Optimization of sorbent sheet geometry for high-throughput targeted odorant analysis

Abstract

Targeted trace level (< mg/kg) quantitative analysis of volatiles in wines, grape, and other matrices is time consuming and expensive. Solid phase microextraction-gas chromatography-mass spectrometry (SPME-GC-MS) is the gold standard for such analyses but is limited to around three samples per hour in typical configuration. Sorbent sheet extraction from headspace direct analysis in real time mass spectrometry (SPMESH-DART-MS) has been put forward as a possible high-throughput alternative. By cutting out chromatography, SPMESH-DART reaches potential throughput of around 120 samples per hour, a 40-fold increase. However, poor sensitivity is reported for some compound classes. SPMESH uses an etched sorbent mesh to facilitate parallel extraction and desorption of headspace volatiles, but thorough optimization of SPMESH mesh pattern geometry to enhance sensitivity is not reported. New SPMESH geometries were designed with varying mesh aperture and surface area. Using a turnkey DART-MS/MS system, performance of these geometries were evaluated using two odorants of particular interest to the wine and grape industry: 3-isobutyl-2-methoxypyrazine (IBMP; “green bell pepper”) and methyl anthranilate (MA; “grape candy”). Improvements in sensitivity were observed for mesh patterns with circular mesh apertures in place of square, and for larger mesh apertures. Increasing surface area did not enhance sensitivity. These results are likely because SPMESH-DART-MS sensitivity is limited by transmission of absorbed volatiles from SPMESH to the MS as opposed to limitations in volatile extraction and desorption. The best performing design improved detection limits by 24-fold for IBMP (LOD decreased to 4.1 ng/kg from 100 ng/kg) and by 6-fold for MA (20.9 µg/kg from 135 µg/kg) as compared to the original SPMESH design.