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It has been found that a reagent containing sulphuric acid, ammonium molybdate and ascorbic acid may be used as a single-solution reagent for the determination of phosphate in sea water. Development of the molybdenum-blue colour is complete in 24 h at room temperature and in 30 min at 60° C; the colour is stable for at least 3 days. Beer's law is obeyed closely up to at least 500 μg PO43−-P/1. The salt error is approximately 4% with sea water of chlorinity 19·3%. The interference due to either arsenate or silicate at their concentrations in sea water is negligible.

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Using a mutant version of E. coli alkaline phosphatase, we succeeded in trapping and determining the structure of the phospho-enzyme intermediate. The X-ray structure also revealed the catalytic water molecule, bound to one of the active site zinc ions, positioned ideally for the apical attack necessary for the hydrolysis of the intermediate.