Determination of Phosphine Residues in Wheat and Yellow Corn with a New Developed Method Using Headspace and SIM Mode GC-MS.

Phosphine is considered the main fumigant material used for long time for controlling insect pests in stored grains. This research was focused on the determination of phosphine residues in cereal matrixes (mainly wheat and corn) after the fumigation process, using a new procedure developed to reduce the number of analytical steps and improve the chromatographic separation, identification, and quantitation of analyte, thus leading to enhanced total efficiency and sensitivity. This method, using gastight vials for extraction with 5% sulfuric acid, a heating extraction sequence, and injection with headspace and GC-MS in selected-ion monitoring mode, gave clean separation and accurate results. Repeatability was achieved for both wheat and corn after spiking samples at the 0.01 mg/kg level, with RSD values of 7.6 and 6.3%, respectively. The LOD and LOQ values were 0.46 and 1.38 µg/kg, respectively. The mean value of phosphine residue in wheat was 8.43 µg/kg, with an RSD of 8.17%, whereas it was 8.09 µg/kg in corn, with an RSD of 7.75%. All residues detected in all the replicates were below the estimated maximum residue limit for wheat and corn (0.1 mg/kg). The highest residue value for wheat was 9.85 µg/kg and the lowest was 7.70 µg/kg, whereas for corn, the highest value was 9.03 µg/kg and the lowest 7.30 µg/kg.