Browsing by Subject "desorption"

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  • Lindfors, Pia (Helsingfors universitet, 2010)
    The most important part in bioanalysis is the sample cleanup process which is usually the most laborious and time consuming part of the analysis and very susceptible to errors. A functional bioanalysis has to be quick, easily automated, sensitive, selective and stable. It also needs to be suitable for high throughput analysis. Desorption atmospheric pressure photoionization (DAPPI) is a novel direct desorption/ionization technique for mass spectrometry that enables direct analysis of solids from surfaces or liquid samples from a suitable sample plate often without any sample preparation. The suitability of DAPPI-MS for biological samples was investigated by measuring the limits of detection for selected opioids and benzodiazepines and screening them from authentic urine samples. Limits of detection were measured for standard solutions and spiked urine. Opioids and benzodiazepines were analyzed from post mortem urine samples with an optimized DAPPI-MS method. Post mortem urine samples were analyzed with and without sample preparation. Sample preparation improved the sensitivity of the method remarkably. About 50 % of the analytes were detected without sample preparation and almost 100 % after sample cleanup. It is however difficult to estimate the suitability of DAPPI-MS as a screening method because not all analyte concentrations of the urine samples were known. Therefore we cannot be certain weither the results obtained without sample preparation are caused by the suppression of the urine matrix or if the concentrations of the analytes are below the limits of detection. The reliability of the method can further be improved by investigating the metabolites of the analytes and improving the system towards automation. On grounds of this research DAPPI-MS should be used cautiously as a screening method for urine samples without sample preparation and with only high enough analyte concentrations. DAPPI-MS shows promise as a screening method for opioids and benzodiazepines from urine when the sample cleanup is used before the analysis.
  • Aalto, Henni (Helsingfors universitet, 2011)
    Lipids are fat soluble compounds that are derived from living tissues. Lipids have many important physiological functions. Developing methods for efficient lipid analysis is important since lipids can function as biomarkers in diseases. Additionally these methods can be used for the discovery of the biological processes of disease development. Lipids comprise of molecules with different polarity and structure. Several mass spectrometric ionization methods have been used in the analysis of lipids but they usually require sample preparation prior to the analysis. Desorption electrospray ionization-mass spectrometry (DESI-MS) and desorption photoionization-mass spectrometry (DAPPI-MS) are novel ionization methods that allow sample analysis straight from the matrix, such as tissue, usually without any sample preparation. DESI-MS has already been used in the analysis of different lipids, but DAPPI-MS has only been used in the analysis of steroids. The ionization of a range of lipid compounds (phospholipids, triglycerides, fat soluble vitamins, fatty acids, and steroids) by DAPPI-MS and DESI-MS was studied. Analysis conditions were optimized for all the different lipid classes with both DAPPI and DESI using standard samples. Some lipids were also analysed straight from pharmaceutical preparations. There were differences in the suitabilities of DAPPI-MS and DESI-MS for the ionization of different lipid classes. DAPPI-MS worked well for the ionization of nonpolar lipids like triglycerides, vitamins and fatty acids, but the phospholipids fragmented in the DAPPI-MS process and showed no molecular ion. Previous studies have shown that DESI-MS works well in the ionization of phospholipids, and this study showed that it works reasonably well for other lipid groups as well, with the exception of some of the nonpolar lipids. New knowledge was acquired especially about the suitability of DAPPI-MS for the analysis of different lipids. Based on the results it can be said that DAPPI-MS works equally well or better than DESI-MS in the ionization of most lipid classes. The DAPPI method should still be further developed so that phospholipids, which are very important lipids in human physiology, could be analysed by DAPPI-MS. As lipids were not analysed straight from a tissue sample, there are no conclusions about the suitability of DAPPI-MS for the analysis of lipids straight from tissue samples.
  • 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.
  • Heikkinen, Janne (Helsingfors universitet, 2011)
    The ambition of the agricultural environmental programme is to reduce nutrient load, because greater part of the diffuse loading of phosphorus is caused by agriculture. A eutrophic influence of the phosphorus in water systems tends to be limited inter alia by constructed wetlands. Their main task is to allow sedimentation of eroded soil into the bottom of the wetlands. There is ambiguity on the findings of the functionality and the importance of the prevention of water loading among scientific research in Finland. The aim of this study is to examine by utilizing soil analyses what happens to the basin water eroded phosphorus in the wetland sediment and wether the sedimentary constituent of the soil be suitable for a substratum of plant production. Comparing the samples of basin soil and wetland sediments revealed that the eroded constituent of the basin soil got assorted on wetlands. The samples collected from the wetlands contained 48 % more clay than the samples collected from the basin soil. The growth of the clay concentration increased the reactive area of the sediment. In consequence, it contained 45 % more hydroxides of aluminium and iron in the samples of the sediment than the samples of the basin soil. Because of the hydroxides, the phosphorus sorption capacity was 52 % higher than in the samples of the basin soil. However, the degree of phosphorus saturation was equal in the sediment and basin soil, because the oxidized sediment contained 50 % more phosphorus extracted from hydroxides of aluminium and iron. At the time of sampling the sediment was in reduced state and the amount of its water extracable phosphorus was significantly higher compared to the oxidized sediment. Correspondingly, when the sediment became oxidized the sorption capacity for phosphorus increased significantly, therefore the phosphorus was desorbed from reduced sediment to the wetlands water. This was also proven in a pot experiment, where rye-grass that grew in the sediment suffered from a severe shortage of phosphorus. In contrast, rye-grass grown in the basin soil didn’t suffer from the deficiency of phosphorus at the same fertilization levels. After threefold extra fertilization of phosphorus, the dry matter yield, concentration of phosphorus and uptake of phosphorus on the second yield grown in sediment were equal to the results of the first yield grown in basin soil. According to the results of the pot experiment, the sediment in reduced state is weakly suitable for the substratum of plant production, because the sorption capacity of phosphorus is high. Instead, sediment suits well to be utilized in the areas wherein the soil includes plenty of easy soluble phosphorus, such as for the material of subgrade for the corral of livestock, because the sediment reduces the load of phosphorus directed to the environment.
  • Ajmalghan, Muthali; Piazza, Zachary; Hodille, Etienne; Ferro, Yves (2019)
    Herein we investigate absorption and desorption of hydrogen in the sub-surface of tungsten via Density Functional Theory. Both the near-surface diffusion and recombination of a bulk hydrogen atom with a hydrogen atom adsorbed upon the W(110) and W(100) surfaces are investigated at various surface adsorption coverage ratios. This study intends to model the desorption processes occurring during Thermal-Desorption Spectroscopy experiments and the absorption of hydrogen during gaseous or low energy atomic exposure. Since the diffusion and recombination processes are expected to change as the hydrogen coverage of the surface varies, different coverage ratios were investigated on both surfaces. We found that at saturation coverage of hydrogen on both surfaces, the activation barriers for the recombination of molecular hydrogen are below 0.8 eV. On the contrary, below saturation, the activation barriers for recombination rise to 1.35 eV and 1.51 eV depending on the coverage and on the orientation of the surface. Regarding the absorption of atomic hydrogen from the surface into the bulk, the activation barrier raises from less than 1.0 eV at saturation to around 1.7 eV below saturation on both surfaces. These results indicate that surface mechanisms certainly play a significant role in the kinetics of desorption of hydrogen from tungsten; it is also expected that surface mechanisms affect the total amount on hydrogen absorbed in tungsten during implantation.
  • Hannula, Juha (Helsingfors universitet, 2015)
    Ambient mass spectrometry includes methods where ions are produced outside of the mass spectrometry in atmospheric pressure direct from the surface of the sample without sample preparation. The first and most popular ambient ionization methods are DESI, desorption electrospray ionization and DART, direct analysis in real time. DAPPI, desorption atmospheric pressure photoionization is an ionization method where samples are desorbed with hot vapor from surface and then ionized by photoionization. The aim of this study was to develop desorption atmospheric pressure photoionization method in transmission geometry. In transmission geometry hot vapor for microchip is directed through metal or polymer meshes to mass spectrometer inlet. Liquid samples can be analyzed either by soaking the mesh to liquid sample or apply a sample droplet to the mesh. Hot vapor desorbs analytes from the mesh and analytes are ionized in a gas phase by photoionization using VUV lamp. In this method optimal positioning of the mesh and the microchip was determined. Additionally optimal microchip heating power, dopant flow rate, nebulizer gas flow rate, capillary voltage and drying gas parameters were determined. Optimized method was applied for analyzing standard samples, vitamin juice samples and milk samples. According the analysis with authentic samples, transmission mode DAPPI can be applied for analyzing liquid samples without sample preparation. According the analysis with standard samples, transmission mode DAPPI can be applied for extraction of hydrophobic analytes from water samples. Comparing to conventional DAPPI, in transmission mode DAPPI spectra, intensities of the background ions are lower resulting higher signal-to-noise ratios with transmission mode DAPPI.