Calcium analysis in seawater by an ion sensitive electrode

Abstract

A newly developed calcium sensitive liquid-liquid membrane electrode is used to analyse seawater off the Oregon coast in waters fed by the Columbia River runoff. For the analysis, an application of the method of standard additions is used requiring the assumption that the seawater is of so high a salt concentration that a small change in the overall ionic strength is insufficient to disturb the electrode response to calcium. Two equations describing the behavior of the electrode are treated and one is found applicable for use in seawater. Analyses by electrode are compared with analyses of the same water by atomic absorption spectroscopy with a degree of scatter in the correlation which is largely accounted for by 10% of calcium accuracy in the electrode readout device. Overall laboratory precision of the electrode and readout was 3% of calcium per standard deviation. The electrode appears to be much better for analytical purposes than ± 10% of calcium concentration.