Qualitative Analysis of Glass Microfragments Using the Combination of Laser-Induced Breakdown Spectroscopy and Refractive Index Data.

We have successfully demonstrated that although there are significant analytical challenges involved in the qualitative discrimination analysis of sub-mm sized (microfragment) glass samples, the task can be solved with very good accuracy and reliability with the multivariate chemometric evaluation of laser-induced breakdown spectroscopy (LIBS) data or in combination with pre-screening based on refractive index (RI) data. In total, 127 glass samples of four types (fused silica, flint, borosilicate and soda-lime) were involved in the tests. Four multivariate chemometric data evaluation methods (linear discrimination analysis, quadratic discrimination analysis, classification tree and random forest) for LIBS data were evaluated with and without data compression (principal component analysis). Classification tree and random forest methods were found to give the most consistent and most accurate results, with classifications/identifications correct in 92 to 99% of the cases for soda-lime glasses. The developed methods can be used in forensic analysis.

Forensic investigation of glass microfragments exposed to heat.

The comparative analysis of glasses based on refractive index (RI) is a widely used method in forensic examinations. However, it cannot be directly applied if the control sample has previously been altered by heat or fire, since RI can change significantly in this process. For this reason, the refractive index of the fragments recovered from the perpetrator's clothing can also differ from the control sample recovered after the fire, although they originate from the same source. In the present study, annealing was used as a possible way for the examination of glass microfragments exposed to heat. The appropriate conditions of annealing were investigated first. Then fragments from a toughened and a non-toughened glass were heated in a furnace for various times at 450 and 650 °C and cooled down immediately to model different heat expositions. It resulted in a significant change in the RIs in all cases. These fragments, together with the non-treated samples from the same pane of glasses, were annealed using the optimized parameters. In a similar process, further glasses exposed to real fire were examined. It was found, both in the model experiments and for the fragments exposed to fire, that - regardless of the heat exposure conditions - annealing resulted in the same RI for fragments from the same source, while for different samples different values were observed. Altogether, 11 glasses were examined in 38 experiments, and it was found that annealing combined with refractive index measurement could be a possible way for the examination of heated fragments. The changes in RIs and standard deviations observed during the experiments are consistent with literature data.

Refractive index measurement of the smallest bulk and surface glass microfragments in a model case.

The refractive index measurement is a widely used investigation method of glass microtraces in forensic laboratories. The advantage of the method, in addition to its cost efficiency and repeatability, is that it is suitable for examining small fragments. In the present study, a real case was simulated, and fragments smaller than 250 micrometers obtained from five pieces of clothing, after breaking a pane of float glass, were investigated. In addition to the known (control) sample, altogether 25 bulk and 83 recovered surface fragments were also examined. In the first step, only one measurement was performed for each fragment to simulate the investigation of small fragments and test their measurability without crushing. All the bulk fragments met with the matching criterion Kmin  ≤ Q ≤ Kmax , in which Kmin and Kmax are the minimum/maximum value of the measured refractive indices of the known sample, while Q is the measured (mean) value of the questioned fragment. However, the matching ratio was only approximately 60% for the surface fragments according to the one-edge measurements. After crushing, the false exclusion rate was significantly reduced, and 79 of the 83 recovered surface fragments met with the matching criterion. As a result of crushing, not only the probability of matching, but also the edge count values improved significantly. Although the refractive index is only one property examined in the totality of glass analysis, the results of the present work can significantly contribute to the determination of the origin of small glass particles in real forensic cases.

Photochemical Formation of Diazenecarbaldehyde (HNNCHO) and Diazenecarbothialdehyde (HNNCHS) in Low-Temperature Matrices.

The photochemical decomposition of 1,2,4-oxadiazole-3,5-diamine and 1,2,4-thiadiazole-3,5-diamine was investigated in low-temperature Ar and Kr matrixes at different wavelengths. The analysis of matrix-isolation infrared (MI-IR) spectra aided by high-level quantum chemical computations showed not only that these photochemical reactions yield [NH2, C, N, X] (X = O, S) isomers but also that the bands of a novel, formerly unobserved species were observed. The comparison of computed IR spectra of potential products with the observed spectra suggests that these species are the diazenecarbaldehyde (HNNCHO) and diazenecarbothialdehyde (HNNCHS). Neither of the reactive HNNCHO and HNNCHS molecules was observed experimentally before. Both molecules are identified in the matrix as a complex with the other photoproduct, NH2CN. Comparison of the present experiments with former photochemical experiments on 1,2,5-oxadiazole-3,4-diamine and 1,2,5-thiadiazole-3,4-diamine and the analysis of the rate of formation of the different photoproducts indicate that HNNCHO and HNNCHS are formed in a different reaction path than H2NNCX and H2NC(NX) (X = O, S), and not by photoisomerization from these latter products.

Macro- and microstructural tracking of ageing-related changes of papaverine hydrochloride-loaded electrospun nanofibrous buccal sheets.

Electrospun papaverine hydrochloride-loaded nanofibrous sheets consist of hydroxypropyl cellulose/poly(vinyl alcohol) composite were prepared for buccal administration for cerebral ischemia. The nanofibrous drug delivery system was subjected to accelerated stability test for four weeks in order to scrutinize the solid state changes relating to the stress induced (40±2°C/75±5% relative humidity) physical ageing. Micro- and macrostructural alterations were detected using scanning electron microscopy (SEM), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR) and positron annihilation lifetime spectroscopy (PALS). Significant changes were revealed at both supramolecular and macroscopic levels. Microscopic morphology uncovered major morphological transitions. Subtle variations of Raman and FTIR spectra indicated that the local chemical environment of papaverine was altered suggesting a partial phase transition of the active. Discrete o-Ps lifetimes and lifetime-distributions unveiled a two-step ageing process of the drug carrier. In addition to the tracking of the glassy-to-rubbery transition of the fiber forming polymers, the Raman spectroscopy enabled monitoring the kinetics of the phase transition observed.

Photochemical generation of H2NCNX, H2NNCX, H2NC(NX) (X = O, S) in low-temperature matrices.

The [NH2, C, N, O] and the [NH2, C, N, S] molecular systems were investigated by computational and matrix-isolation spectroscopic methods. The determination of the equilibrium structures and relative energies by CCSD(T) method was followed by the computation of the harmonic and anharmonic vibrational wavenumbers, infrared intensities, relative Raman activities, and UV excitation energies. These computed data were used to assist the identification of products obtained by UV laser photolysis of 3,4-diaminofurazan and 3,4-diaminothiadiazole in low-temperature Ar and Kr matrices. It is shown that two open-chain H2NNCX and H2NCNX and one cyclic H2NC(NX) (X = O, S) isomers are generated in the case of both systems. Except for H2NNCO and H2NCNS, the present study reports the first generation and spectroscopic identification of these compounds.

Matrix isolation and computational study of the [H, C, N, Se] isomers.

Nine minima on the ground-state singlet and ten minima on the lowest-energy triplet potential energy surfaces of the [H, C, N, Se] system were located at the B3LYP/aug-cc-pVTZ level of theory. The singlet isomers were further investigated by the higher-level CCSD(T) method. Besides their structure and relative energies, isomerization barriers and the dissociation energies of the most important fragmentation channels were determined. Anharmonic vibrational wavenumbers, infrared intensities, relative Raman intensities, and UV excitation energies were also computed to assist the detection of these species. Two of the singlet isomers were generated and investigated by IR and UV spectroscopic methods. First, HNCSe and its deuterated isotopomer, DNCSe, were prepared by the reaction of HBr/DBr with AgNCSe and deposited in an 8 K Ar matrix. Photolysis of (H/D)NCSe at 254 nm led to the formation of the novel (H/D)SeNC isomer, which decomposed upon broad-band UV irradiation.