A comparative study of the determination of phosphorus by electrothermal atomic absorption spectrometry and solution spectrophotometry

Graphite-furnace atomic absorption spectrometry (a.a.s.) and a spectrophotometric AutoAnalyzer method for phosphorus based on molybdovanadophosphate formation are compared. Only slight improvements in accuracy and reproducibility were obtained when SiC- or ZrC-coated graphite tubes replaced uncoated tubes. Perchloric acid enhanced the phosphorus signal in a.a.s. The digestion system was found to be critical for the AutoAnalyzer method. Digetion with nitric/perchloric acids gave higher recoveries than a micro-Kjeldahl digestion for most of the biological samples studied. Better accuracy was obtained by the a.a.s. method, whereas the AutoAnalyzer method was more reproducible. The methods were applied to NBS Oyster Tissue and Spinach, and fish samples.