In-furnace Digestion And In-furnace Preconcentration-for The Determination Of Lead And Cadmium In Beverage Samples By Graphite Furnace Atomic Absorption Spectrometry

With the increasing of the social economy and people’s living level, the requirements of food quantity have been satisfied, and more and more requirements on food quality have been put forward. Beverage is one of the most popular food for people. Beverages are expected to be green and safe, and the quality control is becoming a major concern. Heavy metals such as lead and cadmium have widely used in industry, and caused great harm to human health with a wide range of environmental pollution. Once the lead enter the body, it can damage some of normal physiological functions, and can even cause cancer, threatening human life. With the increasing concern on food safety all over the world, world health organization(WHO) identified the food safety problems as the research focus in recent years. However, the pollution of toxic heavy metals in beverages is becoming more and more serious. Therefore, the accurate determination of heavy metals in beverage samples appears to be particularly important.Wet-digestion is usually employed for the determination of heavy metals in beverage suspension. However, the digestion process is complicated, and likely to cause contamination. For the rapid and accurate determination of heavy metals in beverage suspension, a furnace digestion method was proposed.The content of heavy metals in some beverage samples is too low to be accurately measured. A furnace enrichment method was proposed in this study, which greatly enhanced the sensitivity of graphite furnace atomic absorption spectrometry(GFAAS). The accurate determination of trace heavy metals in bevetage was demonstrated.The beverage samples tested in the experiment include coffee drinks, pure milk and liquor. Standing on the shoulders of references, we have done the following research by GFAAS.(1) Optimization of experimental parameters. The ultrasonic time, concentration of nitric acid, matrix modifier type, modifier concentration, ashing temperature, atomization temperature were investigated. The optimization curve the optimum experimental conditions were obtained.(2)Determination of lead, cadmium in beverage samples by in-furnace digestion GFAAS. The accuracy, precision, and limit of detection of the methods were illustrated. The samples studied include coffee drinks, milk, liquor etc.(3)In order to verify the reliability of the proposed method, a wet digestion method was used to determine lead and cadmium in coffee drinks, milk and other samples, and the results was in good agreement with our method.(4)In-furnace preconcentration. The content of lead and cadmium in some beverage samples is too low to be accurately measured. Thusan in-furnace preconcentraion method was proposed.Multiple injections were employed for the enrichment of lead and cadmium in different liquors. The signal intensity increased linearly with the increase of injection times. In order to verify the accuracy of in-furnace preconcentration method, aspike recovery test was carried out.Through detailed study, the main conclusions are as follows:(1) Determination of lead in beverage samples by in-furnace digestion GFAAS. After optimization, the matrix modifier was 0.1% palladium nitrate; the dilution reagent was 0.2% nitric acid; the surfactant was 0.1% triton-100; the ultrasonic time was 15 minutes;The optimal furnace program was: 900 oC ashing temperature for 20 seconds, and 1500 oC atomization temperature for 5 seconds. The lead in coffee drinks and pure milk was determined under the optimized conditions. The contents of lead in the four coffee drinks were 8.05ng/ml, 9.75ng/ml, 10.85ng/ml, and not detectable. The content of lead in the four milks were 13.90ng/ml, 15.65ng/ml, 13.45ng/ml, and 17.60 ng/ml. The calibration curve was linear from 0ng/ml to 50ng/ml, with the correlation coefficient of 0.9991. The limit of detection was 0.24ng/ml, and the relative standard deviation was less than 3.5%. The recoveries are in the range between 94% and from 0ng/ml to 5ng/ml, with the correlation coefficient of 0.9993. The limit of detection was 0.02ng/ml, and the relative standard deviation was less than 3.0%.The recoveries are in the range between 95% and 108%.(3)Using nitrate acid and perchlorate acid to digest coffee drinks and pure milk, to validate the accuracy of the proposed in-furnace digestion method. A good agreement between wet-digestion GFAAS and in-furnace digestion GFAAS was observed, which demonstrated the accuracy and reliability of the in-furnace digestion method.(4) In-furnace preconcentration for the sensitive determination of lead and cadmium. The content of lead and cadmium in some beverage samples is too low to be accurately measured. Therefore, multiple injections were used to improve the analytical sensitivity. The recoveries was ranged from 94% to 106% by five times injections, demonstrating the accuracy and reliability of the method. The curve of injection numbers vs. signal intensity, and the curve of time vs. signal intensity were constructed.