Measurements of concentration dependent diffusivities of aqueous Metrizamide solution in various buffers by laser microinterferometric technique

Diffusion coefficients of Metrizamide in aqueous solution and three buffer solutions were measured by the microinterferometric technique over a solute concentration range from 0.1054 gm/ml to 0.4862 gm/ml. The three buffers used were 0.005 M phosphate buffer at pH 6.2, 0.5 M acetate buffer at pH 4.6, and 1.0 M borate buffer at pH 8.2.

Empirical formulae for the diffusivities and activity coefficients for Metrizamide diffusing into distilled water at 25°C were obtained as follows:

D*10⁵ =0.1725 + 2.6376C - 4.2399C² + 12.1790C³ - 17.1886C⁴

(cm²/sec)

lnγ^(c) = 16.6350C - 0.3138C² + 19.6243C³ + 50.2210C⁴ -139.7657C⁵ + 225.6294C⁶ - 366.4004C⁷ + 191.9028C⁸

lnγ^(w) = 0.1302 (1.000 + 108.9314w/1.000 - w)^1.027

Empirical formulae for the diffusivities and activity coefficients for Metrizamide in three buffer solutions at 25°C were obtained as follows:

D*10⁵ = 0.1725 + 4.4325C (sc²/sec)

lnγ^(c) 27.2092C + 19.8622C³ + 11.2099C³ + 92.4010C⁴ - 80.0733C⁵

1nγ^(w) = 0.3580 (1.000 45.920w/1.000-w)1.1945

Metrizamide-1.0 M borate buffer at pH 8.2

D*10⁵ = 0.1725 +2.5120C - 5.5755C² + 26.9393C³ - 37.4474C⁴ (cm²/sec)

lnγ^(c) = 16.0823C- 4.76463C² + 44.2267C³ +49.8279C⁴ - 185.5841C⁵ + 448.0136C⁶ - 812.7647C⁷ +422.9421C⁸

lnγ^(w) = 0.3218 (1.000 24.362w/1.000-w)^1.256

Metrizamide-0.5 M acetate buffer at pH 4.6

D*10⁵ = 0.1725 + 2.7395C + 3.0322C^ - 8.3039C² + 1.7456C⁴

lnγ^(c) = 17.3977C + 21.2036C² + 1.6863C³ + 43.0755C⁴ - 0.7004C⁵ - 164.7067C⁶ + 128.8303C⁷ + 19.7101C⁸ lnγ^(w) = 0.141 (84.330w/1.000-w)^2.250

The experiment showed that the diffusivities and activity coefficients of Metrizamide in aqueous solution increased with increasing solute concentration throughout the entire range studied. The buffers seemed to be effecting on the diffusivities and activity coefficients of Metrizamide in aqueous solution; difference in formular weight, valence, ionization constant and density change due to concentration of Metrizamide might be the factors. A correction factor for using buffers had been obtained. Thus, one could evaluate diffusivities of Metrizamide at various concentrations in any buffers from the diffusivity of Metrizamide into distilled water and this correction factors.