85-2 Equation of diffusion current-A basis of Enoaregraphieally quantitative analysis On dropping mercury electrode Mnt ne- +H g M(Hg) RT C Ed,=Eo + In F Where c. is mnt concentration on the electrode surface C. is m concentration in amalgam on electrode surface
§5-2 Equation of diffusion current A basis of polarographically quantitative analysis On dropping mercury electrode: Mn+ + ne- +Hg M(Hg) Ede = Eo + ln RT nF Ce Ca Where Ce is Mn+ concentration on the electrode surface, Ca is M concentration in amalgam on electrode surface
L细它 mo 浓度 Ce 梯我 Diffusion layer Bulk solution 玉滴周的 浓差极化 Concentration polarization Q=o around mercury drop Diffusion layer Bulk solution
Diffusion layer Bulk solution Electrode Diffusion layer Bulk solution Electrode d Concentration polarization around mercury drop
When the applied voltage exceeds the decomposition voltage, diffusion-controlled current is expressed as i=k(C-Ce When the applied voltage gets more negative, Ce-0, then id= kc Ia reaches a limiting value proportional to ion concentration C in bulk solution, and do not changes with applied voltage longer
When the applied voltage exceeds the decomposition voltage, diffusion-controlled current is expressed as: i = K(C-Ce ) When the applied voltage gets more negative, Ce →0, then id = KC Id reaches a limiting value proportional to ion concentration C in bulk solution, and do not changes with applied voltage longer
Ilkovic equation---diffusion current equation In above equations, K is called Ilkovic constant, it is expressed as follows K=607nD12m2/3t16 607nD1/2m2/3t1/6C Concentration of electro-active analyte(mmol L-1) Drop time sec Mercury mass flow lae'i11.se.11 Average limiting hber of transferring Cuillin derating ar al'e ir dris i, ElEctone C'Jlrent an'nerciI" solution(cm. sec-7) reaction(elma)or anal to C drop forming to falling HA)
In above equations, K is called Ilkovic constant, it is expressed as follows: Ilkovic equation---diffusion current equation K = 607 n D1/2m2/3t 1/6 id = 607nD1/2m2/3t 1/6C Average limiting diffusion current denoting average current on mercury drop from drop forming to falling (mA) Number of transferring electrons in electrode reaction(e/mol) Diffusion coefficient of electroactive analyte in solution(cm2 .sec-1 ) Mercury mass flow rate(mg.sec-1 ) Drop time (sec) Concentration of electro-active analyte(mmol.L-1 ) From above equation, we can find that when temperature, matrix solution and capillary characteristic are kept constant, id is proportional to C
Background Current Let's look more closely at the electrode/solution interface 20-300A→ Bulk of Electrode solution 吗 Charge separation)capacitance )charging current ee) 4