IC Determination of Residual Amount of Phosphide in Cereals with Absorption by Acidic Potassium Permanganate Solution

The cereal sample (100.00 g) was reacted with 10.0 mL of 1.0 mg·L^-1 H₂SO₄ solution and 150 mL of water for 30 min in the reaction flask placed in boiling water bath, and the PH₃ liberated was absorbed in 3 portions of an absorption solution containing 5.0 mL of 3.3 g·L^-1 KMnO₄ solution and 0.2 mL of 1.0 mg·L^-1 H₂SO₄ solution, placed separately in 3 gas absorption flasks connected in series. At this moment, PH₃ was oxidized to PO₄^3- by KMnO₄. Excess of the KMnO₄ was destroyed by dropwise addition of 6% (w) H₂O₂ solution until formation of dark-brown colored precipitate was observed and then 0.5 mol·L^-1 KOH solution was added until the formation of bulk of black precipitate. Water was added to make the total volume to 50.0 mL. After centrifugation, the supernatant was taken and used as sample solution for IC analysis under the prescribed conditions. Linear relationship between values of peak area and mass concentration of phosphorus (in terms of PH₃) was obtained in the range of 0.02 to 4.0 mg·L^-1, with detection limit (3S/N) of 0.005 mg·kg^-1. Results of recovery found were ranged from 88.0% to 93.2% and values of RSDs (n=6) found were ranged from 1.6% to 2.3%.