An Examination of the Sequence of Intersecting Lines using Microspectrophotometry

The potential of microspectrophotometry as a technique to determine the sequence of intersecting lines was examined. The technique was used to determine the sequence of heterogeneous line intersections produced using inkpad, stamp‐pad ink and ballpoint pens, gel pens, fountain pens, laser and ink‐jet printers. The study was carried out with an assumption that the peak characteristics of spectra from the point of intersection should correspond to the peak characteristics of pure ink which was executed later. According to spectral reflectance curves, microspectrophotometry was possible to determine whether the ink was above or below the inkpad/stamp‐pad ink seals. In blind testing, microspectrophotometry technique results were directly compared to those obtained by five experienced forensic document examiners using optical microscopy regularly employed in casework. As the results obtained from the study were positive, microspectrophotometry technique was found to be very successful in determining the sequence of heterogeneous line intersections under some conditions.     

Characterization of Printing Inks Using DART‐Q‐TOF‐MS and Attenuated Total Reflectance (ATR) FTIR

The rise in improved and widely accessible printing technology has resulted in an interest to develop rapid and minimally destructive chemical analytical techniques that can characterize printing inks for forensic document analysis. Chemical characterization of printing inks allows for both discrimination of inks originating from different sources and the association of inks originating from the same source. Direct analysis in real‐time mass spectrometry (DART‐MS) and attenuated total reflectance Fourier transform infrared spectroscopy (ATR‐FTIR) were used in tandem to analyze four different classes of printing inks: inkjets, toners, offset, and intaglio. A total of 319 samples or ~ 80 samples from each class were analyzed directly on a paper substrate using the two methods. DART‐MS was found to characterize the semi‐volatile polymeric vehicle components, while ATR‐FTIR provided chemical information associated with the bulk components of these inks. Complimentary data results in improved discrimination when both techniques are used in succession resulting in >96% discrimination for all toners, 95% for all inkjets, >92% for all offset, and >54% for all intaglio inks.     

A Novel Forensic Tool for the Characterization and Comparison of Printing Ink Evidence: Development and Evaluation of a Searchable Database Using Data Fusion of Spectrochemical Methods

A searchable printing ink database was designed and validated as a tool to improve the chemical information gathered from the analysis of ink evidence. The database contains 319 samples from printing sources that represent some of the global diversity in toner, inkjet, offset, and intaglio inks. Five analytical methods were used to generate data to populate the searchable database including FTIR, SEM‐EDS, LA‐ICP‐MS, DART‐MS, and Py‐GC‐MS. The search algorithm based on partial least‐squares discriminant analysis generates a similarity “score” used for the association between similar samples. The performance of a particular analytical method to associate similar inks was found to be dependent on the ink type with LA‐ICP‐MS performing best, followed by SEM‐EDS and DART‐MS methods, while FTIR and Py‐GC‐MS were less useful in association but were still useful for classification purposes. Data fusion of data collected from two complementary methods (i.e., LA‐ICP‐MS and DART‐MS) improves the classification and association of similar inks.     

TDS-GC/MS法检测黑色中性笔墨迹中挥发性溶剂的历时性变化

目的应用热脱附-气相色谱/质谱(TDS-GC/MS)分析,研究7支黑色中性笔墨迹中挥发性溶剂的历时性变化规律。方法选取7支不同品牌的黑色中性笔,分别在A4纸和笔记本上进行一次制样,然后在不同时间点取样,应用所建TDS-GC/MS方法分析墨迹中乙二醇、二甘醇和三甘醇在200余天内的含量变化。结果6支笔中的乙二醇、三甘醇的含量在2个月之内有明显的下降,另1支笔中二甘醇的含量在5个月内还能观察到较明显的下降。目标物的历时性变化趋势能拟合成幂函数或对数函数。不同的纸张、不同的墨水对检测结果均有影响。结论黑色中性笔墨迹中的挥发性溶剂的含量随时间增加而下降,应用所建TDS-GC/MS方法,能为判断需检墨迹是否处于溶剂含量明显变化的阶段提供依据。     

激光显微共聚焦拉曼光谱仪对红色墨迹的研究

目的利用激光显微共聚焦拉曼光谱仪对文书中常见的红色墨迹材料进行表征,研究该方法对红色墨迹材料的区分能力。方法在785nm激发波长,50倍物镜条件下,对49种红色印文,以及9种彩色喷墨打印和13种彩色激光打印的红色墨迹材料进行拉曼光谱表征。结果通过对71种墨迹样品的谱图进行分析,可以发现,红色印文墨迹、喷墨打印红色墨迹及激光打印红色墨迹的拉曼光谱间均存在差异,同时,拉曼光谱可将这三种墨迹材料分别进一步区分。结论显微共聚焦激光拉曼光谱可对红色墨迹材料进行有效表征和区分。这一方法可对红色印文墨迹进行识别,并且可实现对伪造印文文件的鉴别。     

根据印文特征分析印章的材质与制作方法

在文件检验实际鉴定工作中发现,印文特征的形成既与制作方法有关又与印章的材质有关。如果能够通过印文特征确定其检材印文与样本印文是两种不同方法刻制或使用不同材质的印章所盖印,就不难做出正确的鉴定结论。通过分析印文特征的成因,可以确定其所盖印文的印章材质及其制作方法,进而识别印文的真伪。     

基于红外光谱无损区分可擦中性笔墨水色痕的研究

可擦中性笔墨水色痕形成文件的检验是目前法庭经常遇到的问题,建立一种简便、灵敏、快速、定性准确的区分可擦中性笔墨水色痕种类的方法是当前公安实战部门所需要的。研究中利用红外显微镜,采用单点模直接采集可擦中性笔墨水色痕的红外光谱。实验结果表明,根据样品红外吸收光表征的红外吸收峰的位置、数目、强度及形状可将不同品牌的可擦中性笔墨水色痕区分开来。     

Using Raman Spectroscopy to solve crime: inks, questioned documents and fraud

Raman microscopy is becoming a tool of major importance in forensic analysis, particularly of drugs and explosives. It is a non-invasive, non-destructive chemical probe allowing samples to be examined in their entirety without any preparation. This paper demonstrates the use of the technique as a general tool for inks analysis. Furthermore, it addresses two important issues that historically have been extremely difficult for the professional document examiner, namely, comparison of black ballpoint inks and the chronological sequencing of crossed ink lines. We show that Raman can successfully distinguish between a representative sample of commercially available black ballpoint inks. This data has been converted into a database for future reference. A method for chronological sequencing of crossed ink lines has been developed using confocal Raman microscopy. Case study work has shown the feasibility of this approach.     

探析高分辨率指纹特定条件下三级特征的稳定性

目的探索油墨捺印指纹显现三级特征稳定性的影响因素,排除主观条件的影响。方法在最适宜的条件下,通过油墨捺印采集不同压力下的指纹样本,清晰地显出指纹三级特征,用高分辨率扫描仪扫描试验样本,保存指纹样本,最后分析了指纹汗孔、细点线、纹线形态、皱纹等三级特征的反映性及稳定性,确定其鉴定价值。结果油墨捺印法对三级特征的反映性不够理想,汗孔、纹线形态特征、细点线特征及皱纹在不同压力下的稳定性较差。其中,各个三级特征在轻压下的反映性及稳定性较为接近实际,捺印的压力越大则三级特征变形越大,甚至完全变形成为另外一种特征。结论所以如果将此法应用于指纹比对时,仍需进一步的研究与改进。     

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。