Browsing by Subject "desorption atmospheric pressure photoionization"

Sort by: Order: Results:

Now showing items 1-4 of 4
  • Flink, Anu (Helsingfors universitet, 2011)
    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.
  • Sathyanarayanan, Gowtham; Haapala, Markus; Sikanen, Tiina (2018)
    This work describes the interfacing of electrowetting-on-dielectric based digital microfluidic (DMF) sample preparation devices with ambient mass spectrometry (MS) via desorption atmospheric pressure photoionization (DAPPI). The DMF droplet manipulation technique was adopted to facilitate drug distribution and metabolism assays in droplet scale, while ambient mass spectrometry (MS) was exploited for the analysis of dried samples directly on the surface of the DMF device. Although ambient MS is well-established for bio- and forensic analyses directly on surfaces, its interfacing with DMF is scarce and requires careful optimization of the surface-sensitive processes, such as sample precipitation and the subsequent desorption/ionization. These technical challenges were addressed and resolved in this study by making use of the high mechanical, thermal, and chemical stability of SU-8. In our assay design, SU-8 served as the dielectric layer for DMF as well as the substrate material for DAPPI-MS. The feasibility of SU-8 based DMF devices for DAPPI-MS was demonstrated in the analysis of selected pharmaceuticals following on-chip liquid-liquid extraction or an enzymatic dealkylation reaction. The lower limits of detection were in the range of 1-10 pmol per droplet (0.25-1.0 mu g/mL) for all pharmaceuticals tested.
  • Kannela, Niina (Helsingfors universitet, 2013)
    Cortisol is a vital hormone for normal bodily functions. Both physical and mental stress, as well as many diseases like the Cushing syndrome are known to increase the human cortisol levels. These levels can be measured in many biological matrixes, such as saliva. Traditionally, these measurements have been done by using immunoassays or liquid chromatographic-mass spectrometric methods (LC-MS). However, in the last few years, ambient ionization techniques, which are quick and easy to use, have also proven suitable for quantitative analysis of compounds in biological matrixes. Thus, these techniques could offer an alternative to traditional methods in the analysis of cortisol from human saliva. The aim of this study was to investigate the suitability of desorption atmospheric pressure photoionization (DAPPI) for quantitative analysis of steroids in saliva. The investigated steroids were dehydroepiandrosterone (DHEA), cortisol and testosterone. Because of the low quantities of testosterone and DHEA in saliva, the study was mainly focused on cortisol analysis. In this study, the ionization mechanism for the steroids was observed to be proton transfer with every tested spray solvent (acetone, chlorobentzene and toluene). Even though the choice of spray solvent did not change the ionization mechanism, it affected the efficiency of ionization. In cortisol measurements acetone was observed to be the best solvent. The temperature of the microchip, as well as the UV-lamp used (dc- or rf-lamp), only affected the ionization slightly. In this study, measuring cortisol in non-pretreated saliva was not successful. However, solid phase extraction (SPE) method for the pretreatment of saliva was optimized with high recovery for cortisol (106 %). The detection limit for cortisol (50 nM) in water samples and the linear area of cortisol in both water and pretreated saliva samples (500 nM - 10 µM) were also determined. Poor repeatability of DAPPI-system was the main challenge in these measurements. The DAPPI-MS-method developed in this study is suitable for analyzing cortisol in pretreated saliva samples. However, without further development it is not sensitive enough to be used in quantitative analysis of cortisol in salivary levels.
  • Säilä, Pasi (Helsingfors universitet, 2016)
    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.