Flow-injection spectrophotometric determination of paraoxon by its inhibitory effect on the enzyme acetylcholinesterase

Flow injection visible diffuse reflectance quantitative analysis of nickel

Flow injection (FI) methodology, using diffuse reflectance in the visible region of the spectrum, for the analysis of nickel, precipitated in the form of dimethylglyoximate, is presented. A reflectance cell, constructed in polytetrafluoroethylene, using a LED (light emitting diode) as light source and a LDR (light dependent resistor) as detector, is described. The analytical signal (S) correlates with nickel concentration (C) between 1.6 x 10(-4) and 6.6 x 10(-4)molL(-1). This correlation is described by the equation S=-1.108+3.314 x 10(4)C-2.081 x 10(7)C(2) (r=0.9996). The experimentally observed limit of detection is about 1.3 x 10(-4) molL(-1), as in lower concentrations the formation of precipitate is not observed. The experimental quantitation limit is about 1.6 x 10(-4) molL(-1). The mean R.S.D. (relative standard deviation) is about 2.7%. Samples containing nickel were analyzed and the results obtained in this method were compared with those of other methods using the statistical Student's t-test.