Identifying reliable ions for the statistical differentiation of structurally similar fentanyl analogs.

Definitive identification of fentanyl analogs based on mass spectral comparison is challenging given the high degree of structural and, hence, spectral similarity. To address this, a statistical method was previously developed in which two electron-ionization (EI) mass spectra are compared using the unequal variance t-test. Normalized intensities of corresponding ions are compared, testing the null hypothesis (H0 ) that the difference in intensity is equal to zero. If H0 is accepted at all m/z values, the two spectra are statistically equivalent at the specified confidence level. If H0 is not accepted at any m/z value, then there is a significant difference in intensity at that m/z value between the two spectra. In this work, the statistical comparison method is applied to distinguish EI spectra of valeryl fentanyl, isovaleryl fentanyl, and pivaloyl fentanyl. Spectra of the three analogs were collected over a 9-month period and at different concentrations. At the 99.9% confidence level, the spectra of corresponding isomers were statistically associated. Spectra of different isomers were statistically distinct, and ions responsible for discrimination were identified in each comparison. To account for inherent instrument variations, discriminating ions for each pairwise comparison were ranked based on the magnitude of the calculated t-statistic (tcalc ) value. For a given comparison, ions with higher tcalc values are those with the greatest difference in intensity between the two spectra and, therefore, are considered more reliable for discrimination. Using these methods, objective discrimination among the spectra was achieved and ions considered most reliable for discrimination of these isomers were identified.

Optical and spectroscopic characterization of crystalline structures in cannabis extracts.

Marijuana and hemp represent two broad classes of Cannabis sativa plants that are distinguished based on the concentration of the psychoactive cannabinoid delta-9-tetrahydrocannabinol (Δ9 -THC). In this work, solvent extracts derived from marijuana and hemp were characterized using optical and spectroscopic techniques. The crystalline components of the solvent extracts were first analyzed using polarized light microscopy to determine optical properties, namely, crystal system, optical sign, and principle refractive indices. Crystals from the marijuana-derived extracts exhibited an orthorhombic crystal system and were optically negative, with nß between 1.6320 and 1.6330 ± 0.0002. In contrast, crystals from hemp-derived extracts exhibited a monoclinic crystal system and were optically positive, with nß between 1.600 and 1.6040 ± 0.0002. Crystals were further distinguished through infrared spectroscopy, which highlighted structural differences between the two sample types, primarily based on differences in O-H stretching. Finally, single-crystal X-ray diffraction was used to definitively identify the crystalline components, confirming the presence of tetrahydrocannabinolic acid in marijuana-derived extracts and cannabidiol in hemp-derived extracts. Given the differences in crystal structure identified between marijuana-derived and hemp-derived solvent extracts, optical characterization provides a screening method to differentiate visually similar samples prior to confirmatory analysis.

Elemental Characterization and Discrimination of Nontoxic Ammunition Using Scanning Electron Microscopy with Energy Dispersive X-Ray Analysis and Principal Components Analysis.

Concerns over the toxic by-products produced by traditional ammunition have led to an increase in popularity of nontoxic ammunition. In this work, the chemical composition of six brands of nontoxic ammunition was investigated and compared to that of a road flare, which served as an environmental source with similar composition. Five rounds of each brand were fired while a further five were disassembled and the primer alone was fired. Particles collected from all samples, including the road flare, were analyzed by scanning electron microscopy with energy dispersive X-ray analysis. Common elements among the different ammunition brands included aluminum, potassium, silicon, calcium, and strontium. Spectra were then subjected to principal components analysis in which association of the primer to the intact ammunition sample was generally possible, with distinction among brands and from the road flare sample. Further, PCA loadings plots indicated the elements responsible for the association and discrimination observed.

Statistical approach to establish equivalence of unabbreviated mass spectra.

RATIONALE: In many legal and regulatory applications, mass spectral comparison of an unknown or questioned sample to a reference standard or database is used for identification; however, no statistical confidence level or error rate is determined. Therefore, a simple and rapid method to establish the statistical equivalence of mass spectra is needed. METHODS: The standard deviation of the abundance at each m/z ratio was determined from replicate measurements or from a statistical model. These standard deviations were used in an unequal variance t-test to compare two spectra at every m/z ratio over the entire scan range. If determined to be statistically indistinguishable at every m/z ratio, the random-match probability (RMP) that the specific mass spectral fragmentation pattern occurred by chance was calculated. RESULTS: n-Alkane and alkylbenzene standards of varying concentrations were analyzed on the same instrument at different ionization voltages. Using the proposed method, replicate spectra were successfully associated at the 99.9% confidence level, with RMP values less than 10(-29). Despite the similarity in fragmentation patterns, spectra were distinguished from others in the homologous series. Moreover, the n-alkane spectra were appropriately associated to and discriminated from those in a standard reference database at the 99.9% confidence level. CONCLUSIONS: A simple and rapid method to assign statistical significance to the comparison of mass spectra was developed and validated. This method may be useful for legal and regulatory applications, such as the identification of controlled substances, environmental pollutants, and food and drug contaminants.

Effect of evaporation and matrix interferences on the association of simulated ignitable liquid residues to the corresponding liquid standard.

Identification of an ignitable liquid in fire debris evidence can be complicated due to evaporation of the liquid, matrix interferences, and thermal degradation of both the liquid and the matrix. In this research, liquids extracted from simulated fire debris were compared to the original liquid using multivariate statistical procedures. Neat and evaporated gasoline and kerosene standards were spiked onto nylon carpet, which was subsequently burned. The ignitable liquid residues were extracted using a passive headspace procedure and analyzed by gas chromatography-mass spectrometry. Pearson product moment correlation coefficients, hierarchical cluster analysis, and principal components analysis were used to compare the liquids extracted from the carpet to the corresponding neat liquid. For each procedure, association of the extracts according to liquid type was possible, albeit not necessarily to the specific evaporation level. Of the three procedures investigated, principal components analysis offered the most promise since contributions from matrix interferences were essentially eliminated.

Effect of gas chromatography temperature program on the association and discrimination of diesel samples.

Five diesel samples were analyzed by gas chromatography-mass spectrometry (GC-MS) using six GC temperature programs, aiming to investigate the effect of temperature program on association and discrimination of the samples. Temperature programs varied by ramp rate and incorporated one- or two-step temperature ramps. Pearson product moment correlation coefficients and principal components analysis were used to evaluate differences in discrimination among the diesel samples afforded by each temperature program, based on the total ion chromatogram (TIC) and selected extracted ion profiles (EIPs). Association of diesel replicates and discrimination among samples based on the TIC and aromatic EIP were similar for all temperature programs based on scores plots. The alkane EIP was not useful in discriminating samples regardless of temperature program, because of similar alkane content of the diesel samples. The association and discrimination of diesel samples was largely unaffected by temperature programs that incorporated one- or two-step temperature ramps.

Association and discrimination of diesel fuels using chemometric procedures.

Five neat diesel samples were analyzed by gas chromatography-mass spectrometry and total ion chromatograms as well as extracted ion profiles of the alkane and aromatic compound classes were generated. A retention time alignment algorithm was employed to align chromatograms prior to peak area normalization. Pearson product moment correlation coefficients and principal components analysis were then employed to investigate association and discrimination among the diesel samples. The same procedures were also used to investigate the association of a diesel residue to its neat counterpart. Current limitations in the retention time alignment algorithm and the subsequent effect on the association and discrimination of the diesel samples are discussed. An understanding of these issues is crucial to ensure the accuracy of data interpretation based on such chemometric procedures.

Characterization of smokeless powders using nanoelectrospray ionization mass spectrometry (nESI-MS).

Smokeless powder is one of the most common types of explosives used in civilian ammunition and, hence, its detection and identification is of great forensic value. Based on comparison of physical properties, extraction yield in methanol, and the spectra obtained using nanoelectrospray ionization and multistage tandem mass spectrometry (MS/MS) in a quadrupole ion trap mass spectrometer, a method was developed to identify and differentiate unburned smokeless powders from different brands of ammunition. The mass spectrometry method was optimized for the simultaneous detection of the organic stabilizers commonly present in smokeless powders: methyl centralite, ethyl centralite, and diphenylamine. All but two of the powders were differentiated; however, the two that were not differentiated were produced by the same manufacturer. Gunshot residue from the cartridges was deposited on cotton cloth and collision-induced dissociation MS/MS was used to identify low levels of ethyl centralite in the residue, despite the presence of contaminants.

A review of recent advances in impurity profiling of illicit MDMA samples.

Profiling illicit ecstasy tablets has the potential to become an invaluable tool in the crackdown on drug trafficking, but that potential has yet to be fully realized. The impurity profile of an ecstasy tablet can be used to determine the method employed to synthesize the actual controlled substance, which in most cases, is 3,4-methylenedioxymethamphetamine (MDMA). Tablets can then be linked to a common synthetic route, potentially to a common manufacturer, and possibly even to a common manufacturing batch, based on the impurities present. Current methods for profiling MDMA tablets typically involve extracting the organic impurities for analysis by gas chromatography-mass spectrometry. The potential of profiling the trace metals present in tablets has begun to be investigated while more robust statistical and chemometric procedures are being applied to compare and link tablets. This article reviews the recent advances in MDMA impurity profiling from 2002 up to the end of 2006.