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1.
Gholam Hossein Rounaghi Razyeh Sanavi Khoshnood Mohammad Hossein Arbab Zavvar 《Journal of inclusion phenomena and macrocyclic chemistry》2006,54(3-4):247-252
The complexation reactions between Mg2+, Ca2+, Ag+ and Cd2+ metal cations with N-phenylaza-15-crown-5 (Ph-N15C5) were studied in acetonitrile (AN)–methanol (MeOH), methanol (MeOH)–water (H2O) and propanol (PrOH)–water (H2O) binary mixtures at different temperatures using the conductometric method. The conductance data show that the stochiometry of all of the complexes with Mg2+, Ca2+, Ag+ and Cd2+ cations is 1:1 (L:M). The stability of the complexes is sensitive to the solvent composition and a non-linear behaviour was observed for variation of log K
f of the complexes versus the composition of the binary mixed solvents. The selectivity order of Ph-N15C5 for the metal cations in neat MeOH is Ag+>Cd2+>Ca2+>Mg2+, but in the case of neat AN is Ca2+>Cd2+>Mg2+>Ag+. The values of thermodynamic parameters (ΔH
c
o
, ΔS
c
o
) for formation of Ph-N15C5–Mg2+, Ph-N15C5–Ca2+, Ph-N15C5–Ag+ and Ph-N15C5–Cd2+ complexes were obtained from temperature dependence of stability constants and the results show that the thermodynamics of complexation reactions is affected by the nature and composition of the mixed solvents. 相似文献
2.
The isoelectric point (IEP) of rutile is shifted to higher pH values in the presence of greater than 10−4 mol dm−3 Ba2+, Ca2+ and Mg2+, and when a critical concentration (5 × 10−4 mol dm−3 for Ba2+ and 1 × 10−3 mol dm−3 for Ca2+) is exceeded there is no IEP at all and the ζ potential is always positive. A common intersection point for the ζ-potential
curves of the different concentrations of salt is found, but for the various salts the point is shifted from ζ = 0 mV for
Mg2+ up to ζ = 20 mV for Ba2+. Between the IEP and the charge-reversal point a rheologically unstable region is discovered. The shear stress of rutile
dispersions (2.5 g rutile + 4 g electrolyte solution) at shear rates of 116 s−1 shows the same pH dependence irrespective of the concentration of alkaline-earth metal cations up to 10−2 mol dm−3. The shear stress is less than 1 Pa below pH 3.8 and in the pH range 5–12 it assumes a value between 50 and 80 Pa at 116 s−1 with some scatter; however, no systematic trend with concentration of alkaline-earth metal cations and a rather insignificant
decrease with pH at pristine conditions are observed. The acidic branch of the yield stress (pH) and low shear rate viscosity
(pH) curves is insensitive to the presence of alkaline-earth metal cations, and the same behaviour is found for the ζ potential.
The alkaline-earth metal cations induce an increase in viscosity in the basic region and a shift in the pH of maximum viscosity
to high pH values. It was also discovered that the effect different alkaline-earth metal cations have on the rheological properties
at the same concentration is different from the effect induced by indifferent electrolytes. When the ζ potential increases
the viscosity at high pH is increased in a series which follows the increase in size of the cation.
Received: 9 September 1998 Accepted in revised form: 12 January 1999 相似文献
3.
Mohammad Ansarifard Gholamhossein Rounaghi 《Journal of inclusion phenomena and macrocyclic chemistry》2005,52(1-2):39-44
The complexation reactions between Mg2+, Ca2+, Sr2+ and Ba2+ cations with the macrocyclic ligand, 18-Crown-6 (l8C6) in water–methanol (MeOH) binary systems as well as the complexation reactions between Ca2+ and Sr2+ cations with 18C6 in water–ethanol (EtOH) binary mixtures have been studied at different temperatures using conductometric method. The conductance data show that the stoichiometry of all the complexes is 1:1. It was found that the stability of 18C6 complexes with Mg2+, Ca2+, Sr2+ and Ba2+ cations is sensitive to solvent composition and in all cases, a non-linear behaviour was observed for the variation of log K
f of the complexes versus the composition of the mixed solvents. In some cases, the stability order is changed with changing the composition of the mixed solvents. The selectivity order of 18C6 for the metal cations in pure methanol is: Ba2+ > Sr2+ > Ca2+ > Mg2+. The values of thermodynamic parameters (Δ H
c
° and Δ S
c
°) for formation of 18C6–Mg2+, 18C6–Ca2+, 18C6–Sr2+ and 18C6–Ba2+complexes were obtained from temperature dependence of the stability constants. The obtained results show that the values of (Δ H
c
° and Δ S
c
°) for formation of these complexes are quite sensitive to the nature and composition of the mixed solvent, but they do not vary monotonically with the solvent composition.This revised version was published online in July 2005 with a corrected issue number. 相似文献
4.
Shangfen Gao Guangqun Tan Hongyan Yuan Dan Xiao Martin M. F. Choi 《Mikrochimica acta》2006,153(3-4):159-162
A simple and green analytical procedure based on chlorophyll a is presented for the determination of Hg2+ ion. Chlorophyll a was extracted and purified from the leaves of pea and is employed as a reagent for analysis of Hg2+ ion. It displays remarkable fluorescence emission at 674 nm when excited at 412 nm. The emission intensity decreased significantly
on exposure to various concentrations of Hg2+ ion. This forms the basis for the determination of Hg2+ ion. The proposed method was evaluated for sensitivity and selectivity. The linear concentration range was found to be 2.0–10 μM
with r2 = 0.997 and the limit of detection for Hg2+ ion was 1.3 μM. Ions including Pb2+, Cd2+, Ag+, Zn2+, Co2+, Ni2+, Cu2+, Mg2+, Mn2+, Ru3+, Er3+, K+, Na+, NH4+, Cl−, NO3−, CH3COO− and SO42− did not interfere with the measurement of Hg2+ ion even at 500-fold excess. Since chlorophyll a is widely available in the leaves of most plants, and the extraction and purification process is simple, this technique can
provide an alternative, sensitive and economical way to determine Hg2+ ion. 相似文献
5.
A multiscale theoretical investigation has been performed to study the hydrogen and acetylene storage in Ca2+- and Mg2+-doped COFs (COF-105 and COF-108). The first-principles calculations show that the Ca2+ and Mg2+ can be immobilized at the COFs surfaces, and the doped Ca and Mg cations can adsorb five H2 molecules and three C2H2 molecules with ideal binding energies. The Grand Canonical Monte Carlo (GCMC) simulations were carried out to obtain the hydrogen and acetylene uptakes of Ca2+- and Mg2+-doped COFs at room temperature in the different pressure ranges. Our results demonstrate that, at T = 298 K and p = 100 bar, the total gravimetric uptakes of H2 in Ca2+-doped COF-105 and COF-108 reach 6.78 and 6.54 wt%, respectively, and a higher uptakes of 7.14 and 7.27 wt% have been reached for Mg2+-doped COF-105 and COF-108, respectively. At T = 298 K and p = 1 bar, the acetylene uptakes of Ca2+-doped COF-105, Ca2+-doped COF-108, Mg2+-doped COF-105, and Mg2+-doped COF-108 are 406.42, 366.24, 308.07, and 319.88 cm3/g (corresponding to the excess uptakes of 358.37, 316.38, 236.7109, and 245.42 cm3/g), respectively. The Ca2+-doped COF-105 displays a highest acetylene storage capacity among all materials reported. The Ca2+- and Mg2+-doped COFs can be very practical hydrogen or acetylene storage medium in the future. 相似文献
6.
L. S. Nikolaeva A. N. Semenov L. I. Burova 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2010,84(12):2039-2046
Chemical equilibria in the high-molecular-weight heparin (Na4hep)-arginine (HArg)-H2O-NaCl and MCl2-Na4hep-HArg-H2O-NaCl systems of electrolytes (M = Ca2+, Mg2+) were calculated by the method of mathematical simulation of chemical equilibria from representative planned pH-metric titration
experiment at 2.30 ≤ pH ≤ 10.50 in a physiological solution medium in the presence of 0.154 M NaCl as a background electrolyte
at 37°C. The initial concentrations of the basic components were n × 10−3 M (n ≤ 4). 相似文献
7.
Tadasuke Tsuji Shinya Kitagawa Hajime Ohtani 《Analytical and bioanalytical chemistry》2009,394(3):835-843
Voltage-induced impedance variation of the minicolumn (i.d. 0.53 mm, length 2 mm) packed with cation exchanger was investigated
to develop a sensing method. An aqueous sample solution containing the metal cations was continuously supplied to the minicolumn
during the impedance measurement with the simultaneous application of both alternating current voltage (amplitude, 1.0 V;
frequency, 200 kHz to 6 Hz) and direct current (DC) offset voltage (0.1 to 1.0 V). On a complex plane plot, the profile of
the column impedance consisted of a semicircle (200 kHz to 100 Hz) and a straight line (<100 Hz), of which slope varied with the magnitude of the applied DC offset voltage (V
DC). The slope–V
DC relation depended on the kind of the metal cation and its concentration; in particular, the slope–V
DC relations of monovalent cations (Na+ and K+) and divalent ones (Mg2+ and Ca2+) were significantly different. With the change in the concentration of minor divalent salt of MgCl2 or CaCl2 (60 to 140 μM) in the sample solution containing 10 mM NaCl, the slopes showed almost linear relationships between those
with application of V
DC = 0.1 V and 1.0 V both for magnesium and calcium additions. In the case of plural addition of both MgCl2 and CaCl2 to the solution, the data points in the slope0.1
V–slope1.0
V plot were located between the two proportional lines for single additions of magnesium and calcium, reflecting both the mixing
ratio and net concentrations of the divalent cations. Thus, simulations determination of Mg2+ and Ca2+ can be attained on the basis of the slope0.1
V–slope1.0
V relation obtained by the impedance measurements of the minicolumn. Actually, the contents of both magnesium and calcium cations
in the bottled mineral waters determined simultaneously using the proposed method were almost equivalent to those obtained
by the atomic absorption spectrometric measurement. 相似文献
8.
Recep Akkaya 《Journal of Radioanalytical and Nuclear Chemistry》2012,292(2):771-775
In this research, a new composite, poly (hydroxyethylmethacrylate-hydroxyapatite) [P(HEMA-Hap)], was synthesized and its adsorptive
features for natural radionuclides (TI+, Ra2+, Bi3+and Ac3+ in a leaching solution) were investigated at differing initial pH, concentration and temperature ranges. The natural radionuclides
were counted by gamma spectrometer using a type NAI (Tl) detector. The adsorption data obtained were well represented by Langmuir
and Freundlich type isotherms. The magnitude of determined monolayer adsorption capacities (X
L) for the adsorbed radionuclides were TI+ = Ac3+ > Ra2+ = Bi3+. These results demonstrated that P(HEMA-Hap) had high affinity to the natural radionuclide. The thermodynamic parameters
indicated that the adsorption mechanisms were spontaneous (ΔG < 0) in terms of adsorption free enthalpy, and changes in the enthalpy and entropy values showed that the overall adsorption
process was endothermic (ΔH > 0), thus increasing entropy (ΔS > 0). 相似文献
9.
Yves Claude Guillaume Lydie Lethier Claire André 《Biomedical chromatography : BMC》2015,29(9):1338-1342
In a previous paper Guillaume's group demonstrated that magnesium (Mg2+ concentration range 0.00–2.60 mm ) increased the passive diffusion of statins and thus played a role in their potential toxicity. In order to confirm an increase in this passive diffusion by divalent salt cations, the role of calcium chloride (CaCl2) on the statin–immobilized artificial membrane (IAM) association was studied. It was demonstrated that calcium supplementation (Ca2+ concentration range 0.00–3.25 mm ) increases the statin passive diffusion. In addition, it was shown that the Ca2+ effect on the statin–IAM association is higher than that of Mg2+. These results show that Ca2+ enhances the passive diffusion of drugs into biological membranes and thus their potential toxicity. Also, addition of H2O2 to the medium showed a hyperbolic response for the statin passive diffusion and this effect was enhanced for the highest Ca2+ or Mg2+ concentrations in the medium. H2O2 is likely to interact with the polar head groups of the IAM through dipole–dipole interactions. The conformational changes in H2O2–IAM result in a higher degree of exposure of hydrophobic areas, thus explaining why the binding of pravastatin, which showed the lowest logP value, was less affected by H2O2. This result shows the significant contribution of H2O2 and thus the oxidative stress on the statin passive diffusion. Much of the sensitivity derives from the action of Ca2+ or Mg2+, in turn supported the idea that H2O2 may serve a Ca2+ or Mg2+ sensing function in statin passive diffusion Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
10.
Qi Wu Chen Li Chenglei Li Hui Chen Liu Shuliang 《Applied biochemistry and biotechnology》2010,160(1):129-139
The collagenase, produced extracellular by Bacillus pumilus Col-J, was purified by ammonium sulfate precipitation followed by two gel filtrations, involving Sephadex G-100 column and
Sepharose Fast Flow column. Purified collagenase has a 31.53-fold increase in specific activity of 87.33 U/mg and 7.00% recovery.
The collagenase has a relative molecular weight of 58.64 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis.
The optimal temperature for the enzyme reaction was 45 °C. More than 50% of the original activity still remained after 5 min
of incubation at 70 °C or 10 min at 60 °C. The maximal enzyme activity of collagenase was obtained at pH 7.5, and it was stable
over a pH range of 6.5–8.0. The collagenase activity was strongly inhibited by Mn2+, Pb2+, ethylenediamine tetraacetic acid, ethylene glycol tetraacetic acid, and β-mercaptoethanol. However, Ca2+ and Mg2+ greatly increased its activity. The collagenase from B. pumilus Col-J showed highly specific activity towards the native collagen from calf skin. The K
m and V
max of the enzyme for collagen were 0.79 mg/mL and 129.5 U, respectively. 相似文献
11.
The two new compounds Mn(dien)2[MoS4] (1) and Mn(dien)2[Mo2O2S6] (2) (dien = diethylenetriamine) were prepared under solvothermal conditions. Both compounds were obtained as phase-pure products. The structures consist of new [Mn(dien)2]2+ cations and isolated tetrahedral [MoS4]2− (1) or [Mo2O2S6]2− (2) anions. Between the anions and the cations, hydrogen bonding is observed. Compound 1 crystallizes in the tetragonal space group I (a = 10.219(2), c = 9.259(2) ?, Z = 2), whereas 2 crystallizes in the monoclinic space group P21/c (a = 8.703(2), b = 18.390(4), c = 14.603(3) ?, β = 103.18(3)°, Z = 4). The thermal behaviour of the thiomolybdates was investigated using difference thermoanalysis (DTA) and thermogravimetry (TG). Both compounds decompose under argon with a single endothermic signal in the DTA curve (peak maximum: 252 (1) and 242°C (2)). 相似文献
12.
Peter Klampfer Primož Benkič Maja Ponikvar Ana Rahten Antonija Lesar Adolf Jesih 《Monatshefte für Chemie / Chemical Monthly》2003,134(1):1-9
Summary. Hydrazinium(+2) fluoroarsenate(III) fluoride was prepared by the reaction of hydrazinium(+2) fluoride and liquid arsenic
trifluoride. N2H6AsF4F is stable at 273 K, but decomposes slowly at room temperature. N2H6AsF4F crystallizes in the orthorhombic space group Pnn2 with a = 774.0(2) pm, b = 1629.2(4) pm and c = 436.6(1) pm; V = 0.5506(3) nm3, Z = 4 and d
c
= 2.461 g cm−3. The structure consists of N2H6
2+ cations, AsF4
− anions, and F− anions and is interconnected by a hydrogen bonding network. Distorted trigonal-bipyramidal AsF4
− units are very weakly interconnected and form chains along the b axis. Bands in the Raman spectrum are assigned to the vibrations of N2H6
+2 cations and AsF4
− anions.
Corresponding author. E-mail: adolf.jesih@ijs.si
Received April 18, 2002; accepted July 15, 2002 相似文献
13.
A consistent set of G
B
, H
B
, and S
B
parameters have been determined from ion specific electrode, calorimetric, and spectrophotometric studies for the binding of Ca2+ and Mg2+ to bovine calmodulin at pH=7.0 and an ionic strength I of 0.113M. A non-linear least squares analysis of calcium specific ion electrode data yields, on a molar basis, four calcium dissociation constants: 10–7 for the first site, 10–5 for the fourth site, and two constants between these values. Both calorimetric experiments and an indicator method provide evidence that Mg2+ binds to calmodulin, probably at the same sites as Ca2+, but with affinities about 100 times smaller: 4×10–5 for the first site and 2×10–3 for the fourth. Calorimetric titrations on Ca2+ binding to calmodulin in three buffers are consistent with 0.46 protons released upon binding at all four sites and yield an average H
B
per site of 5.6 and 7.9 kJ-mol–1 for Ca2+ and Mg2+, respectively. The entropy of the system increases by 524 and 361 J-K–1-mol–1 when Ca2+ and Mg2+, respectively, bind to four sites on calmodulin, i.e., the selectivity of calmodulin for Ca2+ is primarily derived from entropy effects. Further analysis based on elimination of the entropy term for the metal ions demonstrates that calmodulin bound to Ca2+ has a larger entropy than the unbound calmodulin; the opposite is true for calmodulin bound to Mg2+. These analyses are consistent with the hypothesis that Ca2+ forms tight complexes at all sites on calmodulin and that release of waters of hydration upon binding is the source of the increase of entropy in the system. 相似文献
14.
The complex formation reactions between Mg2+, Ca2+, Sr2+ and Ba2+ metal cations with macrocyclic ligand, 4′-nitrobenzo-15C5, were studied in acetonitrile (AN)-methanol (MeOH) binary mixtures
at different temperatures using conductometric method. The results show that 4′-nitrobenzo-15C5 forms 1:1 [ML] complexes with
Mg2+, Ca2+ and Sr2+ metal cations in solutions. But in the case of Ba2+ cation a 1:2 [ML2] complex is formed in these solvent systems. The stability of the complexes is sensitive to the solvent composition and a
non-linear behavior was observed for variation of logK
f of the complexes versus the composition of the binary mixed solvents. The stability constants of complexes decrease suddenly
with increasing the concentration of methanol in this binary system. The values of thermodynamic parameters (ΔH
c° and ΔS
c°) for formation of (4′-nitrobenzo-15C5.Mg)2+, (4′-nitrobenzo-15C5.Ca)2+ and (4′-nitrobenzo-15C5.Sr)2+ complexes were obtained from temperature dependence of the stability constants and the results show that these parameters
are affected by the nature and composition of the mixed solvents. A non-linear behavior is observed between the ΔS
c° and the composition of the mixed solvents. 相似文献
15.
Summary. The two new compounds Mn(dien)2[MoS4] (1) and Mn(dien)2[Mo2O2S6] (2) (dien = diethylenetriamine) were prepared under solvothermal conditions. Both compounds were obtained as phase-pure products. The
structures consist of new [Mn(dien)2]2+ cations and isolated tetrahedral [MoS4]2− (1) or [Mo2O2S6]2− (2) anions. Between the anions and the cations, hydrogen bonding is observed. Compound 1 crystallizes in the tetragonal space group I (a = 10.219(2), c = 9.259(2) ?, Z = 2), whereas 2 crystallizes in the monoclinic space group P21/c (a = 8.703(2), b = 18.390(4), c = 14.603(3) ?, β = 103.18(3)°, Z = 4). The thermal behaviour of the thiomolybdates was investigated using difference thermoanalysis (DTA) and thermogravimetry
(TG). Both compounds decompose under argon with a single endothermic signal in the DTA curve (peak maximum: 252 (1) and 242°C (2)).
Received November 5, 2001. Accepted December 27, 2001 相似文献
16.
From extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium Mg2+(aq) + 1·Sr2+(nb) ⇆ 1·Mg2+(nb) + Sr2+(aq) taking place in the two-phase water–nitrobenzene system (1 = beauvericin; aq = aqueous phase, nb = nitrobenzene phase) was evaluated as log K
ex (Mg2+, 1·Sr2+) = 0.0 ± 0.1. Further, the stability constant of the 1·Mg2+ complex in nitrobenzene saturated with water was calculated for a temperature of 25 °C as log βnb (1·Mg2+) = 9.1 ± 0.2. By using quantum mechanical DFT calculations, the most probable structures of the non-hydrated 1·Mg2+ and hydrated 1·Mg2+·3H2O complex species were predicted. 相似文献
17.
Ana B. Gaspar M. Carmen Mu?oz Nicolás Moliner Vadim Ksenofontov Georgii Levchenko Philipp Gütlich José Antonio Real 《Monatshefte für Chemie / Chemical Monthly》2003,134(2):285-294
Summary. The monomeric compounds [Fe(abpt)2(NCX)2] (X = S (1), Se (2) and abpt = 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole) have been synthesized and characterized. They crystallize in the monoclinic
P21/n space group with a = 11.637(2) ?, b = 9.8021(14) ?, c = 12.9838(12) ?, β = 101.126(14)°, and Z = 2 for 1, and a = 11.601(2) ?, b = 9.6666(14) ?, c = 12.883(2) ?, β = 101.449(10)°, and Z = 2 for 2. The unit cell contains a pair mononuclear [Fe(abpt)2(NCX)2] units related by a center of symmetry. Each iron atom, located at a molecular inversion center, is in a distorted octahedral
environment. Four of the six nitrogen atoms coordinated to the Fe(II) ion belong to the pyridine-N(1) and triazole-N(2) rings
of two abpt ligands. The remaining trans positions are occupied by two nitrogen atoms, N(3), belonging to the two pseudo-halide ligands. The magnetic susceptibility
measurements at ambient pressure have revealed that they are in the high-spin range in the 2 K–300 K temperature range. The
pressure study has revealed that compound 1 remains in high-spin as pressure is increased up to 4.4 kbar, where an incomplete thermal spin crossover appears at around
T
1/2 = 65 K. Quenching experiments at 4.4 kbar have shown that the incomplete character of the conversion is a consequence of
slow kinetics. Relatively sharp spin transition takes place at T
1/2 = 106, 152 and 179 K, as pressure attains 5.6, 8.6 and 10.5 kbar, respectively.
Corresponding author. E-mail: jose.a.real@uv.es
Received June 12, 2002; accepted July 1, 2002 相似文献
18.
Summary. The influence of reaction conditions (temperature, type of catalyst, time) on the base-catalyzed reaction of mono-, di-,
and trialkylphosphates (alkyl = methyl, ethyl, i-propyl, n-butyl) with Ca2+ ions and on the structure and composition of the reaction products was studied. The composition of the calcium phosphates
depends mainly on the reaction temperature. At temperatures below 100°C, a nanocrystalline solid product transforming into
dicalcium phosphate by heating (calcination) was found. Pure nanocrystalline hydroxyapatite was prepared by hydrothermal synthesis
at 160°C from mono- and dialkylphosphates. The size of hydroxyapatite crystallites was about 1 nm, the particle size about
150 nm. Agglomerated particles of hydroxyapatite larger than 2 μm were prepared at 200°C. Hydrothermal reaction of trialkylphosphates
with Ca2+ ions at 200°C produced CaHPO4. The experimental results were used to propose a reaction mechanism for base-catalyzed hydrothermal reactions of alkylphosphates
with Ca2+ ions.
Received October 4, 2001. Accepted (revised) November 19, 2001 相似文献
19.
The specificity of the exchange between divalent (Di2+ = Ca2+ or Ba2+) and monovalent (M+ = Li+, Na+ or K+) ions onto a polyacrylic chain is examined using conductometric and microcalorimetric techniques. Assuming the formation
of a bidentate complex between the Di2+ and the carboxylate groups, the conductometric data give the exchange ratio (Di2+/M+) and the speciation of the acrylic groups. No significant difference is observed between the three alkali-metal ions for
a given Di2+ ion. Comparisons between Ca2+ and Ba2+ show a stronger hydrophobicity of the former as it precipitates at a complexation ratio r = 0.33 versus r = 0.45 for the Ba2+ salt. Microcalorimetric data show that all Di2+/M+ exchange energies are positive and depend significantly on the type of cations. The largest displacement energy (the more
positive) is found for the binding of Ca2+ with sodium polyacrylate (8.13 kJ · mol−1) and the smallest for Ba2+ with lithium polyacrylate (1.88 kJ · mol−1). The interpretation of the data leads to the conclusion that specificity of the Di2+ binding originates in the dehydration phenomenon and specificity between the three alkali-metal ions is due to the decrease
in the electrostatic bond strength with an increase in the ionic radii. The Di2+/M+ exchange is entropically driven.
Received: 28 January 1999 Accepted in revised form: 7 April 1999 相似文献
20.
We use a multiple-analytical approach based on secondary-ion mass-spectrometry (SIMS), X-ray single-crystal structure refinement
(SREF) and electron-probe micro-analysis (EPMA) to derive the complete crystal-chemical formula of a B-rich kornerupine-group
mineral, prismatine, from Hrarigahy, Madagascar: (Ca0.01Li0.02Mg0.20Fe2+
0.10) (Mg3.57Fe2+
0.06 Al5.37) (Si3.84B0.91Al0.26)O21 (OH1.08F0.07). SIMS matrix effects related to crystal structure were investigated by analyzing two grains with a known crystallographic
orientation relative to the ion beam.
Boron orders at the T3 site. The refined site-scattering for T3, 6.33 eps (electrons per site) agrees well with the mean bond-length for this site (1.512 ?), which indicates nearly complete
occupancy by B (85% rel.). B2O3 (∼ 4 wt%), derived by SREF, agrees with the SIMS data within analytical uncertainty using Si as the inner reference for the
matrix. The occupancy of the X site obtained by combining the SIMS and EPMA data (5.30 eps; electrons per site) agrees with the refined site-scattering
value (5.75 eps). Trace quantities of Li and Ca are ordered at this site. SIMS data for H2O is in accord with the stoichiometric value, indicating complete occupancy at O10 by OH. Fluorine (∼ 0.17 wt%) orders at O10: it corresponds to ∼ 0.07 atoms per formula unit (apfu) vs. 0.15 apfu (atoms per formula unit) by SREF, indicating a slight
overestimation of F with SREF, as previously observed in fluoborite.
Our data show that SIMS chemical matrix effects are well-calibrated, and emphasize the usefulness of independent micro-analytical
techniques in testing the mutual accuracy and consistency of experimental data. 相似文献