Abstract: The method for determination of methanol content in dishwashing detergent adopting ISTD as specified in GB 9985—2000 was improved.Difference between ISTD method and ESTD method for determination of methanol content in dishwashing detergent was compared.Via the spiking of isobutanol and dilution with 75% ethanol up to the specified volume,then filtered through 0.45 μm pinhole membrane,the prepared sample solution was separated by DB-FFAP chromatographic column and detected by FID detector,quantified separately with ISTD and ESTD.Results showed that the detection limit was 0.5 mg/L,the relative standard derivation of ISTD and ESTD were 0.4%~0.9% and 0.6%~1.2% respectively,and the average recovery were 100%~102% and 95%~99% respectively.Both the quantitative results with ISTD and ESTD can satisfy the requirement specified in the National Standard.However,the precision and recovery of ISTD method are better than that of ESTD method.

Key words: dishwashing detergent, gas chromatography, methanol, ISTD, ESTD