Hardness screening of water using a flow-batch photometric system

The versatility of the flow-batch technique has been taken advantage of to implement an extremely simple and fast water hardness screening system. The proposed approach addresses the demand for simple YES/NO responses on water hardness quality control. It is based on monitoring the well-known quantitative reaction of the calcium/magnesium ions with EDTA, in the presence of the Eriocrhome Black T indicator, by monitoring the absorbance of the medium at 650 nm after addition of fixed amounts of the titrant. Performance curves were employed to measure the reliability of the method and to calculate cut-off statistic values. As a real-life problem, river and dam waters from Para?ba, Brazil, were screened and the results were validated by a reference procedure. The high sample throughput (up to 120 samples per hour), low reagent and sample consumption and disposal, high reliability and easy handling make the screening system very promising for routine applications. Advantageously, the same system assembly can still be used to perform quantitative analysis of target-screened water samples.