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

Abstract

Calcium ion (Ca²⁺) 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 Ca²⁺ in our daily life. In this work, a portable gas pressure meter-based method was developed for the detection of Ca²⁺ in water samples and calcium gluconate oral liquids. Ca²⁺ in solution was extracted and precipitated by the addition of Na₂C₂O₄, CaC₂O₄ precipitate was formed and then filtered from the complicated matrix through a filter membrane. The filter membrane (containing CaC₂O₄ precipitate) was then treated by H₂SO₄ solution, CaC₂O₄ precipitate was dissolved during this step and H₂C₂O₄ was formed. In a sealed bottle-in-bottle reaction device, H₂C₂O₄ reacted with acidic KMnO₄ solution to generate CO₂ gas, causing a significant gas pressure increase and it was readout by a hand-held pressure meter. A standard curve with a 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 Ca²⁺ 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 Ca²⁺.