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     

Contributions to the basic problems of complexometry-XXVII. Influence of magnesium on masking of calcium with fluoride in the determination of manganese

Determination of manganese in the presence of calcium and magnesium after their masking with ammonium fluoride was reinvestigated. Normally such a determination gives low results caused by co-precipitation of manganese with calcium fluoride. It has been found that the co-precipitation is highest when magnesium is absent in the solution. With increasing concentration of magnesium ions co-precipitation of manganese decreases and at the ratio ca:Mg = 0.5-1 is entirely eliminated. An explanation of this phenomenon is discussed.     

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.     

The use of Omega Chrome Fast Blue 2G in the microdetermination of some metals

Summary Omega Chrome Fast Blue 2G has been found to be a suitable indicator for the detection of the equivalence point of calcium, magnesium and manganese in the presence of cadmium, nickel, and aluminium, when they are masked by the addition of cyanide or triethanolamine. It is also a suitable indicator for the back titration of aluminium using calcium or magnesium as a back titrant.This dye has also been found to be a suitable reagent for the colorimetric determination of calcium, magnesium, manganese and thorium.     

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。     

FT-Raman spectroscopy of lichens on dolomitic rocks: an assessment of metal oxalate formation

The FT-Raman spectra of five epilithic lichen taxa growing on dolomite and magnesium-rich carbonate rocks have been analysed and interpreted for the key molecular marker bands associated with calcium oxalate monohydrate (whewellite), calcium oxalate dihydrate (weddelite) and magnesium oxalate dihydrate. From the results, it can be concluded that the biomineral product of lichen biodeterioration involves the calcareous part of the substratum only; no trace of magnesium oxalate has been found in the Raman spectra. Two of the species, Lecanora sulfurea and Aspicilia calcarea, produce calcium oxalate monohydrate exclusively, but Dirina massiliensis f. sorediata, D. massiliensis f. massiliensis and Tephromela atra produce significant quantities of the dihydrate. An explanation is advanced for the exclusive accumulation of calcium oxalate into the lichen thallus despite the significant presence of magnesium ions.     

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.     

Atomic-absorption spectrometric determination of calcium, magnesium and potassium in leaf samples after decomposition with molten sodium hydroxide

The decomposition of standard leaf samples of varied origin and nature by fusion with sodium hydroxide in an open system has been studied. The use of sodium nitrate as an auxiliary agent facilitated the mineralization of most of the samples. The solutions obtained were analysed for calcium, magnesium and potassium by flame atomic-absorption spectrometry. The method is fast and quite precise, with absolute standard deviations of 0.04-0.13, 0.002-0.03 and 0.04-0.12% for calcium, magnesium and potassium contents of O.8-5.0, 0.13-0.48 and 0.36-2.2% respectively. The limits of detection (mug/ml) in the determination step were 0.10 for calcium, 0.011 for magnesium, and 0.09 for potassium.     

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.     

An ab initio mo study of calcium and magnesium complexes with malonate and formate

Quantum mechanical SCF calculations were performed on magnesium and calcium complexes of malonate and malonate/formate coordination. The calcium malonate structure is in substantial agreement with recent X-ray results on -ethylmalonate. The magnesium complexes are generally more tightly bound than calcium, although qualitatively, the calcium and magnesium structures are similar. Experimental binding results for divalent ions with malonates and EDTA are discussed in view of the current calculations.     

Masking of manganese in relation to stepwise complexometric determination of calcium, magnesium and manganese

A critical study has been made of the masking of manganese with potassium cyanide in alkaline medium for complexometric titration of calcium and magnesium. It has been found that there is incomplete oxidation to manganese(III) unless the solution is aged for a sufficient period or air is bubbled through the solution at 35 ± 5° for 10 min. The manganese(III) complex can be reduced with ascorbic acid for titration with EDTA. Procedures are given for stepwise titration of magnesium, manganese and calcium in silicate materials. Mixed indicators are used, to improve the end-points.     

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、...     

Differential kinetic analysis and flow injection analysis: Part 2. The (2.2.1) Cryptates of Magnesium and Calcium

Simultaneous differential kinetic analysis for magnesium and calcium ions in solution has been adapted to the flow injection system. The two-point kinetic assay is based on dissociation of the cryptand (2.2.1) complexes of magnesium and calcium ions with sodium ion as scavenger. The ions could be determined reproducibly with phthalein complexone as indicator, at a sampling rate of 80 samples per h with 200-μl sample injections and low reagent consumption. Rules derived from f.i.a. theory were confirmed experimentally.     

聚氧化乙烯絮凝-电感耦合等离子体发射光谱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-4000r/min离心,电感耦合等离子体发射光谱法（ICP-AES）测定土壤水溶性钠钾钙镁硫酸根离子的方法。本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发射光谱法一次性测定钾、钠、钙、镁、硫酸根,相较传统方法简便快速,结果准确可靠。本法各离子检出限为0.37-2.91g/g,相对标准偏差小于5.55%,完全满足检测要求。该法操作简便,快速,实用性强,对环境无二次污染,已成功应用于土壤水溶性钾、钠、钙、镁、硫酸根离子的测试分析中,适合土壤批量样品分析。     

A sequential injection system for the spectrophotometric determination of calcium, magnesium and alkalinity in water samples.

A sequential injection methodology for the spectrophotometric determination of calcium, magnesium and alkalinity in water samples is proposed. A single manifold is used for the determination of the three analytes, and the same protocol sequence allows the sequential determination of calcium and magnesium (the sum corresponds to the water hardness). The determination of both metals is based on their reaction with cresolphtalein complexone; mutual interference is minimized by using 8-hydroxyquinoline for the determination of calcium and ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) for the determination of magnesium. Alkalinity determination is based on a reaction with acetic acid, and corresponding color change of Bromcresol Green. Working ranges of 0.5 - 5 mg dm(-3) for Ca, 0.5 - 10 mg dm(-3) for Mg, and 10 - 100 mg HCO3- dm(-3), for alkalinity have been achieved. The results for water samples were comparable to those of the reference methods and to a certified reference water sample. RSDs lower than 5% were obtained, a low reagent consumption and a reduced volume of effluent have been accomplished. The determination rate for calcium and magnesium is 80 h(-1), corresponding to 40 h(-1) per element, while 65 determinations of alkalinity per hour could be carried out.     

Rapid microchemical method for the determination of magnesium in biological fluids

A photometric method for the determination of magnesium in the presence of up to 50-fold excess of calcium is described. A magnesium-Azovan Blue lake is formed, stabilized with polyvinyl alcohol, and the absorbance is measured (Kodak No. 7 filter). The method has been used to determine magnesium in sera.     

Metal-binding properties of human centrin-2 determined by micro-electrospray ionization mass spectrometry and UV spectroscopy

We analyzed the metal-binding properties of human centrin-2 (HsCen-2) and followed the changes in HsCen-2 structure upon metal-binding using micro-electrospray ionization mass spectrometry (muESI-MS). Apo-HsCen-2 is mostly monomeric. The ESI spectra of HsCen-2 show two charge-state distributions, representing two conformations of the protein. HsCen-2 binds four moles calcium/mol protein: one mol of calcium with high affinity, one additional mol of calcium with lower affinity, and two moles of calcium at low affinity sites. HsCen-2 binds four moles of magnesium/mol protein. The conformation giving the lower charge-state HsCen-2 by ESI, binds calcium and magnesium more readily than does the higher charge-state HsCen-2. Both conformations of HsCen-2 bind calcium more readily than magnesium. Calcium was more effective in displacing magnesium bound to HsCen-2 than vice versa. Binding of a peptide from a known binding partner, the xeroderma pigmentosum complementation group protein C (XPC), to apo-HsCen-2, occurs in the presence or the absence of calcium. Near and far-UV CD spectra of HsCen-2 show little difference with addition of calcium or magnesium. Minor changes in secondary structure are noted. Melting curves derived from temperature dependence of molar ellipticity at 222 nm for HsCen-2 show that calcium increases protein stability whereas magnesium does not. Delta 25 HsCen-2 behaves similarly to HsCen-2. We conclude that HsCen-2 binds calcium and magnesium and that calcium modulates HsCen-2 structure and function by increasing its stability without undergoing significant changes in secondary or tertiary structure.     

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。     

改性硝酸铵爆轰安全性研究 Ⅰ.CaCO3和MgSO4对硝酸铵爆轰安全性的影响

将碳酸钙和硫酸镁改性的硝酸铵按照工业炸药配方配制成铵油(ANFO)炸药，以8号雷管起爆，对硝酸铵的爆轰安全性进行了评价。采用恒温热分解和示差扫描量热法，研究了改性硝酸铵及铵油炸药的热分解行为。测定了改性硝酸铵的比表面积以解释爆轰结果。得出如下结论：硝酸铵含40％的碳酸钙，或25％碳酸钙和5％硫酸镁的混合物，所配制的铵油炸药不能被8号雷管起爆。碳酸钙同硝酸铵发生复分解反应放出NH3、H2O和CO2气体，反应程度与碳酸钙的含量、温度和时间成正比。虽然硝酸铵中加入碳酸钙后提高了ANFO炸药的热稳定性，但由于上述气体的逸出增加了改性硝酸铵的比表面积。因此，在硝酸铵中加入少量的碳酸钙不能达到爆轰安全性的要求。硫酸镁与硝酸铵形成复盐，可减缓硝酸铵和碳酸钙之间复分解反应的速度．有利于降低硝酸铵的起爆感度。