Determination of Calcium by Inductively Coupled Plasma-Atomic Emission Spectrometry, and Lead by Graphite Furnace Atomic Absorption Spectrometry, in Calcium Supplements after Microwave Dissolution or Dry-Ash Digestion: Method Trial

A 3-laboratory method trial was conducted to evaluate 2 sample digestion procedures and instrumental determination parameters for analysis of calcium and lead in Ca supplements. Calcium supplements were treated by dry-ash digestion or microwave dissolution prior to spectrometric analysis. In each case, Pb was determined by graphite furnace atomic absorption spectrometry and Ca by inductively coupled plasma-atomic emission spectrometry. Blind duplicates of 6 Ca supplement samples were analyzed after each sample treatment procedure. Matrix pairs contained dissimilar Pb levels to cover the analyte range encountered during method development. Calcium content of the Ca supplement samples also reflected the range seen during method development. Stock solutions of Ca and Pb were supplied to collaborators for preparation of quantitation standards to remove a variable external to the method. National Institute of Standards and Technology Standard Reference Material (NIST SRM) 1486, bone meal, was included to assess method accuracy and recovery at NIST certificate Ca and Pb levels for this material (26.58 ± 0.24% Ca and 1.335 ± 0.014 µg Pb/g). Analyses of the NIST SRM yielded 25.9 ± 1.1 and 27.2 ± 2.3% Ca and 1.53 ± 0.19 and 1.26 ± 0.19 µg Pb/g for dryash and microwave procedures, respectively. Statistical analyses of data indicated acceptable repeatability and reproducibility for determination of Pb and Ca in various Ca supplements. With either sample preparation technique, the method Received August 27, 1997. Accepted by JS July 2,1998. is appropriate for determining Pb or Ca in Ca supplements.