Silver-EDTA chelate

A common form of EDTA used as a preservative is calcium disodium EDTA (CaNa2EDTA). What metals will this form of the sequestrant scavenge effectively The dissolution of the solid will yield calcium ions, sodium ions, and the EDTA anion. Any metal more effectively complexed than calcium will be readily scavenged, including all ions listed in Table 9.1 except silver (Ag+) and magnesium (Mg2+). (In the absence of the calcium counterion, as in the case of the acid form of EDTA, chelation of calcium in the body can occur. In fact, EDTA administered orally is an FDA-approved treatment for calcium deposits in the bloodstream that lead to cardiovascular disease.) Citric acid (Fig. 9.3.3) is another sequestrant of metal ions in foodstuffs. 

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. 

Sulfur and several sulfides, highly insoluble precipitates with solubility products as low as 1.6 X 10 for mercuric sulfide, have been used to concentrate trace metals from water. Sulfur, produced from (NH4)aS and HNO3 ( 0), coprecipitated several metals including mercury. Iron(III) sulfide (also used in a commercial process SULFEX) removes several metals (61) and is better than hydroxide in the presence of EDTA and other chelating agents (62). Lead sulfide has been used to collect silver for aqueous solution (63), molybdenum sulfide to collect arsenic from 2 M hydrochloric acid solution (64), and copper sulfide to concentrate cobalt and zinc from seawater (65). 

Some of the most successful and widely used chelating reagents include dimethylglyoxime for the gravimetric determination of nickel 1,10-phe-nanthroline and its derivatives for the colorimetric determination of iron and copper dithizone for the separation and colorimetric determination of a number of metals but particularly lead, silver, zinc, cadmium, and mercury the dithiocarbamates such as diethylammonium diethyldithiocarbamate and ammonium pyrrolidinedithiocarbamate, used for colorimetry but more widely applied now as selective extractants and the most successful titrant, EDTA. 

Sihca impregnated with saturated and unsaturated hydrocarbons (squalene, paraffin oil) silicone and plant oils complexing agents (silver ions, boric acid, and borates carbohydrates unsaturated and aromatic compounds) chelating compounds [ethylene diamine tetra-acetic add (EDTA), digitonin] transition metal salt synthetic peptides 18-crown-6 and ammonium sulfate silanized sdica gel impregnated with anionic and cationic surfactants Cross-hnked, polymeric dextran gels (Sephadex)... 

Antimicrobial releasing Organic acids (benzoic acid, sorbic acid, propionic acid, lactic acid), silver salts, sulfur and its compounds, bacteriocins (nisin and lacticin), zeolites, chlorine dioxide, grape seed extracts, lemon seed extracts, spice extracts (thymol, p-cymene, and cinnamalde-hyde), enzymes (peroxidase and lysozyme), chitosan, chelating agents (EDTA), Plant essential oils... 

A titration is the process of determining the quantity of a substance by adding measured increments of another substance, the titrant. The latter is almost always added as a standardised solution (or by electrolyte generation, as in a coulometric titration). The end-point of the titration, which should indicate the addition of an exact chemical equivalence, is recognized by a visual indicator or instrumentally. Titrations are based on acid-base reactions (for determination of acids or bases), redox reactions (for determining oxidants or reductants), chelating reactions (usually with EDTA-type compounds, for determination of metal ions) or precipitations (usually of halides or pseudohalides with silver ions). 

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