Cadmium spectrophotometric determination

Lum and Callaghan [ 140 ] did not use matrix modification in the electother-mal atomic absorption spectrophotometric determination of cadmium in seawater. The undiluted seawater was analysed directly with the aid of Zeeman effect background correction. The limit of detection was 2 ng/1. 

Raman B, Shinde VM. 1990. Extraction, separation and spectrophotometric determination of cadmium and mercury using triphenylphosphine oxide and its application to environmental samples. Analyst 115 93-98. 

Nitrite. This chemical species, formed in-line by passing a potassium nitrate stream through a copperised cadmium solid-phase reactor, was used in the spectrophotometric determination of sulfadiazine in pharmaceutical formulations [99]. A nitrite solution that would normally be stored in a refrigerator, standardised and frequently replaced was therefore not required. 

The spectrophotometric determination of cadmium in natural waters involving in-line formation of an aqueous dithizone suspension [121] illustrates another application of in-line suspension addition. Solid dithizone reagent was packed in a mini-column through which a surfactant (Triton X-100) stream was allowed to flow. The emerging suspension formed was added by confluence to the main analytical channel of a flow-injection system. With this innovation, good sensitivity was achieved without the need for an analyte separation/concentration LLE step and the entire procedure was carried out in the aqueous phase. 

A mono-segmented flow system (see 5.5.1) provides good conditions for organic/aqueous phase interaction the extraction process is carried out between two air bubbles and vortices are established inside the plug. An efficient extraction, with reduced sample dispersion, low carryover and thus a high sampling rate, is achieved, as demonstrated in the spectrophotometric determination of cadmium [195]. 

J.A. Gomes-Neto, A.P. Oliveira, G.P.G. Freshi, C.S. Dakuzaku, M. Moraes, Minimization of lead and copper interferences on spectrophotometric determination of cadmium using electrolytic deposition and ion-exchange in multi-commutation flow system, Talanta 53 (2000) 497. 

Spectrophotometric determination of cadmium with dithizone General remarks... 

Nitrate may also be determined by LC with an anion-exchange column. A comparison has been made between the traditional method of nitrate determination using a reducing cadmium column and spectrophotometric determination with a reversed-phase LC method with orthophosphoric acid adjusted to pH 3.5 with sodium hydroxide as the mobile phase. A high correlation was observed between the nitrate content determined by the two methods. However, LC was found to be more precise, reproducible, and appropriate for routine work. 

The inline conversion of nitrate to nitrite and subsequent spectrophotometric determination after diazotization and coupling reactions is the basis of an important set of analytical methods for the simultaneous determination of both ions. Either homogeneous (titanium(III) chloride, hydrazinium sulfate, etc.) or heterogeneous (zinc, cadmium, amalgamated cadmium, copperized cadmium, etc.) reduction agents, photochemical or enzymatic reactions have been used [157]. The nitrite so produced is determined through spectrophotometric detection of the reddish purple azo dye formed as a result of the modihed Griess chemistry. 

Preconcentration by cloud point extraction of the complex determination by ICP optic emission spectrometry. Simultaneous spectrophotometric determination of cadmium and mercury... 

Spencer and Brewer [111] have reviewed methods for the determination of nitrate in seawater. Classical methods for determining low concentrations of nitrate in seawater use reduction to nitrite with cadmium/copper [ 112,116,117] or zinc powder [113] followed by conversion to an azo dye using N- 1-naphthyl-ethylenediamine dihydrochloride and spectrophotometric evaluation. Malho-tra and Zanoni [114] and Lambert and Du Bois [115] have discussed the interference by chloride in reduction-azo dye methods for the determination of nitrate. 

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. 

The Department of the Environment UK [155] has described a number of alternative methods for the determination of total oxidised nitrogen (nitrate and nitrite) in aqueous solution, while specific methods for nitrate and nitrite are also included. Among the methods for total oxidised nitrogen, one is based on the use of Devarda s alloy for reduction of nitrate to ammonia, and another uses copperised cadmium wire for reducing nitrate to nitrite, which is determined spectrophotometrically. Nitrate may also be determined spectrophotometrically after complex formation with sulfosalicylic acid or following reduction to ammonia, the ammonia is eliminated by distillation and determined titrimetrically. Other methods include direct nitrate determination by ultraviolet spectrophotometry, measurements being made at 210 nm, and the use of a nitrate-selective electrode. Details of the scope, limits of detection, and preferred applications of the methods are given in each case. 

After adjusting to 2 mol 1 1 in hydrochloric acid, 500 ml of the sample is adsorbed on a column of Dowex 1-XS resin (Cl form) and elution is then effected with 2 M nitric acid. The solution is evaporated to dryness after adding 1M hydrochloric acid, and the tin is again adsorbed on the same column. Tin is eluted with 2 M nitric acid, and determined in the eluate by the spectrophotometric catechol violet method. There is no interference from 0.1 mg of aluminium, manganese, nickel, copper, zinc, arsenic, cadmium, bismuth, or uranium any titanium, zirconium, or antimony are removed by ion exchange. Filtration of the sample through a Millipore filter does not affect the results, which are in agreement with those obtained by neutron activation analysis. 

Block diagram of a remote spectrophotometric, flow injection based monitor for the determination of nitrate in river water. Reduction to nitrate by copperized cadmium followed by colour development with sulphanilimide and N-I-naphthylmethylenediamine dihydrochloride. 

Continuous monitoring methods based on amperometric (Nikolic et al. 1992) or spectrophotometric (Kuban 1992 Ma and Liu 1992) techniques for the quantification of free cyanide are also available. Ion chromatography with amperometric determination provides good sensitivity (2 ppb) and selectivity for free cyanide and the weak complexes of cadmium and zinc (Rocklin and Johnson 1983). Postcolumn derivatization and fluorescence detection provides low detection limits as well (0.1 ppb) (Gamoh and Imamichi 1991). 

Lopez Garcia et al., [24] suspended soil samples in water containing 5% (v/v) concentrated hydrofluoric acid before injection into an electrothermal atomic absorption spectrophotometric system. No modifier other than the hydrofluoric acid was required for the determination of lead, cadmium and thallium. 

Garcia Gutierrez [19] has described an azo coupling spectrophotometric method for the determination of nitrite and nitrate in soils. Nitrite is determined spectrophotometrically at 550 nm after treatment with sulfuric acid and N-1 -naphlhylclhylcnediamine to form an azo dye. In another portion of the sample, nitrate is reduced to nitrite by passing a pH 9.6 buffered solution through a cadmium reductor and proceeding as above. Soils were boiled with water and calcium carbonate, treated with freshly precipitated aluminium hydroxide and active carbon, and filtered prior to analysis by the above 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. 

Lopez Garcia et al. [2] have described a rapid and sensitive spectrophotometric method for the determination of boron complex anions in plant extracts and waters which is based on the formation of a blue complex at pH 1 - 2 between the anionic complex of boric acid with 2,6-dihydroxybenzoic acid and crystal violet. The colour is stabilised with polyvinyl alcohol. At 600 nm the calibration graph is linear in the range 0.3-4.5 xg boron per 25 ml of final solution, with a relative standard deviation of 2.6% for xg/l of boron. In this procedure to determine borate in plant tissues, the dried tissue is treated with calcium hydroxide, then ashed at 400 °C. The ash is digested with 1N sulfuric acid and heated to 80 °C, neutralized with cadmium hydroxide and then treated with acidic 2,6-dihydroxybenzoic acid and crystal violet, and the colour evaluated spectrophotometrically at 600 nm. Most of the ions present in natural waters or plant extracts do not interfere in the determination of boron complex anions by this procedure. Recoveries of boron from water samples and plant extracts were in the range of 97 -102%. 

This method can be used to determine the nitrate content in precipitation within the range from 0.02 to 0.23 mg NO3-N/L (0.1-1.0 mg N03/L). Nitrate is reduced to nitrite using cadmium treated with copper sulfate as reducing agent in the presence of ammonium chloride. With this method the sum of nitrate and nitrite is determined. Nitrite and sulfanilamide form a diazo compound that couples with N-(l-naphthyl)-ethylenediamine dihydrochloride to form a red azo dye. The concentration in the solution is determined spectrophotometrically at 520 nm. Note that nitrite will interfere with the determination of nitrate. 

The cationic complex of cadmium with 1,10-phenanthroline forms with acid dyes the ion associates which have become a basis for extraction-spectrophotometric methods of determining cadmium. Among the dyes used are Rose Bengal (CHCI3, e = 1.0-10 ) [58,59], Erythrosin (e = 9.6-10 ) [60], dibromofluorescein [61], Bromophenol Blue (CHCI3, e = 5.6-10 ) [62,63], and Thymol Blue [64]. 

This field provides a brief description of the suggested monitoring and analysis method for quantitative determination of a particular substance. For example, a method for quantitative determination has been developed for cadmium, copper, manganese, and lead in water by means of co-precipitation with zirconium hydroxide followed by subsequent analysis by atomic adsorption spectrometry. An Inductively Coupled Plasma-Atomic Emission Spectrophotometric method has been employed by the Environmental Protection Agency (EPA Method 200.7) for the determination of dissolved, suspended, or total elements in drinking water, surface water, and domestic and industrial wastewaters. 

Bond, A.M. and Wallace, G.G. (1984) Liquid chromatography with electrochemical and/or spectrophotometric detection for automated determination of lead, cadmium, mercury, cobalt, nickel, and copper. Anal. Chem., 56, 2085-2090. 

Burguera and Burguera [16] developed a FI liquid-liquid extraction spectrophotometric method for the determination of cadmium in urine using dithizone. Original urine samples were directly injected into a buffered earner (pH 10.5) containing tartrate, and... 

In view of the high toxicity of cadmium it is necessary to be able to determine very small concentrations in water. AAS techniques (Sections 3.4.7.1 and 3.4.7.2) are particularly suitable for determining cadmium in water. Where no AAS facilities are available, it is still possible to use the classical spectrophotometric technique (Section 3.4.7.3) with dithizone and extraction in chloroform. 

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. 

Inorganic ions in biological systems can be quantified by spectrophotometric methods provided they are present at suitable concentrations (of a few micrograms per milliliter or higher) and other species in the medium exhibit little or no absorption. However, many elements including aluminum, cadmium, chromium, and nickel usually cannot be determined by UV-visible spectrophotometry, because they occur at very low concentrations in biological systems. 

FIGURE 1,6 Example of manifolds developed for flow injection speciation analysis, (a) Manifold of the reversed FIA system for speciation of chromium with pH measurements and spectrophotometric detection, q—peristaltic pumps, V—injection valves, L— reaction coil, M.E.—pH glass electrode. (Adapted from Ruz, J. et al. 1986. J. Autom. Ghent. 8 70-74.) (b) Manifold of branched FIA system for simultaneous biamperomet-ric determination of nitrate and nitrite. (Cd)Cu—reductive column with copperized cadmium, L—mixing coils. (Adapted from Trojanowicz, M., W. Matuszewski, and B. Szostek. 1992. Anal. Chim. Acta 261 391-398.) (c) Example signal recordings obtained in the FIA system shown in (b) 1-6—standard solutions, A-I—natural water samples. Concentration in standard solutions 1—0.075 2—0.050 3—0.025 mM nitrate and 4—7.5 5—5.0 6—2.5 pM nitrite. 

Most spectrophotometric methods consist of colorimetric detection of nitrite at 520-540 nm, based on the classical reaction with N-(l-naphthyl)ethylenediamine and sulfanilamide (Griess reaction). Nitrate is determined colorimetrically in the same way after reduction to nitrite by means of a cadmium column (ISO Standard 14673-1 2004/ IDF Standard 189-1 2004). Different SIA systems based on the Griess reaction have been developed for the determination of nitrate and nitrite in infant formulas and milk powder, in dairy samples, in cured meat and infant formulas and milk powder (Oliveira et al., 2004, 2007 Reis Lima et al., 2006 Piston et al., 2011). 

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