Residue Dynamics Studies of Aluminum Phosphide and Magnesium Phosphide in Stored Rice Utilizing a Sulfuric Acid‐Toluene Extraction Coupled with Gas Chromatography Analysis

Abstract

ABSTRACTA method for determination of aluminum phosphide and magnesium phosphide residues in rice was developed and validated. This work, through good laboratory practices, demonstrated aluminum and magnesium phosphide residue dynamics in stored rice. Rice samples were treated with sulfuric acid, which hydrolyzed phosphides to phosphine (PH3), which was simultaneously trapped in toluene. The organic layer was filtered and then analyzed by gas chromatography with a flame photometric detector. The PH3 calibration curves showed a strong linear relationship in the range of 0.012–1.2 mg/L, with a correlation coefficient of 0.999. The limit of detection of this method was 0.004 mg/kg. The average recoveries from samples fortified with aluminum phosphide and magnesium phosphide ranged from 76.8 to 106.5% with relative standard deviations below 10.2% (n = 5). PH3 was applied separately to rice samples to study dissipation dynamics at application dosages of 9.0 and 12 g/m3, respectively. The results showed half‐lives of aluminum and magnesium phosphide in rice to be 1.84 and 1.53 days, respectively. PH3 was applied once at low and high dosages. The low dosage was 4.5 g/m3 of aluminum phosphide and 6.0 g/m3 of magnesium phosphide, and the high dosage was 9.0 and 12 g/m3 for these two formulations, respectively. The final PH3 residues were below 0.013 mg/kg (limit of quantification).