Dynamic Electrochemistry - University of Sulaymaniyah：动态电化学-大学苏莱曼尼亚.pptVIP

Other types of Polarography Examples refer to polarography but are applicable to other votammetric methods as well all attempt to improve signal to noise usually by removing capacitive currents Normal Pulse Polarography current measured at a single instant in the lifetime of each drop. higher signal because there is more electroactive species around each drop of mercury. somewhat more sensitive than DC polarography. data obtained have the same shape as a regular DCP. NPP advantage IL = nFAD1/2c/(ptm)1/2 (tm = current sampling t) IL,N.P./IL,D.C. = (3t/7tm)1/2 Predicts that N.P.P. 5-10 X sensitive than D.C.P. Differential pulse voltammetry DPP current measured twice during the lifetime of each drop difference in current is plotted. Results in a peak-shaped feature, where the top of the peak corresponds to E1/2, and the height gives concentration This shape is the derivative of the regular DC data. DPP has the advantage of sensitive detection limits and discrimination against background currents. Traditionally, metals in the ppm range can be determined with DPP. Derivative improves contrast (resolution) between overlapping waves DPP vs DCP Ep ~ E1/2 (Ep= E1/2±DE/2) where DE=pulse amplitude s = exp[(nF/RT)(DE/2)] Resolution depends on DE W1/2 = 3.52RT/nF when DE?0 Improved response because charging current is subtracted and adsorptive effects are discriminated against. l.o.d. 10-8M Resolution Square wave voltammetry SWV SWV Response SWV advantage of square wave voltammetry is that the entire scan can be performed on a single mercury drop in about 10 seconds, as opposed to about 5 minutes for the techniques described previously. SWV saves time, reduces the amount of mercury used per scan by a factor of 100. If used with a pre-reduction step, detection limits of 1-10 ppb can be achieved, which rivals graphite furnace AA in sensitivity. data for SWV similar to DPP height and width of the wave depends on the exact combination of experimen