Abstract
Abstract Three interlaboratory studies are described in which AOAC method 2.053 was compared with the neutral ammonium citrate method for direct available P2O5 recommended by the European Economic Community (EEC). The initial study comprised 5 laboratories and 7 samples. Significantly more available P205 was found by the AOAC method in 5 of 7 samples tested. Fifteen laboratories analyzed 8 samples in the second study; only 2 samples yielded more P2O5 by the AOAC method. The final study included 9 samples and 14 laboratories. Results for the AOAC method were higher on 4 samples. Conclusions reached from the 3 studies are (1) The AOAC method gave consistently higher values for available P2O5, especially for triple superphosphate samples; and (2) the difference between methods increased with increasing amounts of citrate-insoluble P2O5. All data were reported to the International Standards Organization Working Group on phosphorus in fertilizer.
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