中国药典采用钙盐法灰化后用古蔡氏法（砷斑法）检测甲紫中砷限量。此法难炽灼完全、耗时长。笔者采用加氧化镁、硝酸镁帮助灰化（称镁盐法）可以消除钙盐法灰化存在的问题，且砷检出量高于药典法，提示有机破坏方法对砷检出量有影响。镁盐法系取甲紫0．20g，氧化镁0·2g，15％ Chinese Pharmacopoeia using calcium salt method after ashing with ancient Chua’s method (arsenic stain method) to detect Arsenic limit. This method is hard to burn completely, long time. The author uses magnesium oxide and magnesium nitrate to help the ashing (called magnesium salt method), which can eliminate the problem of ashing by calcium salt method, and the detection amount of arsenic is higher than that of the pharmacopoeia method, suggesting that the method of organic destruction has an influence on the amount of arsenic detected. Magnesium salt method to take a violet 0.20g, magnesium oxide 0.2 g, 15%