The effect of methanol addition on generation of 40Ar35Cl+ was investigated. Methanol addition increases As signal intensity via conversion of 75As into 75As+ through charge transfer reaction. Methanol addition decreases 40Ar35Cl+ interference via conversion of 40Ar35Cl+ to 12C35Cl+ through substitution reaction. 40Ar35Cl+ decreases more efficiently in a high-As-containing sample than counterparts with low As concentrations.