Interlaboratory Assessment of Dry Calibration Milk Powders for Calibrating Infrared Milk Analyzers

An interlaboratory study was carried out to assess the performance of preformulated, preanalyzed, dry calibration milk powders designed for calibrating infrared milk analyzers. The calibration powders can be reconstituted to produce consistent calibrations within laboratories. The powders met AOAC specifications In terms of accuracy and repeatability, and provide calibrations with performance characteristics comparable to those produced with conventional calibration milks. The reconstituted solutions were shown to be stable for up to 6 h at 40°C, and can be stored under refrigerated conditions and used for repeated analyses for up to 21 days without apparent deterioration In calibration performance. In general, the calibration powders perform as well as, or better than, the conventional calibrants used by the laboratories participating in the study, and the calibrations could be switched without significantly changing the analytical results. Simulation and cross-calibration analyses indicated that the powdered calibrants produced more consistent results overall than fluid calibration milks. The powdered calibrants, as formulated, are shown to be suitable for any application requiring calibrations that meet AOAC specifications, Including payment applications. The calibration powders have the stability and performance characteristics to serve as a consistent, stable reference standard for monitoring instrument performance, and would be a useful tool for Interlaboratory standardization or accrediting payment and dairy herd analysis laboratories.