The heavy metal detector can test the content of heavy metals (cadmium, chromium, mercury, arsenic, lead) in soil, fruits, vegetables, meat and other food products.
（1） After digestion, all forms of heavy metals (including arsenic, lead, cadmium, chromium, mercury, nickel, iron, aluminum, zinc, manganese, copper, etc.) in the sample are transformed into ionic forms, and color is developed after adding relevant detection reagents;
The color depth of a solution within a certain concentration range is proportional to the content of heavy metals, following the Lambert Beer law;
Then, the content value is determined through instruments, and compared with the national standard for agricultural product safety quality, pollution-free vegetable safety requirements and allowable limit standards, to determine the heavy metal content of vegetable samples.
Wet digestion method:
In the detection of heavy metals in food, sample pretreatment is the most crucial step in food inspection, which directly affects the precision and accuracy of the analysis results;
Choosing appropriate pre-treatment methods and shortening the pre-treatment time of samples is an important method to improve inspection efficiency while ensuring inspection quality.
Wet digestion method is to add strong oxidizing acids to an appropriate amount of food samples, heat them to destroy organic matter, release the inorganic components to be tested, and form non-volatile inorganic compounds for analysis and determination.
Wet digestion is a widely used food sample pretreatment method, which has strong practicality and can be used to digest almost all foods.
（2） The detection principles and standards for various heavy metals
1. The detection principle and adopted standards of heavy metal arsenic
The national standard borohydride reduction colorimetric method is adopted, which involves adding potassium iodide thiourea and heating the sample after digestion;
Reduce pentavalent arsenic to trivalent arsenic, and under acidic conditions, potassium borohydride reduces trivalent arsenic to negative trivalent, forming hydrogen arsenide that is introduced into the absorption solution and turns yellow. The arsenic content is determined by instrument detection.
2. The detection principle and standards for heavy metal lead
The national standard dithizone colorimetric method is adopted, which means that after digestion of the sample, under weak alkaline conditions, lead ions and dithizone form a red complex, which is dissolved in trichloromethane and then determined by colorimetry.
3. The detection principle and adopted standards of heavy metal chromium
After digestion, in the presence of divalent manganese, chromium ions react with diphenylcarbazide to form a purple red complex. The color of the complex is directly proportional to the content of hexavalent chromium, and colorimetric determination can determine the chromium content.
4. The detection principle and adopted standards of heavy metal cadmium
Using the national standard colorimetric method, after digestion of the sample, under alkaline conditions, cadmium ions form a red complex with 6-bromophenyl propionazole azonaphthol, which is dissolved in trichloromethane for colorimetric determination.
5. The detection principle and adopted standards of heavy metal mercury
The national standard dithizone colorimetric method is adopted, which means that after digestion of the sample, under acidic conditions, mercury ions and dithizone form an orange red complex, which is dissolved in trichloromethane and then determined by colorimetry.
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