GB/T 38403.3-2025 "Determination of anti-mildew agent in leather and fur, Part 3: Gas chromatograph - Mass spectrometry (methanol extraction) " is a new national standard for anti-mildew agent testing in the leather industry in our country. The standard is proposed by the China Light Industry Federation, centralized by the National Leather Industry Standardization Technical Committee, and jointly formulated by Zhejiang Fangyuan Leather Textile Testing and Certification Co., Ltd., and will be officially implemented on November 1, 2025. The standard innovatively uses gas chromatograph-mass spectrometry technology to detect the content of PCMC, OPP, OIT and other common anti-mildew agents in leather and fur by methanol extraction, which has the characteristics of high detection sensitivity and easy operation. The standard specifies key links such as sample preparation, instrument analysis, quality control, etc., providing a unified technical basis for industry supervision and international trade. It is worth noting that this method is not suitable for the determination of TCMTB anti-mildew agents.