Pitfalls encountered during quantitative determination of 3-alkyl-2-methoxypyrazines in grape must and wine using gas chromatography-mass spectrometry with stable isotope dilution analysis. Comprehensive two-dimensional gas chromatography-mass spectrometry and on-line liquid chromatography-multidimensional gas chromatography-mass spectrometry as potential loopholes.
The analysis of 3-alkyl-2-methoxypyrazines in Vitis vinifera grape must or wine at the low nanogram per liter level failed in several situations when applying a one-dimensional gas chromatographic analysis with mass spectrometric detection (GC-MS). Sample preparation methods such as headspace solid phase microextraction or solid phase extraction were convenient procedures, however lacking extraction selectivity for complex matrices. Analysis by comprehensive two-dimensional gas chromatography with mass spectrometric detection clearly demonstrated the potential for co-elution in such matrices and the risk for erroneous results when applying one-dimensional GC-MS. In one example, matrix problems would have been a challenge even for a comprehensive two-dimensional chromatographic approach with MS detection (GC×GC-MS). A solution to matrix problems was found by protonating the 3-alkyl-2-methoxypyrazines in acidic pH and sample clean-up using solid phase extraction with a mixed-mode polymeric cation-exchange sorbent. Quantification was performed by a stable isotope dilution assay, following analysis by on-line coupled high performance liquid chromatography with multidimensional gas chromatography and detection with mass spectrometry (on-line LC-MDGC-MS). This new approach allowed trace-level analysis of 3-alkyl-2-methoxypyrazines in grape musts and wines and is described for V. vinifera Sauvignon blanc, following 3-alkyl-2-methoxypyrazines concentrations during ripening and in the processed wines.
Schmarr
Hans-Georg
HG
Dienstleistungszentrum Ländlicher Raum (DLR) Rheinpfalz, Abteilung Weinbau und Oenologie, Breitenweg 71, D-67435 Neustadt an der Weinstrasse, Germany. hans-georg.schmarr@dlr.rlp.de
Ganss
Sebastian
S
Koschinski
Stefan
S
Fischer
Ulrich
U
Riehle
Carmen
C
Kinnart
Julian
J
Potouridis
Theodoros
T
Kutyrev
Maria
M
D002853:Chromatography, Liquid / Q000379:methods; D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods*; D007553:Isotope Labeling / Q000379:methods*; D011719:Pyrazines / Q000032:analysis* / Q000737:chemistry; D052616:Solid Phase Extraction / Q000379:methods; D027843:Vitis / Q000737:chemistry*; D014920:Wine / Q000032:analysis*
D011719:Pyrazines