Copper complexes buffers

A technique for the determination of free cupric ions in seawater has been described by Sunda and Hanson [332], The method is based on sorption of copper onto Sep-Pak Cis cartridges and internal free cupric ion calibration. Calibration is accomplished by adding cupric ion buffers and EDTA, which competes with natural organic ligands for copper complexation. The method was used to establish that 0-2% of the copper occurs as inorganic species and 98-100% occurs as organic complexes. 

Copper Complexes. The preparation of copper and nickel complexes of tridentate metallizable azo and azomethine dyes is easily carried out in aqueous media with copper and nickel salts at pH 4-7 in the presence of buffering agents such as sodium acetate or amines. Sparingly water soluble precursors can be metallized in alkaline medium at up to pH 10 by using an alkali-soluble copper tetram(m)ine solution as coppering reagent, which is available by treating copper sulfate or chloride with an excess of ammonia or alkanolamines [3],... 

In the photometric determination of copper, a coupling product formed between the diazonium salt from 2-amino-pyridine and resorcinol, or 4-(2-pyridinylazo)-l,3-benzenediol 21, has been used. Here the formed copper complex under acetate buffer exhibits an absorption peak at 520 nm, which is measured photometrically <2003KPU28>. Similarly for photometric determination of iron(ll), a coupling product formed between the diazonium salt of 2-amino-4,6-dihydroxypyrimidine and 8-hydroxyquinoline, or 6-hydroxy-2-(8-hydroxy-7-quinolinyl)azo-4(l//)-pyrimidinone 22, has been used. This reagent forms a blue complex with iron(n) ions with an absorption maximum at 625 nm that does not interfere with the presence of other metals <2003KD95>. 

A spectrophotometric method for the determination of ampicillin involving initial benzoylation of the side chain a-amino group is described. a-Benzamidobenzylpenicillin so formed is treated with mercuric chloride in acid solution and a-benzamidobenzylpenicillenic acid is obtained. This may be assayed spectrophoto-metricallyl69, Ampicillin is degraded in a buffer solution at pH 5.2 at 75°C and the absorbance is measured at 320 nm. Smith s method for the spectrophotometric determination of ampicillin was adapted to the assay of ampicillin in chicken blood, bile and urine 3-Ampicillin is dissolved in 5N sodium hydroxide and the absorbance is measured at 279 nm 2, Ampicillin is determined spectrophotometrically as its copper complex S. Spectrophotometric and circular dichroism methods for determining the activity of ampicillin are described. A... 

More recently, the activity of serum peptidases was investigated by capillary electrophoresis with electrochemical detection [60]. Increased peptidase activity in blood is characteristic of a number of disease states. In this application, leu-enkephalin was used as a model substrate. Leu-enkephalin and its metabolites were separated and detected with CEEC following on-capillary copper complex-ation. By incorporating copper in the run buffer, peptides were complexed directly on-capillary [61]. The copper(ll) complexes could then be detected at +700 mV by oxidation to Cu(lll). The method shows good selectivity for peptides over amino acids. This method was used to monitor the metabohsm of leu-enkephalin by enzymes present in a serum sample (Eigure 10). 

Supplementing culture media, crude extracts, storage, and assay buffers with copper salts can assist copper complex formation in MCO preparations. In many cases, copper can be added to bacterial and fungal culture supernatants to increase MCO activity and holoenzyme yield [62-67]. Free copper ions are toxic to microorganisms, so copper concentrations must remain low enough during cultivation so that growth is not inhibited [61]. 

Discussion. Minute amounts of beryllium may be readily determined spectrophotometrically by reaction under alkaline conditions with 4-nitrobenzeneazo-orcinol. The reagent is yellow in a basic medium in the presence of beryllium the colour changes to reddish-brown. The zone of optimum alkalinity is rather critical and narrow buffering with boric acid increases the reproducibility. Aluminium, up to about 240 mg per 25 mL, has little influence provided an excess of 1 mole of sodium hydroxide is added for each mole of aluminium present. Other elements which might interfere are removed by preliminary treatment with sodium hydroxide solution, but the possible co-precipitation of beryllium must be considered. Zinc interferes very slightly but can be removed by precipitation as sulphide. Copper interferes seriously, even in such small amounts as are soluble in sodium hydroxide solution. The interference of small amounts of copper, nickel, iron and calcium can be prevented by complexing with EDTA and triethanolamine. 

The reaction is a sensitive one, but is subject to a number of interferences. The solution must be free from large amounts of lead, thallium (I), copper, tin, arsenic, antimony, gold, silver, platinum, and palladium, and from elements in sufficient quantity to colour the solution, e.g. nickel. Metals giving insoluble iodides must be absent, or present in amounts not yielding a precipitate. Substances which liberate iodine from potassium iodide interfere, for example iron(III) the latter should be reduced with sulphurous acid and the excess of gas boiled off, or by a 30 per cent solution of hypophosphorous acid. Chloride ion reduces the intensity of the bismuth colour. Separation of bismuth from copper can be effected by extraction of the bismuth as dithizonate by treatment in ammoniacal potassium cyanide solution with a 0.1 per cent solution of dithizone in chloroform if lead is present, shaking of the chloroform solution of lead and bismuth dithizonates with a buffer solution of pH 3.4 results in the lead alone passing into the aqueous phase. The bismuth complex is soluble in a pentan-l-ol-ethyl acetate mixture, and this fact can be utilised for the determination in the presence of coloured ions, such as nickel, cobalt, chromium, and uranium. 

Figure 8.43 Separation of enantiomers using complexation chromatography. A, Separation of alkyloxiranes on a 42 m x 0.2S mm I.O. open tubular column coated with 0.06 M Mn(II) bis-3-(pentafluoro-propionyl)-IR-camphorate in OV-ioi at 40 C. B, Separation of D,L-amino acids by reversed-phase liquid chromatography using a mobile phase containing 0.005 M L-histidine methyl ester and 0.0025 M copper sulfate in an ammonium acetate buffer at pH 5.5. A stepwise gradient using increasing amounts of acetonitrile was used for this separation.

Mash, H., Chin, Y., Sigg, L., Hari, R., and Xue, H., Complexation of copper by zwitterionic aminosul-fonic (good) buffers, Anal Chem, 75 (3), 671-677, 2003. 

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