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Potentiometric Determination of N-(2- Mercaptopropionyl)-Glycine Using an Electrode with AgI-Based Membrane

Potentiometric methods for determination of N-(2– mercaptopropionyl)-glycine (MPG) using a commercial indicator electrode with AgI-based membrane are described. Heterogeneous and homogeneous chemical reactions important for the response of the sensor are discussed. For direct potentiometric measurements, equilibrium potentials recorded under continuous addition of standard MPG solution into 0.1 mol L^-1 HClO_4 as the background solution were considered relative to pMPG. Linear response with a slope of 59 &plusmn ; ; 0.7 mV was obtained in the concentration range from 2.0 ∙ 10^-5 to 1.5 ∙ 10^-3 mol L^-1. In the "kinetic" potentiometric experiment, the relationship between the potential change and the concentration of MPG was found to be linear for more than a one-decade range of the amount of MPG. The best analytical results were achieved using the potentiometric titration method. This method with 0.1 mol L^-1 HClO_4 as the background solution is recommended for the determination of MPG in pharmaceutical preparations.

N-(2-mercaptopropionyl)-glycine; direct potentiometry; kinetic potentiometry; potentiometric titration

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