Low-level Pesticide Screening and Monitoring Wine Spoilage: Rapid Sample Concentration for Quantitative Analysis by DART Mass Spectrometry

DART is the most popular of the plasma-based ambient mass spectrometry ionization techniques, allowing for direct analysis of a variety of solid, liquid and gaseous samples without sample preparation. It can be used both in quantitative and qualitative experiments, and can provide the information necessary for identifying unknowns when coupled to high resolution accurate mass MS instruments. A major source of wine spoilage worldwide is caused by the yeast Brettanomyces bruxellensis, which is responsible for significant economic loss in the wine and beer industries. Wines exhibiting a “Brett” character generally include medicinal and barnyard odors that are attributed to two volatile phenols, 4-ethylphenol (4-EP) and 4-ethylguaiacol (4-EG). When 4-EP and 4-EG are at levels less than 400 μg/L they contribute positively to the sensory complexity of the wine giving it a spicy, smoky and leather aroma. However, when levels are greater than 620 μg/L, the “Brett” character may be too strong and the wine contains off-flavor notes and is often no longer marketable. A Direct Analysis in Real Time (DART) ambient ionization source was coupled to a high resolution accurate mass (HRAM) quadrupole mass spectrometer for full scan pesticide screening and quantitative targeted MS/MS analysis of 4-EP and 4-EG markers in wine spoilage. Both analyses employed a rapid unattended sample concentration step using Twister stir bar sorptive extraction (SBSE) prior to ambient desorption ionization. The detection limits were in the very low ppb range for the targeted wine analyses and demonstrated an increased detection for a range of pesticides. Sample analysis time using the DART ionization approach was 3 minutes or less per sample to thermally desorb the analytes directly from the Twister sorptive stir bar surface. Rapid monitoring methods enhance consumer safety, protect the integrity of the product and allow the manufacturers to take control to prevent economic losses.