Oxidizing substances determination

CZE-ELD, with a Au microelectrode at —0.6 V vs. SSCE and a Pt wire as auxiliary electrode, using sodium borate buffer and dodecyltrimethylanunonium bromide for dynamic coating of the capillary internal surface, can be applied for separation and determination of ultra-trace amounts of many oxidizing substances. Thus, the concentration of peroxodisulfate (S208 ) and peroxomonosulfate (S05 ) ions in pickling baths can be monitored by this method. The faster emergence of the heavier peroxodisulfate ion is attributed to different adsorption of the two analyte ions by the capillary coating . ... 

Coulometry comprises a set of techniques in which the total charge required (not the current, as in potentiometry) to oxidize or reduce the chemical species of interest is measured. The prime virtue of coulometric techniques is that they link the quantity of substance determined directly to the quantity of electrical charge, and thus expensive and often difficult procedures for standardization or calibration can be minimized or eliminated. 

The direct use of the Hoesch injection technique is useful for trace analysis of oxide substances after fusion [31, 99, 142]. It is possible to take up the fused substance in small quantities (max. 10 ml, usually 1 ml). It is best to use an acid mixture which contains 400ml HC1 (6 = 1.15gml-1) and 40g citric acid in 1000 ml. Generally, 10 pi, and in special cases 50 pi, of the analytical solution are injected. It is thus possible to determine all important ascertainable elements in 1 ml of analytical solution several times over. Salt concentrations of 100 mg ml-1 are no problem for the injection technique. 

The chemical make-up of oxide substances is often very complex and the matrix frequently contains two or three compounds of almost equal concentration. The determination of individual interference effects is very complicated and time consuming, because the composition of these substances can be subject to wide variations. As in the case of steel, pig iron and cast iron the interference effects are generally not determined. 

While analysis in an iron matrix ranges from the trace range to 20%, element concentrations of up to 60% are determined in oxide substances. 

First experiments indicate that a direct determination of trace elements in oxide substances is possible but the determination of matrix elements, because of their high concentrations, should however be left to other methods of analysis, such as solution analysis with AAS or direct X-ray fluorescence spectrometry. 

There are many substances which would appear to be good candidates for LC-EC from a thermodynamic point of view but which do not behave well due to kinetic limitations. Johnson and co-workers at Iowa State University used some fundamental ideas about electrocatalysis to revolutionize the determination of carbohydrates, nearly intractable substances which do not readily lend themselves to ultraviolet absorption (LC-UV), fluorescence (LC-F), or traditional DC amperometry (LC-EC) [2], At the time that this work began, the EC of carbohydrates was more or less relegated to refractive index detection (LC-RI) of microgram amounts. The importance of polysaccharides and glycoproteins, as well as traditional sugars, has focused a lot of attention on pulsed electrochemical detection (FED) methodology. The detection limits are not competitive with DC amperometry of more easily oxidized substances such as phenols and aromatic amines however, they are far superior to optical detection approaches. 

The electrochemical detection system requires reducible or oxidable substances. The eluted substance is reduced or oxidized by an electrode. This not very common detection system is a useful tool for determination of amino-compounds and other organic nitrogen-compounds, phenols and quinones [8],... 

Aggregation and fragmentation of colloidal particles has been investigated further employing natural polyelectrolytes like humic substances. Adsorption of humic acids on aluminum oxide was determined to resemble interfacial deposition on the basis of methods previously employed for the aluminum oxide/polyacrylic acid system [88]. Complexation by soluble aluminum ions produces pH drops that are very similar to that determined for polyacrylic acid, and essentially humic acids were determined to exert effects on the stability of colloidal aluminum oxide particles at pH 5 that are very similar to polyacrylic acid. 

Given a formula for a substance, determine the oxidation number (or oxidation state) for each atom in the formula. 

The difficulties with the COD method as a measure of oxygen demand is that acidified dichromate is such a strong oxidizer that it oxidizes substances that are very slow to consume oxygen in natural waters and that therefore pose no real threat to their oxygen content. In other words, dichromate oxidizes substances that would not be oxidized by O2 in the determination of the BOD. Because of this excess oxidation, namely of stable organic matter such as cellulose to CO2, and ofCU to CI2, the COD value for a water sample as a rule is slightly higher than its BOD. 

A shift in the cellular reduction/oxidation (redox) state has been found to be involved in the process of apoptosis. Generally, the cellular redox state is a balance between the relative quantities of the intracellular oxidative substances (reactive oxygen species, ROS) and reductive substances (reduced glutathione, GSH). A microfluidic device method with laser-induced fluorescence (LIF) detection for simultaneous, rapid determination of intracellular ROS and GSH in apoptotic leukemia cells has been described. 

At low operation temperatures, polarisation losses and the importance of catalysis of the electrode reactions Increase. At the cathode, mixed potentials can arise when traces of combustible substances determine the electrode potential in competition with oxygen, an effect, mentioned near the end of Section 2.3, whose cause was recognised by Hartung in 1981 [143], today the basis of the development of hydrocarbon sensors. For the anodes growing interest is directed to materials which accelerate the electrochemical oxidation of CO and hydrocarbons and is stable against fuel impurities. 

The methods described earlier for determining the total, free, or combined chlorine residual also are used in establishing the chlorine demand of a water supply. The chlorine demand is defined as the quantity of chlorine that must be added to a water supply to completely react with any substance that can be oxidized by chlorine while also maintaining the desired chlorine residual. It is determined by adding progressively greater amounts of chlorine to a set of samples drawn from the water supply and determining the total, free, or combined chlorine residual. 

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