Cadmium reduction procedure

Tecator [20] has described a flow injection system for the determination of nitrate and nitrite in 2 mol/1 potassium chloride extracts of soil samples. Nitrate is reduced to nitrite with a copperised cadmium reductor and this nitrite is determined by a standard spectrophotometric procedure in which the soil sample extract containing nitrate is injected into a carrier stream. Upon the addition of acidic sulfanilamide a diazo compound is formed which then reacts with N-(l-naphthyl)ethylcncdiamine dihydrochloride provided from a second merging stream. A purple azo dye is formed, the intensity of which is proportional to the sum of the nitrate and the nitrite concentration. Nitrite in the original sample is determined by direct spectrophotometry of the soil extract without cadmium reduction. 

A variety of methods has been described for the determination of nitrogen species (Table 4) but not all are routinely used. The cadmium reduction method is widely used in both batch and automated (continuous flow) spectrophotometric methods. In this procedure, nitrate is reduced to nitrite, which is then determined by diazotization with sulfanilamide and coupling with N-(l-naphthyl)ethylenediamine dihydrochloride (NED) to form an intensely pink-colored azo dye. This chemistry can be incorporated in a flow injection manifold to allow rapid, automated, in situ determinations in a robust and portable manner. Other common techniques for nitrogen determination are the nitrate ion-selective electrode and ion chromatography. 

Spencer and Brewer [144] have reviewed methods for the determination of nitrite in seawater. Workers at WRc, UK [ 145] have described an automated procedure for the determination of oxidised nitrogen and nitrite in estuarine waters. The procedure determines nitrite by reaction with N-1 naphthyl-ethylene diamine hydrochloride under acidic conditions to form an azo dye which is measured spectrophotometrically. The reliability and precision of the procedure were tested and found to be satisfactory for routine analyses, provided that standards are prepared using water of an appropriate salinity. Samples taken at the mouth of an estuary require standards prepared in synthetic seawater, while samples taken at the tidal limit of the estuary require standards prepared using deionised water. At sampling points between these two extremes there will be an error of up to 10% unless the salinity of the standards is adjusted accordingly. In a modification of the method, nitrate is reduced to nitrite in a micro cadmium/copper reduction column and total nitrite estimated. The nitrate content is then obtained by difference. 

To prepare metal hexacyanoferrate films, very frequently the following procedure was followed first a film of the respective metal, for example, cadmium [79], copper [80], silver [81], or nickel [82, 83] was elec-trochemically plated on the surface of a platinum electrode, and that was followed by chemical oxidation of the metal film in a solution of K3[Fe(CN)6], leading to the formation of the metal hexacyanoferrates. The same method has been used to produce films of nickel hexacyanoruthen-ate and hexacyanomanganate using the appropriate anions [83]. It is also possible to perform the oxidation of the deposited metals in solutions containing hexacyano-ferrate(II) by cyclic oxidation/reduction of the latter. In a similar way, films of copper heptacyanonitrosylferrate have been deposited [84]. 

Gold nanorods were prepared by the photochemical procedure of Kim et al. [6]. Gold nanocrystals with an average diameter of 2.5 nm were obtained by the reduction of chlo-roaurate ion (0.55 ml of 25 mM aqueous solution) by partially hydrolyzed tetrakis (hydroxymethyl) phosphonium chloride (THPC) [7], CdSe nanocrystals were prepared by the solvothermal procedure starting with cadmium stearate, selenium and tetralin in toluene [8]. SWNTs prepared by the electric arc method with a Y2O3 + Ni catalyst, were purified by acid and hydrogen treatments [9]. 

Two procedures have been adopted to prevent oxidation of excess unreacted iodide by molecular oxygen. Either unreacted iodide is com-plexed with cadmium (Buege and Aust, 1978), or spectrophotometric measurements are made in air-free stoppered cuvettes and development of I3 is followed continuously. The second procedure allows reliable detection of the reaction end point and identifies any oxygen contamination (Hicks and Gebicki, 1979), but it is not applicable to routine measurements of many samples as the time taken for complete reduction of the hydroperoxide is prohibitive. Methods are therefore described which are based only on the procedure utilizing cadmium. 

The results obtained from sorption/desorption edge experiments on Milwhite kaolinite and cadmium are presented in Figure 3.8 as an illustration. The testing parameters of these experiments are tabulated in Table 3.2, and the experimental procedure is detailed in Yeung and Hsu (2005). The low concentration of cadmium in the dissolved phase used in the experiments precludes the formation of cadmium precipitates. Therefore, the reduction in cadmium concentration in the dissolved phase was caused by the sorption of cadmium onto Milwhite kaolinite particle... 

The following procedure is based on a method by Morris and Riley (Anal. Chim. Acta, 29 272, 1963) with some modifications. At the suggestion of GrasshoS (Kiel. Meeresjorsch., 20 5, 1964) we use ammonium chloride. A cadmium-mercury column has been replaced by a cadmium-copper column based on the work of Wood, Armstrong and Richards (/. Marine biol. Assoc. U.K., Al 25, 1967), although we have had trouble with the use of EDTA suggested by these workers and have reverted to ammonium chloride as an activator. Reduction of nitrate to nitrite is nearly complete and the method described below is probably as sensitive as is practicable by a routine spectrophotometric procedure. 

Alfonsi (9,10,11,12,13) has carried out an extensive investigation of the controlled-potential separation and determination of antimony in alloys containing combinations of lead, tin, bismuth, and copper. Tanaka (14, 15), working mainly with synthetic samples, reports conditions for the separation of antimony from gold, silver, mercury, copper, bismuth, cadmium, zinc, and vanadium in a variety of common electrolytes. Very recently, Dunlap and Shults (18) have developed two coulometric procedures which permit the determination of antimony in each of its oxidation states as well as the total antimony present. After pre-reduction of antimony (V) with hydrazine hydrate, the antimony (III) is reduced to the amalgam at a mercury cathode with a potential of —0.28 V vs. SCE in a supporting electrolyte 0.4 m in tartaric add and 1 m in hydrochloric acid. In the... 

---