Mass spectrometry provides rapid, sensitive, and selective analysis. However, the analysis times are extended for complex samples if sample preparation and separation are required beforehand. Various desorption ionization mass spectrometry (DI-MS) methods have recently been presented to provide rapid sampling even of complex samples, with minimal or no sample preparation. At best, the analysis is performed in a few seconds. The aim of this work was to develop and evaluate DI-MS methods for efficient bio- and pharmaceutical analysis exploiting desorption/ionization on silicon (DIOS), desorption electrospray ionization (DESI), and desorption atmospheric pressure photoionization (DAPPI). For DIOS-MS analysis, a method based on micro-scale atmospheric pressure electric discharge was developed for the fabrication of novel sampling surfaces. The electric discharge method was used in two applications: 1) tuning of the wettability (hydrophilic/hydrophobic properties) of black silicon DIOS sample surfaces to improve DIOS-MS sensitivity and repeatability and 2) simplified fabrication of nanocluster silicon (NCSi) surfaces to be used as new DIOS sample surfaces, through surface roughnening of planar silicon. The electric discharge method is simple, rapid, flexible, and cost-effective, requiring only a high-voltage supply and a discharge needle. Potential applications for the created structures are numerous, including microreactors, diagnostic devices, sensors, optoelectronics, and micro- and nanofluidics. In this work, the surfaces were used in DIOS-MS analysis of drugs and small peptides. The capabilities of DESI and DAPPI in the analysis of various lipids and drugs of abuse were investigated with standard, spiked, and authentic biological and pharmaceutical samples. The lipids typically formed multiple, often unpredictable, ions differing according to the spray solvent. Therefore, DESI and DAPPI are more feasibly applied for targeted analysis than for the identification of unknown lipids. Targeted analysis of lipids was demonstrated with pharmaceutical and food products without sample pretreatment. The ionization of the drugs of abuse (benzodiazepines and opioids), on the other hand, was more straightforward. These drugs could be identified in urine without sample pretreatment by DESI and DAPPI, however, in routine analyses of authentic urine samples, the performance of the methods was not acceptable. In conclusion, although many DI-MS methods without sample preparation are powerful and fast tools for direct analysis, their suitability for a particular analysis always needs careful consideration. The true potential of DESI and DAPPI probably lies in imaging and in in situ analysis where sample pretreatment is not possible for example, because it disturbs the chemical integrity of the sample. Also, the unique features of the methods, such as chemical reactions induced by the spray solvent, offer interesting possibilities. DIOS, on the other hand, provides intriguing prospects for on-plate sample manipulation utilizing surface modifications; the high surface area provided by nanostructures offers large sample loading capacity, and the surface is easily modified to contain specific chemical functionalities.
|Place of Publication||Helsinki|
|Publication status||Published - 2012|
|MoE publication type||G5 Doctoral dissertation (article)|
Fields of Science
- 317 Pharmacy