This document describes a method for the quantitative determination of pyrrolizidine alkaloids (PA) in complete and supplementary feed and in forages by liquid chromatography tandem mass spectrometry (LC-MS/MS) after solid phase extraction (SPE) clean-up.
The method has been successfully validated in a collaborative trial for the matrices complete feed for horses, supplementary feed for horses, supplementary feed for rodents, hay, alfalfa and grass silage. Validation was carried out for the PA and concentrations ranges listed in Table 1. It was demonstrated that the PA isomeric pairs senecivernine and senecionine as well as senecivernine-N-oxide and senecionine-N-oxide cannot be determined individually due to insufficient chromatographic separation. However, the sums of the individual PA of the isomeric pairs were quantified with sufficient reproducibility. Co-elution of other PA-isomers not included in the scope of the method shall be taken into account. A list of potentially co-eluting isomers is presented in Annex E.
Although the calibration range of the method protocol is specified from 10 μg/kg to 300 μg/kg, the results of the collaborative study showed, that the dilution of sample extracts with blank sample extracts enables for the quantitation of concentrations exceeding the calibration range. Satisfactory reproducibility was achieved when quantifying up to 1428 μg/kg for individual PA and up to 887 μg/kg for the sum of isomeric pairs.
NOTE 1 A second method was part of the method validation collaborative main trial. For this method PA-N-Oxides are reduced by adding zinc powder to the extract of the feed material. The following steps correspond to the first and main method. Quantitative results for each PA except the otonecine type PA senkirkine represent the sum of the free PA base and its corresponding N-oxide.
NOTE 2 Due to insufficient numbers of data for some analyte-matrix combinations statistical evaluation was not valid for standardization. Received data indicated the methods applicability in experienced laboratories with appropriate quality assurance measures. Therefore, the method description is included as an informative annex (Annex D).