Successive high-precision determination of calcium and magnesium in sea water with a new probe photometer

A high-precision method for determining calcium and magnesium successively in sea water is described. The calcium end-point is evaluated with zinc—zincon as indicator, while magnesium is determined with calcon. The computerized method utilizes a new probe photometer based on modern optoelectronic components. The precision for calcium and magnesium is 0.3 ‰ and 0.4 ‰, respectively.     

Investigation of the Scope of Heterogeneous and Homogeneous Procedures for Preparing Magnesium Chelates of Porphyrins, Hydroporphyrins, and Phthalocyanines

A simple method has been developed for metalation of porphyrinic compounds under homogeneous conditions at room temperature using a stable ethereal solution of MgI(2) and N,N-diisopropylethylamine. A previously developed heterogeneous procedure employs a mixture of a magnesium halide and a nonnucleophilic amine in a noncoordinating solvent at room temperature. The scope of the heterogeneous and homogeneous magnesium insertion procedures has been investigated across a family of 19 porphyrinic compounds, including synthetic porphyrins, synthetic or naturally occurring chlorins, and organic-soluble phthalocyanines. The rate of magnesium insertion increased in the series phthalocyanines < chlorins < porphyrins, which parallels the basicity of the ligands. Though phthalocyanines have the smallest core size, the magnesium phthalocyanines were far more stable than magnesium porphyrins to acid-induced demetalation. The heterogeneous method is broadly applicable to porphyrins, chlorins, and phthalocyanines. The homogeneous method is generally slower than the heterogeneous method, though both afford rapid metalation of most porphyrins, including electron-deficient, peripherally coordinating, or facially encumbered meso-substituted tetraarylporphyrins, and the beta-substituted octaethylporphyrin. Chlorin e(6) trimethyl ester and methyl pyropheophorbide a were metalated cleanly under homogeneous but not heterogeneous conditions, while pheophytin a failed with both methods. The homogeneous method failed altogether with phthalocyanines. Several methods in magnesium chemistry have been developed that augment these procedures, including a mild synthesis of tetraphenylchlorin and a streamlined separation of porphyrin, chlorin, and bacteriochlorins based on selective formation of the magnesium chelates. Collectively, these methods should broaden the scope of model systems based on magnesium chelates of porphyrinic compounds.     

Preconcentration and Quantitative Determination of Esomeprazole Magnesium Present in Water

A simple, accurate, and sensitive preconcentration method for determination of esomeprazole magnesium in treated sewage water was developed based on HPLC. A preconcentration method was developed for aqueous solution containing pure drug using solid phase extraction. Macroporous beads of polystyrene divinyl benzene (PSDVB) polymer were used for preconcentration followed by chromatographic determination. Experimental parameters were optimized. This optimized method can detect esomeprazole magnesium concentration up to 0.003 mg L^?1 after preconcentration. This method was used for determination of esomeprazole magnesium in water collected from a sewage treatment facility. Esomeprazole magnesium could not be detected in the treated sewage water sample collected for the study.     

Bench‐Stable Stock Solutions of Silicon Grignard Reagents: Application to Iron‐ and Cobalt‐Catalyzed Radical C(sp3)–Si Cross‐Coupling Reactions

A robust method for the preparation of silicon‐based magnesium reagents is reported. The MgBr₂ used in the lithium‐to‐magnesium transmetalation step is generated in situ from 1,2‐dibromoethane and elemental magnesium in hot THF. No precipitation of MgBr₂ occurs in the heat, and transmetalation at elevated temperature leads to homogeneous stock solutions of the silicon Grignard reagents that are stable and storable in the fridge. This method avoids the preparation of silicon pronucleophiles such as Si?Si and Si?B reagents. The new Grignard reagents were applied to unprecedented iron‐ and cobalt‐catalyzed cross‐coupling reactions of unactivated alkyl bromides. The functional‐group tolerance of these magnesium reagents is excellent.     

Speciation of magnesium in rat plasma using capillary electrophoresis-inductively coupled plasma-atomic emission spectrometry

A new method for speciation analysis of magnesium species and quantification of free magnesium concentrations in rat plasma was developed by on-line coupling of CE with inductively coupled plasma-atomic emission spectrometry (ICP-AES). Baseline separation of seven magnesium species was achieved by using a 120 cm (100 microm internal diameter) fused-silica capillary, a 20 kV separation voltage and a solution of 50 mmol/L NaAc-HAc (pH 5.5) as electrolyte buffer. CE-ICP-AES analysis of a rat plasma sample showed the presence of seven magnesium species, one of which was identified as free Mg2+ ion by spiking a Mg2+ standard; the migration time of the Mg2+ peak in the standard and the spiked sample matched with each other. One protein-bound magnesium species in rat plasma is associated with albumin, and the other three species are combined with globulin. The concentration of free magnesium in the plasma was 14.0 mg/L. The other six magnesium species were estimated to be 4-15 mg/L. RSDs of migration time and peak area for the magnesium species from ten replicates were less than 5%. The developed method was also applied to speciation analysis of magnesium species in spiked plasma samples. The recoveries of the free magnesium species in four samples ranged from 95.8 to 103.8%.     

Fluorimetric sequential injection determination of magnesium using 8-hydroxiquinoline-5-sulfonic acid in a micellar medium

A fluorimetric sequential injection method for the determination of magnesium is proposed. The system is based on the complex formation between Mg(II) and 8-hydroxyquinoline-5-sulfonic acid (HQS). The reaction was carried out in the presence of ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) as a masking agent. Cetyltrimethylammonium chloride (HTAC) was employed as a fluorescence enhancer. The influence of several variables, such as reagent concentration, volumes and pH has been investigated. The reagent was prepared in a 0.1 M Tris-HCl buffer solution (pH 9). A detection limit of 12 mug l(-1) magnesium was obtained. The proposed method was applied to the determination of magnesium in natural waters.     

Determination of Magnesium in Biological Samples. A Statistical Study on Infant Muscle

Abstract

A simple and rapid method using atomic absorption spectrophotometry for measuring magnesium in micro muscle samples is presented.

The criteria of normality for age of muscle magnesium content were established by means of the statistical analysis of the results obtained in 33 infants aged 2 weeks to 18 months.

The importance of muscle analysis in the diagnosis of magnesium depletion is discussed.     

聚氧化乙烯絮凝-电感耦合等离子体原子发射光谱(ICP-AES)法测定土壤中水溶性钾、钠、钙、镁、硫酸根

建立了聚氧化乙烯絮凝-4000 r/min离心,电感耦合等离子体原子发射光谱(ICP-AES)法测定土壤水溶性钠、钾、钙、镁、硫酸根离子的方法.在常规方法浸提的基础上,加入聚氧化乙烯絮凝剂使溶液中的胶体形成絮凝物聚沉,制得澄清溶液,消除了胶体对钾、钠、钙、镁吸附的干扰;采用电感耦合等离子体原子发射光谱法测定钾、钠、钙、...     

PROTON, Mg2+ AND PROTEIN AS COMPETING LIGANDS FOR THE FLUORESCENT PROBE, MAG-INDO-1: A FIRST STEP TO THE QUANTIFICATION OF INTRACELLULAR Mg2+ CONCENTRATION

Abstract Increasing evidence of the role of magnesium in various cellular mechanisms has led to the need to develop an accurate method for the evaluation of magnesium concentration in cells. 1H-indole-6-carboxylic acid, 2–(4- bis- [carboxymethyl]amino-3–[carboxy]ethoxy) (mag-indo-1) is used as a fluorescent indicator for ionized magnesium concentration. A physicochemical study of this probe has pointed out (1) that at concentrations higher than 10 μ M , the presence of dimers can alter the different equilibria and (2) at concentrations, avoiding the dimer (≤ 10 μ M ), three fluorescent forms are in equilibrium with the deprotonated form of mag-indo-1 (L), which are the protonated form LH, the magnesium-bound form LM and the protein-bound form LP. A model is proposed that takes into account the equilibria between the four species. In a solution containing magnesium and protein, a complex fluorescence spectrum can be resolved by a combination of the three fluorescence spectra (L, LM, LP). However, under these conditions, the LH fluorescence spectrum is not taken into account for the spectral resolution. Finally, from the contribution of characteristic fluorescence spectra in the experimental fluorescence spectrum, the magnesium concentration can be estimated with accuracy. Such a method should be further applied to magnesium determination in different cell lines.     

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.     

Kinetic-fluorimetric determination of magnesium in micellar medium

A simple method for the kinetic determination of magnesium(II) is described. The method is based on the reaction of 2-fluorenaldehyde 2-pyridylhydrazone with magnesium ion to originate a strong green fluorescence that decreases with time. The reaction is monitored at 520 nm, when excited at 375 nm, and the initial rate method is applied to perform the analytical procedure. Magnesium contents between 0.36 and 1.22 μm ml^?1 can be determined. The method is free from interferences of alkaline earth ions.     

Determination of magnesium at trace levels by isotope dilution

A mass spectrometric method for the isotopic analysis of magnesium and its determination at low concentrations in the presence of an excess of other elements is described. The lowest level at which magnesium was determined was 1 ppm with a precision and error +/- 1%.     

Rapid determination of magnesium in the presence of calcium and phosphate by titration with cdta

A method is presented for the accurate determination of magnesium in phosphate rock and phosphoric acid down to 0.03% magnesium oxide in the presence of 0–70% phosphorus pentoxide by titration with cyclohexanediaminetetraacetic acid (CDTA). Interference from heavy metals for which inaccurate empirical corrections have previously been made in the combined magnesium and calcium titration are linearly and unequivocally determined and subtracted from the combined titration. Magnesium oxide is determined in less than 20 min after sample digestion for Ca: Mg ratios from 1:9 to 850:1.     

Spectrophotometric and First Derivative Spectrophotometric Determination of Magnesium with 1-Hydroxy-2-Carboxyanthraquinone

Abstract

1-Hydroxy-2-carboxyanthraquinone reacts with magnesium in ethanol-water mixtures to form a red complex having an absorption maximum at 490 nm in alkaline medium. A detailed study of the characteristics of this complex has been carried out and a spectrophotometric method for the determination of magnesium at the 0.4–4.0 μg ml^?1 level is proposed. The method has been sensitized by employing first derivative spectrophotometry. By the use of the derivative approach magnesium can be determined between 0.08–0.40 μg ml^?1. Statistical analysis of the results is also described.     

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.     

A comparative study of methods for precipitating calcium oxalate from homogeneous solution

A PFHS of calcium oxalate has been examined and the optimum conditions for the precipitation established. This method, and two other methods employing PFHS for the gravimetric determination of calcium as the oxalate are compared with the conventional and acetic acid-medium methods. All the methods work well in the absence of magnesium, but the urea hydrolysis procedure, in the absence of an initial precipitate, is recommended as the best method when magnesium is present. Crystal sizes have been measured by microscopy.     

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.     

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.     

Diphenyl carbazone as an internal indicator in volumetric analysis

Summary A method for the volumetric determination of calcium using diphenyl carbazone as indicator has been described. Calcium is precipitated by excess sodium oxalate, the excess oxalate being determined by standard lead nitrate. A study of the possible interferences of barium and magnesium in the above determination is undertaken and it is shown that the above procedure is applicable to the determination of calcium in the presence of magnesium and barium.Sincere thanks of the authors are due to Professor G. B. Singh for providing the necessary facilities during the course of the above investigation.     

Determination of protein-free and protein-bound calcium and magnesium in biological samples by use of ultrafiltration and ion chromatography

Protein-free and protein-bound calcium and magnesium are determined selectively in biological samples by use of ultrafiltration followed by ion chromatography. A commercial ultrafiltration kit is used to remove proteins of molecular weight > 10 000. The content of protein-bound cation is calculated by subtracting the value of protein-free from that of total cation. A protein-free cation filtrate is prepared by ultrafiltration of a diluted sample; a total cation filtrate is prepared by adding EDTA to the sample and filtering. Calcium and magnesium are determined in each filtrate by single-column ion chromatography with 1 mM EDTA (pH 6.5) as eluent and a conductivity detector. The use of a u.v. detector, in series with the conductivity detector, is useful for monitoring small molecules in the filtrates. The proposed method has been successfully applied to the determination of calcium and magnesium in blood serum, milk and egg white.