Determination of the total hardness in tap water using acoustic wave sensors

The determination of hardness in water is a useful parameter to control the quality of water for households and industrial uses. The present work proposes a new methodology as an alternative to the conventional EDTA titration. The determination of Ca2+ and Mg2+ is performed using two different coated piezoelectric quartz crystals. Poly(vinyl chloride) membranes, incorporating a plasticizer and a Mg or Ca ionophore were used to coat the piezoelectric quartz crystals. Results obtained by this new methodology shows that the tap water found in Portugal can be considered soft in Gouveia (9.4 +/- 0.8 mg L-1 CaCO3) and in Vila Praia Ancora (15 +/- 1 mg L-1 CaCO3) Slightly hard in Leiria (59 +/- 1 mg L-1 CaCO3), moderately hard in Aveiro (74 +/- 1 mg L-1 CaCO3) and in Esposende (104 +/- 1 mg L-1 CaCO3) and very hard in Tomar (225 +/- 1 mg L-1 CaCO3). The results obtained by the proposed method are not significantly different (alpha = 0.05), both in terms of accuracy and precision, from the ones obtained by the conventional EDTA titration method. Besides providing individual concentration of Ca2+ and Mg2+, this new methodology also has the advantage of being less reagent, sample and time consuming. (c) 2007 Elsevier B.V. All rights reserved.