A liquid chromatographic (LC) method for the analysis of lasalocid sodium in premixes, complete animal feeds, and trace-level feeds was collaboratively studied. The method employs a 0.5 HCl acidified methanol extraction followed by 20 min sonication in a water bath heated to 40C. Samples
are then shaken on a mechanical shaker for 1 h and stored overnight, followed by an additional 10 min shaking the following morning. Sample extracts are diluted if necessary with extractant, filtered, and injected onto an LC system. Determination of all lasalocid homologs is by reversed-phase
LC with fluorescence detection at 314 nm excitation and 418 nm emission. Eight samples of drug premixes, medicated feeds, and mineral supplements, along with 2 samples for trace-level analysis were sent to 20 collaborators in the United States, Canada, and The Netherlands. Study data were
returned by 17 laboratories. Two additional supplemental trace-level samples and a blank feed were provided to 15 of the collaborating laboratories, and test data were received from all 15 participants. For the drug premixes, medicated feeds, and mineral supplements, RSDr values
(within-laboratory repeatability) ranged from 1.2 to 19.9, RSDR values (among-laboratory reproducibility) ranged from 3.4 to 32.3, and HorRat values ranged from 0.35 to 3.73. For the trace-level samples, only lasalocid A, the predominant homolog comprising >90 of the sum of all
homolog peak area, was quantified. All laboratories correctly identified the analyte. Although some instrument response was reported by a number of laboratories for the blank feed, all but one laboratory's results were well below the 1 mg/kg limit of quantification. RSDr values
for the initial 2 trace-level samples were excessive, ranging from 51.6 to 64.4. RSDR values ranged from 51.6 to 75.7, and HorRat values ranged from 3.6 to 4.0. Data for the initial trace-level samples indicated that the test samples were improperly prepared to ensure homogeneity,
and a new set of supplemental samples was provided to collaborators, with significantly improved results. RSDr values for the 2 supplemental trace-level samples ranged from 1.6 to 2.5, RSDR values ranged from 5.6 to 9.2, and HorRat values ranged from 0.43 to 0.62.
Document Type: Research Article
Nebraska Department of Agriculture, 3703 S. 14th St, Lincoln, NE 68502.
Publication date: May 1, 2008
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The Journal of AOAC INTERNATIONAL publishes refereed papers and reviews in the fields of chemical, biological and toxicological analytical chemistry for the purpose of showcasing the most precise, accurate and sensitive methods for analysis of foods, food additives, supplements and contaminants, cosmetics, drugs, toxins, hazardous substances, pesticides, feeds, fertilizers and the environment available at that point in time. The scope of the Journal includes unpublished original research describing new analytical methods, techniques and applications; improved approaches to sampling, both in the field and the laboratory; better methods of preparing samples for analysis; collaborative studies substantiating the performance of a given method; statistical techniques for evaluating data. The Journal will also publish other articles of general interest to its audience, e.g., technical communications; cautionary notes; comments on techniques, apparatus, and reagents.