A Simple Flow Injection pH Indicator Method for the Determination of Metal Ions by Urease Inhibition Study

A simple double channel flow injection (FI) pH indicator method based on urease inhibition is described for the determination of Hg+2 Cd+2 and Ze(+2) at microgram level. In urease catalyzed reaction, urea is converted to NH3 and CO2. NH3 released during the reaction increases pH of the reaction mixture, which is immediately detected by pH indicator, bromocresol purple (BCP) due to change in color from reddish yellow (pH 5.2) to purple (pH 6.8). Maximum absorption of BCP at pH 6.8 was found at 588 nm. The method is found very simple, rapid, sensitive and reproducible. The sample through put rate was more than 120 samples per hour. The calibration curves were linear for Hg+2 Zn+2 and Cd+2 in the range of 0.01-4, 1.0-10 and 0.5-10 mM respectively. At 2 mM concentration for each metal ion relative standard deviation (RSD) of three replicate measurements was not more than 0.3 %. The limit of detection, defined as concentration of analyte giving signal (Y) equal to the blank signal (Yb) plus three standard deviations of the blank (Y-Yb = 3Sd), was 0.008, 0.01 and 0.1 mM for He+2 Zn+2 and Ce+2 respectively. The method proves to be suitable for determination of metal ions in environmental and biological samples.