Sequential injection system in flame atomic absorption spectrometry for the determination of calcium and magnesium in mineral waters

A flow set-up based on sequential injection analysis (SIA) is proposed to increase the versatility and robustness of routine flame atomic absorption analytical methods. Four procedures were selected to allow the determinations of calcium within the ranges of 0.03–10.00 and 0.58–200.00 mg l−1, and magnesium within 0.03–1.5 and 0.80–50.0 mg l−1, in mineral waters. The sample aliquots inserted were 70.8 and 12 μl for calcium and 13 and 12 μl for magnesium. Moreover the system developed enabled to restrict the consumption of the releasing agent to respectively 142 and 97 μl in the determinations of calcium and to 26 and 12 μl in the determinations of magnesium. The results obtained in the analysis of 15 mineral waters were compared with those obtained by the corresponding conventional procedures yielding the equations: [Ca mg l−1]SIA=1.008(±0.004)*[Ca mg l−1]conv. −0.3 (±0.3) and [Mg mg l−1]SIA=0.992(±0.006)*[Mg mg l−1]conv. +0.0 (±0.1). In all cases the sampling rates achieved were higher than 110 h−1, and reproducibility being better than 3%.