Preliminary classification scheme of silicone based lubricants using DART-TOFMS

Forensic Discrimination of condom lubricants using ATR-FTIR spectroscopy in combination with chemometrics- effect of matrices, pre-coital and post-coital conditions

The escalating rates of rape and sexual assault cases underscore the essential need to analyze associative evidence of sexual assault to ensure justice. The condom, when used during the act of sexual assault/rape, leaves behind traces of lubricant that could be instrumental in establishing the link between the victim and perpetrator. This leading evidence is crucial especially when the traditional DNA analysis is challenging owing to the lack of biological evidence. The present study employs the use of ATR FTIR spectroscopy coupled with the chemometric, to discern the chemical discrimination of condom lubricants. The study also aimed to investigate simulated real-case scenarios by analysing the effect of different matrices such as vaginal fluid, menstrual blood, and undergarment substrates (cotton, polyester and nylon) on condom traces. The difference in the spectral profile of pre-coitus and post-coitus samples was also investigated. The results of the present study are noteworthy, unveiling the efficacy of discriminating the condom lubricants of different brands and other frequently used household lubricants with 100% sensitivity, specificity, and accuracy. Condom lubricants are detected despite the presence of contaminants such as menstrual blood, and vaginal fluid, across different substrates and, in post-coital conditions. In conclusion, this study presents a comprehensive approach to analysing condom lubricants, offering a potential breakthrough in the investigation of sexual assault cases, coupled with the ability to counter false accusations.

Forensic aspects of condom evidence: Analysis, interpretation, and recent trends

In recent years, collection and analysis of condom evidence in sexual assault investigations are becoming more common in forensic caseworks. Condom analysis can provide investigative leads or establish potential contact between the suspect and victim in the absence of DNA evidence or supplement biological evidence. Recent forensic literature shows significant advancements in the analysis of condom lubricants, including casework samples. There is an increasing trend in the use of chemometric tools for the comparison and interpretation of the results. This review highlights the advances in common analytical techniques used for the analysis of condom lubricants with a particular focus on the developments occurring in recent years, including chemometric interpretation. The analysis of reference and casework samples (swab samples, samples on skin, clothing and fingermark) are discussed separately. For casework samples, the transfer and persistence of different lubricant formulations are discussed, along with their detection with various analytical approaches. The issues with the interpretation of lubricants are also discussed in another section, with particular emphasis on samples such as personal hygiene products which have similar formulations with sexual lubricants and the interpretation of negative profiles. The current challenges in the field and prospects for future research are also discussed.

LMJSSP for analysis of prophylactic lubricants, spermicides and residues

DNA evidence in sexual assault cases have proven increasingly difficult to obtain and analyse due to increased condom use. With more interest in alternatives to DNA evidence, prophylactic lubricants, spermicides and residues may be interesting prospects. Current interest in the analysis of prophylactic residues focuses on the evaluation and identification of lubricants and constituents, primarily through gas chromatography or Fourier transform infrared spectroscopy. Though cost-effective methods, extensive sample preparation and destructive modes of analysis remain an area for improvement. As a result, the focus has since shifted to ambient ionization methods that offer adequate sensitivity and reduced sample preparation. The Liquid Microjunction Surface Sampling Probe (LMJSSP) is a versatile ambient ionization source that employs a probe that supports a continuously flushing droplet that extracts analytes when placed in contact with a surface. The analytes are aspirated into the mass spectrometer with a Venturi pressure. In this work we use the LMJSSP to analyse the trace transfer of condom lubricant to different types of fabric (cotton, cotton-spandex, and denim). Furthermore, we examine the sensitivity and storage conditions for the direct analysis method on different swab types (cotton, silicone, and foam). Additionally, Principal Component Analysis (PCA) and Maximally Collapsing Metric Learning (MCML) are utilized for visualization of differentiability of commercially available condom brands including Durex™ and Trojan™, and product subtypes. The results present an interesting multi-disciplinary approach of using a direct liquid extraction ambient ionization technique and machine learning to improve the overall workflow for the analysis of lubricants, swabs and fabrics. Machine learning algorithms were able to differentiate between inherent differences of Durex™ and Trojan™ condoms.

Application of direct analysis in real-time mass spectrometry (DART-MS) in forensic science: a comprehensive review

Background

As the rate of crime is constantly increasing, the workload on the forensic analyst also piles up. The availability of a limited number of seized samples makes it crucial to directly analyze the sample, thereby preventing wastage in the prior steps of sample preparation. Due to such needs, the forensic community is consistently working on broadening the usage of direct analysis in real-time mass spectrometry (DART-MS). DART-MS is a relatively new technique for rapid mass spectral analysis. Its use for chemical analysis credits its ability to analyze the sample at atmospheric pressure.

Main body

This article gives insight into the ionization mechanisms, data analysis tools, and the use of hyphenated techniques like thermal-desorption-DART-MS, infrared-thermal-desorption-DART-MS, Joule-heating thermal-desorption-DART-MS, etc. This review summarizes the applications of DART-MS in the field of Forensic Science reported from 2005 to 2021. The applications include analysis of drugs, warfare agents, gun-shot residues, ink differentiation, and other forensically relevant samples. The paper also presents the relation between the type of DART-MS technique and the ionization mode used for a particular class of compounds.

Conclusion

The review follows that the high-resolution mass-spectrometers or low-resolution mass-spectrometers systems in the positive or negative mode were highly dependent on the type of analyte under investigation. Drugs, inks, dyes, and paints were mainly analyzed using the positive ionization mode in the HRMS technique. The examinations of fire accelerants predominantly used the positive ionization mode in the LRMS technique. Moreover, the limit of detection values obtained from the qualitative screening of street drugs were of ppb level, indicating high sensitivity of DART-MS. Considering the work done in the past years, there are potential future research needs of this technology, especially in forensic science.

Graphical Abstract

On the impact of DNA extraction procedure on the recovery of condom evidence

On the international level, different protocols exist for sampling condom traces, similarly to DNA traces. Usually collected with cotton swabs, some protocols use nylon swabs, which were found more efficient for the desorption of DNA, because they offer a better desorption of the compounds during the extraction. In addition, not all the protocols do contain swabs for other evidence than DNA. Depending on the protocol, the forensic scientist will either benefit from a swab purely dedicated to condom evidence or will have to prioritize which evidence to analyse first. It is more likely that priority will be set to DNA, but in the eventuality that no DNA would be recovered, it is necessary to know whether the swab can still be used for condom evidence recovery or not. This work aimed to use Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS-FTIR) to investigate whether DNA extraction affects the recovery of condom traces. Traces were simulated by either rubbing condoms on the swabs or soaking the swabs in solutions containing different concentrations of polydimethylsiloxane (PDMS), the most common condom lubricant found on the market. DNA extraction was found to generate a loss of silicones, when processed prior to condom silicone extraction. Therefore, results show that protocols should contain cotton swabs dedicated to condom traces collection.

The use of an optimized DRIFTS-FTIR method for the forensic analysis and classification of silicone condom lubricants

Condom residues may be encountered in forensic investigations as traces left in sexual assault or rape cases. Considering casework samples analysis, where material from swabs will need to be extracted, Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) was reported as the most relevant method for trace evidence analysis. However, there has been no study to identify which specific parameters were the most suitable for the analysis of silicone-based lubricants, especially in terms of repeatability of the analyses. This study looked at the resolution and number of scans with the aim of optimizing these parameters for polydimethylsiloxane (PDMS) analysis and detection. Experimental parameters were refined while performing a full factorial experimental design (FFD) for the screening and extended to a face centered central composite design (FCCD) for the optimisation. Repeatability of the results was also investigated using principal component analysis (PCA) and hierarchical cluster analysis (HCA) in order to select the most relevant analytical parameters. The optimized DRIFTS parameters were then used to collect data from reference material and from traces after a transfer in a vaginal matrix has occurred. Discrimination models were built with DRIFTS data and compared to pre-existing models built with Attenuated Total Reflectance (ATR)-FTIR data. Condom traces were recovered from volunteers who had sexual intercourse using different types of silicone-lubricated condoms. The corresponding traces characteristics were investigated and analysed.

A preliminary investigation of underwear as a support for condom evidence in rape and sexual assault cases

Condom lubricants have been found to be a new type of evidence to investigate and analyze in sexual assaults and rape cases. Casework studies highlighted two main types of trace evidence supports collected from the victim and send to forensic laboratories: cotton swabs and victims' underwear. If cotton swabs have been used in most of the recent published research papers, the underwear and the textile effects on the recovery of condom lubricants are under investigated although such studies are very important for the interpretation of the evidence, as highlighted in the Regina v. Andrew Nicholas Malkinson case. This work employed Diffuse Reflection Infrared Fourier Transform Spectroscopy (DRIFTS-FTIR) and Attenuated Total Reflectance (ATR-FTIR) to investigate the content of various feminine underwear and the effect of a laundry procedure on the recovery of any type of evidence. 7 laundry detergents and 9 slips from common brands/models were purchased for this study. No silicones were detected in the laundry detergents, which indicates they are unlikely to generate false positive in terms of detection of silicones. However, silicones were detected in most of the brand new underwear, which was found to be an issue when interpreting the evidence. The laundry procedure was found to significantly affect the evidence, with a strong decrease of the absorbance pre and post washing. Unfortunately, no trend regarding the temperature or the type of textile could be drawn.

A longevity study to determine appropriate storage conditions for sexual lubricants using spectroscopic and spectrometric techniques

There has been an increase in the number of reported cases in which assailants have used a condom or sexual lubricant. Sexual predators understand that DNA from seminal fluid is one of the main forms of evidence used to connect a suspect to a victim or crime scene; therefore, the use of condoms in sexual assault cases has increased. This dilemma has led to research into other types of trace evidence (e.g., sexual lubricants). The study presented herein was performed to determine the optimal storage time length and conditions appropriate for storing trace lubricant residue. This research project used Fourier transform infrared spectroscopy (FTIR), direct analysis in real time-high resolution mass spectrometry (DART-HRMS), and gas chromatography-mass spectrometry (GC-MS) techniques to analyze the stored swabs containing sexual lubricants at 8 timepoints over 18 months. Blank, personal lubricant, and condom swabs were stored under several environmental conditions. Swab storage allowed for the determination of whether lubricants degraded, thus adversely affecting the ability to recognize the classification patterns. Resulting spectra from each instrument can be used to identify environmental degradation of lubricant samples and generate investigative leads. Pearson Correlation Coefficients and time plots of the chemical components were used to determine if chemical breakdown occurred for each lubricant and if the pattern changed significantly. Results showed that the strongest correlations occur between the initial timepoint (T 0) and one month (T_1m), with correlations decreasing consistently up to eighteen months (T_18m). The best storage conditions were determined to be 22 °C at both 16% and 50% humidity. The ability to understand the effects of environment and time to the analysis of sexual lubricants may offer helpful information when analyzing sexual assault kits.

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.

Chemometrics in forensic science: approaches and applications

Forensic investigations are often reliant on physical evidence to reconstruct events surrounding a crime. However, there remains a need for more objective approaches to evidential interpretation, along with rigorously validated procedures for handling, storage and analysis. Chemometrics has been recognised as a powerful tool within forensic science for interpretation and optimisation of analytical procedures. However, careful consideration must be given to factors such as sampling, validation and underpinning study design. This tutorial review aims to provide an accessible overview of chemometric methods within the context of forensic science. The review begins with an overview of selected chemometric techniques, followed by a broad review of studies demonstrating the utility of chemometrics across various forensic disciplines. The tutorial review ends with the discussion of the challenges and emerging trends in this rapidly growing field.

Condom evidence: Characterisation, discrimination and classification of pyrolysis-GC-MS profiles

Analysis of condom evidence commonly focusses on the detection of silicone-based lubricants, such as polydimethylsiloxane (PDMS). Although various instruments are used to analyse silicone lubricants, pyrolysis-gas chromatography coupled to mass spectrometry (py-GC-MS) is one of the few instruments that presents immediate applicability to casework. However, considering that this technique detects silicone-based evidence, it is important to evaluate the discrimination potential of the method when applied to various samples. Examination of the variability within a large sample set from an international market is needed to evaluate the most distinguishing compounds likely to be detected in casework. In this study, 70 condoms, personal hygiene products, and lubricants, were analysed using py-GC-MS. Resulting pyrograms were characterised using published spectral databases. Pyrolysates data were extracted and evaluated using multivariate techniques. Qualitative visual inspection of the data, as well as statistical analysis, revealed at least five groups within the dataset. Discrimination was based on four main oligomers, as well as six minor compounds from siloxane degradation. Condom lubricants were found to present a very regular pattern, allowing for the majority of them to be differentiated from personal lubricants.

Forensic applications of DART-MS: A review of recent literature

The need for rapid chemical analyses and new analytical tools in forensic laboratories continues to grow due to case backlogs, difficult-to-analyze cases, and identification of previously unseen materials such as new psychoactive substances. To adapt to these needs, the forensics community has been pursuing the use of ambient ionization mass spectrometry, and more specifically direct analysis in real time mass spectrometry (DART-MS), for a wide range of applications. From the inception of DART-MS forensic applications have been researched with demonstrations ranging from drugs of abuse to inorganic gunshot residue to printer inks to insect identification. This article presents a review of research demonstrating the use of DART-MS for forensically relevant samples over the past five years. To provide more context, background on the technique, sampling approaches, and data analysis methods are presented along with a discussion on the potential future and research needs of the technology.

Combined Statistical Analyses of Forensic Evidence in Sexual Assault: A Case Report and Brief Review of the Literature

DNA analysis has been widely used in the forensic field in order to contribute to identifying the perpetrator of a crime. Forensic investigation in sexual assaults usually focuses on locating and identifying biological fluids, followed by DNA analysis. The identification of certain compounds present in condoms can be useful to reconstruct the occurred event, especially in cases of sexual assaults where the DNA analysis did not show the presence of a male profile and where RNA analysis did not show the presence of sperm markers. Herein we describe the case of a woman reporting to be victim of sexual assault, who was not able to provide accurate information concerning the dynamics of the event; she remembered only forced penile-vaginal penetration by a single perpetrator. We performed short tandem repeat (STR) analyses and mRNA typing for forensic genetics testing on vaginal and rectal swabs collected on the victim, and Fourier-transform infrared spectroscopy (FTIR) followed by chromatographic analyses for the detection of condom compounds on the same swabs. The STR analysis showed only the victim's genetic profile, and RNA analysis showed only the presence of vaginal and skin markers. In this situation, the identification of condom compounds residues on vaginal swabs became important as it complemented other collected evidences allowing the Court to reconstruct the events. A proposal of likelihood ratio (LR) calculation for the assessment of the weight of evidence in this case is described.

Temperature-Dependent DART-MS Analysis of Sexual Lubricants to Increase Accurate Associations

The analysis of lubricant evidence is a recent development in sexual assault investigations and in the absence of any biological evidence may assist in linking an assailant to the victim or crime scene. An ambient ionization technique, high-resolution direct analysis in real-time mass spectrometry (HR-DART-MS), was employed to characterize a sample set of 33 water-based lubricants. As lubricants are complex multicomponent mixtures, this study investigated if different thermal desorption temperatures could elucidate different additives and provide additional information. A low-temperature, high-temperature, and thermal desorption/pyrolysis DART-MS protocol was used to characterize the water-based lubricant sample set. The strength of the methodologies was evaluated using positive and negative likelihood ratios that were calculated from inter- and intra-pairwise comparisons using Pearson correlation coefficients. The low-temperature DART-MS protocol afforded valuable information pertaining to volatile additives (e.g., flavors and fragrances) and provided positive likelihood ratios that would provide strong support for true positive and negatives than the high-temperature protocol when associating between individual samples and samples to their respective sub-groupings. The thermal desorption/pyrolysis DART analytical protocol provided enhanced differentiation between samples due to the precise temperature control using a thermal gradient. Moreover, the total ion spectra obtained from the thermal desorption/pyrolysis protocol, not only had high positive and negative likelihood ratios, this method also provided the most discrimination as determined by empirical cross entropy plots. Graphical Abstract.