（活塞） （螺线管） （金属垫圈）） （聚氨酯） 0.05~ 0.5mm diameter (iii) Easy to remove diffusion layer on mercury drop surface when the drop falls Hg microelectrodes
（活塞） （螺线管） （金属垫圈）） （聚氨酯） 0.05~ 0.5mm diameter (iii) Easy to remove diffusion layer on mercury drop surface when the drop falls Hg microelectrodes
Advantages of DME (compared to planar electrode) ● clean surface generated ● rapid achievement of constant current during drop growth ● remixing of solution when drop falls to remove previous diffusion layer ● high Hg overvoltage means even metals with high –Ve E0 can be measured without H2 formation Disadvantages of DME ● Hg easily oxidized, limited use as anode(E < +0.4V) 2Hg + 2Cl- -2e →Hg2Cl2 ●nonfaradaic residual currents limit detertion to > 10-5 mol.L-1 . ●cumbersome(笨重的,尴尬的) to use(toxic mercury) ●sometimes produce current maxima for unclear reasons( use maxima suppressor)
Advantages of DME (compared to planar electrode) ● clean surface generated ● rapid achievement of constant current during drop growth ● remixing of solution when drop falls to remove previous diffusion layer ● high Hg overvoltage means even metals with high –Ve E0 can be measured without H2 formation Disadvantages of DME ● Hg easily oxidized, limited use as anode(E < +0.4V) 2Hg + 2Cl- -2e →Hg2Cl2 ●nonfaradaic residual currents limit detertion to > 10-5 mol.L-1 . ●cumbersome(笨重的,尴尬的) to use(toxic mercury) ●sometimes produce current maxima for unclear reasons( use maxima suppressor)
Sample Cells
Sample Cells
Sample cell Drop knocker Dropping Hg Bectrode SCE reference Inert gas electrode purge Sample
Polarogram For Cd2+: 20 For a reversible system: 15 Limiting current Eoppl =Eo- (0.0592/n)Log(i/04-i) 至 10 Half-wave Diffusion So,ati:音id potential current.l Eappl (=E)=Eo /2 B Residual current 0 0.3 0.6 -0.9 -12 Applied potential,V vs.SCE