Determination of zinc phosphide residues in the California ground squirrel (Spermophilus beecheyi) by gas chromatography-flame photometric detection

Zinc phosphide (Zn 3 P 2 ) recovery from small mammal tissues is assessed for the first time by an analytical method developed for the determination of Zn 3 P 2 residues in the gastrointestinal (GI) tracts of California ground squirrels (Spermophilus beecheyi) by gas chromatography-flame photometric detection (GC-FPD). GI tracts from field-collected squirrels were removed, and the stomachs and intestines were separated. Emptied stomachs were fortified with varying combinations of Zn 3 P 2 and partially digested range grass ; intestines were fortified with Zn 3 P 2 only. Tissues were processed and acid hydrolyzed in a sealed flask to produce phosphine (PH 3 ) gas, and samples of the PH 3 -containing headspace gas were analyzed by GC. Recovery data were used to develop predictive linear equations relating tissue weights and Zn 3 P 2 observed with actual Zn 3 P 2 residues. The validated linear range was 0.1-103.4 μg of Zn 3 P 2 /mL headspace (0.102-100.3 mg of Zn 3 P 2 /sample, r 2 = 0.9993). The limits of detection of the method were 0.015 mg (250 ppb) and 0.013 mg (154 ppb) in stomachs and intestines, respectively. No chromatographic interferences were observed.