Submitted to: Journal of Separation Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/13/2005
Publication Date: 6/21/2005
Citation: Cajka, T., Mastovska, K., Lehotay, S.J., Hajslova, J. 2005. Use of automated direct sample introduction with analyte protectants in the gc-ms analysis of pesticide resides. Journal of Separation Science. 28. pp. 1048-1060.
Interpretive Summary: In the gas chromatographic analysis of pesticide residues in food, maintenance of the instrument is a major limitation in routine practice. In this study, we investigated a novel approach called difficult matrix introduction (DMI) that can eliminate the need for frequent instrument maintenance while also improving detectability for the pesticides in complex food matrices. The results indicated that DMI worked well for this purpose, especially in combination with a unique approach developed in our laboratory to deactivate exposed glass surfaces in the system. Those laboratories that implement this approach will benefit by the improved analytical performance and ease of use to conduct trace residue analysis of pesticides in food.
Technical Abstract: Automated large-volume direct sample introduction, or difficult matrix introduction (DMI), was investigated in the determination of 44 pesticide residues possessing a wide range of physico-chemical properties (volatility, polarity, pKa) in fruit-based baby food by means of gas chromatography'mass spectrometry (GC-MS) with a quadrupole mass analyzer. DMI has advantages over traditional injection because large volumes (up to 30 'L) of potentially dirty sample extracts can be injected into the GC'MS, but nonvolatile matrix components that would normally contaminate the inlet are removed after every injection. The extra matrix and glass surfaces involved in DMI, however, make the system more prone to the matrix-induced chromatographic enhancement effect, which adversely affects quantification of several pesticides. To overcome this problem, matrix-matched calibration standards and/or the use of analyte protectants were applied in the DMI approach, and the analysis of extracts were also compared before and after undergoing clean-up by dispersive solid-phase extraction. For best quantification, clean-up was still needed, and the combination of matrix-matching with analyte protectants gave the most reproducible results. Depending on the application, however, the addition of analyte protectants (a mixture of 3-ethoxy 1,2-propanediol, Lgulonic acid '-lactone, and D sorbitol) to sample extracts and calibration standards in solvent (non-matrix matched), gave satisfactory quantification for most of the 44 pesticides tested. The lowest calibration levels for 25 of the 44 pesticides were '10 ng/g, which meets the standard required by the European Union Baby Food Directive (1999/39/EC).