Abstract
A method was developed to analyze various calcium supplements for Ca and Pb content. The analysis involves a dry ash of the supplements followed by wet digestion. The Pb is determined by graphite furnace atomic absorption spectro–photometry (GFAAS). Analysis of Ca is by inductively coupled plasma–atomic emission spectrometry (ICP–AES). Ca supplements fortified with Pb at levels ranging from 0.25 to 10.0 μg/g yielded recoveries ranging from 82.7 ± 4.2 to 105.0 ± 1.7%. To test accuracy, the method was applied to National Institute of Standards and Technology standard reference materials (NIST SRMs) 1572 citrus leaves and 1486 bone meal. GFAAS analysis of SRM 1572 averaged 13.1 ± 0.6 μg Pb per g (certificate value, 13.3 ± 2.4 (μg Pb per g), and analysis of SRM 1486 averaged 1.34 ± 0.11 μg Pb per g (certificate value, 1.335 ± 0.014 μg Pb per g). ICP–AES analysis of SRM 1572 averaged 3.12 ± 0.01% Ca (certificate value, 3.15 ± 0.10% Ca by weight), and analysis of SRM 1486 averaged 27.63 ± 0.27% Ca (certificate value, 26.58 ± 0.24% Ca). The method's limit of quantitation (LOQ), on supplement Ca basis and a 1 g sample, averaged 0.75 μg Pb per 1 g Ca for supplements containing 9 to 35% Ca by weight. At a Pb level of 0.663 μg/g Ca, the reproducibility relative standard deviation (RSDr) averaged 7.3% and the repeatability relative standard deviation (RSDr) averaged 8.0%. It is recommended that the method be studied collaboratively.
