Application of the precolumn back-flush technology in pesticide residue analysis: a practical view

Precolumn back-flushing is a matrix minimization technique in GC in which the carrier gas flow of the precolumn is reversed after the transfer of the highest boiling analyte to the analytical column. Practical details concerning this technology have rarely been published although it is widely used. This paper now focuses on the practical implementation of precolumn back-flushing for pesticide residue analysis of complex food matrices. Fitting the analytical column into the precolumn was found to be essential for comparable analyte responses with and without back-flushing. The effectiveness of the reverse column flow technique is mainly affected by the transfer time after which back-flushing starts. The transfer time was found to depend on which kind of injected matrix is used and the state of the precolumn. For the regular adaptation of the transfer time in routine analysis, a simple test was introduced in which 13-C-labeled deltamethrin and indeno[1,2,3-c,d]pyrene were added to the prepared extract. Chromatograms, LOQ and RSD of up to 99 pesticides in citrus oil and liver extracts proved a clearer identification and enhanced quantification using precolumn back-flushing compared to measurements without this technology. Furthermore, reduced system maintenance could be achieved through back-flushing.