Browsing by Subject "desorption atmospheric pressure photoionization"

Here, we demonstrate the application of desorption atmospheric pressure photoionization (DAPPI) as a screening method at the Criminal Laboratory of the Finnish National Bureau of Investigation for samples confiscated by the Finnish criminal police. DAPPI is a fast mass spectrometric technique to analysis compounds directly from the sample surface in ambient atmosphere. In DAPPI, the sample is thermally desorbed from the sample surface using hot solvent vapor, after which the analytes are ionised in the gas-phase by photon-initiated gas-phase reactions. DAPPI was applied to the direct analysis of confiscated drugs, anabolic steroids and explosives of various matrices without any sample preparation. Confiscated drug samples included e.g. tablets, powders, herbal mixtures, herbal products [Catha edulis (khat) leaves, opium, Cannabis sativa, Psilocybe mushrooms] and ampules and tablets containing anabolic steroids. Powders were sprinkled on a 2-sided tape on a microscope slide, after which the excess powder was shaken away from the tape surface. Liquid samples were analysed from a kitchen paper, after application of 1 Äl of oil from ampules. Other samples were analysed by simply placing them on the DAPPI sampling stage and by directing the solvent plume on the sample surface. DAPPI proved to be a fast and specific analysis technique to this type of forensic analysis. DAPPI does not require any sample preparation, which therefore is well suited for fast forensic analysis, especially for plant samples and oily anabolic steroids, which are considered very challenging with conventional methods. Contamination of the mass spectrometer could be avoided by adjustment of the distance of the sample from the mass spectrometer inlet. Memory effects or contamination of the MS instrument were not observed even after several weeks of DAPPI measurements. DAPPI was also used for trace detection of the explosives trinitrotoluene (TNT), nitroglycol (NK), nitroglycerine (NG), penitrit (PETN), cyclonite (RDX), octogen (HMX) and picric acid. These organic explosives are nitrated compounds, which are divided based on their chemical structure into nitroaromatics (TNT and picric acid), nitroamines (RDX and HMX) and nitrate esters (PETN, NG and NK). Explosive dilutions were analysed with DAPPI from a polymer surface [poly(methyl methacrylate), PMMA] after application and drying of 1 Äl of sample. Also forensic analysis of post-blast residues from different matrices were done. DAPPI was effective in the ionisation of nitroamines and nitrate esters as their adducts with anions such as nitrate, acetate, formate and acetate. TNT used to form negative molecular ions through electron capture and picric acid formed deprotonated molecules through proton transfer. A DAPPI-MS method was developed for all explosives but the identification of the very low concentration explosive traces from wild variety of matrices proved to be difficult.

Oxysterols and vitamin D related compounds are found to be biologically active in brain. They might be involved in different psychiatric and neurodegenerative diseases. These compounds have traditionally been analysed from tissues using somewhat laborious and time-consuming gas chromatograpy and liquid chromatography mass spectrometric methods. To the side of these methods ambient desorption ionization methods have been developed. The advantage of these methods is rapid and easy operation. Usually minimal or no sample pretreatment is required. In addition these methods can be applied to imaging of for example tissues. The aim of this work was to study if it is possible to detect certain oxysterols and vitamin D related compounds from rat brain tissue samples with desorption atmospheric pressure photoionization (DAPPI). The compounds chosen to this study were cholesterol, vitamin D3, 25-hydroxyvitamin D3, 7-dehydrocholesterol, desmosterol and 7-ketocholesterol. DAPPI is especially suitable for efficient ionization of this kind of neutral and non-polar compounds. Detected MS and MSn spectras of the brain tissue samples were compared to those obtained from standard compounds. As a result we could not detect vitamin D3, 25-hydroxyvitamin D3, 7-dehydrocholesterol, desmosterol from rat brain samples with DAPPI. Excluding vitamin D3 it is possible that those other analytes are present at the spectras of brain samples but there is some other compound with same mass which makes the reliable identification of studied compounds impossible. 7-ketocholesterol and cholesterol were the only compunds we detected from brain tissue sections. 7-ketocholesterol can be formed via auto-oxidation in samples containing excess amount of cholesterol. According to this study it is impossible to say if the detected 7-ketocholesterol is formed endogenously or during sample preparation and analysis.