Solution-phase ferricyanide

Figure 21.24. (a) Magnitude (dashed line) and phase (solid line) spectra of ferricyanide and ferrocya-nide with hexacyanoferrate adsorbed on the electrode surface (b) in-phase spectrum after phase rotation of solution-phase ferricyanide and ferrocyanide bands into the quadrature channel. 10 mM ferrocyanide 1 Hz modulation frequency potential modulation limits, 0.02 to 0.42 V versus SCE. (Reproduced from [20], by permission of the American Chemical Society copyright 1997.)... 

In redox electrodes an inert metal conductor acts as a source or sink for electrons. The components of the half-reaction are the two oxidation states of a constituent of the electrolytic phase. Examples of this type of system include the ferric/ferrous electrode where the active components are cations, the ferricyanide/ferrocyanide electrode where they are anionic complexes, the hydrogen electrode, the chlorine electrode, etc. In the gaseous electrodes equilibrium exists between electrons in the metal, ions in solution and dissolved gas molecules. For the half-reaction... 

All. three-necked flask is fitted with an efficient stirrer, a dropping funnel, and a gas inlet tube connected to a stream of purified nitrogen. A solution of 5 g of potassium hydroxide in 200 ml of water, 8 g (0.04 mole) of 4-bromo-2.6-xylenol and 200 ml of benzene is introduced. The stirrer is started and 1.3 g of potassium ferricyanide in 20 ml of water is added dropwise over a period of 30 minutes. After an additional 15 min of stirring, the mixture is transferred to a separatory funnel and the aqueous phase is drawn off the bottom. The yellow benzene solution is transferred to a 300 ml distilling flask and concentrated to 50 ml under water pump... 

Vitamin Bi, vitamin B2, and nicotinic acid, all of which frequently occur together in foods, were separated by TLC and fluorimetrically determined by using a commercially available fiber optic-based instrument. A fluorescent tracer (fluoresceinamine, isomer II) was used to label the nicotinic acid. Vitamin B1 was converted to fluorescent thiochrome by oxidizing with potassium ferricyanide solution in aqueous sodium hydroxide. These vitamins were separated by HPTLC on silica gel using methanol-water (70 30 vol/vol) as mobile phase. Under these conditions, the Rf values of the vitamin Bi, vitamin B2, and nicotinic acid derivatives were 0.73, 0.86, and 0.91, respectively. 

B) In-phase spectrum after phase rotation of solution ferricyanide and ferrocyanide bands into the quadrature channel. Reprinted from Ref. [30] with permission. 

The magnitude of the signal represents the total optical response of the system to the modulation frequency d>, while the phase represents the phase delay. Provided the phase delay across the solution band is constant (the species is in a homogeneous environment), the value of is measured for a solution species, and then the entire complex spectrum is rotated into the quadrature channel, as shown in Fig. 3.50. As a result, only the absorption due to surface species with different phase delays remains in the in-phase channel. This technique was used for disentangling strong bands due to the ferro/ferricyanide Faradaic species that were superimposed on weak bands of these species in the adsorbed state on a Pt electrode [263]. 

CPE followed by spectrofluorimetry was applied to analyse the concentration of vitamin Bi in samples of urine (Tabrizi 2006). In this method, Triton-XI14 surfactant was used for CPE. The procedure was accomplished by adding an aqueous solution of thiamin, ferricyanide and Triton-X114 in an alkaline medium. The surfactant-rich turbid phase and diluted aqueous phase were attained after centrifugation of the mixture. The surfactant-rich phase was collected and diluted in an ethanol water mixture prior to measurement of the fluorescence excitation and emission intensity. Thiamin was oxidized by ferricyanide under alkaline conditions to form thiochrome, which is a fluorescent species. During the extraction procedure, thiochrome was entrapped in surfactant micelles. Thus, thiamin was separated from the biological matrix after derivatization. The fluorescence intensity responded linearly with the concentration of thiamin under optimized conditions. 

If the monomer sample contains up to 0.005% of inhibitor then pipette 0.1 to 2 cm of the sample directly into a 100 cm separatory funnel, make the volume up to 2 ml with toluene. Into a second (reagent blank) separatory funnel pipette 2 cm of pure toluene. To each funnel add 1 cm of freshly prepared iron III chloride solution (0.5%) and shake for one min. Add 10 cm water and allow the phases to separate. Run the aqueous phases into two 100 cm volumetric flasks. Into each volumetric flask pipette 1 cm of potassium ferricyanide solution and dilute to 100 cm. ... 

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