Detection of Ca2+ in water samples and calcium gluconate oral liquids using gas pressure meter as portable detector

Calcium ion (Ca 2+ ) is one of the important nutrients for humans, excessive and insufficient intake may both cause diseases, so that it is of great importance to analysis of Ca 2+ in our daily life. In this work, a portable gas pressure meter-based method was developed for the detection of Ca 2+ in water samples and calcium gluconate oral liquids. Ca 2+ in solution was extracted and precipitated by the addition of Na 2 C 2 O 4 , CaC 2 O 4 precipitate was formed and then filtered from the complicated matrix through a filter membrane. The filter membrane (containing CaC 2 O 4 precipitate) was then treated by H 2 SO 4 solution, CaC 2 O 4 precipitate was dissolved during this step and H 2 C 2 O 4 was formed. In a sealed bottle-in-bottle reaction device, H 2 C 2 O 4 reacted with acidic KMnO 4 solution to generate CO 2 gas, causing a significant gas pressure increase and it was readout by a hand-held pressure meter. A standard curve with linear range of 1–80 mmol L −1 and a limit of detection of 0.4 mmol L −1 were obtained. This system was subsequently applied to the detection of Ca 2+ in several water samples and oral liquids, recoveries of 92–110 % were obtained for their spiked samples. Only a few reaction bottles and a gas pressure meter were required in this system. It is a low-cost, sensitive, rapid and easy-used analytical method for on-site determination of Ca 2+ .