A FI-Electrochemoanalytical System and Its Application to In-Situ Supervising Analysis in the Process of Preparation of Calcium Citrate by Cation Exchange

A flow-injection electrochemoanalytical system was proposed and applied to in-situ supervising analysis for content of the product and state of production in the process of preparation of calcium citrate by cation exchange. As shown by the experimental results, the optimized testing conditions were given as follows: ① a mixed solution containing 80 mmol of Tris, 175 mmol of boric acid, 1.0 mmol of KCl and 0.025 mmol of CaCl2 in 1 L of solution was used as TISAB (pH 8.0) in the analysis; ② 150 μL was taken as the volume of sample injection; ③ total flow-rate taken was 2.26 mL·min-1; and ④ length of the mixing coil taken was 120 cm (with i.d. 0.5 mm). Linearity ranges found for determination of Na+ ion and Ca2+ ion were between 2.0-1 000 mmol·L-1 and 0.2-50.0 mmol·L-1 respectively. Values of lower limits of determination found for the ISE of Na+ and Ca2+ were 1.12 mmol·L-1 and 0.09 mmol·L-1 respectively. Tests for precision were made with mixtures of standard solutions of Na+ and Ca2+ at low and high concentrations, values of RSD′s (n=11) found were all less than 0.7%.