Bottle-in-bottle reaction device: Portable gas pressure meter for rapid and on-site analysis of oxalate in spinach and tea beverages.

A gas pressure meter-based portable/miniaturized analytical kit was established for rapid and on-site detection of oxalate. Potassium permanganate (KMnO) and oxalate solution were mixed together in bottle-in-bottle reaction device, a simple oxidation reaction process occurred within 6 min and carbon dioxide (CO) was generated, inducing the pressure of the sealed bottle changed, which was measured by a portable gas pressure meter. A detectable range of 0.1-6 μmol mL and a detection limit of 0.064 μmol mL were achieved. The proposed analytical method was further used for the analysis of several real samples (spinach, beverages and water samples), with the recoveries of 89-111%. Considering the interferences from the complicated matrix, calcium chloride (CaCl) was served as a precipitant, oxalate (CO ) was precipitated with Ca to form precipitation (CaCO), CaCO was then separated from the matrix by centrifuge/filter, eliminating the interferences. It is a rapid, easy-used and interference-free analytical system/device for oxalate on-site and real time analysis.