建立了超高效液相色谱-串联质谱法（UHPLC-MS/MS）测定淋洗类化妆品中甲基异噻唑啉酮（MI）和甲基氯异噻唑啉酮（MCI）含量的方法。将0.2 g样品经10%（体积分数）甲醇溶液超声提取10 min后，依次加入100 g·L^-1亚铁氰化钾溶液0.2 mL和200 g·L^-1乙酸锌溶液0.2 mL，用于沉淀样品中的蛋白质等大分子杂质。静置5 min后取上清液过0.22 μm滤膜，滤液中的2种目标物在Waters ACQUITY UPLC HSS T3色谱柱上用不同体积比的甲醇和0.1%（体积分数，下同）甲酸溶液的混合溶液进行梯度洗脱，前4.5 min仅用0.1%甲酸溶液洗脱，用于除去表面活性剂等水溶性杂质，分离后的目标物在电喷雾离子源正离子（ESI⁺）模式下电离，采用多反应监测（MRM）模式进行质谱检测。结果显示：MI和MCI的质量浓度分别在0.8~200 μg·L^-1和1.6~400 μg·L^-1内与其对应的峰面积呈线性关系，检出限（3S/N）分别为0.02，0.01 μg·g^-1；对空白样品进行加标回收试验，回收率分别为94.3%~107%和93.4%~106%；实际样品6次重复测定的测定值的相对标准偏差（RSD）分别为0.70%，2.1%；方法用于90批沐浴、洗发和洁面类化妆品的分析，有1批婴童类沐浴产品的MI检出量接近我国《化妆品安全技术规范》规定的限值（0.01%），有7批沐浴和4批洗发类产品中MI检出量超过欧盟化妆品法规EC 1223/2009规定的限值（0.001 5%）；8批产品MI含量是MCI的5倍以上，怀疑同时添加了MI和卡松，不符合《化妆品安全技术规范》的规定；在90批产品中，有25批产品存在实际检出成分与标签标识不一致的情况。

A method for determination of methylisothiazolinone (MI) and methylchloroisothiazolinone (MCI) in rinse-off cosmetics by UHPLC-MS/MS was established. The sample (0.2 g) was ultrasonically extracted for 10 min with 10% (volume fraction) methanol solution, then 100 g·L^-1 potassium ferrocyanide solution (0.2 mL) and 200 g·L^-1 zinc acetate solution (0.2 mL) were used to precipitate large molecular impurities such as protein in the sample. The supernatant obtained after settling for 5 min was filtered through a 0.22 μm filtering membrane, and the two target compounds were eluted on a Waters ACQUITY UPLC HSS T3 column by mixed solutions composed of methanol and 0.1% (volume fraction, the same below) formic acid solution with different volume ratios. For the first 4.5 min in the elution program, only 0.1% formic acid solution was used to remove water-soluble impurities such as surfactants. The separated targets were ionized in ESI⁺ mode, and MRM was adopted in MS/MS for detection. The results showed that linear relationships between values of peak area and mass concentration of MI and MCI were found in the ranges of 0.8-200 μg·L^-1 and 1.6-400 μg·L^-1, with detection limits (3S/N) of 0.02, 0.01 μg·g^-1, respectively. The spiked recovery tests were made on the blank samples, giving values of recovery in the ranges of 94.3%-107% and 93.4%-106%. RSDs of the determined values obtained from 6 repeated test on actual samples were 0.70% and 2.1%. The method was applied to the analysis of 90 batches of bath, hair washing and facial cleansing cosmetics:the content of MI in one batch of baby and child bath product was close to the limit value (0.01%) of Safety and Technical Standards for Cosmetics; the content of MI in 7 batches of bath and 4 batches of hair washing products exceeded the limit value (0.001 5%) of the European cosmetics regulation EC 1223/2009; the content of MI in 8 batches of products was above 5 times more than that of MCI, and it was suspected that MI and kathon were added to the sample at the same time, which did not comply with the provision of Safety and Technical Standards for Cosmetics; in the 90 batches of products, compositions of 25 batches of products were found to be inconsistent between the identification of the label and the actual detection.