Direct and rapid analysis of trace levels steroids in water by thermal desorption atmospheric pressure photoionization mass spectrometry

Abstract

Rapid analysis of steroids at a low concentration level in natural matrices by ambient mass spectrometry is still challenging. Here thermal desorption atmospheric photoionization (TD-APPI) was developed for direct analysis of steroids at trace levels from a 10 μL water sample. The thermal process is based on the Leidenfrost phenomenon, which can enable soft desorption of the water sample. The utilization of APPI can realize the highly efficient ionization of non-polar steroids. The quantification capability of TD-APPI for five steroids in water was tested, where satisfactory correlation coefficients (R² > 0.996) for standard curves and limits of detection (LODs in the range of 50–500 fg) were determined. In addition, the applicability for steroid analysis was also evaluated with three real water samples (tap water, surface water and river water). Due to the matrix effect, a factor of 2–10 decrease in sensitivity was obtained with real water. We show that TD-APPI can serve as a complementary tool for fast steroid analysis without any chemical pretreatment.