A negative-pressure flow-injection micro-electrode system for rapid and simultaneous determination of four electrolytes in human serums.

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(2)B(4)O(7)-H(3)BO(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.