Analysis of streptomycin and dihydrostreptomycin in milk by liquid chromatography

A method developed for the determination of the aminoglycoside antibiotics streptomycin and dihydrostreptomycin in tissues was applied to the analysis of fluid milk. Samples are extracted with 3.6% perchloric acid, and then injected onto a trace enrichment column, from which they are eluted onto a reversed-phase analytical column. The analytes are detected by fluorescence following postcolumn derivatization with 1,2-naphthoquinone-4-sulfonic acid. Recovery of analytes was in the range of 50-65% for skim or partially defatted fluid milk, while recoveries for homogenized whole milk were lower. Limits of quantitation were 10 ppb for streptomycin and 20 ppb for dihydrostreptomycin.