Potentiometric flow titration of iron(II) and chromium (VI) based on flow rate ratio of a titrant to a sample

摘要

A new potentiometric flow titration has been proposed based on the relationship of two flow rates between titrant and sample solutions. A sample solution is pumped at a constant flow rate. The flow rate of the titrant solution is gradually increased at regular time invervals and a flow rate for the titrant solution in the vicinity of the equivalence point is obtained. The concentration of the sample is calculated by C_s (mol 1~(-1)) = R(_T (ml min~(-1)) * C_T (mol 1~(-1)))/R_S (mol min~(-1)), where C_S, C_T, R_S, and R_T denote the unknown sample concentration, titrant concentration in the reservoir, the flow rate of the sample solution which is a constant rate, and the flow rate of the titrant solution at an inflection point, respectively. The potentiometric flow titration of iron(II) with cerium(IV) and of chromium(VI) with iron(II) has been presented. The titration time of the proposed method is about 10 min per samples. An R.S.D. of the method is 0.77% for seven determinations of 1 * 10~(-3) mol 1~(-1) iron(II). Similarly, the flow titration of chromium(VI) with iron(II) is carried out over the range 1 * 10~(-4)-1 * 10~(-3) mol 1~(-1) chromium(VI) and is successfully applied to the determination of chromium in high carbon ferrochromium.