Speciation Analysis of Calcium in Milk by Flame Atomic Absorption Spectrophotometry

An effective method was developed for speciation analysis of calcium in milk by flame atomic absorption spectrophotometry.The effects of ethanol concentration,centrifuge temperature,centrifugal force and centrifugation time on protein sedimentation were discussed.The best conditions for separating calcium from samples were found to be protein sedimentation with 50% and centrifugation at 2 ℃ and 6000 × g for 6 min.The best La(NO3)3 concentration for releasing bound calcium was 6.00 mg/mL as determined by analyzing the effect on absorbance.Under the optimized conditions,the total calcium concentration of milk was determined to be 808.6 μg/mL and the bound and free calcium concentrations were 641.8 μg/mL and 173.0 μg/mL,which accounted for 79.4% and 21.4% of the total calcium,respectively.The precision(RSD) of the developed method was less than 3.3%,and the limit of detection was 0.11 μg/mL.The average spike recoveries of calcium was 97.0% with a RSD of 1.7%.This method was accurate,stable and applicable.