Metals spectrophotometric method

EDTA forms colored complexes with a variety of metal ions that may serve as the basis for a quantitative spectrophotometric method of analysis. The molar absorptivities of the EDTA complexes of Cu +, Co +, and Ni + at three wavelengths are summarized in the following table (all values of e are in cm )... 

Nickel also is deterrnined by a volumetric method employing ethylenediaminetetraacetic acid as a titrant. Inductively coupled plasma (ICP) is preferred to determine very low nickel values (see Trace AND RESIDUE ANALYSIS). The classical gravimetric method employing dimethylglyoxime to precipitate nickel as a red complex is used as a precise analytical technique (122). A colorimetric method employing dimethylglyoxime also is available. The classical method of electro deposition is a commonly employed technique to separate nickel in the presence of other metals, notably copper (qv). It is also used to estabhsh caUbration criteria for the spectrophotometric methods. X-ray diffraction often is used to identify nickel in crystalline form. 

Table. Extraction-spectrophotometric methods of metals determination...

Y K Agarwal and G D Mehd, Solvent extraction and spectrophotometric methods for the determination of some toxic metal ions, Rev. Anal. Chem., 1983, 6(3), 185... 

Pectins in the acidic form were dissolved either in pure water or in 0.1 M NaNOs and put to pH -7.2 by adding 0.05 M NaOH. Various amounts of metal ions were added to pectins solutions at two different concentrations, for 2 h under stirring at 25.0 0.1°C. Concentration of metal ions in solution at equilibrium was determined either by a potentiometric method using ion-selective electrodes for Cu2+ and Pb2+ or by a spectrophotometric method using tetramethylmurexide dye (Kwak Joshi, 1981) for Ni2+, Tsfi and Ca2+. 

Kwak J.C.T. Joshi Y.M. (1981) The binding of divalent metal ions to polyelectrolytes in mixed counterion systems. I. The Dye Spectrophotometric Method. Biophys. Chem. 13, 55-64. 

Fernandez-Gonzales et al. [16] described a method for determination of OTC in medicated premixes and feeds by second-derivative synchronous spectrofluorome-try. The assay based on the reaction of oxytetracycline with divalent metal ion (Ca2+) at pH 6-10 to form a yellow complex that can be analyzed by synchronous spectrofluorometry (AX = 115 nm). Rao et al. [17] described a spectrophotometric method for the determination of OTC in pharmaceutical formulations based on the color reaction with uranium, which was detected at 413 nm. 

Rapid equivalent methods - Generally based on a principle different from that of the corresponding laboratory method, alternative or surrogate systems are used more and more often for on-line and off-line monitoring. For example, the spectrophotometric methods or biosensors proposed for the measurement of organic compounds or electrochemical techniques for metals must be considered as alternative methods. 

Samarium may be analyzed by spectrographic and spectrophotometric methods. In solution, the trivalent samarium shows sharp and intense absorption bands at 362.5, 347.5 and 402.0 nm. Trace analysis may be carried out most accurately by flame AA, ICP-AES, ICP/MS and neutron activation analysis. ICP/MS is the most sensitive method. The metal and its insoluble salts may be solubilized by digestion with acids and diluted appropriately for most instrumental measurements. 

Tellurium and its compounds can be analysed by AA, ICP-AES and other spectrophotometric methods. Also, the metal can be identified by volumetric, gravimetric, and simple colorimetric measurements. 

The section Analysis starts with elemental composition of the compound. Thus the composition of any compound can be determined from its elemental analysis, particularly the metal content. For practically all metal salts, atomic absorption and emission spectrophotometric methods are favored in this text for measuring metal content. Also, some other instrumental techniques such as x-ray fluorescence, x-ray diffraction, and neutron activation analyses are suggested. Many refractory substances and also a number of salts can be characterized nondestructively by x-ray methods. Anions can be measured in aqueous solutions by ion chromatography, ion-selective electrodes, titration, and colorimetric reactions. Water of crystallization can be measured by simple gravimetry or thermogravimetric analysis. 

Salama et al. [34] developed and validated a spectrophotometric method for the determination of omeprazole and pantoprazole sodium via their metal chelates. The procedures were based on the formation of 2 1 chelates of both drugs with different metal ions. The colored chelates of omeprazole in ethanol were determined spectrophotometrically at 411, 339, and 523 ran using iron(III), chromium(III), and cobalt(II), respectively. Regression analysis of Beer s plots showed good correlation in the concentration ranges 15-95, 10-60, and 15-150 /ig/ ml of pure omeprazole using iron(III), chromium(III), and cobalt(II), respectively. 

VIII. EVALUATION OF STABILITY CONSTANTS OF METAL COMPLEXES IN THE ION-EXCHANGER PHASE USING A SPECTROPHOTOMETRIC METHOD... 

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