Ethylenediaminetetraacetate

The bivalent radical —NH— linked to two identical radicals can be denoted by the prefix imino-, as well as when it forms a bridge between two carbon ring atoms. A trivalent nitrogen atom linked to three identical radicals is denoted by the prefix nitrilo-. Thus ethylenediaminetetraacetic acid (an allowed exception) should be named ethylenedinitrilotetraacetic acid. 

Properly called dihydrogen ethylenediaminetetraacetate (Na2H2EDTA 2H2O). U1... 

Standard EDTA Solutions. Disodium dihydrogen ethylenediaminetetraacetate dihydrate is available commercially of analytical reagent purity. After drying at 80°C for at least 24 hr, its composition agrees exactly with the dihydrate formula (molecular weight 372.25). It may be weighed directly. If an additional check on the concentration is required, it may be standardized by titration with nearly neutralized zinc chloride or zinc sulfate solution. 

Using the ladder diagram in Figure 6.7, predict the result of adding 0.080 mol of Ca + to 0.060 mol of Mg(EDTA). EDTA is an abbreviation for the ligand ethylenediaminetetraacetic acid. 

Ladder diagram for metal-ligand complexes of ethylenediaminetetraacetic add (EOTA) with Ca + and Mg +. 

The utility of complexation titrations improved following the introduction by Schwarzenbach, in 1945, of aminocarboxylic acids as multidentate ligands capable of forming stable 1 1 complexes with metal ions. The most widely used of these new ligands was ethylenediaminetetraacetic acid, EDTA, which forms strong 1 1 complexes with many metal ions. The first use of EDTA as a titrant occurred in... 

Ethylenediaminetetraacetic acid, or EDTA, is an aminocar-boxylic acid. The structure of EDTA is shown in Eigure 9.25a. 

Ethylenediaminetetraacetic acid, H4Y, is a tetraprotic weak acid with successive acid dissociation constants of 0.010,... 

Actinide ions of the 111, IV, and VI oxidation states can be adsorbed by cation-exchange resins and, in general, can be desorbed by elution with chloride, nitrate, citrate, lactate, a-hydroxyisobutyrate, ethylenediaminetetraacetate, and other anions (11,12). 

Certain compounds, known as chelating agents (qv), react synergisticaHy with many antioxidants. It is beheved that these compounds improve the functional abiUties of antioxidants by complexing the metal ions that often initiate free-radical formation. Citric acid and ethylenediaminetetraacetic acid [60-00-4] (EDTA), C2QH2gN20g, are the most common chelating agents used (22). 

Other Additives. To provide and maintain the clarity of clear shampoos, the use of either ethyl or isopropyl alcohol maybe employed. Perfumes are added to make shampoos more pleasing in terms of odor, while dyes are incorporated to give visual aesthetics to the products. Salts of ethylenediaminetetraacetic acid are found to sequester and prevent formation of insoluble alkaline-earth metal salts. 

EthylenediaminetetraaceticAcid. Ethylenediaminetetraacetic acid (EDTAH has six potential donor groups two nitrogen atoms and four carboxylate groups. If EDTA 4— acts as a hexadentate ligand to a metal, the resulting complex contains five five-membered chelate rings and has a charge that is four less than that of the metal ion. 

The lanthanides form many compounds with organic ligands. Some of these compounds ate water-soluble, others oil-soluble. Water-soluble compounds have been used extensively for rare-earth separation by ion exchange (qv), for example, complexes form with citric acid, ethylenediaminetetraacetic acid (EDTA), and hydroxyethylethylenediaminetriacetic acid (HEEDTA) (see Chelating agents). The complex formation is pH-dependent. Oil-soluble compounds ate used extensively in the industrial separation of rate earths by tiquid—tiquid extraction. The preferred extractants ate catboxyhc acids, otganophosphoms acids and esters, and tetraaLkylammonium salts. 

Chromium (ITT) can be analy2ed to a lower limit of 5 x 10 ° M by luminol—hydrogen peroxide without separating from other metals. Ethylenediaminetetraacetic acid (EDTA) is added to deactivate most interferences. Chromium (ITT) itself is deactivated slowly by complexation with EDTA measurement of the sample after Cr(III) deactivation is complete provides a blank which can be subtracted to eliminate interference from such ions as iron(II), inon(III), and cobalt(II), which are not sufficiently deactivated by EDTA (275). 

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. 

Coordination Complexes. The abiUty of the various oxidation states of Pu to form complex ions with simple hard ligands, such as oxygen, is, in order of decreasing stabiUty, Pu + > PuO " > Pu + > PuO Thus, Pu(Ill) forms relatively weak complexes with fluoride, chloride, nitrate, and sulfate (105), and stronger complexes with oxygen ligands (Lewis-base donors) such as carbonate, oxalate, and polycarboxylates, eg, citrate, and ethylenediaminetetraacetic acid (106). The complexation behavior of Pu(Ill) is quite similar to that of the light lanthanide(Ill) ions, particularly to Nd(Ill)... 

EDTA (ethylenediaminetetraacetic acid, [60-00-4]) chelates any trace metals that would otherwise decompose the hydrogen peroxide [7722-84-1]. The amine is preheated to 55—65°C and the hydrogen peroxide is added over one hour with agitation the temperature is maintained between 60 —70°C. The reaction is exothermic and cooling must be appHed to maintain the temperature below 70°C. After all the peroxide has been added, the temperature of the reaction mixture is raised to 75°C and held there from three to four hours until the unreacted amine is less than 2.0%. The solution is cooled and the unreacted hydrogen peroxide can be destroyed by addition of a stoichiometric amount of sodium bisulfite. This may not be desirable if a low colored product is desired, ia which case residual amounts of hydrogen peroxide enhance long-term color stabiUty. 

A method suitable for analysis of sulfur dioxide in ambient air and sensitive to 0.003—5 ppm involves aspirating a measured air sample through a solution of potassium or sodium tetrachloromercurate, with the resultant formation of a dichlorosulfitomercurate. Ethylenediaminetetraacetic acid (EDTA) disodium salt is added to this solution to complex heavy metals which can interfere by oxidation of the sulfur dioxide. The sample is also treated with 0.6 wt % sulfamic acid to destroy any nitrite anions. Then the sample is treated with formaldehyde and specially purified acid-bleached rosaniline containing phosphoric acid to control pH. This reacts with the dichlorosulfitomercurate to form an intensely colored rosaniline—methanesulfonic acid. The pH of the solution is adjusted to 1.6 0.1 with phosphoric acid, and the absorbance is read spectrophotometricaHy at 548 nm (273). 

A mixture of dimethyl sulfate with SO is probably dimethyl pyrosulfate [10506-59-9] CH2OSO2OSO2OCH2, and, with chlorobenzene, it yields the 4,4 -dichlorodiphenylsulfone (153). Trivalent rare earths can be separated by a slow release of acid into a solution of rare earth chelated with an ethylenediaminetetraacetic acid agent and iodate anion. As dimethyl sulfate slowly hydrolyzes and pH decreases, each metal is released from the chelate in turn and precipitates as the iodate, resulting in improved separations (154). 

The most well known of the tri- and polycarboxylates is the tetracarboxyUc acid ethylenediaminetetraacetic acid (EDTA),... 

Calcium and magnesium can be titrated readily with disodium ethylenediaminetetraacetate, with Eriochrome Black T as the indicator. The solution is buffered at pH 10.0. Certain metal ions interfere with this procedure by causing fading or indistinct end points. Cyanide, sulfide, or hydroxjiamine can be used to eliminate or minimise the interferences. 

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