Determination of harmful metal elements in food

Shanghai Fisheries University Food Faculty Jiangjinjin Stepping Cun Temple In recent years, due to the increased environmental pollution, the large amount of pesticides used in cultivation and the food processing process are becoming more and more complex, often lead, cadmium, arsenic, mercury and other elements enter human food. These metal elements are not physiologically essential elements of the human body and are considered to be toxic elements.

Under normal circumstances, the body's tolerance to these elements is small. When they are too high in food or they are taken in small amounts over a long period of time, they will cause harm to the human body and must be tested frequently. This article will describe the conventional methods for determining these four elements and some improvements.

Lead is widely distributed in nature, and lead in food is the main source of human lead.

Immature lead can cause harm to the nervous system, digestive system and hematopoietic system.

Both the national standard method and the American AOAC standard method use dithizone colorimetry and atomic absorption spectrometry. The former is based on the principle of the formation of red complexes of lead and dithizone in PH 8.5-9.0 solution, the complex is dissolved in organic solvents, colorimetric after extraction. This method has high sensitivity and simple instrument, but the analysis process is very long, and dithizone is a broad coordination agent. Masking agent must be added to prevent interference from other metal ions. The sensitivity of the latter cannot meet the requirement for determining the content of lead in foods, so it is generally determined by solvent extraction to increase the sensitivity. Here, the iodide MIBK extraction method identical to the chelation extraction method of copper is described. This method can simultaneously extract copper, lead, and cadmium, and perform the measurement under the same conditions. After extraction, no flame atomic absorption spectrometry was used to measure the sample. The sensitivity was very high. When the lead was measured, a small amount of solvent was extracted and the graphite furnace was atomized.

Cadmium is very toxic to the human body. Excessive intake can cause chronic kidney toxicity, hypertension and atherosclerosis. Under normal circumstances, the content of cadmium in foods is very low, and it is required to use a method with high sensitivity and accuracy. Dithizone colorimetry is generally no longer used because of its low sensitivity. At present, the representative method is atomic absorption spectrophotometry. The method is simple and accurate. When the flame atomic absorption spectrophotometry still cannot meet the measurement requirements, it needs to be extracted and concentrated first. The national standard method (C; B5 (X9.15-%) is an iodide MIBK extraction method. This method is most stable for determination of cadmium and has high sensitivity. Sample preparation is based on the characteristics of the sample selected dry ashing and lmol/LHCL leaching law.

Total arsenic includes inorganic arsenic and organic arsenic. Inorganic arsenic is more toxic than organic arsenic, and trivalent arsenic in inorganic arsenic is more toxic than pentavalent arsenic. Arsenic in food mainly comes from the direct pollution of arsenic-containing pesticides. General foods contain only trace amounts of arsenic. Its quantification method must be trace quantification. For example, the ancient Chow method (arsenic spot method), multi-blue method, silver diethyldithiocarbamate method (silver salt method), hydride generation atomic absorption spectrometry. Among them, the silver salt method has high precision, and it is one of the standard methods of food hygiene testing in China (the other is the arsenic spot method).

Total mercury, including inorganic and organic mercury, can cause harm to the central nervous system of the organism. Methylmercury can enter the human fetus through the placenta and cause fetal congenital mercury poisoning.

Mercury in food mainly comes from pollution. Mercury in the water can accumulate in the fish through the food chain. In addition to quantifying total mercury, aquatic products often use methylmercury for children. Mercury in foods is commonly determined by cold atomic absorption spectrometry. The method has high sensitivity, less interference, and simple operation. The principle is: The sample is oxidized and decomposed by sulfuric acid, nitric acid, and potassium permanganate. All the mercury compounds are oxidized to form high-valence mercury ions. Stannous chloride is added in the decomposing solution, and mercury ions are reduced to metal mercury. The generated mercury vapor was introduced into the quartz ion chamber, and the absorbance was measured at a wavelength of 253.7 tnm while the AOAC in the United States used a dithizone colorimetric method to determine the mercury content of the food.

The detection of harmful metal elements in food is a necessary means for understanding the quality of food from a macroscopic perspective to a microscopic perspective. It is also an important basis for evaluating the quality of life and the quality of the environment in all grass-roots units. In recent years, many measures have been taken at home and abroad to ensure food safety, such as food hygiene standards, Good Manufacturing Practices (GMP) and HACCP. It is of great significance to strengthen food safety inspections and pay attention to prevent problems before they occur, which is of great significance for improving people’s health, improving quality of life, and promoting economic development and social stability.

Civil Military Medical Press. 199328―43 published by Science and Technology Press. 1993298―31 1. Chief editor of Lu Changhao, a physics and chemistry tester of food, published by People's Medical Publishing House.

5. Food Safety Yang Jiebin et al., published by China Light Industry Press.

6 Laboratory technicians Zhang Tiejun, Cheng Quanshou et al., Water Resources Press c1988D