Document authentication at molecular levels using desorption atmospheric pressure chemical ionization mass spectrometry imaging

Molecular images of documents were obtained by sequentially scanning the surface of the document using desorption atmospheric pressure chemical ionization mass spectrometry (DAPCI‐MS), which was operated in either a gasless, solvent‐free or methanol vapor‐assisted mode. The decay process of the ink used for handwriting was monitored by following the signal intensities recorded by DAPCI‐MS. Handwritings made using four types of inks on four kinds of paper surfaces were tested. By studying the dynamic decay of the inks, DAPCI‐MS imaging differentiated a 10‐min old from two 4 h old samples. Non‐destructive forensic analysis of forged signatures either handwritten or computer‐assisted was achieved according to the difference of the contour in DAPCI images, which was attributed to the strength personalized by different writers. Distinction of the order of writing/stamping on documents and detection of illegal printings were accomplished with a spatial resolution of about 140 µm. A Matlab® written program was developed to facilitate the visualization of the similarity between signature images obtained by DAPCI‐MS. The experimental results show that DAPCI‐MS imaging provides rich information at the molecular level and thus can be used for the reliable document analysis in forensic applications. © 2013 The Authors. Journal of Mass Spectrometry published by John Wiley & Sons, Ltd.     

The use of laser desorption/ionization mass spectrometry in the analysis of inks in questioned documents

Determination of the age of a handwritten or ink printed questioned document can be an important consideration in forensic cases. Most often the age of a document is determined by the chemical behavior of the dyes that make up the ink. Exposure of the dyes to environmental factors such as oxygen and ultraviolet or visible light cause them to degrade. Often this degradation can be correlated to the time since the exposure of the ink to the elements began. A number of methods have been used to track the aging of inks on paper. This paper reports the use of laser desorption mass spectrometry as a valuable tool in not only elucidating the structures of dyes used in inks but tracking the change in their chemistry as they age. This study also explores methods for artificially aging documents using ultraviolet and visible light.     

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。     

蓝色圆珠笔字迹色痕傅里叶变换显微红外光谱法的无损分析

利用傅里叶变换显微红外光谱法中的微区衰减全反射采样技术无损测定了纸张上圆珠笔油墨所形成的字迹色痕,获得了１０种不同圆珠笔字迹的显微红外光谱图。结果表明,笔迹色痕的微区衰减全反射谱图可明显地识别色料和溶剂的结构组成;快速地分辨各生产厂家油墨的差异。同时,纸张的不同,字迹书写的深浅均可快速,准确地进行无损分析。     

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。     

显微共聚焦拉曼光谱结合群分析的黑色直液笔墨迹鉴别研究

黑色直液笔是一种新型书写工具,目前对该种笔墨迹的相关研究较少。为给文件检验工作中墨迹的分析提供新的参考依据,本实验使用显微共聚焦拉曼光谱技术,采集了30支不同品牌、型号的黑色直液笔墨迹光谱数据,进行Savitzky-Golay卷积平滑处理后,依据光谱图的拉曼位移及拉曼谱峰差异对墨迹进行初步分析。设置聚类方法为组间联接,区间距离测量方式为平方欧式距离,对采集的光谱数据进行群分析,将30支黑色直液笔墨迹样本分成了3类,并与品牌建立了相关联系;同时通过主成分分析验证了群分析的可靠性和准确性。研究表明,显微共聚焦拉曼光谱技术结合群分析方法可实现对黑色直液笔墨迹的无损分析及有效鉴别,该方法操作简便、结果准确,适用于法庭科学文件检验。     

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.     

Classification and dating of black gel pen ink by ion-pairing high-performance liquid chromatography

A novel approach for classification and dating of the black gel pen ink entries on document was developed based on ion-pairing high-performance liquid chromatography (IP-HPLC). Ninety-three black gel pens were collected and divided into two groups, dye-based and pigment-based, by preliminary solubility test. The chromatographic conditions for separation of the dye-based black gel pen inks were optimized and the dye components in inks were satisfactorily separated by using 40 mmol/L tetrabutylammonium bromide as ion-pairing reagent. According to the number and the chromatographic retention times of the main dye components, the 50 dye-based inks were categorized into four classes. The inks within a class can be further identified by the percentage of each dye component. The compositional changes of the dye components in the black gel pen ink entries on paper were investigated in light and natural aging conditions and it has been found that the dye components in the ink entries underwent obvious decomposition, and the decomposing extent of the dye components was related to the aging time. The results can provide scientific evidences for dating of the suspicious black gel pen ink entries on documents.     

基于高光谱成像结合分光光度技术的喷墨打印墨水种类鉴别方法

在法庭科学实践中,往往需要通过对文件中字迹墨水的成分分析来精确地判定检材和样本文件的同一性。利用高光谱成像和分光光度技术结合化学计量法,提出了一种对喷墨打印墨水分类的方法。采集14台不同品牌、型号的四色喷墨打印墨水高光谱数据和色度值。计算出平均色度值后进行PCA降维处理和K-Means聚类分析,将样品初步分类。之后应用LightGBM模型、XGBoost模型和SVM模型共三种分类模型,以1:4的比例确定测试集和训练集,对聚类分析结果中每一类别的样品进行逐一鉴别。结果表明,LightGBM和XGBoost对四色样品的分类精度都能达到95%以上,SVM的分类精度为100%。提出的方法能够做到无损、准确、快速地将不同品牌乃至型号的喷墨打印墨水进行区分。     

Study of the copper effect in iron-gall inks after artificial ageing

Iron-gall inks consist of a mixture of vitriols (sulphates of certain metals), gall nut extracts and arabic gum. The association of the iron(II) sulphate present in vitriols, and the gallic acids present in the gall nut extracts induces, after exposure to oxygen, the formation of dark coloured compounds of ink. In addition to iron, this kind of inks contains other metals, such as copper, zinc, and nickel. Among them, copper could be considered the most important because, owing to its catalytic ability, it can be involved in the processes concerning formation and stability of iron complexes, which are responsible for the ink dark colour. For this purpose, four different iron-gall inks containing increasing amounts of copper sulphate were prepared according to a traditional receipt and applied on paper supports. The ink-stained paper specimens were subjected to an intense analytical program to investigate their chemical and physical modifications after artificial ageing (both temperature/humidity and ultraviolet light ageing). The role of copper in the iron-gall inks was evaluated using optical microscopy, colorimetric measurements, X-ray fluorescence (XRF), X-ray diffraction analysis (XRD), scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM–EDX) and Fourier transform infrared spectroscopy (FTIR). For the evaluation of the oxidation state of iron and copper, X-ray absorption spectroscopy (XANES) was used. All results indicate that the presence of copper in iron-gall ink causes colour variation, affects the migratory behaviour of iron in the paper, increases the formation of secondary products particularly when ageing process based on temperature/humidity variations is considered.     

A multi-analytical approach for the characterization of powders from the Pompeii archaeological site

Nine black powders found in Pompeii houses in three different types of bronze vessels (cylindrical theca atramentaria, unguentaries, and aryballoi) were characterized in order to assess a correspondence between the composition and the type of vessel and, possibly, to verify if these powders were inks or not. For the compositional characterization, a multi-analytical approach was adopted, which involved the use of scanning electron microscopy-energy dispersive X-ray, Fourier-transformed infrared spectroscopy, Raman, X-ray diffraction, electron paramagnetic resonance spectroscopy, thermogravimetric analysis, gas chromatography coupled with mass spectrometry (GC/MS), and pyrolysis GC/MS. Powders contained in cylindrical theca atramentaria form a homogeneous group, and their organic and inorganic compositions suggest that they were writing inks, while powders contained in unguentaries and aryballoi could have had several different uses, including writing inks and cosmetics. Furthermore, the composition profile of the powders found in cylindrical cases shows that, at 79?AD: , in Pompeii, carbon-based inks were still used for writing, and iron gall inks had not been introduced yet.     

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.     

Preparation of photoluminescent nanocomposite ink toward dual-mode secure anti-counterfeiting stamps

Fluorescent photochromism has been applied as an attractive approach for the production of effective authentication substrates to show dual-mode secure encoding. In the current study, novel photochromic and fluorescent nanocomposite ink was developed to introduce a stamped film with strong dual-mode emission for anti-counterfeiting purposes. Inorganic/organic nanocomposite ink was developed from lanthanide-doped aluminate (LDA) dispersed in poly(acrylic acid)-based binder. To produce a transparent film, LDA must be dispersed well in the poly(acrylic acid)-based ink solution. The fluorescent and photochromic nanocomposite ink was stamped effectively onto cellulose documents followed with thermal fixation. Homogeneous fluorescent and photochromic layer was stamped onto paper surface providing a transparent look with the ability to switch to green beneath ultraviolet as illustrated by CIE Lab. The stamped documents were studied by photoluminescence spectra to show an absorption peak at 364 nm, and fluorescence band at 438 nm. The induced security encoding was transparent beneath visible light turning into visible greenish-yellow beneath ultraviolet light indicating a bathochromic shift. LDA was synthesized in the nanoparticle form and characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS). The morphological properties of the stamped documents were examined by infrared spectroscopy (FTIR), scan electron microscope (SEM), EDS, and X-ray fluorescence (XRF). The stamped paper sheets displayed an efficiently reversible photochromism without fatigue under visible and ultraviolet lights. The rheologies of the prepared photoluminescent nanocomposite inks as well as the mechanical performance of the stamped sheets were investigated.     

Studies into the Early Degradation Stages of Cellulose by Different Iron Gall Ink Components

Selective fluorescence labelling of oxidized cellulose functionalities followed by GPC-MALLS was used to get a deeper insight into ink-induced degradation processes. As the method is very sensitive towards oxidation and molecular weight changes, slight variations at the very beginning of aging processes, e.g. during ink corrosion of cellulose, can be studied. Five different ink modifications were applied on model papers and underwent mild accelerated aging at 55 °C and cycling humidity (7 days) followed by a short period of static humid aging at 80 °C (2 days). Pure ink constituents like tannic acid or iron sulphate do not result in the same degree of oxidation or chain scission as complete inks. Balanced ink degrades paper more than single compounds, but less than unbalanced inks. Interestingly, some degradation occurs already during or shortly after the application process of unbalanced inks on paper. It could be demonstrated that this oxidation proceeded in a rather high Mw area, while the subsequent aging steps affected predominantly regions of shorter cellulose chains.     

Ink dependence of poly(dimethylsiloxane) contamination in microcontact printing

Poly(dimethylsiloxane) (PDMS) is the most widely used stamp material in microcontact printing. It has excellent properties with respect to versatility, chemical inertness, and mechanical stability. However, it has an inclination to contaminate printed substrates with low molecular weight siloxane fragments. In this study, it is shown, by a combination of lateral force microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy, that the extent of the PDMS-induced contamination is dependent on the nature of the ink used. The highest degree of contamination was found for relatively polar inks, whereas apolar alkanethiol inks were found to shield the substrate from contamination. This is interpreted in terms of the contaminating species being polar in nature.     

Multivariate classification of pigments and inks using combined Raman spectroscopy and LIBS

The authenticity of objects and artifacts is often the focus of forensic analytic chemistry. In document fraud cases, the most important objective is to determine the origin of a particular ink. Here, we introduce a new approach which utilizes the combination of two analytical methods, namely Raman spectroscopy and laser-induced breakdown spectroscopy (LIBS). The methods provide complementary information on both molecular and elemental composition of samples. The potential of this hyphenation of spectroscopic methods is demonstrated for ten blue and black ink samples on white paper. LIBS and Raman spectra from different inks were fused into a single data matrix, and the number of different groups of inks was determined through multivariate analysis, i.e., principal component analysis, soft independent modelling of class analogy, partial least-squares discriminant analysis, and support vector machine. In all cases, the results obtained with the combined LIBS and Raman spectra were found to be superior to those obtained with the individual Raman or LIBS data sets.     

Advanced Polymer Designs for Direct-Ink-Write 3D Printing

The rapid development of additive manufacturing techniques, also known as three-dimensional (3D) printing, is driving innovations in polymer chemistry, materials science, and engineering. Among current 3D printing techniques, direct ink writing (DIW) employs viscoelastic materials as inks, which are capable of constructing sophisticated 3D architectures at ambient conditions. In this perspective, polymer designs that meet the rheological requirements for direct ink writing are outlined and successful examples are summarized, which include the development of polymer micelles, co-assembled hydrogels, supramolecularly cross-linked systems, polymer liquids with microcrystalline domains, and hydrogels with dynamic covalent cross-links. Furthermore, advanced polymer designs that reinforce the mechanical properties of these 3D printing materials, as well as the integration of functional moieties to these materials are discussed to inspire new polymer designs for direct ink writing and broadly 3D printing.