Semiautomated Method for Simultaneous Determination of Phosphorus, Calcium, and Crude Protein in Animal Feeds

Abstract

A semiautomated method was developed for the simultaneous determination of phosphorus, calcium, and crude protein in animal feeds. Samples are digested with a block digestor, diluted to volume, and analyzed at the rate of 40 samples/hr. Protein is determined by the official AOAC method, by measuring the absorbance of an ammonia-salicylate complex at 660 nm. Phosphorus and calcium are determined by measuring the absorbances of the molybdovanadophosphate and calcium-cresolphthalein complexes at 420 and 570 nm, respectively. Samples are weighed according to the amount of protein they contain. Over 90% of the mixed animal feed samples analyzed for phosphorus and calcium fall within the range of the instrument; provisions are made for single determinations on those samples that fall outside the specified ranges. Results correlate well for the semiautomated method and official AOAC methods on mixed feed check samples and NBS Standard Reference Orchard Leaves.