Electrochemical determination of para-nitrophenol at apatite-modified carbon paste electrode: application in river water samples.

The behavior of a modified carbon paste electrode (CPE) for para-nitrophenol detection by cyclic and square wave voltammetry (SWV) was studied. The electrode was built by incorporating the hydroxyapatite (HAP) to carbon paste. The overall analysis involved a two-step procedure: an accumulation step at open circuit, followed by medium exchange to a pure electrolyte solution for the voltammetric quantification. During the preconcentration step, para-nitrophenol was adsorbed onto hydroxyapatite surface. The influence of various experimental parameters on the HAP-CPE response was investigated (i.e. pH, carbon paste composition, accumulation time). Under the optimized conditions, the reduction peak shows that the peak height was found to be directly proportional to the para-nitrophenol concentration in the range comprised between 2x10(-7) mol L(-1) and 1x10(-4) mol L(-1). With this, it was possible to determine detection limit (DL), which resulted in 8x10(-9) mol L(-1) for peak 1. The proposed electrode (HAP-CPE) presented good repeatability, evaluated in term of relative standard deviation (R.S.D.=2.87%) for n=7 and was applied for para-nitrophenol determination in water samples. The average recovery for these samples was 86.2%.