Determination of High Concentration of Ca(Ⅱ) in Geothermal Water with Flow Injection-Micro-flow-through Ion Selective Electrode

The FI-micro-flow-through Ca(Ⅱ) selective electrode (FI-MF-Ca(Ⅱ) ISE) was applied to the determination of high concentration of Ca(Ⅱ) in geothermal water. Various influential factors were studied. The optimized conditions were as follows: ① length of the mixing coil: 30 cm; ② flow rate of the carrier: 0.99 mL·min-1; ③ sampling volume: 60 μL; ④ total ionic strength adjusting buffer solution (pH 9.7): a mixed solution containing 0.02 mol·L-1 sodium borate, 0.02 mol·L-1 sodium hydroxide, 10 mg·L-1 Ca(Ⅱ) and 0.60 mol·L-1 sodium chloride, with a flow-rate of 0.88 mL·min-1. Linearity range of the method was kept between 0.16-20.00 g·L-1. Precision of the method was tested at the concentration levels of 1.00 and 2.00 g·L-1 of Ca(Ⅱ) for 11 determination. Values of RSD′s were found to be 2.8% and 1.8%, respectively. The proposed method was used in the analysis of samples of geothermal water, giving values of recovery by standard addition method in the range of 102%-111%.