Atmospheric Solid Analysis Probe and Modified Desorption Electrospray Ionization Mass Spectrometry for Rapid Screening and Semi-Quantification of Zilpaterol in Urine and Tissues of Sheep.

Ambient ionization mass spectrometric methods including desorption electrospray ionization (DESI) and atmospheric solid analysis probe (ASAP) have great potential for applications requiring real-time screening of target molecules in complex matrixes. Such techniques can also rapidly produce repeatable semiquantitative data, with minimal sample preparation, relative to liquid chromatography-mass spectrometry (LC-MS). In this study, a commercial ASAP probe was used to conduct both ASAP-MS and modified DESI (MDESI) MS analyses. We conducted real-time qualitative and semiquantitative analysis of the leanness-enhancing agent zilpaterol in incurred sheep urine, kidney, muscle, liver, and lung samples using ASAP-MS and MDESI MS. Using ASAP, limits of detection (LOD) and quantitation (LOQ) in urine were 1.1 and 3.7 ng/mL, respectively, while for MDESI MS they were 1.3 and 4.4 ng/mL, respectively. The LODs for tissues were 0.1-0.4 ng/g using ASAP, and 0.2-0.6 ng/g with MDESI MS. The LOQs of the tissues in ASAP were 0.4-1.2 ng/g and 0.5-2.1 ng/g in MDESI MS. Trace levels of zilpaterol were accurately analyzed in urine and tissues of sheep treated with dietary zilpaterol HCl. The correlation coefficient ( R2 ) between semiquantitative ASAP-MS and MDESI MS results of urine samples was 0.872. The data from ASAP and MDESI MS were validated using LC-MS/MS; urinary zilpaterol concentrations ≥5.0 ng/mL or tissue zilpaterol concentrations ≥1.5 ng/g were detected by ASAP and MDESI MS, respectively, 100% of the time. Forty samples could be analyzed in triplicate, directly from biological matrixes in under an hour.