Direct determination of Calcium in milk by atomic absorption spectrometry using flow-injection analysis

Abstract

A flow-injection system with sample and reagent addition by the synchronousmerging zones approach for calcium determination in milk by flame AAS is proposed. Mainparameters were optimized using a factorial design with central point. The optimum conditionswere 2.5% (m/v) for La concentration, 8 mL min -1 for the carrier flow-rate, 20 cm for coiledreactor and 250 ìL for sample volume. Different sample preparation procedures were evaluatedsuch as dilution in water or acid and microwave-assisted decomposition using concentratedor diluted acids. The optimized flow system was applied to determine Ca in eleven commercialmilk samples and two standard reference materials diluted in water. Similar calcium levelswere encountered comparing the results obtained by the proposed method (dilution in water)with those obtained using microwave-oven digestion. Results obtained in two standard referencematerials were in agreement at 95% confidence level with those certified. Recoveries of spikedsamples were in the 93% - 116% range. Relative standard deviation (n = 12) was < 5.4%and the sample throughput was 150 measurements per hour, corresponding to a consumptionof 250 μL of sample and 6.25 mg La per determination.