Development and validation of an LC-APCI-MS-MS analytical method for the determination of streptomycin and dihydrostreptomycin residues in milk.

An analytical method for the quantification and identity confirmation of streptomycin and dihydrostreptomycin residues in pasteurized milk using liquid chromatography (LC)-atmospheric pressure chemical ionization (APCI)-tandem mass spectrometry (MS-MS) was developed and validated. Method validation was performed according to the recommendations of the international agencies European Community and IUPAC, and the following parameters were evaluated: analytical curve, linearity, sensitivity, precision (intra- and inter-day repeatability), accuracy, and the limit of detection (LOD) and limit of quantification (LOQ). Simple sample preparation was followed by the LC-APCI-MS-MS analysis. The method presented adequate linearity with correlation coefficients above 0.99 for both analytes in the dynamic range of 50-400 microg/kg, and average accuracies between 84-110%. The LOD and LOQ were, respectively, 25 microg/kg and 50 microg/kg for both analytes. Method selectivity was verified by the absence of interfering peaks in the retention regions of the analytes and the internal standard when a blank sample was tested. The results qualified the method for the quantification and confirmation of the analytes in milk at concentrations inferior to the established maximum residue limits (200 microg/kg).