Measurement of amorphous ferric phosphate to assess iron bioavailability in diets and diet ingredients

A method of measuring amorphous ferric phosphate in the presence of crystal line ferric phosphate is described. This procedure is important because the re appears to be a big difference in availability between the amorphous and crystalline forms of ferric phosphate. This difference has been proven for two situations. In the first situation, when amorphous ferric phosphate is used as the source of iron for gypsy moths, growth is normal, but if the c rystalline form is used, results are identical to the case when no iron is used. In the second situation, several plant species have been reported to grow much better when amorphous ferric phosphate is used instead of crystal line ferric phosphate as the source of phosphate in fertilizer. Differentia tion of the amorphous from the crystalline uses citrate solutions that extr act the amorphous form but not the crystalline form. The procedure was opti mized for three different sample forms: agar based artificial diet, Wesson salt dagger (a salt mixture containing all recommended minerals for insect diets), and pure ferric phosphate. A method for overcoming a problem with t urbidity that occurs when analyzing some prepared diets is also described.