Detection of sodium dithionite

In the preceding sections, it was mentioned several times that the limiting-current of the first wave of the sodium dithionite oxidation is suitable for electroanalytical purposes because of the transport-controlled nature of this limiting-current. Indeed, it was proven earlier that this limiting-current can be correlated with the Levich equation (1.15), showing a linear relationship between limiting-current and sodium dithionite concentration. 

However, it is not ideal to use cyclic or linear-sweep voltammetry as a method for analytical purposes. A more suitable method is chronoamper-ometry, which in fact is the application of a constant potential located in the limiting-current plateau and measurement of the limiting-current as a function of time. With this method, it is possible to measure continuously, and the required equipment setup becomes much more simplified. 

11 Chronoamperometric experiment at F=0.45V vs. AglAgCI recorded at a rotating platinum-disc electrode in an alkaline solution (pH = 12.5) at a rotation rate of 400rpm for dithionite concentrations of (1) 6.0x10 4, (2) 1.2x10 3, (3) 1.8x10 3, 

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Simultaneous detection of sodium dithionite, sulphite and indigo at a wall-jet electrode... 

For the simultaneous detection of sodium dithionite, sulphite and indigo, a multistep amperometric method was worked out and optimised, as outlined in Table 6.4. It is clear that after each measuring step, the electrode surface should be cleaned to remove indigo that is oxidised at all applied... 

In this chapter, it will be shown that the detection of sodium dithionite on bare gold electrodes can be improved by electrocatalysis using a cobalt(II)tetrasulphonated phthalocyanine, sodium salt (CoTSPc) or a 5,10,15,20-tetrakis-(4-sulphonatophenyl)porphyrin cobalt(II), tetrasodium salt (CoTSPor) as catalyst. The selection of these catalysts was based on... 

Note Phosphoric acid [8] and hydrochloric acid [6, 9] have both been suggested in the literature as substitutes for phthalic acid. The addition of sodium dithionite [9] is also occasionally mentioned and sometimes no additives are employed [10]. The alternative reagents offer no advantages over the phthalic acid containing reagent since they usually cause more background coloration. The limits of detection are about 0.1 —0.5 pg per chromatogram zone [5]. 

In this section, the use of a wall-jet electrode (with optimal values for its parameters as described in section6.7.2) and the method to detect simultaneously sodium dithionite, sulphite and indigo (see section6.7.4) are evaluated as a function of reproducible dyeing processing. In order to evaluate this, a spectrophotometric method was used to measure the amount of dye absorbed and/or adsorbed by the dyed fabric. 

Materials and Methods section). To deactivate WT hydrogenases, a controlled amount of 02 was added to the anaerobic cell suspension in the sealed vial and incubated under vigorous mixing for 2 min. Anaerobic conditions were then rapidly re-established, and methyl viologen (reduced by addition of sodium dithionite) was added to serve as the electron donor to the hydrogenase. The mixture was then incubated in the dark for 15 min at 30°C, and the reaction was stopped by the addition of trichloroacetic acid. The amount of H2 produced was detected by gas chromatography. 

The parent acid has no independent existence and has not been detected in aqueous solution either. Sodium dithionite is widely used as an industrial reducing agent and can be prepared by reduction of sulfite using Zn dust, Na/Hg or electrolytically, e.g. ... 

The first step of the reaction involves nitration of the aromatic skeleton of the substance to be detected. Then the aromatic nitro derivatives so produced are reduced with sodium dithionite, in acid medium, to the corresponding amines these are then diazotized and coupled with N-(l-naphthyl)-ethylenediamine to yield an azo dye (cf. Fig. 21). 

A nitrochromone has three easily reducible functions and, for its reduction, conditions and reagents which have little or no effect on the carbonyl or the 2,3-double bond should be chosen. Nitrochromones are reduced by tin-hydrochloric acid, zinc-ammonium chloride, iron-acetic acid, iron-hydrochloric acid or sodium dithionite. It may be easier to control the severity of the conditions in catalytic hydrogenation. Scheme 29 shows that with proper choice of conditions (temperature, pressure, solvent, catalyst), it is often possible to optimize the yield of the desired product (527). Extending the reaction time from about 30 min to 2.5 h increased the yield of the chromanone (528) and none of the hydroxylamine (529) was then detected (70JCS(C)2230). 

Simultaneous detection of indigo and sodium dithionite for control of dyeing processes... 

The aim of an indigo sensor is to keep the leuco-indigo concentration in the solution at a constant value. In the past, different methods were developed for detection of the indigo and sodium dithionite concentration, but up to now with limited success. The sodium dithionite concentration can be determined by volumetric titration with iodine2 22 or with K3[Fe(CN)6]23. The endpoint detection of these titrations can be done visually22,24"25 or... 

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