镉离子选择电极电位滴定测定钙镁

建立了以镉离子选择电极极作指示电极ＥＤＴＡ、ＥＧＴＡ电位滴定测定钙、镁的方法，详细考察了电位滴定的适宜条件，干扰离子的影响及消除办法。在四硼酸钠－氢氧化钠缓冲介质中，ＥＧＴＡ滴定钙，ＥＤＴＡ滴定钙镁含量，测定矿泉水及硅酸盐样品中钙镁含量，结果符合要求。     

Compleximetric determination of calcium in impure calcium carbonate and limestone

Calcium is determined in impure calcium carbonate and limestone samples by titrating with 0.01 M disodium EGTA at pH 12 in the presence of at least 0.6 mg of magnesium and a maximum of 500 μg of iron(III), using a pH 12.5 sodium hydroxide-potassium cyanide-sodium sulfide buffer and Calcon indicator. The results of such titrations are compared with those obtained by titrating at pH 10 the calcium perchlorate solutions derived from calcium oxalate, and with those of a modified LEWIS AND MELNICK method. The results for magnesium (% MgO) obtained by difference are in fair agreement. Magnesium can be titrated compleximetrically as magnesium perchlorate, but the reagent blank must be determined.     

Preconcentration and determination of calcium and magnesium in brine with flow-injection systems

On-line preconcentration on a chelating resin (Dowex A-1) and elution with 0.1 M hydorchloric acid is followed by spectrophotometry based on the metal complexes formed with 1- (2-hydroxy-4-diethylamino-1-phenylazo)-2-hydroxynaphthalene-3,6-disulfonic acid. The total concentration of calcium and magnesium is determined; in a second sample, calcium is masked with a ligand buffer containing excess of barium(II) and EGTA, and magnesium is determined. The calcium concentration is measured by difference. Magnesium (1–30 μg l^?1 and calcium (8– 10 μg l^?1) in 2.5 M sodium chloride can be determined. Calcium and magnesium in analytical reagent-grade sodium chloride and potassium chloride and primary standard sodium chloride are aslo determined. The method based on the exchange between calcium ions and Mg(EDTA) is proposed to enchance the sensitivity for calcium.     

The titrimetric determination of calcium and magnesium in silicate rocks

A cation-exchange scheme is described for the separation of calcium and magnesium from interfering elements in rapid silicate analysis. Interfering elements can be eluted from the ammonium form of Zeo-Karb 225 with a solution of the ammonium salt of ethylenediaminetetraacetic acid at pH 4.5. Calcium and magnesium are not eluted with this reagent but can be eluted consecutively with ammonium chloride solution and titrated photometrically with EDTA. Calcium and magnesium can be separated quantitatively from Al, Fe, Ti, Mn, Bi, Cd, Cr, Co, Cu, Pb, Mo, Ni, U, V, rare earths, and Zn.     

Contributions to the basic problems of complexometry-XXVI determination of calcium in the presence of large amounts of magnesium

Two methods for the determination of calcium in the presence of very large amounts of magnesium are proposed. Both are based on back-titration of excess of EGTA, Thymolphthalexone being used as indicator. In the one method the titrant is a zinc solution, in the other a calcium solution is used, with a small amount of zinc present for end-point indication. Both titrations can be performed either visually or spectrophotometrically.     

Complexometric titration of calcium in the presence of larger amounts of magnesium

A simple and accurate titrimetric determination of calcium in the presence of larger amounts of magnesium is proposed. Calcium is extracted into a small volume of organic solvent as its glyoxal-bis(2-hydroxyanil) complex, and the calcium is titrated with EGTA. The end-point is sharp, and occurs when the red colour of the organic layer vanishes. This method has been successfully applied to the determination of calcium in sea-water with an error less than 0.1%.     

EDTA络合滴定法快速测定矿石中钙、镁

试样用盐酸、硝酸、氢氟酸、高氯酸分解,在pH值为6～9时,经六次甲基四胺-铜试剂分离铁、铝、镍、钴、铅、锌、铜、镉、锰等干扰元素后,在pH=10的氨水和氯化铵缓冲溶液中,以酸性铬蓝K-萘酚绿B为指示剂,用EDTA络合滴定法测定钙镁合量;另在氢氧化钾溶液中,用钙试剂为指示剂,以EDTA络合滴定法测定钙量,从而计算镁的含量。当样品钙高镁低或者镁高钙低时,低含量的镁量或钙量(<5%)可用电感耦合等离子体原子发射光谱(ICP-AES)法准确测定,使结果更准确。实验中对三个标准样品中的钙和镁进行多次测定,结果与认定值相符,相对标准偏差在0.69%～1.3%(n=7),加标回收率在99%～102%。方法实用性强,已经成功应用于各类矿石中钙镁的检测。     

Dosage amperometrique rapide et directe de calcium et de magnesium dans l'eau,les ciments et le sol

An amperometric method for thé successive titration of calcium and magnesium with EGTA and EDTA respectively is proposed. The method is direct and rapid. Calcium and magnesium can be determined in waters (41.5 mg/l and 4.6 mg/l with a precision of ±1.15% and ±6.70%), in cements (66.7% CaO and 1.70% MgO with a precision of ±2% and ±8%), and in soils (16.5% CaCO₃ and 1.8% MgCO₃ with a precision of ±2.6% and ±5.5%). The results obtained are compared with those obtained by gravimetric or titrimctric methods.     

Extraction with long-chain amines--VI. Separation of manganese as Mn(CNS)4-(6) complex and its complexometric determination in calcareous material

Manganese is quantitatively extracted into a benzene solution of trioctylmethyl-ammonium chloride from a solution at least 0.25M in potassium thiocyanate and at pH 2.5-7. After stripping into dilute ammonia containing triethanolamine (TEA) and hydroxylamine hydrochloride, manganese is determined by EDTA titration. Calcium and magnesium are not extracted even in traces. Iron is co-extracted with manganese and is masked with TEA during the stripping. Aluminium also does not interfere. In the aqueous phase, after the extraction of manganese, calcium or magnesium can be determined by the usual EDTA titration. The method described permits highly selective individual determination of manganese and calcium and/or magnesium in all materials rich in manganese.     

Dosage electrochimique rapide,en une seule operation et sans separation,du calcium et du magnesium en presence lún de láutre: Application aux dosages de ces elements dans le serum sanguin et dans lúrine

An important simplification is proposed for the simultaneous electrochemical titration of calcium and magnesium in blood serum and urine. By using platinum wire and mercury electrodes, calcium can be titrated with EGTA and then magnesium with EDTA in the presence of a buffer (pH 10.5) and possibly a citrate-tartrate masking agent. A current due to oxidation of mercury in presence of EGTA or EDTA marks the end-point, and can be read directly or recorded. For blood serum, no preliminary operation is needed; for urine, prior addition of a little silver nitrate makes the method satisfactory.     

Comparative study of metomega chrome blue BBL, calcon, eriochrome blue S.E. and omega chrome black blue G as indicators in the complexometric titration of calcium and magnesium

Conclusion It can be concluded that for the determination of calcium and magnesium in mixtures two separate titrations are to be done in case of Calcon, Erio SE, BBG. Total calcium and magnesium was determined first and then calcium in a separate titration. Magnesium is found by differences whereas in the case of BBL, the mixture was first titrated for its calcium content, then the solution is made acidic with hydrochloric acid and then alkaline with ammonia buffer solution pH 10 and magnesium is determined in the same sample.It is also noticed that Erio SE can work in sodium hydroxide or potassium hydroxid medium as well as in diethyl amine; but its drawback is the red hue which can be overcome by the addition of a green component, whereas BBL is spoilt in sodium hydroxide or potassium hydroxide medium.In comparing the first 3 indicators (Calcon, Erio SE, BBG) we find that BBG is the best one in the titration of calcium and magnesium using either EDTA on Complexion IV, and its endpoint has no red hue as that found in Erio SE; also the recovery of calcium is quantitative in any ratio of magnesium.

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Vergleichende Untersuchung von Metomega Chromblau BBL, Calcon, EriochromblauS.E.und Omega-ChromschwarzblauG als Inidicatoren bei der komplexometrischen Bestimmung von Calcium und Magnesium

     

Microdetermination of calcium and magnesium in a mixture

Summary A procedure is presented for the chemical separation and determination of mg quantities of calcium and magnesium, which is based on the selective carrying of calcium by ignited strontium sulphate leaving magnesium in the solution phase; the carried calcium is recovered by leaching with alcoholic sulphuric acid solution. Calcium and magnesium in the separated fractions are determined complexometrically using Eriochrome Black T as the indicator.

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Zusammenfassung Ein Verfahren zur chemischen Trennung und Bestimmung von mg-Mengen Calcium und Magnesium wird vorgeschlagen, wobei Ca selektiv mit geglühtem Strontiumsulfat abgetrennt wird, während Mg in Lösung bleibt. Ca wird mit alkoholischer Schwefelsäure eluiert. Beide Metalle werden getrennt gegen Eriochromschwarz T komplexometrisch titriert.

     

Fluorometric titration of calcium, magnesium and iron using calcein blue as indicator

Calcium, magnesium and iron can be determined by successive fluorometric titration without separation. Calcium is titrated directly with EGTA at a pH 13; magnesium is determined by a substitution reaction with copper-EDTA complex at a pH of about 11 ; and iron is titrated directly with EDTA in the presence of hydrogen peroxide at a pH of 10.5, after destroying its triethanolamine complex. Calcein Blue serves as an indicator in all of the titrations and as a fluorescent standard. The end-points are sharp and the accuracy is good for various proportions of the metal ions. The method is simple, reproducible and inexpensive. Standard solutions of ions, limestone, cement and serum samples have been analysed by the proposed method.     

Determination of calcium and magnesium in limestone and dolomite by enthalpimetric flow-injection analysis

A flow-enthalpimetric method for the determination of calcium and magnesium in limestone and dolomite is described. Calcium is determined by measuring the heat evolved from the substitution reaction with Mg-EDTA. The amount of magnesium is calculated from the calcium content and the enthalpimetric signal for the reaction of the sample solution with disodium-EDTA, which gives the total concentration of calcium and magnesium. Analysis of reference materials and other samples indicates an error not exceeding 0.3% of CaO and MgO, and a sampling rate of 100 samples per hour.     

Successive substitution titration of calcium and magnesium with EGTA using thallium oxide electrode for indication

Summary It is demonstrated that magnesium can be titrated with EGTA in the presence of CaEDTA complex. On the basis of this substitution reaction, calcium and magnesium are successively titrated with EGTA, if an appropriate amount of CaEDTA is added after having reached the end point for calcium. Both end points are indicated amperometrically using a thallium oxide anode. The method has been tested for analysis of tap and mineral water. Larger amounts of manganese(II) render the calcium result too high. Moreover, the indication of both end points is affected by the electrode position of an inactive MnO₂-layer onto the Tl₂O₃-layer. Reducing agents destroy the Tl₂O₃-layer. These interferences can be overcome by addition of an appropriate amount of manganate(VII) to the sample.

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Sukzessive Substitutionstitration von Calcium und Magnesium mit ÄGTA, indiziert mit der Thalliumoxidelektrode

Zusammenfassung Magnesium kann mit ÄGTA in Gegenwart des CaÄDTA-Komplexes titriert werden. Auf der Grundlage dieser Substitutionstitration können Calcium und Magnesium nacheinander mit ÄGTA titriert werden, wenn nach dem Endpunkt für Calcium eine ausreichende Menge CaÄDTA zugesetzt wird. Beide Endpunkte werden amperometrisch mit Hilfe einer Thalliumoxidelektrode angezeigt. Die Methode wurde an Leitungswasser und Mineralwasser geprüft. Größere Mengen Mangan(II) bewirken zu hohe Calciumwerte. Darüber hinaus wird die Indikation beider Endpunkte dadurch beeinträchtigt, daß sich eine inaktive MnO₂-Schicht auf der Tl₂O₃-Schicht elektrolytisch abscheidet. Reduzierende Stoffe zerstören die Tl₂O₃-Schicht. Diese Störungen können durch Zugabe von Permanganat vermieden werden.

     

Determination of calcium,magnesium, and phosphate in the presence of iron and each other

Excess EDTA and MgSO₄ solution is added to a mildly acidic solution of the sample containing calcium, magnesium, iron, and phosphate ions. Addition of NH₄OH to this solution results in the precipitation of MgNH₄PO₄·6H₂O and various iron compounds. Calcium ions and a portion of the magnesium ions stay in the solution as the respective EDTA chelates. The mixture is adjusted to a known volume and filtered. The EDTA content of the filtrate with the exception of the EDTA tied up as calcium-EDTA chelate, is titrated with standard CaCl₂ solution at pH 12.5–13.0 in the presence of hydroxy naphthol blue indicator. The calcium content of the sample can be calculated from the result of this titration.     

Amperometric complex-formation titration of traces of alkaline earths

Alkaline earth metals were determined in microgram quantities by complexometric titration with EDTA, EGTA and DTPA. The end-point was detected by following the anodic wave of the chelating agent at the rotating mercury electrode. All the alkaline earths can be titrated at the microgram level with reasonable accuracy, and calcium may be titrated with EGTA in the presence of a 1000-fold excess of magnesium.     

EDTA titration of calcium and magnesium with a calcium-selective electrode

Direct semi-automatic and automatic derivative potentiometric EDTA procedures for the determination of calcium and/or magnesium with a calcium-selective electrode are described. Calcium is titrated in the presence of magnesium at pH 12.0 and the total calcium and magnesium is determined at pH 9.7. Calcium in the range 1-8 mg and magnesium in the range 0.7-5 mg are determined semi-automatically with average errors of about 0.2 and 0.3% respectively and automatically with average errors of 0.4 and 0.7%. Titration times vary from a few seconds to a few minutes.     

Microdetermination of magnesium in biological fluids

A modified procedure for the spectrophotometric determination of serum magnesium is described in which a direct addition of serum is made to a two-piece color reagent system. One solution contains an optimized concentration of the color reagent Magon, 1-azo-2-hydroxy-3-2-(2,4-dimethylcarboxanilido)-naphthalene-1′-(2-hydroxybenzene-5-sulfonate) sodium salt, in a dimethyl sulfoxide medium for binding magnesium and also EGTA, ethylene-bis(oxyethylenenitrilo)-tetraacetic acid, for binding calcium. The other is an alkaline solution of dilute cyanide to bind copper and iron and provide the optimum reaction pH. By means of these ingredients the simple procedure involves a reaction with serum magnesium while masking the interference of calcium and trace metals and allowing the reaction to take place without either separation or deproteinization steps. Optimized characteristics are shown for a linear reaction involving a variable reaction blank in the procedure where calcium is measured against a blank that is constant in its makeup. The linearity of the procedural reagent blank, with respect to its own concentration, helps attain the required linear results for the overall system and this is described by spectral studies.     

Rapid visual compleximetric titration of calcium in natural waters

Visual compleximetric methods for the titration of calcium in the presence of magnesium have been based either on masking the magnesium or using an indirect indicator procedure, e.g., the system Zn-EGTA-Zincon. In the proposed method these two approaches are combined. Zn-EGTA complex is added to the mixture and the zinc liberated in the calcium replacement reaction is titrated with EGTA after the magnesium has been masked with fluoride ion.