Catechols, determination electrodes

Specific catechol determination is demanded in the photographic, paint, and pharmaceutical industries. Neujahr (1980) combined immobilized catechol-1,2-oxygenase with an oxygen electrode and employed the sensor for catechol measurement. The sensor was selective for catechol and 3- and 4-methylcatechol. Phenol, resorcinol, cresol, vanil-line, and dihydroxyphenylalanine (DOPA) did not interfere. 

Van den Berg and Huang [292] determined uranium (VI) in seawater by cathodic stripping voltammetry at pH 6.8 of uranium (Vl)-catechol ions. A hanging mercury drop electrode was used. The detection limit was 0.3 nmol/1 after... 

The conditions for reliable cyclic voltametry determination of trace Sn concentrations in sea water were investigated. All organotin compounds should be converted to Sn(II) by UV-photolysis adsorption on mercury drop in the presence of 40 pM of tropolone (1) cyclic voltametry stripping shows two cathodic peaks, corresponding to the two-step process Sn(IV) — Sn(II) -> Sn(0)29. A complex of Sn ions with catechol can be accumulated in a glassy carbon mercury film electrode, followed by stripping voltametry measurement in the cathodic direction, at pH 4.2-4.7. Interference occurs when Cu, Cd and Cr are present LOD 0.5 pg/L for 300 s accumulation30. 

Ivanov and Kaplun [76] used catechol in the determination of vanadium by adsorptive stripping voltammetry. It has been shown that the studied electrode process comprised one-electron reversible reduction of vanadium (IV) triscatecholate, previously accumulated at the electrode. It has also been found that the reduced... 

Carbon electrodes exhibit a wide range of electron transfer rates for benchmark redox systems, depending on carbon material and surface history. Two examples are shown in Figure 10.2, which compares two carbon surfaces with very different k° for Fe(CN) /4. In some cases, the variations in electrode kinetics have been particularly important to analytical applications. For example, carbon paste and carbon fiber electrodes have been used to monitor neurotransmitters in living animal brains [5,6]. The determination of catechol transmitters in the presence of relatively large amounts of interferents (e.g., ascorbate) de-... 

Phenolic substances are for the most part readily oxidized at a graphite electrode. The oxidation potentials for phenols vary widely with structure, and some (hydroquinones and catechols) are far more readily oxidized than others (cresols). Many compounds of biological interest (catecholamines, pharmaceuticals, plant phenolics) [32] and industrial interest (antioxidants, antimicrobials, agricultural chemicals) [33] are phenolic, and trace determination based on LCEC is now quite popular. 

The tissue-based amperometric electrodes for the determination of catechol [13,14], dopamine [15] and phenol [16] shown in Table 17.2 operate on the same principle as the biosensor for L-ascorbic acid [11],... 

Salicylate is determined in blood serum using immobilized salicylate hydroxylase electrodes (243-245). This enzyme is a mixed function monooxygenase that converts salicylate to catechol in the presence of NAD(P)H and molecular oxygen ... 

ZnO nanoparticles dispersed CH composite films deposited onto glassy carbon electrode (GCE) have been used for immobilization of tyrosinase enzyme for phenol detection. This biosensor shows 95% of steady-state current within 10s, sensitivity as 182 pA mmol"1 L with a detection limit of 5.0 x 10"8 mol/L, exhibits maximum response at 50°C and retains 91% current after about 20 days [39], A sol-gel derived ZnO matrix has been used to immobilize tyrosinase for determination of phenol concentration from 1.5 x 10"7 to 4.0 x 10"5 mol L"1 with detection limit of 8.0 x 10 s mol L"1 and sensitivity of 168 pA mmol L"1. This biosensor shows 95% of steady-state current within 15s after 2 weeks [40], Chen et al. have immobilized mushroom tyrosinase oxidase onto ZnO nanorods for the phenol and catechol detection. The linear concentration ranges have been obtained from 0.02 to 0.1 mM and 0.01 to 0.4 mM, for phenol and catechol, respectively. The apparent Km has been estimated as 0.24 mM for phenol and 1.75 mM for catechol [59],... 

An indirect electrochemical method developed for nitrite determination may be of general applicability for PAA determination, as shown in equation 13. A nitrite sample is placed into a cell containing a known amount of 3-sulfanilic acid in dilute HC1 at pH 3. After 5 min the diazonium ion formation is complete an excess of catechol (109) is added and the concentration of the remaining 3-sulfanilic acid is determined at +0.12 V with a GCE vs. standard calomel electrode, by measuring the adduct (110) formed between the aromatic amine and the quinone derived from catechol in the diffusion layer of the electrode. The 3-isomer of sulfanilic acid was chosen among the three isomers, aniline and 4-nitroaniline for its highest sensitivity and its lowest LOD, 0.7 pM, with linearity from 20 to 80 pM. A spectrophotometric assay may be carried out for nitrite by measuring at 516 nm the azo dye derived from catechol and the diazonium ion after 3 h ... 

Biosensors based on a Clark oxygen electrode, coupled to tyrosinase immobilized by three different methods, were investigated for the determination of phenol in real matrices, such as water of various natural sources, industrial wastes and oil press. The feasibility study included direct use of the biosensors and in situ analysis. An integrated system, incorporating SPE, desorption, fractionation and biosensor detection, was validated for screening phenolic compounds in water. Two types of electrode were tested, solid graphite and CPE incorporating tyrosinase. Correct analyses were found for river water samples spiked with phenol (10 p.gL ), p-cresol (25 p.gL ) and catechol (1 A mul-... 

The constant potential amperometric detector determines the current generated by the oxidation or reduction of electoactive species at a constant potential in an electrochemical cell. Reactions occur at an electrode surface and proceed by electron transfer to or from the electrode surface. The majority of electroactive compounds exhibit some degree of aromaticity or conjugation with most practical applications involving oxidation reactions. Electronic resonance in aromatic compounds functions to stabilize free radical intermediate products of anodic oxidations, and as a consequence, the activation barrier for electrochemical reaction is lowered significantly. Typical applications are the detection of phenols (e.g. antioxidants, opiates, catechols, estrogens, quinones) aromatic amines (e.g. aminophenols, neuroactive alkaloids [quinine, cocaine, morphine], neurotransmitters [epinephrine, acetylcoline]), thiols and disulfides, amino acids and peptides, nitroaromatics and pharmaceutical compounds [170,171]. Detection limits are usually in the nanomolar to micromolar range or 0.25 to 25 ng / ml. 

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