Construction of an Optical Sensor for Cobalt Determination Based on Methyltrioctylammonium Chloride Immobilized on a Polymer Membrane

Abstract

An optical sensor has been designed for the determination of cobalt by spectrophotometry. The sensing membrane is made by immobilizing methyltrioctylammonium chloride on a triacetylcellulose membrane. In the presence of Co(II) and thiocyanate ions, the colorless membrane changes to blue. The response time of the optode was about 7 min. The sensor can readily be regenerated with 0.02 mol L−1 sodium oxalate solution. This optode is stable and can be stored under water for more than a month without reagent leaching. The calibration curve was linear in the range of 8.5×10−6–1.3×10−4 mol L−1 of Co(II) ion with a limit of detection 5.9×10−6 mol L−1. The relative standard deviations for seven replicate measurements of 3.4×10−5 and 1×10−4 mol L−1 of Co(II) were 1.58 and 1.10%, respectively. The sensor was successfully applied to the determination of cobalt in food samples and vitamin B12 ampoule.