-performance thin-layer chromatography

The differentiation of inks on a questioned document can highlight a fraudulent insertion and is usually carried out by optical comparison and thin-layer chromatography (TLC). Laser desorption ionization mass spectrometry (LDI-MS) may also be used for the analysis of dyes from ink. This analytical technique was compared with a standard method of high-performance TLC (HPTLC) according to their capacity to differentiate blue ballpoint inks. Ink entries on paper from 31 blue ballpoint pens have been analyzed and their dye ink formulations compared. The pens were classified into 26 classes by LDI-MS against 18 for HPTLC. LDI-MS proved to be a more powerful method for differentiating ink formulations because it provides information about dye structures (molecular weights) and relative quantification of dye classes (peak areas). Sample preparation was minimal and analysis time was short in contrast to the more complex extraction, application, and development steps of the HPTLC method. However, only basic dyes and pigments were identified using positive mode LDI-MS, while HPTLC did yield additional information about acid dyes.     

Differentiation of inks on documents by dequenching of ultraviolet fluorescence: A case report

Detection of chemical erasure and differentiation of inks by examination under long- and short-wave ultraviolet light generally solves many Questioned Documents problems. Many dyestuff-based inks fluoresce when examined under ultraviolet light, when the dye component fluoresces under the direct ultraviolet light. Sometimes, however, this fluorescence becomes quenched when the dye becomes bonded to some other, non-fluorescent compound, and does not fluoresce under ultraviolet rays. When the dye is freed from its bonded state it regains its fluorescence.In a recent case, two specimens of writing in ink of apparently the same colour were differentiated when aqueous spots of the ink from the disputed and original entries were transferred direct to a filter paper and examined under ultraviolet rays. The spots from the fraudulent entry fluoresced under the ultraviolet, but not the spots from the original entry. Neither the original nor the fraudulent entry showed any fluorescence when examined directly under ultraviolet light.     

Differentiation of black gel inks using optical and chemical techniques

Gel ink pens have become a common writing instrument in the United States. Questioned document examiners often attempt to optically differentiate gel inks from each other and from other non-ballpoint ink writings (e.g., those from roller-ball pens). Since early formulations were primarily pigment-based, they do not elute when analyzed by thin-layer chromatography. However, recent gel ink formulations (i.e., within the past five years) include dye-based inks that can be easily separated. This study differentiates black gel inks using optical and chemical techniques. The techniques include: microscopy, visible and near infrared reflectance, near infrared luminescence, thin-layer chromatography (TLC), spot tests, and gas chromatography/mass spectrometry (GC/MS). As a result of this study a flow chart has been developed allowing for a systematic determination of a questioned ink. In addition, an analysis of volatile compounds found in gel inks revealed that there are some unique ingredients that may be found in gel inks that are not typically found in other non-ballpoint inks.     

Experimental Research on Class Identification with a New Type of Erasable Gel Pens

A new type of erasable gel pen ink is becoming increasingly popular because of the modifiable characteristics for writing on documents. This study attempts to distinguish 12 types of blue and black erasable gel pens produced by mainstream stationery manufacturers using infrared (IR) visual analysis, Fourier transform infrared (FTIR) analysis, fluorescence analysis, and microspectrophotometry. The results demonstrate that IR visual, FTIR, and fluorescence analysis can be used to help distinguish each type of erasable gel ink. While microspectrophotometry can be used to effectively differentiate the blue gel inks in this study, there are limitations with respect to distinguishing black erasable gel pens. When these four optical analyses methods were used in combination, the gel inks could be accurately distinguished.     

Identification and dating of the fountain pen ink entries on documents by ion-pairing high-performance liquid chromatography

A novel approach for the identification and dating of the fountain pen ink entries on paper has been established by ion-pairing high-performance liquid chromatography (IP-HPLC). Twelve black and six red fountain inks have been collected, and their ink entries have been prepared by drawing lines on paper. The chromatographic conditions for separation of their dye components after extraction with solvents were optimized. Under the optimized conditions, the 18 fountain pen inks were differentiated individually by comparing the number of detectable main or minor dye components, and the relative peak intensities of each component. The ink entries were artificially and naturally aged, and the analysis results showed that the ink dye components were significantly decomposed when exposed to UV or fluorescent light compare to those of inks stored under natural condition. The changes of the relative peak height for the dye components were linearly related to the aging time, especially under natural aging conditions. The degradation characteristics of the dye components under different aging conditions provide scientific evidences for dating of the suspicious fountain pen ink entries on document.     

Differentiation of ballpoint pen inks by thermodesorption and gas chromatography-mass spectrometry

Differentiation and classification of ink entries with dated samples of a reference collection are important aspects in the examination of questioned documents. Classification of writing inks is presently achieved by analysis of dyes and colorants contained in the ink. This technique has its limitations in newly developed ink formulations with identical dye composition but differing in their solvents and binder resins. This paper introduces a method for the determination of solvents and binder resins of an ink sample directly from paper without sample preparation. This aim is accomplished by thermodesorption of the sample followed by gas chromatography/mass spectroscopy. The method was tested on numerous samples of ballpoint pen inks, which were subsequently grouped into several solvent and resin subgroups. A case study shows the applicability of the newly developed method.     

Dating of Iron Gall Ink Using the Dissolution‐Diffusion Method

In many criminal and civil cases, some questioned documents are written with iron gall ink. Determining the date when an iron gall ink entry was written can be important to assess the authenticity of a document. A dissolution‐diffusion method was successfully employed to draw aging curves of iron gall ink entries stored in controlled conditions over 40 months. Calibration curves were created to indicate the relationship between the average dissolution‐diffusion rate of ink components and the age of ink entries stored under natural aging conditions. As preliminary findings of this study, the mixed solution of dimethyl formamide (DMF) and anhydrous ethanol was suitable to dissolve the dye of iron gall ink strokes made at different time. It was also determined that brands of iron gall inks, types of paper, and thickness of iron gall ink strokes had varying impacts on estimating the dates of iron gall ink strokes.     

Application of laser induced breakdown spectroscopy to examination of writing inks for forensic purposes

The research was focused on the analysis of writing inks using the laser induced breakdown spectroscopy (LIBS) technique. 34 samples of blue, 30 of black, and 21 of red writing inks were analyzed under optimized conditions to determine the variation of chemical composition of inks between different colours, brands and types. Nine elements (Ba, Cr, Cu, Fe, Li, Mo, Mn, Ni and W) were taken into account during comparative analysis of inks. Because of the strong effect of the paper spectrum, elements often found in inks (Ca, Al, Mg, Na, Ti, and Si) were eliminated from LIBS analysis of inks. It was determined that the LIBS method is capable of revealing qualitative elemental differences between ink samples. The discrimination power of this method was found to be 83, 82 and 61% for blue, black and red inks, respectively. Inks produced by the same producer were able to be differentiated in some cases. The results showed the potential of LIBS for forensic purposes as an effective and robust technique, requiring a small amount of sample and giving analytical information in a very short time.     

How Much Can a Forensic Laboratory Do to Discriminate Questioned Ink Entries?

Questioned document examiners are frequently required to determine whether the questioned ink entries on a document are written with the same ink, either for forged document identification or relative ink dating. How many methods are sufficient to discriminate potentially different inks? In this paper, 18 blue ballpoint inks were first nondestructively examined with a video spectral comparator. The ink entries were subsequently extracted with organic solvents for analysis of the volatile solvents and dyes by GC/MS, TLC, and LC‐MS/MS. The 18 ink samples were divided into 10, 9, 12, and 14 categories by these four methods, respectively. With the combined results, there were only two inks that remained indistinguishable, but they were further differentiated by microscopy. Therefore, to achieve effective discrimination of ballpoint ink entries, the authors suggest that a complete examination should include an analysis of their optical features, volatile solvents, and dyes as well as the ink quality.     

Evaluation of laser desorption mass spectrometry and UV accelerated aging of dyes on paper as tools for the evaluation of a questioned document

Laser desorption mass spectrometry (LDMS) may be used for the detection and identification of dyes found in inks. Naturally-aged and artificially-aged blue and black ballpoint pen inks containing the cationic dye methyl violet were analyzed on paper. The average molecular weight of the dye sample was calculated from LD mass spectral data and plotted versus time. The resulting aging curves demonstrate that, as dye degradation increases, the average molecular weight of the dye decreases. Typical variables involved in ink aging, such as the type of paper and ink formulation, were investigated. Results show that these variables influence the rate of dye degradation. Furthermore, UV accelerated aging has been developed and tested as an alternative to thermal approaches.