Cadmium reductions

Sample Number IC Methyl thymol blue IC Cadmium reduction... 

Elemental compostion Ce 25.56%, H 1.47%, N 20.44%, 0 52.53%. The aqueous solution of the compound may be analyzed for Ce by AA or ICP spectrophotometry. Also, the solution may be measured for NH4 ion by ammonium ion-selective electrode and the NO3 ion by nitrate ion-specific electrode, ion chromatography or cadmium-reduction colorimetry. For all these measurements, the solution may require sufficient dilutions. For quantitation, its solution may be standardized by titration with a reducing agent such as sodium oxalate in the presence of iron and ferroin indicator. 

Influence of a Catalyst Erom the data obtained with impedance and demodulation voltammetry for a solution of x M KCl + (1 -x) M KF [40], it follows that chloride ions catalyze the Cd(II)/Cd(Hg) process (Fig. 3) the cadmium reduction proceeds according to several chemical (C) and charge transfer (E) steps, so-called CE-CEC mechanism. The catalyst accelerates specifically the first chemical and the first electrochemical step. 

With the completion of steps one and two, in June 1988 Phase I - Cadmium Reduction commenced. 

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. 

Nitrate is reduced to nitrite (by cadmium reduction reaction), which is then determined by diazotization (pH = 2.0-2.5) with sulfanilamide and coupling N-( 1 -naphthyl)-1,2-ethylendiamine hydrochloride to form an intensely pink colored azo dye (540 nm) Brucine oxidation by nitrate ion in H2S04 at 100°C to form a yellow compound (cacoteline), which is measured at 410 nm... 

Nitrate can also be converted to N02 using cadmium reduction (columns or spongy cadmium) as described above. Once the NOa" is in the form of N02, the N02 can be isolated via organic extraction (e.g., Olson, 1981) or with SPE after the N02 is converted to an azo dye (Kator et al, 1992). Nitrate can be isolated by conversion to N2O via sodium azide in an acetic acid buffer solution (Mcllvin and Altabet, 2005). Another approaches uses a genetically engineered denitrifier to convert N03 to N2O (Sigman et al, 2001) the bacteria wiU denitrify NOa" in a sample to N2O, but lacking nitrous oxide reductase the bacteria cannot take the reaction to completion and form N2. The N2O produced by either approach can then be analyzed on a mass spectrometer. A more detailed discussion of these methods is presented in Chapter 31 by Lipschultz, this volume. 

In the case of multiply unsaturated carbonyl compounds, regioselectivity is also sensitive to the nature of the catalyst, to reaction conditions, and to the structure and degree of substitution of the hydrogenated double bonds. For example, hydrogenation of 3,5-heptadien-2-one over nickel on alumina or nickel on zinc oxide occurs mainly at the y,8-double bond. But if the catalyst is modified by the addition of lead or cadmium, reduction occurs mainly at the a,p-double bond (Scheme 24). 

N-Ammonia. The NHs yields associated with the cadmium reduction column (41) suggest that this technique might be applicable to synthesis of however, the experimental parameters have not yet... 

The salts associated with cured meats, nitrates and nitrites, are assayed by aqueous extraction and colorimetric determination. The ISO methods involve extraction in hot water containing borax solution and deproteination of a portion of the extract with Carrez reagents. Nitrite (ISO 2918 1975) is determined directly by formation of an azo dye with sulfanilamide and N-(l-naphthyl)ethylenediamine dihydrochloride which is measured at 538 mn. Nitrate (including nitrite) (ISO 3091 1975) is determined by cadmium reduction to nitrite and azo dye formation. Reduction of nitrate to nitrite may be carried out on a special column (as in the ISO method) or using spongy cadmium. Care must be taken to prevent interference from ascorbic acid if it is present in the sample at relatively high levels (>20pgml ). 

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. 

Figure 5.9 (a) Working curve showing the dependence of AE on y/. (b) Dependence of AE on V for cadmium reduction. Adapted with permission from Ref. [25]. Copyright 1965 American Chemical Society. 

This analytical instrument was successfully used in several cruises for real-time monitoring of nutrient concentrations in seawater, incorporating a sampling unit for the in situ collection and online determination of phosphate, nitrate, and nitrite. The method is based on the initial determination of phosphate as its phosphoantrmonylmolybdenum blue complex, which is then oxidized online by nitrite and the decrease in absorbance is monitored at 880 nm. Nitrate is determined as the difference between total and initial nitrite content in a separate flow after reduction to nitrite in a cadmium-reductive column. 

C. Gal, W. Frenzel, J. Moeller, Re-examination of the cadmium reduction method and optimisation of conditions for the determination of nitrate by flow injection analysis, Microchim. Acta 146 (2004) 155-164. 

S.M. Oliveira, T.I.M.S. Lopes, A.O.S.S. Rangel, Sequential injection determination of nitrate in vegetables by spectrophotometry with inhne cadmium reduction, Commun. Soil Sci. Plant Anal. 38 (2007) 533 544. 

USEPA Method 353.3 Analysis of Nitrate-Nitrite by Cadmium Reduction and Colorimetry. http //www.caslab.com/EPA-Method-353 3/ (accessed September 16, 2015). 

ISO Standard 14673-1 2004/IDF Standard 189-1 2004. Milk and Milk Products— Determination of Nitrate and Nitrite Contents. Method Using Cadmium Reduction and Spectrometry. Geneva, Switzerland International Organization for Standardization, Brussels, Belgium International Dairy Federation, 2004. 

Sulphate, chloride (Cl ), nitrate (NO ), and ammonium (NH ) in water were measured with a Technicon Autoanalyzer II system by the methylthymol blue, mercuric thiocyanate, cadmium reduction and sodium nitroprusside methods, respectively. Sulphate and Cl in highly colored samples were measured by means of ion chromatography. Cations were analyzed with an atomic-absorption spectrophotometer by means of flame-emission spectrophotometry for potassium (K ) and... 

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