Sodium dithionite detection

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]. 

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... 

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 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. 

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... 

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