Application of Atomic Absorption Spectrophotometers in Food Testing

In recent years, both domestically and internationally, relatively mature analytical methods have been established for the detection and testing of trace elements in foodstuffs, with significant advances also made in sample preparation and data processing methodologies. It has been established that metallic elements such as mercury, lead, cadmium, and arsenic in food can exert significant toxic effects on the human body even at low intake levels. These toxic trace elements exhibit strong accumulation properties, bioaccumulation characteristics, and often cause harm through chronic poisoning. The potential threat to human health posed by trace element contamination has become a serious food safety issue. Consequently, the testing of trace elements in food has become a crucial aspect of food analysis and inspection. This paper briefly outlines the fundamental principles and applications of atomic absorption spectrophotometry (AAS) for detecting trace elements in food.

　　Atomic absorption spectrophotometry is a relative measurement technique based on the absorption of characteristic light by atoms. Its fundamental principle involves passing the characteristic spectral lines of the target element emitted by a light source through the vapour of the sample. These spectral lines are absorbed by the ground-state atoms of the target element. Under specific conditions, the degree of attenuation of the incident light due to absorption is directly proportional to the concentration of the target element in the sample. This relationship enables the determination of the target element's concentration within the sample. This method exhibits high sensitivity, strong selectivity, a broad analytical range, excellent precision, and good accuracy. Atomisation devices typically comprise three types: flame atomisation systems, graphite furnace atomisation systems, and hydride generators.

(1) Concentrated Fruit Juice

　　Sample Preparation: Weigh 0.5000g of sample into a microwave digestion vessel. Add 6ml nitric acid and 2ml hydrogen peroxide for microwave digestion (Table 1). Heat to evaporate acid until a small residual solution remains. Add 1ml of a 10% ascorbic acid and thiourea mixture, then dilute to 10ml.

(2) Milk Powder

　　Sample Preparation: Weigh 0.25g of milk powder into a microwave digestion vessel. Add 6ml nitric acid and 2ml hydrogen peroxide separately, then microwave digest (Table 3). Heat until a small residual solution remains, then dilute to 15ml.

Sample Analysis Results: Analysis of trace metal elements in milk powder using flame and graphite-sheathed methods yielded the following results.

(3) Tea Leaves

Sample Preparation: Chromium – Weigh 0.5g into a porcelain crucible, add 2ml nitric acid and soak for 60minutes. Dry the crucible on an electric stove until carbonised and smoke-free, then transfer to a muffle furnace at 550°C for 3 hours. Cool, dissolve in nitric acid, and dilute to 50 ml. Lead: Weigh 0.2g into a conical flask, add 10 ml nitric acid-perchloric acid (4:1), soak thoroughly, evaporate to dryness on an electric furnace, then digest and dilute to 10ml.

Sample Analysis Results: Chromium and lead content in tea samples were analysed using graphite furnace atomic absorption spectroscopy, yielding the following analytical results.