电位滴定法测定石膏中三氧化硫的方法研究

研究了ＥＤＴＡ滴定Ｐｂ＾２＋过程中溶液的电位变化，建立了以双液接饱和甘汞电极为参比电极，铅电极为指示电极，ＥＤＴＡ为滴定剂电位滴定法测定石膏，水泥中三氧化硫，方法准确度高，结果稳定，操作简便。     

示波滴定法测定合金中铜

利用Ｚｎ＾２＋ｄＥ／ｄｔ～Ｅ曲线上有敏锐的切口并可指示波滴定终点的性质提出了用硫脲释放出Ｃｕ－ＥＤＴＡ配合物中的ＥＤＴＡ，再用Ｚｎ＾２＋示波滴定该ＥＤＴＡ以测定铜含量的新方法，方法不用指示剂，溶液有颜色不影响测定，进行了多种合金中铜的测定，结果令人满意。     

pH电位滴定法测定溶液中钙、镁离子与聚天冬氨酸的生成稳定常数

pH电位滴定法测定溶液中钙、镁离子与聚天冬氨酸的生成稳定常数;pH电位滴定;聚天冬氨酸;配位化学;钙离子;镁离子     

硅钙合金中钙含量的快速测定方法

硅钙合金中钙含量的测定一般采用ＨＮＯ3 ＨＦ ＨＣｌＯ4 溶样 ,ＨＣｌＯ4 冒烟除硅 ,氨水分离以除去铁铝等干扰后用ＥＤＴＡ直接滴定的方法[1] 。该方法须经ＨＣｌＯ4 两次冒烟、两次氨水分离 ,手续较繁琐、费时 ,成本高、操作不便 ,且易造成测定误差。本文研究了硅对钙测定的干扰及ＥＤＴＡ、磺基水杨酸、三乙醇胺(ＴＥＡ)与钙、铁、铝等离子间的络合平衡关系 ,制定出硅钙合金中钙含量快速测定方法。1　试验部分1.1　主要试剂磺基水杨酸 (ＳＳＡ)溶液 :10 0ｇ·Ｌ- 11.2　试验方法移取含一定量硅、钙、铁、铝离子的试液于铂皿中 ,加入一定…     

偶氮胂-DCS作为钙镁络合滴定指示剂的研究及其应用

研究了利用光度显色剂偶氮胂－ＤＣＳ作为钙镁联合滴定指示剂的可能性及使用该指示剂滴定钙镁的准确性,与常用的钙镁络合滴定指示剂进行了比较,并成功地应用于水泥试样中钙镁含量测定。结果表明,偶氮胂－ＤＣＳ是一种良好的钙镁络合滴指示剂。     

热解-电位滴定(或酸碱滴定)快速测定萤石中氟化钙

萤石中氟化钙的测定,多是通过测定钙换算成样品中氟化钙含量。这些测定方法操作繁琐,准确度低。近年来有人试图用氟离子选择性电极测定氟矿中的氟含量,只是应用上的报导还不多。本文研究了热解-电位滴定及酸碱滴定测定萤石中氟化钙的适宜条件,并提出了简单快速、切实可行的分析方法。     

离子选择电极在教学中的应用——钙镁的连续电位滴定

EDTA配位滴定法测定钙镁含量是配位滴定实验教学中的重要内容。为了开拓学生知识面,培养学生的研究和动手能力,我们设计了用钙电极作指示电极,在氨性缓冲溶液中,以EGTA和DCTA为络合剂,在一份试液中连续电位滴定法测定钙镁的实验。通过本实验我们体会有下列优点:相应改善了目前定量分析教学中有关电位滴定实验较少的状况;本实验仪器简单、操作方便,但又包括了容量分析实验的基本操作内容,综合练习多;将本法用于硅酸盐的矿物测定,结果重现性好,准确度较高,有一定的实用性。     

用钙离子选择电极测血清中的总钙——两种钙电极及几种测量技术的比较

测定血清中的钙,对许多疾病的诊断具有重要意义。因测定其中游离的钙离子含量很难测准,故测定总钙含量的方法仍被采用。目前国内采用EDTA滴定目视指示终点,终点不明显,误差较大。文献介绍在酸性下使血清中的总钙全部成为游离的钙离子,用直接电位法测总钙。本文中将中性载体(ETH1001)及磷酸醋两种钙电极,使用几种测量技术测定血清中的总钙,进行比较。ETH1001钙电极比磷酸酯钙电极性能优良,表现在电极电位稳定性     

5－Br－PADAP作指示剂络合滴定法连续测定矿石中的锌和铜

本文在ｐＨ５．５的乙酸－乙酸钠介质中，对以５－Ｂｒ－ＰＡＤＡＰ作指示剂络合滴定法连续测定锌和铜进行了研究，对滴定的ｐＨ值及指示剂用量进行了选择，试验了锌、铜不同配比的滴定结果，研究了共存离子的干扰。实验表明，用５－Ｂｒ－ＰＡＤＡＰ作指示剂、ＥＤＴＡ作滴定剂连续测定锌和铜，滴定终点颜色变化敏锐，准确度高，锌和铜均在０～２０ｍｇ范围内与ＥＤＴＡ用量成正比，锌、铜比例在１：１０～１０：１范围内相互无影响，方法用于标样及金矿中锌、铜的连续测定，结果满意。     

饲料中钙的快速测定

混合饲料和单一饲料中 ,钙是重要的营养成分。ＧＢ/Ｔ 6436- 1992方法用高锰酸钾法间接滴定钙的含量 (容量法 )或用ＥＤＴＡ络合滴定钙 (络合法 )。考虑到容量法测定钙操作繁琐 ,且高锰酸钾溶液要经常标定 ,滤纸要做空白测定 ,耗时较长。而络合法饲料中各类添加剂影响终点的判定。本文提出用原子吸收光谱法测定饲料中钙的含量。通过多次试验证明 ,本法简便、快速 ,检测结果与国家标准分析方法结果比较 ,准确度、精必度均符合要求。1　试验部分1.1　仪器与试剂ＷＦＸ 1Ｂ2型原子吸收分光光度计ＥＤＴＡ溶液 :0 .1ｍｏｌ·Ｌ- 1氯化锶溶液 :2 …     

Contributions to the basic problems of complexometry-XX Determination of calcium and magnesium

A new method for the determination of magnesium in the presence of calcium is described. Calcium is masked with EGTA whilst magnesium is titrated with DCTA with Methylthymol Blue as the indicator. Calcium can be determined in the same solution by back-titration of the excess EGTA with calcium chloride solution. The usual masking agents for iron, aluminium and other heavy metals can be used.     

Contributions to the basic problems of complexometry-XXVIII New method for successive determination of calcium and magnesium

A new method for successive determination of calcium and magnesium is proposed. It is based on the indirect determination of calcium in borax media by back-titration of excess of EGTA with lead nitrate. Magnesium is then determined in ammonia buffer with DCTA. For both titrations Thymolphthalexone is used as indicator. The exceptional role of DCTA in direct titration of magnesium is established experimentally and explained.     

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.     

Determination of exchangeable calcium and magnesium in soil by ion-selective electrode method

The potentiometric measurement of calcium ion activity with a calcium ion electrode and of magnesium ion activity with a divalent cation electrode in the presence of EGTA at pH 7 has been successfully applied to the determination of exchangeable calcium and magnesium in soil after the soil sample is extracted with ammonium acetate and the soil extract is evaporated to dryness and ignited. The results obtained by the ion-selective electrode methods are in good agreement with those obtained by the reference methods.     

Potentiometric and spectrophotometric flow-injection determinations of metal ions with use of metal ion buffers

Potentiometric and spectrophotometric flow-injection determinations of metal ions, based on metal ion buffers, are described. A copper(II) ion-selective electrode and copper(II) ion buffers containing nitrilotriacetic acid (NTA) or ethylenebis(oxyethylenedinitrilo)tetraacetic acid (EGTA) are used for determination of ca. 10^?3 M transition metal ions or of calcium in the presence of magnesium. Spectrophotometric determination of transition metal ions is achieved by using a zinc ion buffer solution containing NTA and xylenol orange as indicator. Zinc concentrations up to 2 M can be determined by using large dispersion in the manifold. The factors influencing the sensitivity of the proposed methods are discussed.     

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.     

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.     

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.     

Determination of calcium in silicate rocks by potentiometric titration with ethyleneglycol-bis-(2-Aminoethylether)tetraacetic acid and a calcium-selective electrode

The method reported for the determination of calcium in silicate rocks involves titration with ethyleneglycol-bis(2-aminoethylether)tetraacetic acid (EGTA) to a potentiometric end-point. A Crytur calcium-selective electrode is used; the selectivity constants (K_ca,x) are less than 10^-3 for Mg, Ba, Sr, K and Na. The method can be used for calcium contents of 2% or higher (and exceptionally for lower contents), in the presence of up to 60% Mg, 33% AI, 17% Fe, 5% Ba, 5% Ti, and 2.5% Mn. Al, Fe and Ti are masked with sulphosalicylic acid, barium is precipitated as its sulphate, and manganese is bound as its cyanide complex. If the magnesium content is less than that of calcium, EDTA can be used as titrant, magnesium being masked with acetylacetone.