Determination of phytic acid in feeds and faeces of pigs and poultry by capillary isotachophoresis

A method for phytic acid determination in the feeds and faeces of pigs and poultry has been developed on the basis of capillary isotachophoresis. Phytic acid was extracted by 0.95  M HCl and separated from interfering compounds by iron precipitation. Complete formation of ferric phytate required 7 mol FeCl 3  mol −1 phytic acid. Residual Fe 3+ was estimated colorimetrically by the tiron reagent, and ferric phytate was dissolved in 1.5  M NaOH at 9 mol NaOH mol −1 Fe precipitated. Analyses were carried out using an electrolyte system with Cl − as the leading anion, bis‐tris‐propane, and 2‐morpholinoethanesulphonic acid as the terminating anion. The recovery of phytic acid (added to hen faeces) using this procedure was 962 ± 24 g kg −1 . The limit of determination of phytic acid was 0.3 µmol ml −1 extract. The amount of phytic acid in feeds ranged from 8.3 to 10.8 g kg −1 on a dry matter basis. Phytic acid P represented 112 g kg −1 total P in faeces of young pigs (40–60 kg) fed a feed with supplemental phytase (490 U kg −1 ), 153 g kg −1 total P in faeces of finishing pigs and 185 g kg −1 total P in faeces of non‐lactating sows. Excreta of laying hens contained 23.7 g phytic acid kg −1 dry matter (362 g kg −1 total P). The isotachophoretic method is sufficiently simple and reproducible to be used for routine analyses of feeds and faeces. © 2000 Society of Chemical Industry