POTENTIOMETRIC STUDY FOR RAPID CONTINUOUS MONITORING OF TRACE LEVEL THIOCYANATE USING SOLID AND CONVENTIONAL TYPES PVC MEMBRANE SENSORS
A comparative study using two different thiocyanate electrode designs was conducted; a solid type electrode (type A) and conventional
liquid inner contact electrode (type B). The fabrication of these electrodes was based on Al (III) [4-(2-Pyridylazo) resorcinol] (Al/PAR) and Mg (II) phthalocyanine (MgPC) complexes as a charged carrier, aliquate 336S and TDMAC as ion exchangers in plasticized poly (vinyl chloride) membrane. Electrodes type (A) revealed significantly enhanced response towards SCNions with displayed near-Nernstian slope of -53.7 - -55.8 mV decade-1 over the concentration range 5.0x10-6 -1.0x10-2 mol L-1 and a detection limit of 0.4-3.7 µg mL-1. Type (B) sensors revealed near-Nernstian potential response to SCN- with a slope of -45.9 - -62.4 mV decade-1 over a linear range of 5.0x10-5- 1.0x10-2 mol L-1 and a detection limit of 0.12-0.3 µg mL-1. Membrane sensors based on (Al/PAR) and (MgPC) using the so called "fixed interference method" (FIM) exhibited a good selectivity over different anions which differ significantly from the classical Hofmeister series. All sensors were integrated in a flow system for continuous monitoring of thiocyanate under hydrodynamic mode of operation. The sensors revealed a frequency of ~ 54 samples h-1. Application of the proposed sensors for SCN- determination in biological fluid samples such as saliva collected from some non-smoker and smoker donors. Determination of cyanide content in electroplating wastewater samples after its conversion into thiocyanate was also applied. The results obtained from the proposed sensors were agreed with that obtained using the standard methods of thiocyanate and cyanide analysis.