Therapeutic drug monitoring (TDM) is a quantitative test that measures drug dosage to prevent underdose or overdose in clinical practice . Ultrahigh sensitivity and selectivity techniques such as mass spectrometry has superior advantages over traditional immunoassay technique in the diagnosis and quantification of therapeutic drug . While liquid chromatography coupled with mass spectrometry has shown to be a "golden standard" for TDM [1,2], it requires complex sample preparation and chromatographic separation that may affect clinical demand time [2,9]. Therefore, the development of quick and simple direct sampling mass spectrometry method is essential . Ambient ionization was introduced into the literature in the early 2000s as a method that allows ionization of unmodified or minimally modified sample . More recently, researchers have been working on developing ambient ionization mass spectrometry (AIMS) method with little to no sample preparation that provides rapid results in a short time. In preliminary studies, AIMS has shown to effectively detect and quantify low concentration samples [5-10]. Studies have also shown how AIMS combined with ion mobility provides rapid diagnosis of complex or isomeric compounds without chromatographic separation [6,8,10]. The utilization of direct sampling technique such as desorption electrospray ionization (DESI), direct analysis in real time (DART), and paper spray (PS) coupled with mass spectrometry have advantageous for drug monitoring.
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 Roscioli, K. M.; Tufariello, J. A.; Zhang, X.; Li, S. X.; Goetz, G. H.; Cheng, G.; Siems, W. F.; Hill, H. H. Desorption Electrospray Ionization (DESI) with Atmospheric Pressure Ion Mobility Spectrometry for Drug Detection. The Analyst 2014, 139 (7), 1740–1750.