| Advances continue in direct desorption/ionization (DI) methods for mass spectrometry (MS) in which the goal is a reduction or elimination in sample handling/preparation steps to simplify chemical analysis using MS. Desorption electrospray ionization (DESI) is one such DI method. The collection and analysis of dried blood spots (DBS) has been utilized routinely in neonatal screening for in-born errors of metabolism for nearly 40 years. The coupling of direct analysis using DESI to DBS sampling offers several inherent advantages. These include: 1) Ease of sample handling, storage and shipment of biological specimens; 2) No requirement for sample preparation; 3) Reduced analysis times. The summation of these advantages results in significant savings in time and cost, and removes the requirement for arduous sample handling procedures currently employed for conventional DBS analysis. We describe here approaches and first results using DESI-MS on making direct measurements of xenobiotics in 1) plasma; 2) whole blood; 3) urine and 4) saliva for a variety of potential applications, including pharmacokinetics, toxicology, substance of abuse screening, and therapeutic drug monitoring. Examples include the direct analysis of whole blood (ala DBS) and plasma dried onto specialty papers for the quantitative analysis of sitamaquine, terfenadine, and prazosin over the range 10-10000 ng mL-1 and the analysis of opiates and prescription drugs in urine directly from a solid-phase microextraction probe or test strip. The intricate details of each approach will be presented. Performance parameters including precision, accuracy, linearity, matrix effects etc. and variations on the experiment will be presented. In some studies, LC-MS/MS was performed in parallel and the DESI-MS/MS results compared favorably. |
|
