Laser-induced acoustic desorption coupled with electrospray ionization mass spectrometry for rapid qualitative and quantitative analysis of glucocorticoids illegally added in creams.

We present a strategy for the coupling of laser-induced acoustic desorption (LIAD) with electrospray ionization (ESI) mass spectrometry. Different from desorption electrospray ionization (DESI) or paper spray ionization (PSI), the technique decouples the desorption of analytes from the subsequent ionization. The desorption is initiated by a shock wave induced in 10 μm titanium (Ti) foil coated with the sample, irradiated from the rear side by a laser beam, and then the desorbed neutral analytes are post-ionized by ESI and finally characterized by quadrupole/time-of-flight (Q-TOF) mass spectrometry (MS). Separating desorption from the ionization event makes this technique flexible and decreases the matrix effect and salt effect. Various kinds of common creams containing glucocorticoids are investigated using LIAD/ESI/MS without sample pretreatment. The results show that volatile and nonvolatile analytes in creams are sampled simultaneously by LIAD, providing a convenient way for high-throughput screening of the target compounds. In addition, quantitation of glucocorticoids in creams was performed by analyzing samples with decreasing concentrations of analytes (dexamethasone (20 μg g-1) used as an internal standard (IS)), until no more signal was observed. The limits of detection (LODs) of glucocorticoids were determined experimentally to be ranging from 0.7 μg g-1 for triamcinolone acetonide to 10 μg g-1 for beclomethasone dipropionate, which are two orders of magnitude lower than the regular usage of glucocorticoids (beclomethasone dipropionate 0.25 mg g-1, triamcinolone acetonide 0.25 mg g-1). Overall, LIAD/ESI/MS is demonstrated to be of great practical importance for rapid qualitative and quantitative analysis of glucocorticoids in creams, and good sensitivity can be achieved without tedious sample pretreatment and time-consuming chromatographic separation, irrespective of the presence of complex matrices.