THE PROTONATION CONSTANTS OF GLYCINE IN ARTIFICIAL SEAWATER AT 25-DEGREES-C

The ionization constants of glycine in artificial seawater containing NaCl, KCl, CaCl2, MgCl2 and Na2SO4 were potentiometrically determined at 25<degrees C by using a commercial glass electrode. Measurements we re carried out at different salinities, and thus ionic strengths, to s imulate seawater and estuarine waters. The experimental data were fitt ed using different equations as functions of the salinity based on Mil lero (1979). Comparisons were made between the parameters obtained by changing the variables and also the parameters yielded by the Fitter i nteraction model, which was previously applied by Millero to seawater systems. After considering all the proposed models we found the functi on in S-1/2 to give the best fit and the smallest standard deviation o f the parameters, although the extrapolated pK is not as good as the o ne obtained by the use of Fitter's model. Some of the models we used y ielded extrapolated pKs closer to the values in the literature (2.36 a nd 9.78) but higher standard deviations in the parameters.