A DETERMINATION OF TOTAL PHOSPHORUS BY SPECTROPHOTOMETRY

1 In an acidic medium, orthophosphates form a yellow-coloured complex with molybdate ions. The combination of P, Sb and Mo leads after reduction with ascorbic acid to the formation of a very stable blue-coloured phosphormolybdenum complex. At a wavelength of 880 nm a very sensitive and stable measurement of P 

2 This determination may be carried out on digest 2.1 (digestion with Hj,SO - salicylic acid - HjOj - Se) and digest 2.2 (digestion with Hj,SO., - salicylic add - H OJ. 

1 This procedure yields a standard curve that is linear up to approximately 5 mg/L 

2 The detection limit is approximately 0.03 mg/L in the digest. The determination limit is approximately 0.1 mg/L (0.2 respectively 0.5 mmol/kg in the dried plant material). 

1 Arsenic and Silica - As and Si form similarly coloured complexes under these conditions. Both interferences are negligible at the low concentrations, which are normally present in these plant material digests. 

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