A rapid complexometric scheme for analysis of iron, aluminium, calcium and magnesium in slags

A simple and rapid complexometric method has been developed for the simultaneous determination of iron, aluminium, calcium and magnesium in a single solution in slags. Phosphorous and small amounts of chromium (1.5 mg) and vanadium (1 mg) do not interfere in the titration. Titanium and manganese are suitably masked with lactic acid and tetra sodium pyrophosphate, respectively. In a suitable aliquot, iron is titrated at pH 2 with EDTA, using sulphosalicylic acid as indicator. To this solution, excess disodium 1,2-cyclohexane diamine tetra acetic acid (DCTA) is added and aluminium is titrated by titrating the excess DCTA with standard copper sulphate solution at pH 3.5, using 1-(2-pyridylazo)-2-naphthol (PAN) as an indicator. A known excess of EDTA is added, the pH is raised to 10 and calcium and magnesium are jointly titrated by titrating the excess EDTA with copper sulphate solution, using PAN indicator. The Ca-EDTA complex is demasked with ammonium oxalate at pH 5 and the released EDTA equivalent to calcium is titrated with copper sulphate solution at pH 10 with PAN indicator. Results of analysis compare favourably with certified values and values obtained by standard methods for BCS and other slags. A set of five samples can be analysed for iron, aluminium, calcium and magnesium in four hours as compared to three days by the classical conventional method.     

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.     

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.     

Simultaneous determination of calcium and magnesium by derivative spectrophotometry in pharmaceutical products

First- and second-derivative spectrophotometric methods for the simultaneous determination of calcium and magnesium in their mixtures are described. The methods are based on the colored complexes formed by calcium and magnesium with bromopyrogallol red in presence of Tween 80 as a surfactant. The zero-crossing method has been utilized to measure the first- and second-derivative value of the derivative spectrum. Calcium (0.8-4.8microgml(-1)) is determined in the presence of magnesium (0.5-3.5microgml(-1)) at the pH 10 and vice versa at zero-crossing wavelengths of 544.5 and 570nm in the first-derivative procedure and 574 and 531nm in the second-derivative procedure, respectively. The detection limits achieved were 0.0575microgml(-1) of calcium and 0.03microgml(-1) of magnesium. The relative standard deviations were in all instances less than 2%. The proposed method has been applied to the simultaneous determination of calcium and magnesium in different samples: commercial multivitamin, human serum and drinking water where excellent agreement between reported and obtained results was achieved.     

Complexometric estimation of ferric iron

Summary Ferric iron has been determined alone or in presence of barium chloride, calcium chloride, magnesium sulphate, mercuric chloride, manganese sulphate, strontium nitrate, chromic sulphate or zinc sulphate by titrating it with EDTA, using potassium thiocyanate-p-anisidine indicator. In these complexometric titrations, the quantitative results obtained by using potassium thiocyanate-p-anisidinie indicator are comparable with those obtained with Bindschedler's green indicator; and the metallic salts mentioned above do not interfere in the estimation of ferric iron by this method.     

Atomic absorption spectrometric determination of calcium and other metallic elements in some animal protein sources

The phosphorus content of some animal protein sources was determined in order to identify the sample with the highest phosphorus content for use as a pilot sample. Varying concentrations of strontium and lanthanum were added to solutions of the ashed pilot sample for the determination of calcium and magnesium using flame atomic absorption spectrophotometry operated on the air-acetylene mode. At least 3000 ppm of strontium or lanthanum was required to completely overcome the interference of phosphate ion, PO(4)(3-), and give peak values for calcium. The presence of strontium or lanthanum did not affect the amount of magnesium obtained from the analyses. Based on this, a procedure is proposed and the results obtained by this procedure for calcium are more enhanced than those obtained without the addition of strontium or lanthanum for the same samples whereas comparable results were obtained for all other elements whether strontium or lanthanum was added or not. The method gives more accurate results and is reproducible. The coefficients of variation calculated using one of the samples were 0.58% for magnesium, 3.12% for zinc; 0.44% for calcium, 11.06% for lead, 22.22% for nickel, 3.53% for manganese and 3.50% for iron at the concentration levels found in that sample. Recoveries of spiked calcium, magnesium and zinc were quantitative. Also, for selected elements, results from the procedure compared well with those from chemical analysis.     

Simultaneous spectrophotometric determination of calcium and magnesium with chlorphosphonazo-III by flow injection analysis

In this flow-injection method, the total concentration of calcium and magnesium is determined by using triethanolamine/hydrochloric acid buffer (pH 7.0) and chlorphosphonazo-III (CPA-III) in the flow streams, and the concentration of calcium alone is determined by using 1.6×10^?3 M hydrochloric acid and CPA-III in the flow treams. At pH 7.0, medium, the linear calibration ranges were 0–2.00 mg l^?1 for both calcium and magnesium and the detection limits were each 0.02 mg l^?1; at pH 2.2, the linear calibration range for calcium and the detection limit were 0.20–2.00 mg l^?1 and 0.1 mg l^?1, respectively. Injection rates are 200 h. The method is suitable for analyzing natural waters.     

1,5-bis(dicarboxymethylaminomethyl)-2,6- dihydroxynaphthalene as a selective spectrofluorimetric reagent for calcium

1,5-Bis(dicarboxymethylaminomethyl)-2,6-dihydroxynaphthalene (BDDN) forms fluorescent complexes with aluminium, barium, beryllium, calcium, magnesium and strontium. All the complexes have 2:1 metal :ligand ratios. Barium, calcium, magnesium and strontium exhibit maximal fluorescence at pH 11.7, with excitation and emission maxima at 385 and 445 nm respectively. Aluminium and beryllium show maximal fluorescence at pH 5.8 and 5.2 respectively, the excitation and emission maxima being at 370 and 405 nm. The formation of the calcium complex provides a highly sensitive and selective determination of calcium in the range 10/2-500 ng. The fluorescence measurement of calcium should be made within 5 min of mixing the solutions because of the instability of the reagent at the given pH. Potassium cyanide may be used as a masking agent and ter- or quadrivalent cations should be removed by preliminary extraction with 8-hydroxyquinoline in chloroform at pH 6.0. In such conditions, of 33 cations studied, only magnesium (>20 ng), strontium (>70 ng) and barium (>150 ng) caused interference in the determination of 300 ng of calcium. Among 16 anions examined, only EDTA interfered seriously.     

A chemometric study of the simultaneous determination of calcium and magnesium in natural waters

A method for the simultaneous spectrophotometric determination of calcium and magnesium in mineral waters with an FIA system is tested. The method is based on the reaction between the analytes and arsenazo(III) at pH 8.5. The calculations of the amounts of both analytes in the samples are carried out with the H-point standard addition method (HPSAM) for ternary mixtures, and with a partial least squares (PLS) model after a proper variable selection. The results obtained for the determination of calcium were comparable using both methods. The employment of the HPSAM brings to our attention the influence of the calcium concentration in the sample to the development of the reaction between magnesium and arsenazo(III). HPSAM also permits to estimate the concentration of magnesium in the samples.     

Bismuthiol as an analytical reagent

Summary Lead can be determined from its Bismuthiol II complex volumetrically by dissolving it in an excess of EDTA at a p_H of about 10 and titrating the excess of the EDTA against a magnesium or lead solution. In the same way silver can be determined by dissolving the complex in an excess of cyanide and back titrating the excess against a standard silver nitrate with iodide as the indicator. The results of the former are fairly accurate while those due to latter are highly satisfactory with silver less than 20 mg. With higher amounts of silver, however, the results are within +2%.Part VIII see Z. analyt. Chem. 156, 103 (1957).     

Determination and differentiation of nitrilotriacetic acid and ethylenediaminetetra-acetic acid

Ethylenediaminetetra-acetic acid (EDTA) and nitrilotri-acetic acid (NTA) can be differentiated and determined by titration with metal ions to visual metallochromic dye end-points. EDTA can be determined without interference from NTA, either by titrating with copper(II) at pH 5 using PAN indicator, or by titrating with iron(III) at pH 6 and 70 degrees using Tiron indicator. The total chelating power (EDTA + NTA) can be determined either by titrating with lead(II) at pH 4.4 using dithizone indicator, or by titrating with iron(III) at pH 3.5 using Tiron indicator ; NTA is determined by difference. The lowest concentration at which NTA can be determined in EDTA by titration to the iron(III)-Tiron end-point is about 1 wt.%. The apparent stability constants of the iron(III)-Tiron complexes under the conditions of the titration at pH 3.5 and pH 6 have been determined using the method of continuous variations.     

Determination of traces of calcium, magnesium, iron and nickel in aluminium salts by atomic-absorption spectrophotometry with a microwave-excited source and hollow-cathode lamps

The determination of trace amounts of calcium and magnesium in solutions containing large concentrations of aluminium salts may be accomplished by co-precipitating their hydroxides on iron(III) hydroxide, dissolving the precipitate, and extracting the 8-hydroxyquinolates of calcium and magnesium into methyl isobutyl ketone at about pH 11. The extract may be sprayed into the airpropane flame of a simple unmodulated spectrophotometer and atomic-absorption measurements for calcium and magnesium made at 4227 and 2852 A respectively. The limits of determination correspond to 10 and 1 ppm of calcium and magnesium in solid alumina. Iron and nickel may be co-precipitated on hydrated manganese(IV) oxide and their 8-hydroxyquinolates extracted at pH 4.5. Measurements of atomic absorption for these elements at 2483 and 2320 A respectively yield limits of determination corresponding to 10 ppm in alumina. Hollow-cathode lamps may be used for calcium, magnesium and nickel, but a simple microwave-excited discharge tube gives much better sensitivity than a hollow-cathode lamp for iron.     

Construction and evaluation of ion-selective electrodes for potassium and calcium with a summing operational amplifier. Application to wine analysis

Electrodes selective to potassium and calcium with improved senstivity were constructed like conventional electrode (ISEs), but used an operational amplifier to sum the potentials supplied by the four membranes (ESOAs). The results obtained during the evaluation of their working characteristics were compared to those obtained by conventional ISEs and were found to be similar, but with higher precision. The electrodes were used in the potentiometric determination of potassium, calcium and magnesium in wines. The results given by ESOAs were more precise than those from ISEs. The results obtained by potentiometry were in good agreement with those from AES for potassium and AAS for calcium and magnesium.     

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.     

Effect of pH and washing on calcium and magnesium distribution between pulp and filtrate

The impact of pH and washing procedure on calcium and magnesium distribution between pulp and filtrate in pulp processing was investigated. Depending on media pH, the elements are present in the form of ions (Ca²⁺, Mg²⁺) and hydrated oxides (Ca(OH)₂, Mg(OH)₂). Distribution was monitored using binary systems of CaCl₂ and MgCl₂ dissolved in deionized water or Ca²⁺ and Mg²⁺ ions present in filtrates from an industrial pulp mill. Complying with the relevant standards in force, Ca and Mg contents are expressed as CaO and MgO. The study was aimed at obtaining mathematic relations between pH and calcium and magnesium, as two important non-process elements, sorption on pulp. Distribution of the elements between pulp and liquid (filtrate or water) was determined with analytical procedures and simulation of pulp washing. It was found that both pH and filtrate composition influenced sorption/desorption of the elements on/from pulp. Filtrate from a pulp mill, mainly content of organic substances in liquid phase, affects their sorption on pulp and desorption to liquid. The higher the pH value the more efficient the sorption of the elements, magnesium being sorbed on pulp in higher amounts than calcium. Prevalence of the sorbed magnesium is preserved even at lower concentrations of both elements. Distribution of the elements between pulp and solution is expressed through mathematic relations which, in turn, can be employed to purposefully modify or optimize the distribution between the solid (pulp) and liquid (filtrate) media. Moreover, rationalized exploitation of mathematical relations enables balancing the elements within a cellulose manufacture, regulating media recycling, and predicting an eventual impact on technological processes.     

Arsenazo III as metallochromic indicator for complexometric determination of calcium in slightly alkaline medium

Arsenazo III is proposed as metallochromic indicator for calcium in slightly alkaline medium. The visual titration with EDTA was performed at pH 8 and 40 microg-12 mg of calcium were determined. The interference of some ions was considered and it was found that phosphate does not interfere appreciably. Spectrophotometric detection of the end-point was used for titration of calcium in the presence of magnesium at pH 9. For the estimation of the titration error, the conditional stability constants of the calcium-arsenazo III complex were found.     

Magnesium and calcium surfactants Ternary phase diagrams of magnesium and calcium dodecylsulphate with decanol and water

The isothermal ternary phase diagrams for the systems magnesium dodecylsulphate-decanol-water at 40 °C and calcium dodecylsulphate-decanol-water at 50 °C are determined by water deuteron NMR and polarizing microscopic studies. In the magnesium system, three liquid crystalline phases (lamellar and normal and reverse hexagonal) and two isotropic (normal and reverse) solution phases are characterized and their ranges of existence are obtained. The calcium system yields the same liquid crystalline phases, but only the lamellar liquid crystalline phase is investigated in detail. The important observations made are: (i) The lamellar liquid crystalline phase for the magnesium and calcium systems can incorporate, respectively, a maximum of 22.5 and 14.3 mole water per mole surfactant ion against 139 mole water for the corresponding sodium system. (ii) The reverse hexagonal liquid crystalline phase is formed for both the magnesium and calcium systems while no such liquid crystalline phase exists for the corresponding sodium system. (iii) The²H NMR quadrupole splittings obtained in the liquid crystalline phases for C₈SO ₄ ^– and C₁₂SO ₄ ^– surfactant systems with different counterions (Ca²⁺,Mg²⁺,Be²⁺,Na⁺) reveal that surfactant hydration is almost independent of alkyl chain length and counterions.     

Construction and evaluation of ion-selective electrodes for potassium and calcium with a summing operational amplifier. Application to wine analysis

Electrodes selective to potassium and calcium with improved senstivity were constructed like conventional electrode (ISEs), but used an operational amplifier to sum the potentials supplied by the four membranes (ESOAs). The results obtained during the evaluation of their working characteristics were compared to those obtained by conventional ISEs and were found to be similar, but with higher precision. The electrodes were used in the potentiometric determination of potassium, calcium and magnesium in wines. The results given by ESOAs were more precise than those from ISEs. The results obtained by potentiometry were in good agreement with those from AES for potassium and AAS for calcium and magnesium. Received: 27 June 1997 / Revised: 29 September 1997 / Accepted: 3 October 1997     

Automatic determination of calcium and magnesium in water

Magnesium and calcium may each be determined in water by an automatic spectrophotometric method. At 571 nm with an excess of Eriochrome Black T as metallochromic agent, the variation m absorbance is proportional to the magnesium concentration regardless of the calcium concentration. By addition of MgEDTA to displace the calcium from its CaEBT complex, this element may be determined at the same wavelength. For 3-25 ppm of magnesium and 5-40 ppm calcium, the standard deviation was about 4%. The apparatus is described.     

Analyses of the temperature and pH effects on the complexation of magnesium and calcium in human blood plasma: an approach using artificial neural networks

The temperature and pH effects on the equilibrium of a blood plasma model have been studied on the basis of artificial neural networks. The proposed blood plasma was modeled considering two important metals, calcium and magnesium, and six ligands, namely, alanate, carbonate, citrate, glycinate, histidinate and succinate. A large data set has been used to simulate different concentrations of magnesium and calcium as a function of temperature and pH and these data were used for training the neural network. The proposed model allowed different types of analyses, such as the effects of pH on calcium and magnesium concentrations, the competition between calcium and magnesium for ligands and the effects of temperature on calcium and magnesium concentrations. The model developed was also used to predict how the variation of calcium concentration can affect magnesium concentrations. A comparison of neural network predictions against experimental data produced errors of about 3%. Moreover, in agreement with experimental measurements (Wang et al. in Arch. Pathol. 126:947–950, 2002; Heining et al. in Scand. J. Clin. Lab. Invest. 43:709–714, 1983), the artificial neural network predicted that calcium and magnesium concentrations decrease when pH increases. Similarly, the magnesium concentrations are less sensitive than calcium concentrations to pH changes. It is also found that both calcium and magnesium concentrations decrease when the temperature increases. Finally, the theoretical model also predicted that an increase of calcium concentrations will lead to an increase of magnesium concentration almost at the same rate. These results suggest that artificial neural networks can be efficiently applied as a complementary tool for studying metal ion complexation, with especial attention to the blood plasma analysis. Figure Artificial neural networks for predicting the behavior of calcium and magnesium as a function of pH and temperature in human blood plasma