Determination of fumigant residues of cyanogen and its metabolite hydrogen cyanide in wheat by headspace gas chromatography

A method for the determination of fumigant residues of cyanogen(C2N2) and hydrogen cyanide(HCN) in wheat using headspace(HS) capillary gas chromatography(HS-GC) with nitrogen- phosphorus detection(NPD) was developed.The separation efficiency and sensitivity for C2N2 and HCN were improved by using a GS-Q megabore capillary column and by injection of 60 μL of HS gas with a splitting ratio of 4.Optimum HS conditions were found to be incubation at 25 ℃ for 4 hours in the presence of 50% phosphoric acid as an acidifying reagent.The distribution coefficient (k) was 0.44 and 48.82 for C2N2 and HCN,respectively.C2N2 showed a different vaporization behaviour to HCN with respect to temperature and matrix effect.The salting-out effect was relatively small for C2N2 and HCN.Optimum release into the headspace of C2N2 and HCN in aged wheat after solvent extraction with 50% phosphoric acid for 72 hour were obtained.C2N2 and HCN residues in aged wheat were estimated by using fortified wheat as standards.The calibration graph was linear over 1.2-500 μg/L of C2N2 and 1.0-500 μg/L of HCN with correlation coefficients(R2) of 0.999 7 and 0.999 8,respectively.The limits of detection(LOD) of C2N2 and HCN were 0.032 mg/kg(RSD 4.6%) and 0.145 mg/kg(RSD 7.4%),the limits of quantitation(LOQ) of C2N2 and HCN were 0.107 mg/kg and 0.483 mg/kg,respectively.This method was also proved to be convenient in operation,high in sensitivity and effective in purificatio,and applicable for determination of C2N2 and HCN residues in aged wheat.