Decreasing the number of points in the standard curve for determining iron in flour: summary of collaborative study

Seven laboratories participated in a collaborative study conducted to (1) evaluate the effects of reducing the number of points for the standard curve in the AOAC Official Method for iron in flour 944.02A-944.02C(a) from 10 points to 5 points, and (2) compare the levels of iron found in foods by using the 10-point and 5-point standard curves. The 5 points (0.2, 0.6, 1.0, 1.4, and 1.8 micrograms Fe/mL) were selected by eliminating every other standard point from the 10-point curve after correction for the reagent blank. No differences in the performance parameters between method versions were found when blind duplicate analysis was used to estimate the performance parameters for each sample analyzed. Results from 2 laboratories were excluded from statistical calculations because of failure to follow the specific instructions to increase the dilution when sample absorbance readings exceeded the highest standard point reading. The 5-point standard curve has been adopted first action in method 944.02 by AOAC INTERNATIONAL.