A Simple and Fast Method for Determination of Phosphorus in Fish Diets and Faeces Used in Animal Nutritional Studies

The optimization and validation of a simple and fast analytical method for the determination of phosphorus in fish diets and faeces used in animal nutrition studies are shown in this paper, starting with the validation of a pre-optimized digestion procedure for biological samples, choice of the best chemical modifier and the minimal sample amounts. The digestion procedure consisted of an acid dissolution of a minimal of 100 mg of dry sample in a domestic microwave system using Parr Teflon bombs at high pressure. The P levels were determined by atomic absorption spectrometry with electrothermal atomisation, using an absorbance of 213.6 nm, a slit width of 1.0 nm, a current lamp of 20 mA and a deuterium lamp for background correction. Different furnace temperature programmes were used, and a final temperature programme was optimized. The optimization stages suggested the use of a 1,000 μg/ml La solution as chemical modifier and 1,600 and 2,700 °C as, respectively, the best pyrolysis and atomisation temperatures. The optimized analytical method was applied to different types of fish diets and faeces, and the percentages of recovery of P in spiked samples were, respectively, 94 ± 11% ( n = 3) and 100 ± 12% ( n = 3). The detection limit was 0.15 mg P/g of dry sample. The optimized methodology is simpler, faster and has less sample mass consumption than normally used colorimetric methods.