Abstract: A method has been established for the determination of calcium in protein power using microwave digestion-flame atomic absorption spectrophotometry with La(NO3)3 as the releasing agent. Digestion efficiency was investigated with respect to four variables including digestion system, digestion pressure, digestion time and pressurization style. The effect of La(NO3)3 concentration on the release of calcium was discussed. Under optimal conditions, the linear range of this method for calcium was 1－20μg/mL and the detection limit was 0.15μg/mL. The average calcium content in a commercial protein powder sample determined by this method was 0.46% with a relative standard deviation of 1.63% (n = 6). The average recovery rate of calcium in a protein powder sample with a calcium content of 9.10μg/mL across the spike levels of 0.5, 1.5μg/mL and 2.0μg/mL was 96.8% with a relative standard deviation of 2.34%. Therefore, this method has a wide linear dynamic range, good correlation, high accuracy and precision, and high practical application value. 

Key words: microwave digestion, releasing agent, flame atomic absorption spectrophotometry(FAAS), protein powder, calcium