Determination of perchlorate and thiocyanate ions by ion-selective membrane and bulk optode techniques using experimental design approach

Abstract

This research aimed to develop the detection method for perchlorate and thiocyanate in aqueous solutions using potentiometric and colorimetric techniques. The optimum conditions were designed by the central composite design (CCD) with response surface methodology (RSM). The potentiometric response of perchlorate‒selective electrode using di‒tripodal amine calix[4]arene copper(II) complex (L1-Cu) in PVC membrane was studied. The optimized pH, ion exchanger and ionophore concentrations were found at pH 8.0, 3.25 mmol/kg and 13.25 mmol/kg, respectively. The optimized condition performed a Nernstian slope of –58.02 mV/decade with R2=0.9994 in a working concentration range of 1.00×10‒6 – 1.00×10‒2 M, and the detection limit was 3.00×10‒5 M. This membrane showed the highest selectivity toward perchlorate in comparison with other anions. Moreover, the paper‒based optode sensing device was successfully developed for the determination of thiocyanate in aqueous solution based on colorimetric analysis. The metalloporphrin ionophores including 5,10,15,20‒tetrakis(4‒methoxyphenyl)porphyrine cobalt(II) complex (L2) and 5,10,15,20‒tetrakis(4‒octhyloxyphenyl)porphyrine cobalt(II) complex (L3) were used and coupled with ion exchanger in PVC optode. Optical responses were detected by a digital camera and color intensity was calculated by imageJ program. The paper‒based optode were responded to thiocyanate by changing its color from pink to green. The CCD with RSM was also used to investigate the optimized concentration of ion exchanger and ionophore resulting in the lowest Blue value. In addition, the paper‒based optode responses to thiocyanate with the highest selectivity among other anions with the dynamic range 1.00×10‒7 – 1.00×10‒2 M. The LOD of the paper‒based optode containing L2 and L3 ionophore were 7.00×10‒6 and 1.26×10‒6 M of SCN‒, respectively. Furthermore, this study was successfully applied as a sensing device to detect thiocyanate in urine sample from smoker and non‒smoker with favorable agreement with ion chromatography technique.