With more and more exploitation and utilization of seawater and geothermal water, the demand of determining the concentration of K+, Na+, Ca2+ and Cl- in them has been increased. A method of flow-injection serial- ion selective electrodes (FI-ISE-S) for simultaneous and rapid determination of K+, Na+, Ca2+ and Cl- in sea water and geothermal water was established. In the research, various influence factors of the FI-ISE-S system were investigated and optimized, including flow rate of system, sampling volume, the length of mixing coil, interfering substances, the acidity and ion concentration of the total ion strength adjusting buffer solution. Among the optimal conditions, the analysis speed of the system is 100 samples · h-1; the consumption of the sample is only 160 μL per time; the relative standard deviation (RSD) is less than 1.96% (n=11); the recoveries obtained by adding K+, Na+, Ca2+ and Cl- in the samples are in range of 91.9%~109.6%; and the linear determination ranges of the method are 1.0~8.0 mmol · L-1 for K+, 50~290 mmol · L-1 for Na+, 3.2~16.0 mmol · L-1 for Ca2+, 70~430 mmol · L-1 for Cl-. It has been successfully applied in the determination of seawater and geothermal water.

10.3969/j.issn.1003-9015.2013.03.001

An automatic system for simultaneous determination of K^+, Na^+, Cl^− and Ca^2+ in serums was established on the basis of a negative-pressure flow-injection using micro-electrodes, and parameters of the system were optimized. The total ionic strength adjustment buffer consisted of 0.25 mmol L^−1 K^+, 48.6 mmol L^−1 Na^+, 2.56 mmol L^−1 Cl^−, 0.25 mmol L^−1 Ca^2+ and 23 mmol L^−1 Na_2B_4O_7-H_3BO_3; the flow rate was 1.58 mL min^−1, the sampling volume was 45 μL, and the mixing coil length was 30 cm. The system could conduct 480 detections h^−1, and its RSD was less than 1.6%. Recoveries were 97.3 – 103.6%, and linear responses were 2.0 – 22.0 mmol L^−1 for K^+, 89.6 – 253.0 mmol L^−1 for Na^+, 20.1 – 248.2 mmol L^−1 for Cl^−, and 0.35 – 10.0 mmol L^−1 for Ca^2+, respectively. The ion concentration ranges were in ranges of human serum electrolytes. The system features minimized sorption of fibrin in sensors and prolonged sensor life.

In order to simplify the device configuration, reduce the cost, improve the instrument stability and anti-interference ability, a new type of double-line flow-injection ion-selective electrode method was proposed, and determination conditions of the method,, such as the carrier composition and flow rate, acidity adjusting liquid composition and flow rate, and reaction coil length were optimized. The method was successfully used in simultaneous determinations of K＋、Na＋、Cl-、Ca2＋ in serums. Linear ranges of the method were in 2.0 -24.0 mmol· L-l for K ＋ , 102-252 mmol · L-1 for Na ＋ , 20 -300 mmol · L-1 for C1- and 0.7 - 8.0 mmol · L-l for Ca2＋ , respectively. The relative standard deviation was less than 1.3% （n = 11 ） , the recoveries obtained by adding K＋、Na＋、Cl-、and Ca2＋ in serum samples were in range 96% - 104% , the analysis speed was 480 detections/h, and the consumption of the sample was only 45μL per time. These determination ranges were in normal ranges of human serum＇ s electrolyte concentrations.

A new automatic analysis method and system for simultaneous determination of K+, Na+, Cl- and C2+ in serum was proposed on the basis of flow-injection micro-electrode dynamic electrochemical technology (FI-ME-ECA). To stabilize baseline potentials of four electrodes and to accelerate response of the electrodes, we have examined various components in the carrier of the FI-ME-ECA and optimized experimental conditions. Obtained results were as follows: 23 mmol/L, of Na2B4 O-7-H3BO3 (pH 7. 40) was used as the buffer solution, the carrier solution are consist of 0. 25 mmol/L K+, 48.6 mmol/L Na+, 2.5 mmol/L Cl- and 0.25 mmol/L Ca2+, and its flow rate is selected 1.56 mL-/min. The length of mixing coil was 30 cm (I. D. 0. 5 mm). The linear determination ranges of the method are 3.0-6.0 mmol/L for K+, 90-253 mmol/L. for Na+, 20-248 mmo/L- for Cl- and 0.35-10 mmol/L for Ca2+, respectively, the relative standard deviation (RSD) is less than 1.1% (n=11), the recoveries obtained by adding K+, Na+, Cl- and C2+ in serum samples are in range of 96. 7% 103. 7%, analysis speed of the system is 1.20 samples/h (480 detections/h), consumption of the sample is only 45 mu L at a time. Main merits of the FI-ME-ECA are injection of micro-volume sample and continuous flow of the Carrier solution. It has achieved automatic cleaning of the FIA manifold, and has avoided carryover between the samples, and has removed sorption and stemming of fibrin on the sensor channels, and has prolonged life of the electrodes.