Spatially Resolved Headspace Extractions of Trace-Level Volatiles from Planar Surfaces for High-Throughput Quantitation and Mass Spectral Imaging.

The use of headspace thin-film microextraction devices (SPMESH) for parallel extraction of trace-level volatiles prior to direct analysis in real-time mass spectrometry (DART-MS) has been reported previously, in which volatiles were extracted from samples in multi-well plates. In this report, we demonstrate that headspace extraction of volatiles by SPMESH sheets can be performed directly from planar surfaces. When coupled with DART-MS, this approach yields volatile mass spectral images with at least 4 mm resolution. When samples were spotted onto general-purpose silica gel thin-layer chromatography (TLC) plates, the SPMESH extraction could reach equilibrium within 2-4 min and 48 samples could be extracted and analyzed in 14 min. Because volatilization of analytes from TLC plates was very rapid, SPMESH extraction was delayed by the addition of 5% polyethylene glycol. Good linearity was achieved in the microgram per liter to milligram per liter range for four odorants (3-isobutyl-2-methoxypyrazine, linalool, methyl anthranilate, and o-aminoacetophenone) in several matrices (water, 10% ethanol, juice, and grape macerate) using 5 μL sample sizes. Detection limits as low as 50 pg/spot (10 μg/L in grape macerate) could be achieved. In contrast to many reports on headspace solid-phase microextraction, negligible matrix effects were observed for ethanol and grape macerates compared to water. SPMESH can preserve volatile images from planar surfaces, and SPMESH-DART-MS from TLC plates is well-suited for rapid trace volatile analysis, especially with small sample sizes.