Amperometric detection oxidation with

Figure 27.16 Potential-time (E - t) waveforms. Processes Elt anodic detection E2, oxidative cleaning E3, cathodic reactivation. Waveforms are (A) pulsed amperometric detection (PAD) with a short current sampling period, (B) PAD with a long current integration period, and (C) integrated PAD with a long integration period. [Reproduced with permission from Ref. 31.]...

Fig. 10 HPLC chromatograms of supercritical fluid extracts of (A) an unfortified wheat sample and (B) a vitamin A-fortified bran-based ready-to-eat breakfast cereal. Column, 5-/rm Altex C8 (octyl) (150 X 4.6-mm ID) mobile phase, acetonitrile/2-propanol/aqueous 25 mM sodium perchlorate (45 45 10), 2.0 ml/min amperometric detection (oxidative mode), glassy carbon electrode, +1.2 V, vs saturated calomel electrode. Peak (1) retinyl palmitate. (Reprinted from Ref. 90, Copyright 1997, with the kind permission of Elsevier Science-NL, Sara Burgerhartstraat 25, 1055 KV Amsterdam, The Netherlands.)...

Mycotoxins are toxic chemical metabolic products produced by microscopic mold fungi that colonize cereal crops, fruits, and vegetables and some of them exhibit carcinogenic and mutagenic properties. The allowed maximum levels in foodstuffs are very low and exhaustive exU action, preconcentration, and clean-up processes are required to attain the desired sensitivity. The alternative of ED (amperometric detection) combined with HPLC can be useful to simplify the detection of such low concentration levels. However, it has been used rarely for the analysis of these compounds in food because many of these compounds can be elecfrochemically oxidized or reduced at extreme potentials. Visconti et al [144], analyzed... 

The following antibiotics have been determined the aminoglycoside tobramycin by chromatography on a pellicular anion-exchange resin, post-colunm addition of alkali, and pulsed amperometric detection pseudouridine with S-fluorouridine as an internal standard on a reversed-phase column with post-column periodate oxidation, derivatization with meso-... 

Wangfuengkanagul and Chailapakul [9] described the electroanalysis of ( -penicillamine at a boron-doped diamond thin film (BDD) electrode using cyclic voltammetry. The BDD electrode exhibited a well-resolved and irreversible oxidation voltammogram, and provided a linear dynamic range from 0.5 to 10 mM with a detection limit of 25 pM in voltammetric measurement. In addition, penicillamine has been studied by hydrodynamic voltammetry and flow injection analysis with amperometric detection using the BDD electrode. 

A study was made of RP-HPLC with constant-potential (1.2 V vs SCE) and pulsed-potential amperometric detection using platinum or gold electrodes, of the derivatives of the common amino acids, obtained from phenyl and methyl isothiocyanates. All the thiohydantoins (98) were oxidized at both electrodes LOD was less than 0.2 pM for lysine and glycine, for 50 pL injection268. 

Fluorescence detection is sensitive to naturally fluorescent analytes or to fluorescent derivatives. Amperometric detection is sensitive to analytes that can be oxidized or reduced at an electrode (Figure 26-29). Conductivity detection with ion-exchange suppression of the background electrolyte (as in Figure 26-4) can detect small analyte ions at 1-10 ng/mL. Electrospray mass spectrometry (Figure 22-18) provides low detection limits and gives qualitative information about analytes.33... 

Copper electrodes have been used to determine amino acids and carbohydrates [10]. Metal oxide electrodes (including thin-film semiconductors) show some promise, but nothing of substance has yet been published with regard to LCEC. Pulsed amperometric detection (PAD) takes advantage of metal oxides formed in situ. This approach is discussed later. 

The problem associated with amperometric detection of NADH is similar to that of H202, with a very high overpotential required [3,4] and with electrode fouling due to the presence of radical intermediates produced during NADH oxidation that then interfere with the measurement [5]. 

A glassy C electrode, which was immobilized with tyrosinase, was used for amperometric detection of phenol in a polyimide chip. Phenol was enzymatically converted to catechol, which was then oxidized to quinone during detection. Chlorophenol can also be detected, but this is achieved after a dechlorination step (to phenol) using a Mg/Pd metal catalyst [229]. 

Iodide in vitamin tablets can be found by amperometric detection [88]. Nonaqueous eluents of methanol-containing ammonium perchlorate, which are relatively oxidant resistant, have been used in conjunction with a silica column to detect a wide range of drugs [89]. The use of higher potentials not possible in totally aqueous mobile phases allows for the detection of secondary and tertiary aliphatic amines 462 drugs have been detected in this manner. For compounds that are not electroactive, a procedure using a postcolumn photolysis can generate electroactive species [90] for penicillins [91], proteins [92], and barbiturates [93]. 

Rao, T.N., Terashima, C., Sarada, B.V., Tryk, D.A. and Fujishima, A. (2002) Electrochemical oxidation of chlorophenols at a boron-doped diamond electrode and their determination by high-performance liquid chromatography with amperometric detection. Anal. Chem. 74,... 

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