Rapid DC polarography

Rapid DC polarography These principles can be 5. Linear-sweep 1. Polarography with 2. Oscillographic ... 

In practice, derivative polarography must be carried out on a smooth curve such as is obtained in current-sampled, current-averaged or rapid DC... 

This is the case for 11,13a-c, 13B2 and 13B3, but not for 13d and 13e Isomers with N—CH3 in position 1 had to be excluded because of rapid dimethylation even in organic solvents. In Table 2 results of rapid cyclic voltammetry are accumulated, which conespond to those obtained earlier by DC-polarography... 

The classical dc polarography of vitamins A, B, B2, B6, BI2, and C, nicotinamide, tocopherols, and naphthoquinones has been reviewed [55]. Other studies have examined in detail the cyclic voltammetry of vitamin B12 employing rapid-scan voltammetry at the DME [90] and the HMDE [91]. Vitamin B12 is complexed with trivalent cobalt ion at the heterocyclic nitrogen atoms. As a result of the complexation, a catalytic hydrogen wave is formed for the compound. In addition to the catalytic wave, a wave corresponding to the reduction of the trivalent cobalt to the monovalent state is observed. 

DC polarography of three aryl-substituted cyclopropenyl cations (40) revealed that a reversible potential could not be obtained due to a rapid dimerization of the intermediate radical formed to give 41. When fast sweep cyclic voltammetry was employed both cathodic and anodic waves were observed, indicating that the radical can be reoxidized before dimerization. 

Why did dc polarography rapidly disappear from analytical laboratories in the mid-1950 s The main application of dc polarography in analysis was to heavy metal cation analysis and the detection limit here is about 10 mol dm - (ca 6 ppm for copper). In the mid 1950 s atomic absorption spectroscopy (AAS) became available and was routinely used to analyse for heavy metal cations at <1 ppm. Atomic absorption spectroscopy, although more expensive in initial costs, is an easier technique to use than polarography. Atomic absorption spectroscopy became rapidly established as the method of choice and has remained so until the present day. It is only in recent years that advanced forms of polarography using pulse techniques have begun to become competitive with AAS (see Section 3.0 and 4.0). 

Direct current (DC) polarography is a simple method for the determination of cyanide in the presence of sulfide [58]. Cyanide gives anodic polarographic waves corresponding to mercury compound formation. At normal drop times, sulfide produces up to four DC waves spread over a very large potential range. Under rapid conditions, however, fewer sulfide waves are recorded, which reduces the possibility of interference from cyanide ions which also give anodic waves. 

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