The detection of calcium in food is of great significance for nutritional reinforcement assessment, quality control, and safety supervision. The accuracy of its detection results directly depends on the sensitivity and stability of the instrument. This article refers to the "GB 5009.92-2016 National Food Safety Standard for Determination of Calcium in Foods" to conduct precision testing and verification of the standard substance for calcium component analysis in milk powder.

1、 Instruments and reagents

·Instrument:A500 Zeeman flame atomic absorption spectrophotometer, muffle furnace, electric heating plate

·Reagent:Hydrochloric acid, nitric acid, lanthanum oxide

·Standard:GBW (E) 080118 Calcium Monoelement Solution Standard Reference Material, GBW (E) 100596 Calcium Composition Analysis Standard Reference Material in Milk Powder: Reference Value 3.2mg/g (Uncertainty 0.35mg/g)

2、 Experimental conditions

3、 Sample pre-treatment

Accurately weigh 0.5g (accurate to 0.001g) of solid sample in a crucible, heat over low heat, carbonize until smokeless, transfer to a muffle furnace, ash at 550 ℃ for 3-4 hours, cool and remove. For samples with incomplete ashing, add a few drops of nitric acid, heat over low heat, carefully evaporate, then transfer to a 550 ℃ muffle furnace and continue ashing for 1-2 hours until the sample turns white ash. After cooling, remove it. Dissolve and transfer an appropriate amount of nitric acid solution (1+1) to a graduated tube, and make up to 25mL with water. Dilute according to actual measurement needs, and add a certain volume of lanthanum solution to the diluent to make its concentration in the final diluent 1g/L. Mix well and set aside for later use. This is the sample to be tested. Simultaneously conduct a reagent blank test.

4、 Experimental results

4.1 Standard Curve:

4.2定量限：

4.3 Stability testing quality control sample test results:

4.4 Calculation of Stability Test Results:

Note: Conduct testing every 5 minutes, with each group testing for 30 minutes

V. Conclusion

The A500 Zeeman flame type atomic absorption spectrophotometer has a precision range of 0.18% to 0.49% in the calcium element interval test, good test stability, and good reproducibility of intra day and inter day standard curve sensitivity, meeting the stability requirements of users for calcium element testing.