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.