FLOW-INJECTION ANALYSIS-METHODS FOR DETERMINATION OF DIFFUSION-COEFFICIENTS

Two flow injection analyses (FIA) methods for the determination of dif fusion coefficients in a straight single tube FIA system were develope d. Based on the analytical solution of the convection-diffusion equati on, linear relationships of the logarithmic values of the dispersion c oefficient (D) and the half-peak width (W-1/2) with the diffusion coef ficient (D-m) were obtained. Experiments were designed to verify these methods. For example, for potassium hexacyanoferrate (III) a D-m valu e of 0.72 x 10(5) cm(2) s(-1) was found versus a literature value of 0 .76 x 10(5) cm(2) s(-1) (error, 5%). For potassium hexacyanoferrate (I I) a D-m value of 0.67x10(5) cm(2) s(-1) was obtained versus a literat ure Value of 0.63x10(5) cm(2) s(-1) (error, 6%). The diffusion coeffic ients of some important biomedical compounds, such as dopamine, epinep hrine, norepinephrine and ascorbic acid, were then determined. The val ues of 10(5) D-m/cm(2) s(-1) are 0.60+/-0.03, 0.44+/-0.02, 0.60+/-0.01 and 0.68+/-0.06, respectively.