Interferences chelating agents

The procedure followed entails the removal of gross interferences by solvent extraction, and the selective extraction and concentration of the trace metal by use of a chelating agent. The alloy used should not contain more than 0.1 g of copper in the sample weighed out. 

In order to suppress interferences due to the presence of inorganic species and reliably determine the proteinaceous composition of the sample, a clean-up step has often been introduced in the analytical procedure. This step may include the extraction of the proteinaceous matter by an ammonia solution [8], the use of a cation-exchange resin [8,55], a chelating agent [9,41,44], the use of a Cig resin or the use of barium chloride solution to suppress sulfates [10,81,82]. Table 9.1 reports the methods used to overcome such problems. 

Mg(II) forms a complex with 8-hydroxyquinoline-5-sulfonic acid (37) at pH 9.0 with Tris-HCl buffer, which can be determined by ELD (X x = 388 nm, ka = 495 nm) with micellar enhancement by cetyltrimethylammonium chloride (38). Masking of Ca(II) is achieved by EGTA (19). The method was applied in a SIA system for analysis of natural waters . After elution of the Mg(II) ions adsorbed on an alkali-activated PTFE tube with 0.1 M HCl and addition of A,A -bis(salicylidene)-2,3-diaminobenzofuran (39), the end analysis was by fluorometric determination of the Mg(II) complex (kex =475 nm, kfl = 545 nm). Possible interference of Ca(II) is masked on addition of the chelating agent... 

Hung et al. (1982) developed a sensitive and selective method for silver analysis by reacting silver (I) with 2(3,5-dibromo-2-pyridylazo)-5-diethyl amino phenol in the presence of an anionic surfactant, sodium lauryl sulfate. The ternary complex formed is red and exhibits an absorption peak at 570 nm. Hung and his co-workers employed EDTA as a chelating agent, thereby reducing the interference of common ions. Recoveries were good, and a detection limit of 0.39 ppm of silver was achieved. 

A number of procedures for the determination of metals and biological samples call for the extraction of the metal with an organic chelating agent in order to remove interferences and concentrate the metal to enable detection of low levels. The urine or blood sample may be first subjected to wet ashing to enable extraction of the metal. Beryllium from an acid-digested blood or urine sample may be extracted by acetylacetone into methylisobutyl ketone prior to atomic absorption analysis. Virtually all of the common metals can be determined by this approach using appropriate extractants. 

Cu, Ni, Zn, Mn — Post-column reaction studied interference by chelating agents Spectrometric [27]... 

In the case of a neutral non-ionic chelating agent we have neutral carrier-selective electrodes transport is achieved by selective complexa-tion of certain ions. The best-known electrode of this kind is the potassium-selective electrode, whose membrane consists of a valinomycin macrocycle immobilized in phenylether. The important criterion appears to be the size of the cavity in the centre of the macrocycle and interferences are from cations with similar hydrated ionic radius, such as Rb+ and Cs+. 

Avoidance of interference of other milk constituents with measurements is also of importance for example, dissociation of casein micelles by calcium-chelating agents, such as trisodium citrate or ethylenediamine tetra-acetic acid (EDTA), may used to avoid interference of the micelles in particle size measurement, while clusters of fat globules can be disrupted by adding a low level of sodium dodecyl sulphate (SDS). 

Plant use of iron depends on the plant s ability to respond chemically to iron stress. This response causes the roots to release H+ and deduct ants, to reduce Fe3+, and to accumulate citrate, making iron available to the plant. Reduction sites are principally in the young lateral roots. Azide, arsenate, zinc, copper, and chelating agents may interfere with use of iron. Chemical reactions induced by iron stress affect nitrate reductase activity, use of iron from Fe3+ phosphate and Fe3+ chelate, and tolerance of plants to heavy metals. The iron stress-response mechanism is adaptive and genetically controlled, making it possible to tailor plants to grow under conditions of iron stress. 

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