Direct Determination of Pb in Cosmetics by Graphite Furnace Atomic Absorption Spectrometry with Suspension Sampling
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摘要: 化妆品样品中金属元素的分析一直存在着样品消解过程繁琐、易爆沸等问题,前处理过程不易控制,试剂消耗大,同时也易带入铅的空白污染;且现有化妆品中铅的含量远远低于国家标准规定的限量要求( < 40 mg/kg),火焰原子吸收光谱法无法准确检测。本文建立了悬浮进样-石墨炉原子吸收光谱仪直接测定化妆品中铅的方法。样品无需消解,采用0.2%硝酸和0.1%曲拉通X-100对样品进行悬浮后直接导入石墨炉原子吸收光谱仪进行测定。在石墨炉灰化过程中不使用常规的高纯氩气,而是使用具有氧化能力的干燥压缩空气,消除了单次分析超过50个样品时产生的碳残留,保证长期分析的稳定性;采用硝酸钯作为基体改进剂,钯能与铅形成铅钯金属互化物,非常稳定,显著提高了原子化温度;采用标准加入法消除基体干扰,保证分析数据的准确性。方法检出限为0.003 mg/kg,加标回收率为91.6%~106.8%,精密度为1.5%~2.1%(n=6)。该方法应用于分析国家标准物质GBW(E) 090028(霜铅)和GBW(E) 090027(粉铅),铅的测定值与标准值吻合;与国家标准方法的测定结果进行比较,无显著性差异。本方法的检出限低,可以满足化妆品中痕量铅的检测需求。Abstract: There have been many difficulties surrounding cumbersome digestion processes and explosive boiling when attempting to detect metal elements in cosmetics. It is difficult to control the pretreatment process and it is necessary to use a lot of reagents, which easily leads to the high reagent blank. Content of lead (Pb) in cosmetics is far below the national limits (≤40 mg/kg), which cannot accurately be determined by flame atomic absorption spectrometric. In this paper a method is described for direct determination of Pb in cosmetics by Graphite Furnace Atomic Absorption Spectrometry with suspension sampling. Sample digestion was not required as the cosmetics samples to be determined were directly placed into the Graphite Furnace Atomic Absorption Spectrometer after suspension by 0.2% nitric acid and 0.1% Triton X-100. The instrument conditions were optimized and high pure argon was added to the drying compressed air in the graphite furnace ashing process, in order to eliminate the carbon residue when the number of samples was over 50, and to ensure the stability for long-term analysis. The matrix modifier was palladium nitrate. Palladium and Pb can form a stable palladium Pb metal compound, and significantly improve the atomic temperature. Standard addition method was conducted to eliminate the matrix interference. The detection limit of this method was 0.003 mg/kg.The recovery of Pb was in the range of 91.6%-106.8%, precision was in the range of 1.5%-2.1% (n=6). National standard reference materials GBW (E) 090028 (cream) and GBW(E) 090027 (powder) were determined by using this method and the results were consistent with the standard value. Compared with the results using the national standard method for detection, the results showed no significant difference. This method has low detection limit, can meet the testing requirements of trace Pb in cosmetics.
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表 1 石墨炉原子吸收光谱仪工作条件
Table 1. Working parameters of the atomic absorption spectrometer
工作参数 设定条件 波长 283.3 nm 狭缝宽度 0.7 nm 灯电流 10 mA 信号测量 峰面积 测量方式 AA-BG 积分时间 4 s 表 2 各种消解方法所需时间、所用器皿、所用试剂的比较
Table 2. Comparison of required digestion time,utensils,reagents for different digestion methods
比较项目 直接进样 湿法消解 微波消解 浸提法 消解时间 0.2 h 2~4 h 2 h 3 h 所用器皿 具塞塑料管 聚四氟乙烯
溶样杯,容量瓶微波消解管,
容量瓶比色管 所用试剂 硝酸、
曲拉通 X-100硝酸、高氯酸、
氢氟酸硝酸、双氧水 硝酸、双氧水、
盐酸羟胺、辛醇表 3 石墨炉原子吸收光谱仪检测条件
Table 3. Measurement conditions of the graphite furnace atomic absorption spectrometer
步骤 温度
θ/℃升温时间
t/s保持时间
t/s气流量
v/(mL·min-1)气体类型 干燥 110 5 30 250 氩气 干燥 130 15 30 250 氩气 灰化 450 15 15 50 空气 灰化 600 10 20 250 氩气 原子化 1800 0 4 0 氩气 清洗程序 2500 1 5 250 氩气 表 4 自动进样器取样程序
Table 4. Sampling procedure of automatic sampler
加入的试剂 吸取体积/μL 样品空白 10 μg/L 20 μg/L 30 μg/L 化妆品悬浮样品 12 12 12 12 稀释溶液 12 8 4 0 标准溶液 0 4 8 12 基体改进剂 5 5 5 5 采集总体积 29 29 29 29 表 5 采用两种不同前处理手段检测结果对比
Table 5. Analytical results of Pb in different samples with two different pretreatment methods
样品名称 直接进样 湿法消解 测试值(mg/kg) 加标量(mg/kg) 回收率/% 加标量(mg/kg) 回收率/% 测试值(mg/kg) 丁家宜防晒修颜隔离霜 0.970 1.0 98.0 2.0 99.6 0.987 李氏防晒霜 0.432 0.5 102.6 1.0 105.3 0.457 红景天幼白抗氧修颜乳 0.140 0.2 106.8 0.4 101.6 0.142 美加净保湿润肤霜 0.0076 0.05 97.5 0.10 98.5 0.00316 李医生美白润肤水 0.0075 0.05 91.6 0.10 92.6 0.00258 隆力奇蛇油膏 0.0124 0.05 97.3 0.10 98.4 0.037 雅漾防晒霜 0.512 0.5 99.6 1.0 101.6 0.509 GBW(E) 090027(粉铅) 15.9 - - - - 15.5 GBW(E) 090028(霜铅) 30.2 - - - - 30.5 注:“-”表示未检测。 表 6 国家标准物质的检测结果和方法精密度
Table 6. Analytical results of Pb in national standard reference materials and the precision of the method
标准物质编号 w(Pb)/(mg·kg-1) RSD/% 标准值 本法分次测定值 GBW(E) 090028
(霜铅)31.0±2.4 30.2 31.5 29.9 31.2 30.1 30.8 2.1 GBW(E) 090027
(粉铅)16.1±2.2 16.5 16.4 15.9 16.0 16.4 16.2 1.5 -
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