Food (lead) testing

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Lead is a key indicator for daily food sampling and monitoring, and there are sporadic releases of unqualified information, such as fresh vegetables, dried vegetable products, algae products, smoked and roasted meat products, tea, health food, candied fruits, etc. The current national standard for determining food safety for lead in China is GB 2762, and the detection method is GB 5009.12-2017. The method standards stipulate the determination of lead content in food by graphite furnace atomic absorption spectrometry, inductively coupled plasma mass spectrometry, flame atomic absorption spectrometry, and dithizone colorimetry. This time, we will focus on interpreting the commonly used inductively coupled plasma mass spectrometry and graphite furnace atomic absorption spectroscopy, as well as the applicable scope, operational precautions, and key points for determining the results of analytical detection methods

Standard application scope

The two methods are applicable to all foods.

Inductively Coupled Plasma Mass Spectrometry: The standard directly references the corresponding detection method in GB 5009.268. After digestion, the sample is determined by inductively coupled plasma mass spectrometry. Qualitative analysis is carried out based on the specific mass number (mass charge ratio) of the element, while quantitative analysis is carried out using the external standard method. The intensity ratio of the mass spectrum signal of the element to be measured and the internal standard element mass spectrum signal is directly proportional to the element concentration. The digestion methods involved in this method include microwave digestion and pressure vessel digestion

Graphite furnace atomic absorption spectroscopy: After digestion treatment, the sample is atomized in a graphite furnace to absorb the 283.3nm resonance line emitted by a hollow cathode lamp. Within a certain concentration range, the absorbance value of the element is directly proportional to the element content, and is quantitatively compared with the standard series. The digestion methods involved in this method include wet digestion, microwave digestion, and pressure vessel digestion

Operating precautions

Sample preparation.

. Lead is a pollutant in food, and the following points should be noted in sample preparation. One is to determine the limit of lead in the edible part of the sample, and impurities and non edible parts should be removed during sample preparation. The preparation requirements for different types of food are different. For example, vegetables and fruits need to be washed and dried, and edible portions should be homogenized to avoid soil and debris pollution; After removing impurities, grains and legumes are ground to a particle size of no more than 0.425mm. The second is the representativeness of the sample. Pollutant detection is trace analysis, and sample uniformity and representativeness play a crucial role in indicator detection. Whether the samples belong to the same batch or not, and whether the samples are evenly divided and shrunk during sample preparation may cause deviation in the test results. When preparing the samples, attention should also be paid to the uniformity of crushing; Some food varieties involve sampling sites, such as filling products that require full sample preparation for the determination of lead element. The third is to avoid pollution. During the sampling and sample preparation process, it is necessary to effectively avoid incomplete equipment cleaning or contamination caused by metal materials and equipment. Fourthly, attention should be paid to the particularity of health food. According to the "Technical Guidelines for the Inspection and Evaluation of Physical, Chemical and Hygienic Indicators of Health Food (2020 Edition)", the detection of heavy metals in capsule samples needs to be carried out as a whole, or the detection results should clearly indicate the relevant detection sites

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