Complexone III

Haar, K. ter, and J. Bazen The titration of complexon III with thorium... 

As with EDTA (Complexone III), DCTA ( Complexone IV) has also been used as a spectrophotometric reagent for chromium [13,14,17,31,32]. The Cr(III)-DCTA complexes have been extracted with chloroform solutions of Aliquat 336 [13,14]. 

Complexones such as EDTA (complexone III) [1-3] and DCTA (complexone IV) [4,5] are suitable eluents, but other complexing agents, such as citrate [3,6] and sulphate [7] are also applied. Barium has been separated from strontium and other metals by cation-exchange chromatography using mixed HCl-organic solvent eluents [8]. Strontium has been enriched and determined in sea water [5] and in milk [2]. 

Direct complexlmetrlc tltratron of lead with 0.07 N complexon III in.the presence of Erichrome Black T as an. indicator has been proposed (Zl). The equivalence point is reached when the color changes from violet to bluegreen. 

Masking by ethylenediaminetetraacetate is conveniently accomphshed by means of its disodium salt (Versene, Complexone III). This action does not extend to Be+ , Ti+, Sn+ and Cr+ ions. Among their hydroxides, only Be(OH) a is brought to a green-yellow fluorescence, which is stable against ammonia. This behavior is the basis of a specific test for beryllium. 

Procedure. A drop of the neutral or weakly acid test solution is placed in a depression of a spot plate and treated with three drops of Complexone III solution, one drop of a 0.02 % acetone solution of morin and one drop of concentrated ammonia. The mixture is transferred by means of a pipette to the filtering device shown on page 44, filtered, and the precipitate washed successively with two drops each of Complexone solution, water, and finally acetone. On examination in ultraviolet light, the filter paper, used in place of asbestos, shows a green-yellow fluorescing zone. 

Procedure. The sample should be divided into as small pieces as possible. One or two milligrams are sintered in a platinum spoon with ammonium fluoride, or fused with sodium pyrosulfate, or dissolved in hydrochloric acid and evaporated. The product is rinsed into a micro crucible with as little water as possible. A drop of the liquid is transferred to a depression of a spot plate and the following are stirred in three drops of a saturated solution of Complexone III (versene) in ammonia (1 10) one drop of 0.002 % solution of morin in acetone then one drop of concentrated ammonia. If beryllium is present, the mixture exhibits a strong yellow-green fluorescence in ultraviolet light. 

Hg + can be detected with dithizone. A yellow-orange precipitate forms that is extractible into carbon tetrachloride or chloroform in acidic medium (1 < pH < 4). The reaction is quasi-specific at pH < 1.5 in the presence of complexone(III) in order to complex other cations, in particular Cu +. 

It is the same state of affairs with iodide ions. The yellow precipitate of lead iodide PW2 is soluble in the presence of an excess of iodide ions by formation of the triiodoplombate(II) complex [PbIs]", poorly stable. By cooling, lead iodide crystallizes as yellow grains. This reaction is carried out to detect Pb + in mineralization liquids used in analytical toxicology. The lead iodide precipitation is inhibited by the addition of complexone(III). 

With sodium diethyldithiocarbamate, bismuth yields a yellow compound extractible into carbon tetrachloride. In the presence of complexone(III), of alkaline cyanide, the reaction is quasi-specific since only lead and mercury are disturbing. 

Ca + may also be detected via precipitation with oxalic acid as calcium oxalate, which is very poorly soluble. In a first reaction, barium and strontium must be eliminated as sulfates and other disturbing ions must be complexed by complexone(III). The latter, if added in excess, must not prevent the calcium precipitation. Its excess is eliminated by adding aluminum nitrate. 

The titration of Ca + in the presence of Mg + is of practical importance. The best results are obtained with complexone(III) as the titrant and with calcein or calcon as the indicator. Murexide, as an indicator, is obsolete since both preceding indicators have been introduced. In any case, titrand solutions must be alkaline for the titration reaction to be sufficiently quantitative. Pb + and Zn + must be masked with 2,3-dimercaptopropanol. Some other heavy metal ions must also be masked with potassium cyanide. Fe + and Mn + can be masked by eomplexation with triethanolamine. Here, again, we find what we have already stressed several times about an interest of the eomplexation phenomenon that can be used to dissimulate disturbing ions. Ba +, Sr +, and Ca + are titrated simultaneously. 

With calcein (a derivative of fluoresceine), the titration is very sensitive. Titrations with complexone(III) solutions of concentrations of about 10 mol/L can be carried out. At the endpoint, the yellow-green fluorescence disappears, whereas a violet color appears quasi-simultaneously. 

The hardness of water is a function of its Ca + and Mg + contents. The separated titrations allow us to determine the hardness due to Mg + and that due to Ca . To clarify what has just been said, the total hardness is determined by a titration carried out at 40 °C (for kinetic reasons) with complexone(III) at pH 9-10 in the presence of eriochrome black T and of magnesium complexonate [Mg(EDTA)] . In an alternative way to determine Mg +, it proceeds as before but after Ca + has been removed by precipitation as oxalate. 

Pb + may be directly titrated with complexone(III) in hexamethylenetetramine medium with xylenol orange as indicator. The pH value is located about 5.6. A similar titration of Zn + can be carried out at pH about 6 with xylenol orange or methyl thymol blue as the indicator. Hexamine is then the buffer. This titration is also possible in ammonia buffer (pH about 10) in the presence of eriochrome black T. 

Bi is also directly titrated by complexone(III) in the pH = 0-1 range with xylenol orange or methyl thymol blue as the indicator. 

Na+ may also be titrated with the help of EDTA. At first sight, this is a surprising fact because EDTA gives very weak complexes with alkaline ions. (Actually, their formation is not even taken into account when complexone-III— which is a sodium salt—is used ) But the evoked titration is an indirect one. In a first stage, Na+ is precipitated as sodium, zinc, and uranyl acetate Na(U02)3[Zn(H20)6](C2H302)9. In a second stage, the precipitate is destroyed and the liberated Zn + ions are directly titrated with a 10 moI/L EDTA solution in the presence of eriochrome black T. 

W l,2-Ethanediylbi (carboxymethyl)]glycine, 9CI. Ethylenedinitrilotetraacetic acid, SCI. EDTA. Edetic acid, BAN, INN. Versene acid. Sequestrene. Tetracemin. Complexone III. Many other synonyms [60-00-4]... 

Complexlng agents that form weak complexes with uranium and relatively strong complexes with other metallic Ions make separation possible between the two uranium Is precipitated by a suitable reagent the other Ions remain in solution. Ethylenedlamlnetetracetlc acid (complexone II) and Its dlBodlum salt (complexone III) have been used successfully In this respect. Uranium has been precipitated with ammonia In the px esence of complexones without Interference from Al, Cf, Min, Fe, Co, Nl, Cu, Zn, Cd, La, Ce, Hg, Pb, Bl,... 

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