Rapid scan 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. 

For the fast-scan technique in HPLC, in which the potential is varied rapidly across its full range, the method of square-wave voltammetry (- Analytical Voltammetry and Polarography) has provided the basis for the development of a rapid-scan square-wave voltammetric detector ... 

The so-called rapid polarography operates with very short drop-times (several milliseconds) produced under mechanical [47] or optical [48] control. This technique permits the application of scan rates up to several hundreds mV per second. The advantage of this technique is evident maxima are suppressed and formation of surface-blocking films is minimized the damping of oscillations is not necessary and the application in flowing and agitated media is possible. These favorable effects are devaluated by the decrease of the faradaic-to-charging current ratio. Therefore, the detection of electroactive substances in solutions below 10 " M is impossible [82]. 

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