Determination of total phosphorus in foods by colorimetric measurement of phosphorus as molybdenum blue after dry-ashing: NMKL interlaboratory study.

A spectrophotometric method in which the sample is dry-ashed in the presence of zinc oxide, and total phosphorus content is measured colorimetrically as molybdenum blue was evaluated by 12 participating laboratories from the Nordic countries. The study included potato flour, sausage, cold ham, infant formula powder, cheese, and skimmed milk powder. The materials were presented to the participants as 12 randomly coded samples of 2 blind duplicates of each material. The phosphorus content of the materials varied between 0.076 and 0.96 g/100 g. The relative standard deviation for repeatability of the method varied from 1.1% for 0.96 g phosphorus/100 g to 5.4% for 0.29 g phosphorus/100 g. The relative standard deviation for reproducibility varied from 3.6% for 0.96 g phosphorus/100 g to 7.7% for 0.23 g phosphorus/100 g.