蓝色圆珠笔字迹的高效液相色谱分析与模式识别研究

该文收集市售蓝色圆珠笔样品16份,结合模式识别技术对其高效液相色谱数据进行研究。利用相关系数法计算色谱图相对峰面积的相似度,定量地评价样品间的差异性。选取16个样品3个批次间的最小相似度(λ=0.92)作为判定是否源于同种样品的阈值,相似度小于0.92的数据为89份,占全部比对样品的74.2%;根据液相色谱图的保留时间、峰数及峰形差异将所有样品分为3类,进一步利用系统聚类法依据相似度的大小将第一类样品分为3小类。该文提出的采用相对峰面积相似度评价样品差异的方法,能够显著提高分辨能力,促进圆珠笔字迹的自动化识别。高效液相色谱法获取数据,模式识别技术分析数据的方法为圆珠笔字迹的分类与鉴别提供了新思路。     

Nondestructive classification and identification of ballpoint pen inks by Raman spectroscopy for forensic document examinations

As a non-destructive analytical method, Raman spectroscopy often provides insufficient information to identify or differentiate the ink used for the preparation of a questioned document. In this study, blue and black ballpoint pen inks deposited on paper substrate were examined in situ by conventional Raman spectroscopy. Inks were successfully classified based on the total number of prominent bands in Raman spectra. It was found that more than 90% of the samples of the same type and color could be differentiated visually using only Raman spectra, i.e. 94 and 95% for blue and black inks, respectively. As a result of this study, a flow chart has been constructed for blue and black ballpoint pen inks allowing their systematic identification. Raman spectroscopy proved to be a fast and precise technique for forensic ink analysis.     

Forensic Identification of Dyes in Ballpoint Pen Inks Using LC–ESI–MS

The aim of this work was to develop a new technique using flow injection analysis combined with LC–ESI–MS which allows identification of dyes in ballpoint pen inks. A sample preparation procedure for the extraction of dyes from ballpoint pen strokes has been developed. The characteristic group of ions for each sample of 21 studied ballpoint pen inks corresponding to the present dyes has been determined using flow injection method. LC separation conditions for identified dyes have been optimized on reversed-phase sorbent based on silica gel. The best composition of the mobile phase for the dyes mixture LC separation was 0.1% aqueous formic acid and acetonitrile. Detection of dyes was carried out using mass spectrometry with electrospray ionization in positive and negative modes after reversed-phase liquid chromatography separation. Dye composition of ink was additionally confirmed comparing the data obtained from the literature. Flow injection analysis allows obtaining intensive ions of unknown strokes. It is difficult to get this information using only chromatographic methods, because dyes peak intensity can be low and noise of basic line high. Flow injection method allows distinguishing the analyzed 21 ballpoint pens by determining a characteristic set of dyes. The developed flow injection technique is very simple and quick. As a result, a novel approach for the identification of dyes in the ballpoint pen inks by flow injection analysis with LC–ESI–MS and UV detection without using standard dye samples has been established. It can be an effective alternative to the existing LC–DAD–MS and IR spectroscopy methods.     

Micro-spectrochemical analysis of document paper and gel inks by laser ablation inductively coupled plasma mass spectrometry and laser induced breakdown spectroscopy

Current methods used in document examinations are not suitable to associate or discriminate between sources of paper and gel inks with a high degree of certainty. Nearly non-destructive, laser-based methods using laser induced breakdown spectroscopy (LIBS) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) were used to improve the forensic comparisons of gel inks, ballpoint inks and document papers based on similarities in elemental composition. Some of the advantages of these laser-based methods include minimum sample consumption/destruction, high sensitivity, high selectivity and excellent discrimination between samples from different origins. Figures of merit are reported including limits of detection, precision, homogeneity at a micro-scale and linear dynamic range. The variation of the elemental composition in paper was studied within a single sheet, between pages from the same ream, between papers produced by the same plant at different time intervals and between seventeen paper sources produced by ten different plants. The results show that elemental analysis of paper by LIBS and LA-ICP-MS provides excellent discrimination (> 98%) between different sources. Batches manufactured at weekly and monthly intervals in the same mill were also differentiated. The ink of more than 200 black pens was analyzed to determine the variation of the chemical composition of the ink within a single pen, between pens from the same package and between brands of gel inks and ballpoint inks. Homogeneity studies show smaller variation of elemental compositions within a single source than between different sources (i.e. brands and types). It was possible to discriminate between pen markings from different brands and between pen markings from the same brand but different model. Discrimination of ~ 96–99% was achieved for sets that otherwise would remain inseparable by conventional methods. The results show that elemental analysis, using either LA-ICP-MS or LIBS, provides an effective, practical and robust technique for the discrimination of document paper and gel inks with minimum mass removal (9–15 μg) and minimum damage to the document's substrate.     

Analysis of Dye Components in Red Ballpoint Pen Inks by Nonaqueous Micellar Electrokinetic Chromatography with LIF Detection

An effective and economical nonaqueous micellar electrokinetic chromatography (NAMEKC) method was developed for the analysis of dye components with similar structure in red ballpoint pen inks. The new NAMEKC method using sodium dodecyl sulfate (SDS) micelle as pseudo-stationary phase in formamide/H₂O medium provided higher resolution and better selectivity than other conventional capillary electrophoresis methods. In this study, the experimental parameters including solvent medium, acid concentration, SDS concentration, separation voltage and temperature, were optimized. The optimized conditions were formamide/H₂O (90/10, v/v) with SDS at concentration of 100 mmol and 3.5 % acetic acid (v/v). The separation voltage and temperature were of 20 kV and 25 °C, respectively. Under the optimized conditions, a good separation of three red color dyes with similar structure was achieved. This method was successfully used to analyze several red ballpoint pen inks from different manufacturers with satisfactory result. Therefore, the proposed method could be useful for the discrimination of red ballpoint pen inks in questioned documents examination.     

Applicability of surface-enhanced resonance Raman scattering for the direct discrimination of ballpoint pen inks

In situ surface-enhanced resonance Raman spectroscopy (SERRS) with excitation at 685 nm is suitable for the direct discrimination of blue and black ballpoint pen inks on paper. For black inks, shorter excitation wavelengths can also be used. For blue inks, SERRS at 514.5 and 457.9 nm does not provide adequate discriminative power. At these excitation wavelengths, the SERRS signals of the Methyl Violet derivatives present in inks easily dominate the overall spectrum because of resonance enhancement and preferential interaction with silver sol particles. At 685 nm, this problem is not encountered as the Methyl Violet derivatives do not show resonance enhancement, while other components may still exhibit resonance. Thirteen blue and thirteen black ink lines were examined. For the blue and black inks, on the basis of the 685 nm SERR spectra, eight and six groups of spectra, respectively, could be distinguished. This discrimination largely agrees with information from thin layer chromatography (TLC) experiments, although some differences in group compositions are found. The in situ SERR spectra show good repeatability with regard to the Raman frequencies, band shapes and relative intensities of the spectral bands. However, absolute intensities cannot be used for discrimination purposes.     

Determining the relative age of blue ballpoint ink by gas chromatography

A method for identifying the writing age of blue ballpoint pen ink has been established due to the imperative demand in forensic laboratories. The content of the volatile components in blue ballpoint pen ink were determined by gas chromatography (GC). The absorbance of dye in blue ballpoint pen ink was measured by UV-Vis spectrometry A writing age curve of the ink was established using the ratio of the content of the volatile components to the dye, based on the identification of 74 kinds of blue ballpoint pen ink of domestic and international origins. The change of benzene alcohol or phenoxetol with the writing age was also tested. Different kinds of blue ballpoint pen ink were detected and the repeatability of the experiment was investigated. The results indicate that the method is reliable, sensitive, systematic and is especially suitable for practical use. __________ Translated from Chinese Journal of Chromatography, 2005 (3)(in Chinese)     

NACE Discrimination of Black Ballpoint Pen Inks

A non-aqueous capillary electrophoresis (NACE) method was developed for analyzing seven basic dyes contained in black ballpoint pen inks. Baseline separation of the studied compounds was achieved on a 57 cm × 75 μm capillary by using a non-aqueous solution composed of 1.0% acetic acid and 60 mM ammonium acetate in methanol medium. Based on the pattern of NACE electropherograms, 120 black ballpoint pens from different manufacturers were divided into six groups in terms of dye categories. Moreover, the black ballpoint pens from the same group may be further distinguished by cluster analysis based on the content of different dyes and some unknown peaks. Our results indicated that the developed NACE method is a credible warrant for investigation of the fraudulent documents.     

Classification of Aurantii Fructus samples by multivariate analysis

Twenty commercial samples of Aurantii Fructus Immaturus (Poncitrus trifoliata) and 30 of Aurantii Fructus Maturus (Citrus aurantium and C. wilsonii) were collected from the Taiwan and China herbal markets. The contents of 12 constituents in these samples were determined by HPLC and were used to assess the potential relationships with their plant origins. Multivariate analysis including principal component analysis (PCA), cluster analysis (CA), and linear discriminant analysis (LDA) were used as classification procedures. Natural groupings of the samples divided into three sets successfully, 20 P. trifoliata, 15 C. aurantium, and 15 C. wilsonii, were observed by using PCA and CA. The application of LDA gave correct assignation percentages of 100.0% for all three groups.     

气相色谱法确定蓝色圆珠笔油墨字迹的形成时间

选择适当的内标物,利用气相色谱法测定蓝色圆珠笔油墨中展色剂苯甲醇和苯氧基乙醇这两种组分的含量(以峰面积计),以展色剂的峰面积、内标物的峰面积与紫外-可见光谱测得的参比物墨水中的染料的吸光度值这三者之比为纵坐标,以字迹形成时间为横坐标,确定了字迹形成曲线,从而建立了确定字迹形成时间的方法。选择了不同种类的蓝色圆珠笔油墨进行检测,获得了良好的实验效果,为圆珠笔油墨字迹形成时间的推断建立了一种可靠而又系统的方法。该方法适用于实际办案。     

Multivariate statistical analysis of tobacco of different origin, grade and variety according to polyphenols and organic acids

The aim of this work was to determine the concentration of polyphenols, organic acids in tobacco of different areas, grades and varieties by ultra-performance liquid chromatography tandem mass spectrometry (UPLC/MS/MS) and to achieve statistical classification by principal component analysis (PCA) and linear discriminant analysis (LDA). The obtained results revealed that tobacco of different varieties can be correctly classified according to the contents of polyphenols or organic acid. The results of PCA showed that different grades and geographic regions cannot completely be discriminated using polyphenols or organic acid as independent variables. However, there were marked differences in special class from the same type or grade tobacco. At the same time, the results of LDA also showed that the samples were correctly classified at 100% for different varieties of tobacco, but only 55.3% and 60% for different grades and areas, respectively. These results demonstrated that the composition of polyphenols and organic acids can be used as the useful variables to characterize the type and the special class or grade of tobacco.     

Studies on the degradation of blue gel pen dyes by ion-pairing high performance liquid chromatography and electrospray tandem mass spectrometry

Ion-pairing high performance liquid chromatography (IP-HPLC) was utilized to monitor the composition changes of blue gel pen ink entries on paper stored in different light conditions and natural environment. The chromatographic conditions were optimized by comparing the separation efficiencies of the blue gel pen inks using a series of ion-pairing reagents, including ammonium carbonate, ammonium acetate, triethylamine acetate, tributylamine acetate, tetrabutylammonium bromide and dihexylammonium acetate. It has been found that tributylamine acetate was a suitable ion-pairing reagent for separation of the inks on the common C18 column. The analysis results of the ink entries on paper in different aging conditions showed that the tendency of composition change in natural aging condition was similar with those in fluorescent light and UV light conditions, respectively. One main component dye of the blue gel pen ink, Acid Blue 9, and its degradation products were identified by ion-pairing high performance liquid chromatography coupled with electrospray tandem mass spectrometry. The results showed that the main degradation products originated from the Acid Blue 9. It gave a reasonable explanation for the changing rules of the relative content of the dyes in the blue gel pen ink. The results obtained can provide scientific evidences for dating of the blue gel pen ink entries on documents.     

裂解气相色谱法分析蓝色中性笔字迹的书写墨水种类及墨迹随书写时间的变化规律

中性笔是当前比较流行的一种书写工具,其墨水多采用颜料作为色料成分,很难用水和有机溶剂进行提取,故无法利用分析圆珠笔油墨和水性笔墨水所采用的气相色谱或高效液相色谱等方法进行检验。目前在法庭科学领域内还没有一种有效的方法用于分析中性笔字迹的书写墨水。采用裂解气相色谱法分析了蓝色中性笔字迹的书写墨水,根据色谱峰的个数和保留时间将收集的65个样品分成3类,其中大部分样品属于具有铜酞菁颜料主要色谱峰的第二大类。色谱峰的保留时间和峰面积比值的分析结果表明所建立的分析方法重现性好且稳定。在此基础上,对蓝色中性笔墨迹随书写时间的变化规律进行了初步研究,得出了老化曲线。     

Rapid classification of White Oak (Quercus alba) and Northern Red Oak (Quercus rubra) by using pyrolysis direct analysis in real time (DART™) and time-of-flight mass spectrometry

Thirty-four samples of Red Oak (Quercus rubra) and fifty samples of White Oak (Quercus alba) were analyzed by pyrolytic direct analysis in real time (DART) ionization coupled with time-of-flight (TOF) mass spectrometry. Although significant differences were not observed in the positive-ion mass spectra, the negative-ion mass spectra showed clear differences. Principal component analysis (PCA) and linear discriminant analysis (LDA) were calculated for the relative abundances of 11 peaks in the negative-ion mass spectra including peaks tentatively assigned as representing deprotonated acetic, malic, gallic, dimethoxycinnamic, and ellagic acids. Leave one out cross validation (LOOCV) was 100% successful in classifying the samples for both PCA and LDA.     

薄层色谱法分析圆珠笔色痕形成时间

 利用薄层色谱法对 70种市售的蓝色圆珠笔油墨的染料成分进行了研究。通过与染料标样的薄层色谱数据比较 ,发现国内圆珠笔厂生产的圆珠笔所用的油墨中的染料主要包括碱性紫、碱性蓝及铜酞菁 ,只是不同厂家的油墨中几种染料的配比不同。根据薄层扫描仪对油墨各斑点的扫描结果 ,确定了圆珠笔油墨成分中碱性紫和铜酞菁染料的峰高比值随着书写时间变化的关系 ,从而为法庭科学工作中鉴定圆珠笔字迹的色痕形成时间提供了可靠的依据。     

DATINK pilot study: An effective methodology for ballpoint pen ink dating in questioned documents

Establishing the approximate age of an ink entry from a questioned document is often a complicated task and a controversial issue in forensic sciences. Among the existing approaches, the analysis of solvents in ballpoint inks may be a useful parameter for determining the age of ink on paper. In recent years, several ink dating methods have been proposed. These methods have been based on the analysis of common ink solvents using gas chromatography/mass spectrometry (GC/MS) as the analytical platform. Despite these recent methods, several questions remain. The aim of this work was to develop an ink dating methodology (DATINK) for documents written by ballpoint pens based on the disappearance of volatile solvents from the ink entry. Multiple solid-phase microextraction (MHS-SPME) coupled to GC/MS was used to measure the solvents from ink entries made with four BIC^® ballpoint pens. The β parameter, the remaining fraction of the analyte in the system after one equilibration, corresponding to the successive extractions was considered for modelling a mathematical equation for later ink age dating. Preliminary tests of DATINK method showed that it was possible to detect the presence of ink solvents on documents up to the studied five years. The analyses of different real samples of known age were analyzed in terms of β values, which provided a mean relative error of 21%. The proposed use of β parameter for estimating the absolute age of ballpoint ink entries has shown promising results with a standard deviation of β ranging from 0.002 to 0.004.     

Benefits of applying combined diffuse reflectance FTIR spectroscopy and principal component analysis for the study of blue tempera historical painting

This paper explores the application of diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) to the examination of historic blue pigments and blue tempera paintings commonly found on works of art. The discussion is mainly focused on the practical benefits of using this technique joined to principal component analysis (PCA), a powerful multivariate analysis tool. Thanks to the study of several replica samples that contain either pure blue pigments (azurite, lapis lazuli and smalt), or pure binder (rabbit glue) and mixtures of each of the pigments with the binder (tempera samples), different aspects of these benefits are highlighted. Comparative results of direct spectra and multivariate analysis using transmittance-Fourier transform infrared spectroscopy (T-FTIR) are discussed throughout this study. Results showed an excellent ability of PCA on DRIFT spectra for discriminating replica samples according to differing composition. Several IR regions were tested with this aim; the fingerprint IR region exhibited the best ability for successfully clustering the samples. The presence of the binder was also discriminated. Only using this approach it was possible to completely separate all the studied replica samples. This demonstrates the potential benefits of this approach in identifying historical pigments and binders for conservation and restoration purposes in the field of Cultural Heritage.     

Forensic analysis of inks by imaging desorption electrospray ionization (DESI) mass spectrometry

Desorption electrospray ionization mass spectrometry (DESI-MS) is employed in the forensic analysis of documents. Blue ballpoint pen inks applied to ordinary writing paper are examined under ambient conditions without any prior sample preparation. When coupled to an automated moving stage, two-dimensional molecular images are generated. Proof-of-principle experiments include characterization of a simulated forged number and examination of older written records. This application of DESI has advantages over extractive techniques in terms of speed and sample preservation. The effects of the desorbing solvent composition, in this case a mixture of methanol and water, and of flow rate, are evaluated. Results suggest that the solubility of the analyte (dyes Basic Blue 7, Basic Violet 3 and Solvent Blue 26) plays an important role in desorption from the paper surface.     

Application of multivariate methods to scalp hair metal data to distinguish between drug-free subjects and drug abusers

Human scalp hair samples of drug-free subjects and drug abusers (heroin and cocaine-heroin abusers) were analysed for trace metals by flame atomic absorption spectrometry (FAAS), flame atomic emission spectrometry (FAES) and electrothermal atomic absorption spectrometry (ETAAS). The classification of drug-free subjects and drug abuses groups with four multivariate methods using the metal contents in hair samples as discriminant variables has been discussed. Principal component analysis (PCA), cluster analysis (CA), linear discriminant analysis (LDA) and soft independent modelling of class analogy (SIMCA) allow distinguishing the two groups correctly. However, predictions by SIMCA are less satisfactory. Thirteen elements (Ag, Al, Ca, Cd, Cr, Cu, K, Mg, Mn, Na, Ni, Pb, and Zn) were determined by FAAS/FAES/ETAAS in 53 hair samples (16 samples of drug-free people and 37 samples of drug abusers). Human hair samples were prepared as aqueous slurries as sample pre-treatment and they were analysed using the slurry sampling technique. The half-range central value transformation was novelty used as data pre-treatment to homogenise the data. Grouping in the samples (drug-free people and drug abusers) were observed by using PCA and CA (squared Euclidean distance between objects and Ward method as clustering procedure). The application of LDA gave a correct recognition assignation percentage of 91.7 and 100.0% for the drug-free people and drug abusers, respectively, at a significance of 5%, while SIMCA offered recognition percentages of 83.3 and 91.3% for drug-free people and drug abusers, respectively, also at 5%. Finally, some studies were developed to classify heroin abusers and polidrug abusers (cocaine-heroin abusers) by the cited multivariate statistical methods. Recognition percentages of 90.9 and 100.0% were reached for heroin abusers and polidrug abusers groups, respectively, after LDA, while these percentages decreased to percentages lower than 90.0% when SIMCA was applied.