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In this article, the effect of spray solvent on the analysis of selected lipids including fatty acids, fat-soluble vitamins, triacylglycerols, steroids, phospholipids, and sphingolipids has been studied by two different ambient mass spectrometry (MS) methods, desorption electrospray ionization-MS (DESI-MS) and desorption atmospheric pressure photoionization-MS (DAPPI-MS). The ionization of the lipids with DESI and DAPPI was strongly dependent on the spray solvent. In most cases, the lipids were detected as protonated or deprotonated molecules; however, other ions were also formed, such as adduct ions (in DESI), [M-H](+) ions (in DESI and DAPPI), radical ions (in DAPPI), and abundant oxidation products (in DESI and DAPPI). DAPPI provided efficient desorption and ionization for neutral and less polar as well as for ionic lipids but caused extensive fragmentation for larger and more labile compounds because of a thermal desorption process. DESI was more suitable for the analysis of the large and labile lipids, but the ionization efficiency for less polar lipids was poor. Both methods were successfully applied to the direct analysis of lipids from pharmaceutical and food products. Although DESI and DAPPI provide efficient analysis of lipids, the multiple and largely unpredictable ionization reactions may set challenges for routine lipid analysis with these methods., (Copyright © 2012 John Wiley & Sons, Ltd.)

We have studied the matrix effect within direct analysis of benzodiazepines and opioids from urine with desorption electrospray ionization-mass spectrometry (DESI-MS) and desorption atmospheric pressure photoionization-mass spectrometry (DAPPI-MS). The urine matrix was found to affect the ionization mechanism of the opioids in DAPPI-MS favoring proton transfer over charge exchange reaction. The sensitivity for the drugs in solvent matrix was at the same level with DESI-MS and DAPPI-MS (LODs 0.05-6 μg mL(-1)) but the decrease in sensitivity due to the urine matrix was higher with DESI (typically 20-160-fold) than with DAPPI (typically 2-15-fold) indicating better matrix tolerance of DAPPI over DESI. Also in MS/MS mode, DAPPI provided better sensitivity than DESI for the drugs in urine. The feasibility of DAPPI-MS/MS was then studied in screening the same drugs from five authentic, forensic post mortem urine samples. A reference measurement with gas chromatography-mass spectrometry (GC-MS) (including pretreatment) revealed 16 findings from the samples, whereas with DAPPI-MS/MS after sample pretreatment, 15 findings were made. Sample pretreatment was found necessary, since only eight findings were made from the same samples untreated., (Copyright © 2011 Elsevier B.V. All rights reserved.)

This study presents a new, simple, and low-cost technique to fabricate a nanocluster silicon (NCSi) surface on planar silicon using a micro-scale direct current (DC) discharge under ambient conditions. The method requires no masks, chemicals, vacuum environment, or laser, but only a high-voltage supply. The NCSi surfaces, characterized by scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy, consist of oxidized silicon nanoclusters 50-200 nm in diameter, likely formed by melting due to high temperatures in the discharge. The minimum size of the NCSi spot is determined by the size of the discharge tip (approximately 90 microm). Arbitrary NCSi areas can be produced on a silicon wafer by moving the discharge needle on the surface with the help of a computer-controlled xyz stage. NCSi surfaces can also be formed on three-dimensional (3D) surfaces, as demonstrated with silicon micropillars. NCSi surfaces can be used, for example, in various analytical applications. In this study, we demonstrate their use as sample plates in the analysis of drugs and peptides with desorption/ionization on silicon-mass spectrometry (DIOS-MS).