Rapid and nondestructive analysis of lipstick on different substrates using ATR-FTIR spectroscopy and chemometrics

Lipstick can be an important piece of evidence in crimes like murders, rapes, and suicides. Due to its prevalence, it can be an important corroborative evidence in crime reconstruction. The analysis of such evidence can provide an evidentiary link between the suspect, the victim, object, or the crime scene. We report the use of nondestructive ATR-FTIR spectroscopy combined with chemometrics for the classification of 10 brands of lipsticks with nine samples each. Chemometric method of partial least square-discriminant analysis (PLS-DA) has been employed to interpret the data and classify the samples into their respective classes. The PLS-DA model provides an AUC figure above 0.99 in all brands except one; for which it is slightly less at 0.94. We have also tested the traces of these lipstick samples on different substrates treating them as unknowns in the already trained PLS-DA model. 100% of the samples on nine substrates viz. a cotton, nylon, plastic, dry tissue, denim (blue jeans), wet tissue, nitrile gloves, white paper, and polyester were correctly attributed to their source brand. In conclusion, the results suggest that ATR-FTIR combined with the chemometrics is a rapid, nondestructive, and accurate method for the discrimination and source attribution of lipstick. This study has potential for use in actual forensic casework conditions.     

汽车罩光漆的ATR-FTIR法检验

目的通过对油漆样品罩光漆成膜物质的检验以区分不同汽车厂家的油漆样品。方法采用衰减全反射红外光谱法（Fourier Transform Infrared Spectroscopy Attenuated Total Reflection Spectroscopy,ATR-FTIR）研究15个汽车厂家提供的356份油漆样品的罩光漆成膜物质。结果在所有油漆样品中,丙烯酸漆出现的频率最高,氨基漆出现的频率最低;在所有厂家中,使用丙烯酸漆的厂家最多,使用氨基氨酯混合漆的厂家最少;在使用相同罩光漆的不同厂家的油漆样品中,通过比较红外谱图可以对样品进一步区分。结论 ATR-FTIR法能够在一定程度上区分不同汽车厂家的油漆样品,从而大大缩小侦查范围,对于涉车案件的快速侦破具有非常重要的作用。     

A comprehensive ATR-FTIR spectroscopic analysis for the identification and differentiation of lip balms

Lip balm may be encountered as physical evidence in cases involving sexual assaults, homicides, and kidnappings. Lip balm can be used as corroborative evidence by providing a potential link between the victim, accused, and the crime scene. For lip balms to be used as evidence, it is important to understand the diversity and their aging process under different conditions. Therefore, in this study, ATR-FTIR spectroscopy in conjunction with chemometric tools such as principal component analysis (PCA) and linear discriminant analysis (LDA) has been used for the objective identification and differentiation of 20 brands of lip balms. Moreover, lip balms on different substrates and wearing effects over time were also investigated. The results show that the PCA-LDA training accuracy was 92.5%, whereas the validation accuracy comes out to be 83.33%. A blind study using pristine samples was also performed which resulted in 80% PCA-LDA accuracy. PCA-LDA prediction of samples on various substrates showed a higher chemometric prediction accuracy for nonporous substrates (glass, plastic, and steel), than for porous substrates (cotton cloth, cotton swab stick, dry tissue paper, and white paper) for samples kept in room temperature and under sunlight for 15 days. The substrate study showed that the samples from various substrates could effectively generate respective spectra which can help in brand-level identification even after several days. The present method demonstrates a potential for lip balm samples to be used in forensic casework applications.     

On the spectroscopic cum chemometric approach for differentiation and classification of inkjet,laser and photocopier printed documents

The potential of ATR-FTIR spectroscopy combined with chemometric methods is explored for the rapid and no-destructive forensic investigation of inkjet, laser and photocopier printed documents. The aim of the present study is to ascertain the source of origin of unknown printed documents, i.e., whether it belongs to the laser or inkjet or photocopier devices and also to visualize the intra-variations present in the same types of printed documents. It is observed that these printing inks contain polystyrene, bisphenol A, methyl acrylate and aromatic ethers as the main chemical constituents. The standard normal variate normalization is performed in order to eliminate the differences caused by the amount of toner powder/inks. The discrimination among printed documents is achieved by using chemometric methods including hierarchal cluster analysis and principal component analysis. Further, linear discriminant analysis is used to classify the unknown printed documents into its respective class of printing devices. The present methodology provides robust, non-destructive, reproducible, and simultaneous identification methods for printed documents.     

A forensic international market survey of condom lubricants and personal hygiene products using ATR-FTIR coupled to chemometrics

Condom residues may be encountered in forensic investigations as traces in sexual assault or rape cases. Casework studies have shown the value of distinguishing condom residues from other types of personal products used by women. However, up to now, there has been no investigation of their chemical variability within an international context. This work employed attenuated total reflectance Fourier transform infrared spectroscopy with chemometrics to provide objective characterisation of condom lubricants and personal hygiene products from the international market. 166 samples were obtained covering five major classes of products likely to be used by women. Principal component analysis distinguished most major classes based on their spectral profiles, with subsequent support vector machine models yielding discrimination accuracies over 90%. A two-step approach was subsequently developed and enabled both classification and a discrimination accuracy of 100%. This could provide greater confidence in chemical discrimination of residues from these products when conducting investigations and help assess the origin of the chemical profile obtained. Further testing using three validation sets produced an identification accuracy of 100% for generic classes, which may allow investigative leads to be more readily obtained from recovered evidence.     

Rapid detection of synthetic cannabinoid receptor agonists impregnated into paper by attenuated total reflectance Fourier transform infrared spectroscopy

The last few years have witnessed the change in the modalities of smuggling of synthetic cannabinoid receptor agonists (SCRAs) by impregnating them in mail envelopes and fast parcels. Considering the aforementioned scenario, it is important to develop a portable technique to identifying SCRAs through packages. The purpose of this research was to detect SCRAs impregnated into substrates of paper using attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. Three SCRAs that included 5F-PB-22, AB-FUBINACA and AKB-48 were purchased from Sigma Aldrich. The three SCRAs and four cutting agents were impregnated into paper of variable thickness at four concentrations (10, 15, 20, and 25 mg/mL). Spectra were collected over the wavenumber range of 650–4000 cm⁻¹ using ATR-FTIR spectroscopy and were exported to Matlab 2020b where data analysis was applied. The FTIR spectral data was able to show the three SCRAs could be detected on paper using ATR-FTIR spectroscopy and quantitatively modeled using the partial least squares regression algorithm. Principal component analysis showed separate clustering for the compounds that crystallized (5F-PB-22, AB-FUBINACA and caffeine) onto the papers surface from those impregnated into the bulk of the paper (AKB-48 and procaine) with the latter situated near blank papers in score plots. In summary, ATR-FTIR spectroscopy has proven to be a successful non-destructive technique in detecting and quantifying a selection of SCRAs impregnated into paper.     

Assessing the potential fire risk of laundered fabrics after contamination with emollients using ATR-FTIR spectroscopy and chemometrics

Since 2010, more than 50 UK fire deaths, have been reported as linked with emollients. This prompted the Medicines and Healthcare products Regulatory Agency (MHRA) to issue advice on their safer use in 2018. The advice was in response to concerns raised by the National Fire Chiefs Council, coroners’ reports, and flammability tests. The test results show a significant reduction in ignition time of fabrics contaminated with paraffin-based and paraffin-free skin care product residues. The MHRA report also included advice on washing clothing and bedding at high temperatures but warned this may not remove all emollient residues. This paper reports on new research on the removal of skin care products from clothing investigated by laundering contaminated 100% cotton fabric at 30, 40 and 60 °C using both biological and non-biological based detergents. As part of the experiment, non-contaminated (blank) napkin samples were included in the wash experiments to assess the possible transfer from fabrics contaminated with emollients to uncontaminated clean fabrics during washing. Washed and dried fabrics were analysed using Attenuated Total Reflectance, Fourier Transform Infrared (ATR-FTIR) spectroscopy and further interpreted via principal component analysis (PCA) and network analysis. Results suggest that the majority of the 6% white soft paraffin-based lotion and paraffin-free cream were removed at all temperatures. Residues of 21% paraffin-based cream (6% light paraffin/15% white soft paraffin) remain, and more residues persist of the 100% paraffin-based ointment (5% light paraffin/95% white soft paraffin) after washing at 30, 40 and 60 °C. The wash experiments show unequivocal transfer of the 100% ointment from the contaminated napkins to clean control napkins placed within washes at 30 °C. Furthermore, residues of the ointment were observed within the machine drum, and washing machine door seal, though this did not cause secondary transfer to subsequent wash experiments. There were no differences observed when using biological versus non-biological detergents, nor when employing a pre-wash treatment in the removal of residues of the 21% cream and 100% ointment. These results suggest that a single application of an emollient when soaked and dried into a fabric is not removed by a single wash at 30, 40 or 60 °C. Instead, the residue remains a persistent potential fire risk and, its high paraffin content presents an additional fire risk via contamination of other fabrics.     

Rapid and non-destructive approach for characterization and differentiation of sealing wax using ATR-FTIR spectroscopy

Sealing wax is used for maintaining the integrity and authenticity of a document or physical evidence. Any tampering with the seal calls into question the overall integrity and authenticity of the tangible evidence or document. In these circumstances, determining the authenticity of the sealing material (physical and chemical) becomes imperative. In this study, ATR-FTIR spectroscopy supported by chemometrics has been used to differentiate sealing wax samples belonging to 12 different brands available across India. All the samples were first melted, cooled, and then analyzed using ATR-FTIR spectroscopy in the mid-infrared region (4000–600 cm⁻¹). The obtained spectra were first examined visually for the presence of different functional groups. Principal component analysis (PCA) and principal component analysis-linear discriminant analysis (PCA-LDA) were employed to analyze the sample clustering patterns and to categorize them into their respective groups, respectively. For classification, a PCA-LDA training model was applied, and it demonstrated 95.83% accuracy. The validation test resulted in an accuracy of 83.33%. PCA-LDA model offered 100% accurate prediction for samples on various substrates, including cloth, cardboard, and paper. A blind study was also performed using five unknown samples, which were accurately classified into their respective groups. PCA-LDA model will be helpful in providing investigative leads by linking a questioned sealing wax sample with its respective group.     

二维红外光谱用于急性心肌缺血猝死的鉴别研究

目的采用衰减全反射-傅里叶变换红外光谱(ATR-FTIR)技术检测急性心肌缺血猝死大鼠的血清分子特征,探讨二维红外光谱鉴别急性心肌缺血猝死的法医学价值。方法成年雄性SD大鼠随机分为急性心肌缺血猝死组(实验组)和空气栓塞死组(对照组),血清样本行ATR-FTIR检测,应用OMNIC软件进行光谱预处理并求二阶导数光谱,分别计算两组原始光谱及二阶导数光谱的相似度,并应用Matlab R2010a软件建立二维光谱模型。结果实验组与对照组的大鼠血清的原始红外光谱在峰形、峰位、峰强度均极其相似,相似度达99.78%,二阶导数光谱显示出两者相似度降至98.62%,二维光谱模型显示两组光谱在1 625cm~(-1)、1 550cm~(-1)、1 080cm~(-1)及860cm~(-1)附近的成分差异,且它们的自动峰个数不相同,提示两组在蛋白质、糖原、核酸等分子含量存在较明显差异。结论仅从一维光谱上难以区分出两组的分子差异,二维红外光谱可以直观、有效地反映出急性心肌缺血猝死与空气栓塞死的大鼠血清分子差异,有望应用于法医学死因鉴别。