Pyrolysis gas chromatographic-mass spectrometric identification of poly(dimethylsiloxane)s

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.

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.

Carbon Nanotubes Readily Disperse in Linear Silicones and Improve the Thermal Stability of Dimethylsilicone Elastomers

Stable silicone fluid-carbon nanotube dispersions were prepared in minutes by simple mixing processes, without the addition of solvents or surfactants and without the chemical modification of the nanotubes. With linear silicones of sufficient viscosity, a dual asymmetric centrifuge (SpeedMixer) was sufficient for dispersion; lower viscosity silicones required a brief ultrasound treatment. Optical microscopy indicates a homogeneous dispersion of multiwalled carbon nanotube (MWCNT) bundles in linear poly(dimethylsiloxane) (PDMS) oils. The facile dispersion of carbon nanotubes in PDMS has been reported in several previous publications and this appears to be general for silicones. MWCNTs also disperse readily, and to a greater extent, as assessed by optical microscopy, in poly(methylphenylsiloxane) and, in particular, poly(diethylsiloxane). Linear PDMS/MWCNT dispersions are stable against agglomeration for months. Platinum-catalyzed hydrosilylation of MWCNT-containing vinyl-/hydride-functionalized PDMS liquids yielded filled elastomers that unexpectedly exhibit significantly increased thermal stability. This enhancement occurs with only fractions of a weight percent of MWCNTs. Thermal gravimetric analysis shows a 54 °C increase in peak weight loss temperature (446-500 °C), an increased decomposition activation energy (158-233 kJ/mol), a second higher temperature decomposition process, and doubled char formation (20-40%) with only 0.5 wt %-added MWCNT. Pyrolysis combustion flow calorimetry confirmed the enhancement in thermal stability. Improvements in electrical conductivity were observed at loadings as low as 0.025 wt %. Spontaneous adsorption of dialkylsiloxane chains to MWCNT surfaces (wetting) and the resulting changes in the composite structure are implicated as the basis for dispersion and thermal behavior changes.

Identification and hazard prediction of tattoo pigments by means of pyrolysis-gas chromatography/mass spectrometry

The implementation of regulation for tattoo ink ingredients across Europe has generated the need for analytical methods suitable to identify prohibited compounds. Common challenges of this subject are the poor solubility and the lack of volatility for most pigments and polymers applied in tattoo inks. Here, we present pyrolysis coupled to online gas chromatography and electron impact ionization mass spectrometry (py-GC/MS) as quick and reliable tool for pigment identification using both purified pigments and tattoo ink formulations. Some 36 organic pigments frequently used in tattoo inks were subjected to py-GC/MS with the aim to establish a pyrogram library. To cross-validate pigment identification, 28 commercially available tattoo inks as well as 18 self-made pigment mixtures were analyzed. Pyrograms of inks and mixtures were evaluated by two different means to work out the most reliable and fastest strategy for an otherwise rather time-consuming data review. Using this approach, the declaration of tattoo pigments currently used on the market could be verified. The pyrolysis library presented here is also assumed suitable to predict decomposition patterns of pigments when affected by other degradation scenarios, such as sunlight exposure or laser irradiation. Thus, the consumers’ risk associated with the exposure to toxicologically relevant substances that originate from pigment decomposition in the dermal layers of the skin can be assessed. Differentiation between more or less harmful pigments for this field of application now will become feasible.

Characterization by mass spectrometry of an unknown polysiloxane sample used under uncontrolled medical conditions for cosmetic surgery

For a complete understanding of the raw material used for cosmetic surgery under uncontrolled medical conditions, an unknown sample of polydimethylsiloxanes has been investigated utilizing a combination of analytical techniques: pyrolysis/gas chromatography/mass spectrometry (Py/GC/MS), electrospray ionization (ESI)-MS, matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF)MS, and liquid chromatography (LC)/MS. Among these techniques, the LC/APCI-MS coupling allowed the fastest and more effective analysis. In addition, the complexity of the mass spectra deduced from these LC/MS experiments was simplified compared to the mass spectra obtained by MALDI-TOF. In this work, we have demonstrated how the LC/APCI-MS coupling applied to polydimethylsiloxane samples permits the full characterization of samples where end groups of different nature can be present in very small quantities.

Analysis of Condom Lubricants for Forensic Casework

The detection of DNA is inhibited in cases of sexual assault involving condom use. Trace evidence, including condom lubricant residues, provides crucial associative evidence in such cases. The existing Fourier transform infrared spectroscopy (FTIR) methods for lubricant analysis and detection are limited with regard to sensitivity and discrimination. The aim of this research was to establish a new method as an alternative to FTIR for the analysis of condom lubricant residues. Pyrolysis gas chromatography-mass spectrometry (PyGC-MS) and GC-MS are highly sensitive methods of analysis for a wide range of chemical substances. PyGC-MS and GC-MS were used to analyze condom lubricants in standard solution, from clean swabs and from postcoital swabs. Pyrolysis of polydimethylsiloxane (PDMS) lubricant forms cyclic products known as cyclic dimethyl siloxanes (DMS), which are separated and detected by the GC-MS. The polyethylene glycol (PEG) lubricant can be analyzed by GC-MS directly from solution. The methods of extraction and analysis presented in this paper were shown to be significantly more sensitive than FTIR for the analysis of PDMS and PEG condom lubricants. PDMS was detected as low as 1 mug in standard solution and from clean swabs using the PyGC-MS method. PEG was detected as low as 0.5 microg from standard solution and 50 mug from clean swabs using the GC-MS method. Unfortunately, we were unable to provide further discrimination between condom brands and subbrands. The methods established throughout the research were used successfully to detect condom lubricants from donated postcoital swabs. Lubricants were detected in abundance on swabs 12 h postcoitus. Recommendations are made regarding implementation of new methods for routine analysis of casework samples along with strict pyrolysis interpretation criteria to minimize the possibility of misinterpretation of false positives.

Mass spectrometry and scanning electron microscopy study of silicone tunneled dialysis catheter integrity after an exposure of 15 days to 60% ethanol solution

Anti-infectious lock is an emerging therapeutic option for preventing and/or controlling catheter-associated infection. Ethanol has widespread bactericidal activity, limited side effects, and low risk of inducing antimicrobial resistance. However, concerns have been raised about ethanol-induced catheter structural degradation. In this study, silicone catheters were immersed at 37 degrees C in three different solvents: 0.9% sodium chloride, 60% ethanol, and 95% ethanol for 4 h, 15 days and 15 days after a first storage of 4 h. Scanning electron microscopy (magnification 1000-20 000 times) of the inner surface of the catheter revealed no damage to the lumen surfaces of catheters immersed in 95% ethanol for 15 days compared with the reference catheter. Gas chromatography/mass spectrometry (GC/MS) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) analysis of the storage solutions revealed a significant release of polydimethylsiloxanes having a number of dimethylsiloxane units lower than 30 in the 95% ethanol solution and a structure highly consistent with a cyclic structure. Most release occurred within the first 4 h of exposure. In contrast, there was no difference in the small amounts of silicone released in 0.9% sodium chloride as reference and 60% ethanol solution, whatever the exposure time. These results should allow the development of clinical trials to assess the efficacy of the 60% ethanol lock technique in preventing or controlling the infectious complications of silicone dialysis catheters.

A protocol for the forensic analysis of condom and personal lubricants found in sexual assault cases

In sexual assault cases, lubricant trace evidence may supplement biological evidence, or may be the primary physical evidence where biological evidence is unavailable. This study considered a total of 50 lubricants from condoms and personal lubricant products available in Australia. Differentiation of the samples was attempted using fluorescence examination, Fourier transform infrared spectroscopy (DRIFTS), gas chromatography-mass spectrometry, liquid chromatography-tandem mass spectrometry, and pyrolysis gas chromatography-mass spectrometry. Eleven of the samples were uniquely identified by the analysis scheme, while the remainder of the samples were separated into nine groups. As a result of this study, a recommended protocol for the detection and analysis of an "unknown" biological swab was produced.

Identification of polydimethylsiloxane lubricant traces from latex condoms in cases of sexual assault

A polydimethylsiloxane (PDMS) liquid is used as a lubricant by many condom manufacturers. Because the use of condoms in sex crimes is likely to increase, a protocol was developed that could extract PDMS and the spermicide nonoxynol-9 from evidence items and separately identify them by Fourier transform infrared spectroscopy. Additionally, at least some discrimination was provided by microscopically identifying insoluble lubricants such as corn starch, lycopodium, silica, and talc which are added to some brands. Desorption chemical ionization mass spectrometry was used to compare the PDMS used by different manufacturers and to detect as little as 20 ng. The protocol was successfully used in two actual cases, one in which the assailant wore a lubricated condom, and a second in which he did not, but claimed to have done so.