Abstract: Objective To develop an oil based headspace-gas chromatography-mass spectrometry technique for the determination of free formaldehyde in water-based coatings. Methods N,N-dimethylformamide was treated to remove formaldehyde background and used as a sample dispersant extraction agent,the deuterated methanol was used as an internal standard,and formaldehyde in water-based coatings was detected by headspace-gas chromatography-mass spectrometry. The internal standard method was used for the quantitative analysis. Results In the range of 1-400 mg/L,the ratio of peak area to internal standard peak area of formaldehyde had a good linear relationship with formaldehyde concentration,and the correlation coefficient（r） was 0.999 4. The recoveries of formaldehyde at low,medium,and high concentration levels in different dosage forms of water-based coatings ranged from 97.5% to 101.8%,with a relative standard deviation between 1.8% and 2.6%. The detection limit was 5 mg/kg,and the quantitative limit was 10 mg/kg. Six different type of water-based coatings in the market were tested,among which formaldehyde was detected in four samples,with the content ranging from 21.5 to 41.8 mg/kg. Conclusions In this method,N,N-dimethylformamide is used as extractant and achieved good dispersion effect for various matrix water-based coating samples,because it has strong dissolving ability for both fat-soluble and water-soluble compounds. Furthermore,it has strong high boiling point and low saturated vapor pressure,which is beneficial to formaldehyde escaping from solution and improved the sensitivity of the method. The matrix interference is effectively reduced by headspace purification and tandem mass spectrometry. The deuterated methanol with molecular structure close to formaldehyde is used as internal standard,which corrects the influence of sample matrix and improved the quantitative accuracy. The method has advantages of simple operation,strong anti-interference ability,high sensitivity,accuracy and reliability.

Key words: Formaldehyde, Water-based coatings, Oil based headspace, Internal standard method, Gas chromatography-tandem mass spectrometry