Direct method for determining inorganic phosphate. Inorganic phosphate reacts in acid medium with ammonium molybdate to form a phosphomolybdate complex with yellow color. The intensity of the color formed is proportional to the inorganic phosphate concentration inthe sample at 340 nm.
Ammonium molybdate + Sulphiric acid + Phosphate — Inorganicphosphate molybdate complex
Most of the phosphorus in the body (80% to 85%) is calcium-bound and is found in the bones as hydroxyapatite crystals.The remainder is distributed throughout other cells of the body primarily as organic phosphorous in phospholipids and phosphoproteins. Plasma contains approximately 1% of total phosphate as inorganic phosphate, the fraction measured in routine biochemical analysis.
Serum phosphorus may increase in hypervitaminosis D, hypoparathyroidism and renal failure. Decreased serum phosphorus is seenin rickets(vitamin D deficiency), hyperparathyroidism and Fanconi syndrome.