恒温平台石墨炉原子吸收光谱法分别测定食品中总铬及六价铬

Simultaneous Determination of Total Chromium and Hexavalent Chromium in Foods by Stabilized Temperature GraphiteFurnace-Atomic Absorption Spectrophotometry

三价铬及六价铬是食品中微量元素铬的两种主要存在价态。本文根据其性质及其在食品中的存在形式,研究确定了其分别定量测定的方法。采用10％四甲基氢氧化铵(简称TMAH)于60℃超声波振荡水浴中溶解样品,使铬离子完全溶提出来并不改变其原价态。取一部分样液直接利用石墨炉原子吸收光谱法测定总铬,取另一部分样液,加稀H_2SO_4将溶液pH调至3左右,定容过滤除去大分子沉淀物,然后在pH4.8～5.0下,用EDTA掩蔽三价铬,用DDTC—MIBK螯合萃取分离浓缩六价铬,最后再用石墨炉原子吸收光谱法测定有机相中的六价铬含量,从而达到分别测定六价与三价铬的目的。其中重点探讨研究了样品的前处理方法、六价铬的分离测定条件,干扰因素的消除及标准加入法的应用,并粗略讨论了仪器测定条件。研究结果表明,本方法的准确度、精密度及灵敏度均达到了食品检测的要求。其总铬及六价铬的样品最低检出浓度分别为0.01ppm和0.004ppm;总铬及六价铬的加标平均回收率分别为99.8±5.8％和98.3±6.4％。重复测定红烧赤贝及NBS—SRMl1566标准样品中总铬的结果分别是:0.333±0.017ppm,C.V.5.1％(H_2 SO_4-H_2 O_2法:0.333±0.011,C.V.3.3％);0.593±0.037ppm,C.V.6.2％(H_2SO_4-H_2O_2法:0.557±0.020ppm,C.V.4.0％,保证值为0.69±0.27ppm)。

Trivalent chromium and hexavalent chromium are two main states of the chromium in foods. According to the nature and form of the chromium in foods, this paper deals with studies on the analytical method used for determination of the Cr (Ⅲ) and Cr (Ⅵ) in foods. The sample is treated with 10% aqueous tetramethyl ammonium hydroxide (TMAH) in an ultrasonic water bath at 60±2℃ until all solid material are dissolved, that results in all chromium ion have been extracted into alkaline solution without any change of it's original valent states.Using one part of the sample solution, total chromium is determinated directly by graphite furnace-atomic absorption spectrophotometry with standard addition method (GFAAS-SAM). The dilute sulfuric acid is added into another part of the sample solution until its pH to 3 , remove precipitates of the large molecular compounds, added EDTA at pH 4.8-5.0 to mask the Cr (Ⅵ) presented in sample solution, then extract Cr (Ⅵ) by DDTC-MIBK, finally determine the absorbance of Cr(Ⅵ)in MIBK layer by GFAAS-SAM again, thus we developed a new method of simultaneous determination of total chromium and hexavalent chromium in foods.The important contents of this study are including the method of sample treatment, condition of separation and determination for Cr (Ⅵ), removal of the interference factor and adoption of the standard addition method. The results showed that sensitivity, precision and accuracy of this method are satisfactory agreement with the requirement of food detection. The minimum detectable concentration of total chromium and hexavalent chromium is 0.01 PPm and 0.004ppm respectively; The recoverly of total chromium and hexavalent chromium is 99.8± 5.8% and 98.3±6.4% respectively;The reproducibility of determination is excellent, results for total chromium determination in stewed baby clams arid NBS-SRM1566 is 0.333±0.0l7ppm, c.v.5.1%(H2SO4-H2O2 method: 0.333± 0.011ppm, c.v.3.3%) and 0.593±0.037ppm, c.v.6.2% (H2SO4-H2O2 method. 0.557±0.02ppm, c.v.4.0%, certified value is 0.69± 0.27ppm) respectively. Result for hexavalent chromium determination in stewed baby clams and fish with tomato juice is 0.036± 0.002ppm, c.v.5.6% and 0.018±0.002 ppm , c.v. 11.1% respectively. This method is successfully used for the various animal food samples, but can not be used for plant food, such as mushroom and gluten.