Study On Determination Of Trace Copper, Cadmium , Zinc In Food Samples By Flae Atomic Absorption Spectrometry After Liquid-Liquid Extraction

In recent years, with the development of society and improvement of living standards, there is increasing demand of food safety. It is hoped that the food we eat is healthy, safe and hygienic in our daily life. But heavy metals pollution of food get more and more seriously. So some sensitive, rapid, simple and accurate analytical methods are required for the determination of heavy metals in food samples. Due to the levels of heavy metals in some food samples are lower than the detection limits of instrumental techniques, the separation and precon-centration techniques are necessary to detect trace heavy metals in food samples.In this paper based on the research of heavy metals in food samples in documents, methods have been developed for the determination of copper, cadmium, zinc in food samples combined liquid-liquid extraction with FAAS. The major contents of this paper are described as follows:(1) Determination of copper in food samples by flame atomic absorption spectrometry after liquid-liquid extractionA new method was established for the determination of copper in food samples by FAAS after liquid-liquid extraction. In the proposed approach, zincon was used as chelating agent, and methyl isobutyl ketone (MIBK) was selected as the extractant. Some factors including the pH of analytical solution, concentration of the chelating agent, temperature and time, which would affect the extraction efficiency and subsequent determination of copper, were studied and optimized. Under the optimized conditions, the calibration graph was linear in the range of 7.0×10-3～2.0μg·mL-1 and the detection limit was 6.7×10-3μg·mL-1, the relative standard deviation was 3.0%. The proposed method was applied to the determination of copper in food samples, and satisfactory results were obtained.(2) Determination of cadmium in food samples by flame atomic absorption spectrometry after liquid-liquid extractionA sample method was developed for the determination of cadmium in food samples by FAAS after liquid-liquid extraction. In the proposed approach, diphenyl semicabazide was used as chelating agent, and methyl isobutyl ketone (MIBK) was selected as the extractant. The sensitivity could be enhanced by adding the cetyltrimethylammonium bromide (CTMAB) into the solution. Some factors were studied and optimized. Under the optimized conditions, the calibration graph was linear in the range of 2.0×10-3～0.24μg·mL-1 and the detection limit was 1.5×10-3μg·mL-1, the relative standard deviation was 1.0%. The proposed method was applied to the determination of cadmium in food and water samples, and results were satisfactory.(3) Determination of zinc in food samples by flame atomic absorption spectrometry after cloud point extractionA new cloud point extraction preconcentraction of trace level of zinc as a prior step to its determination by FAAS has been developed. The cloud point extraction method was based on employing 1-(2-pyridylazo)-2-naphthol as complexing reagent and emulsifier OP as nonionic surfactant. Some conditions that would affect on the complex formation and separation were researched in detail. The optimum conditions were pH 9.0,1.0mL2.0×10-3mol·L-1 PAN,0.5 mL 10% OP, 1.0 mL20% NaCl in 10mL solution, and heated in a thermostated bath at 90℃for 120 min. Under the optimized conditions, the calibration graph was linear in the range of 5.0×10-3～0.8μg·mL-1, and the detection limit was 3.4×10-3μg·mL-1, the relative standard deviation was 3.3%. The proposed method was applied to the determination of zinc in food samples, and results were satisfactory.