Rapid Analysis of Volatile Phenols from Grape Juice
by Immersive Sorbent Sheet Extraction Prior to Direct Analysis in
Real-Time Mass Spectrometry (DART-MS)
posted on 2021-10-07, 20:05authored byJessica
P. Rafson, Gavin L. Sacks
Poly(dimethylsiloxane)-based
thin-film sorbent sheets (SPMESH)
have previously been used for parallel headspace (HS) extraction prior
to direct analysis in real-time mass spectrometry (DART-MS) for rapid
quantitation of odorants in complex matrices. However, HS-SPMESH extraction
is poorly suited for less volatile odorants, e.g., volatile phenols.
This report describes modifications to the previous SPMESH extraction
device, which make it amenable to parallel extraction of low-volatility
analytes from multiwell plates under direct immersion (DI) conditions.
Optimization and validation of the DI-SPMESH-DART-MS approach were
performed on four volatile phenols (4-ethylphenol, 4-ethylguaiacol,
4-methylguaiacol, and guaiacol) of relevance to the quality of grape
juices. Negative-ion mode DART-MS spectra showed a series of oxygenated
adducts [M + nO – H]− for
all analytes, but isobaric interferences could be limited for three
of the four analytes by selecting an appropriate MS/MS transition.
Signal suppression from nonvolatiles (sugars, acids) could be overcome
by a rinse step. DI-SPMESH-DART-MS analysis of 24 samples could be
performed in ∼45 min (30 min extraction, 16 min DART analysis)
with 0.5–3 μg/L detection limits in aqueous and model
juice solutions. In real grape juices (n = 5 cultivars),
good accuracy (72–137%) could be achieved for two of the four
volatile phenols initially investigated, 4-ethylphenol and 4-ethylguaiacol.
However, poor accuracy was observed for guaiacol in some cultivars,
and 4-methylguaiacol could not be quantitated due to interferences
with other volatile phenols. Despite these limitations, DI-SPMESH-DART-MS/MS
may be useful for prescreening a large number of samples prior to
more selective conventional analyses.