Direct-current plasma emission spectrometry determines food calcium and phosphorus, faecal calcium and chromium, and urinary calcium and phosphorus accurately, precisely and rapidly without acid digestion or dry ashing. Food and faeces are homogenised, diluted and aspirated directly into the plasma. The method makes metabolic balances swifter and less labour-intensive; it enables the use of chromium sesquioxide as an inert marker, for perchlorate digestion is avoided. Both plasma emission (–9.9%) and a dry ashing procedure (–13.5%) give lower values for food phosphorus than those derived from food tables.
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