共查询到20条相似文献,搜索用时 343 毫秒
1.
Redondo R Machado VC Baeza M Lafuente J Gabriel D 《Analytical and bioanalytical chemistry》2008,391(3):789-798
Biogas is produced by biological processes under anaerobic conditions and may contain up to 20,000 ppmv hydrogen sulfide (H2S), a corrosive substance that attacks power engines and can affect the health of the industrial staff. H2S must be removed from the biogas, especially in co-generation facilities where the biogas is burnt for energy production.
Nowadays, biofiltration is being studied and considered as an interesting alternative for removing H2S from the biogas besides classical chemical processes. The novelty of this work is the design and construction of an automated
H2S on-line analyser to assess the composition of the liquid and gas phases of gas-phase bioreactors. The analyser is made of
two parallel flow configurations which share the same detection device. The first configuration is a single-channel flow injection
analyser (FIA) to detect S2− in the liquid phase. The second configuration is a continuous flow analyser (CFA) with a gaseous diffusion step (GD–CFA)
for detecting H2S in the gas phase. The diffusion step enables separation of the H2S(g) from the sample and its conversion into a detectable chemical species (S2−). S2− detection was performed with an Ag2S ion-selective electrode (ISE) selective to . The main response parameters of the FIA system are a linear range between 3 × 10−5 and 1 × 10−1 mol L−1 S2− (0.61–3,200 mg L−1), with a sensitivity of 27.9 mV decade−1 and a detection limit of 1.93 × 10−5 mol L−1 S2−. The GD–CFA configuration presents a linear range between 400 and 10,000 ppmv H2S(g) with a sensitivity of 26.1 mV decade−1 and a detection limit of 245 ppmv H2S. The proposed analyser was used by analysing real gas and liquid samples with optimal results at a full-scale biotrickling
filter for biogas treatment at a municipal wastewater treatment plant.
Figure The novelty of this work is the design and construction of an automated H2S on-line analyzer to assess the composition of the liquid and gas phases of gas-phase bioreactors. The analyser is made of
two parallel flow configurations which share the same detection device. The first configuration is a single-channel flow injection
analyser (FIA) to detect S2- in the liquid phase. The second configuration is a continuous flow analyser (CFA) with a gaseous diffusion step (GD-CFA)
for detecting H2S in the gas phase. 相似文献
2.
Samuel Melaku Ilse Gelaude Frank Vanhaecke Luc Moens Richard Dams 《Mikrochimica acta》2003,142(1-2):7-12
Microwave digestion reduction-aeration and pyrolysis combined with cold vapour atomic absorption and cold vapour atomic fluorescence
are compared for the determination of total mercury in several biological and environmental matrices. The biological samples
were digested in a mixture of HNO3/H2O2, the environmental samples in a mixture of HNO3/HClO4. After reduction with SnCl2, the mercury was collected by two-stage gold amalgamation. After microwave digestion reduction-aeration, detection limits
of 1.4 ng g−1 and 0.6 ng g−1 were obtained for cold vapour atomic absorption spectrometry (CVAAS) and cold vapour atomic fluorescence spectrometry (CVAFS),
respectively, for 250 mg of environmental samples. For biological samples (500 mg) the detection limits were 0.7 ng g−1 (CVAAS) and 0.4 ng g−1 (CVAFS). After pyrolysis, detection limits of 3.5 ng g−1 and 1.6 ng g−1 for CVAAS and CVAFS, respectively, were obtained for a 10 mg sample. Pyrolysis can only be applied when the organic content
of the sample is not too high. Accurate results were obtained for 8 certified reference materials of both environmental and
biological origin. In addition, a real sludge sample was analysed.
Author for correspondence. E-mail: richard.dams@rug.ac.be
Received September 18, 2002; accepted December 3, 2002
Published online May 5, 2003 相似文献
3.
Timothy J. Johnson Robert L. Sams Sarah D. Burton Thomas A. Blake 《Analytical and bioanalytical chemistry》2009,395(2):377-386
We report quantitative infrared spectra of vapor-phase hydrogen peroxide (H2O2) with all spectra pressure-broadened to atmospheric pressure. The data were generated by injecting a concentrated solution
(83%) of H2O2 into a gently heated disseminator and diluting it with pure N2 carrier gas. The water vapor lines were quantitatively subtracted from the resulting spectra to yield the spectrum of pure
H2O2. The results for the ν6 band strength (including hot bands) compare favorably with the results of Klee et al. (J Mol. Spectrosc. 195:154, 1999) as well as with the HITRAN values. The present results are 433 and 467 cm-2 atm−1 (±8 and ±3% as measured at 298 and 323 K, respectively, and reduced to 296 K) for the band strength, matching well the value
reported by Klee et al. (S = 467 cm−2 atm−1 at 296 K) for the integrated band. The ν1 + ν5 near-infrared band between 6,900 and 7,200 cm−1 has an integrated intensity S = 26.3 cm−2 atm−1, larger than previously reported values. Other infrared and near-infrared bands and their potential for atmospheric monitoring
are discussed. 相似文献
4.
Matthias Weil Franz Werner Frank Kubel 《Monatshefte für Chemie / Chemical Monthly》2002,229(1):267-275
Single crystals of MgAl2F8(H2O)2 have been obtained under hydrothermal conditions (250°C, 14 d) from a starting mixture of AlF3 and MgAlF5(H2O)2 in a 5% (w/w) HF solution. The crystal structure has been determined and refined from single crystal data (Fmmm (#69), Z = 4, a = 7.2691(7), b = 7.0954(16), c = 12.452(2) ?, 281 structure factors, 27 parameters, R(F 2 > 2σ (F 2)) = 0.0282, wR(F 2 all) = 0.0885). The obtained crystals were systematically twinned according to (010/100/001) as twinning matrix, reflecting the pseudo-tetragonal metric. The crystal structure is composed of perowskite-type layers built of corner sharing AlF6 octahedra with an overall composition of AlF4 − which are connected via common fluorine atoms of [MgF4/2(H2O)2/1] octahedra. Group-subgroup relations of MgAl2F8(H2O)2 to WO3(H2O)0.33 and to other M(II)M(III)2 F8(H2O)2 structures are briefly discussed. Above 570°C, MgAl2F8(H2O)2 decomposes under elimination of water into α-AlF3, β-AlF3, and MgF2. 相似文献
5.
Weichun Ye Yongjie Li Bo Yang Chunming Wang 《Journal of Solid State Electrochemistry》2007,11(9):1347-1351
Pd/Ag films were electrolessly deposited onto p-silicon (100)-activated seed layers of Ag and Pd, respectively, in the solution
of 0.005 mol l−1 AgNO3 + 0.005 mol l−1 PdCl2 + 4.5 mol l−1 NH3 + 0.16 mol l−1 Na2EDTA+0.1 mol l−1 NH2NH2 (pH 10.5) at room temperature. The morphology and composition of the films were studied comparatively by using atomic force
microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). Cathodic polarization curves for hydrogen evolution were recorded
in 0.5-mol l−1 H2SO4 without illumination, in which the obtained films served as working electrodes. The experimental results show that the film
obtained on the Ag seed layer was rather a pure Ag film and not a Pd/Ag film, and the Ag deposition rate on Pd sites was much
faster than that on Ag sites. 相似文献
6.
Harrison AG 《Journal of the American Society for Mass Spectrometry》2012,23(1):116-123
The doubly-protonated peptides Ala-Ala-Xaa-Ala-Ala-Ala-Arg show extensive loss of H2O when Xaa = Ser or Thr. Using quasi-MS3 techniques the fragmentation reactions of the [M + 2H – H2O]+2 ions have been studied in detail. For both Ser and Thr, the [M + 2H – H2O]+2 ions show three primary fragmentation reactions, elimination of CH3CH = NH, elimination of one Ala residue, and elimination of two Ala residues, in all cases forming doubly-charged products.
From a study of the further fragmentation of these products, it is concluded that elimination of two Ala residues results
in formation of a three-membered aziridine ring by interaction with the adjacent amide function as H2O is lost. The elimination of one Ala residue results in formation of a five-membered oxazoline ring through interaction with
the N-terminal adjacent carbonyl function as H2O is lost. The elimination of CH3CH = NH appears to involve formation of an eight-membered ring by interaction with the remote N-terminal carbonyl function
as H2O is lost. However, this initial structure undergoes rearrangement through interaction with the adjacent C-terminal carbonyl
function prior to further fragmentation. The [MH – H2O]+ ion of Ala-Ala-Ser-Ala-Ala-Ala also shows elimination of CH3CH = NH, one Ala residue and two Ala residues. 相似文献
7.
Sensitive fluorescent probes for determination of hydrogen peroxide and glucose based on enzyme-immobilized magnetite/silica nanoparticles 总被引:2,自引:0,他引:2
Qing Chang Lihua Zhu Guodong Jiang Heqing Tang 《Analytical and bioanalytical chemistry》2009,395(7):2377-2385
Sensitive fluorescent probes for the determination of hydrogen peroxide and glucose were developed by immobilizing enzyme
horseradish peroxidase (HRP) on Fe3O4/SiO2 magnetic core–shell nanoparticles in the presence of glutaraldehyde. Besides its excellent catalytic activity, the immobilized
enzyme could be easily and completely recovered by a magnetic separation, and the recovered HRP-immobilized Fe3O4/SiO2 nanoparticles were able to be used repeatedly as catalysts without deactivation. The HRP-immobilized nanoparticles were able
to activate hydrogen peroxide (H2O2), which oxidized non-fluorescent 3-(4-hydroxyphenyl)propionic acid to a fluorescent product with an emission maximum at 409 nm.
Under optimized conditions, a linear calibration curve was obtained over the H2O2 concentrations ranging from 5.0 × 10−9 to 1.0 × 10−5 mol L−1, with a detection limit of 2.1 × 10−9 mol L−1. By simultaneously using glucose oxidase and HRP-immobilized Fe3O4/SiO2 nanoparticles, a sensitive and selective analytical method for the glucose detection was established. The fluorescence intensity
of the product responded well linearly to glucose concentration in the range from 5.0 × 10−8 to 5.0 × 10−5 mol L−1 with a detection limit of 1.8 × 10−8 mol L−1. The proposed method was successfully applied for the determination of glucose in human serum sample. 相似文献
8.
Wolfgang Preis Michael Holzinger Werner Sitte 《Monatshefte für Chemie / Chemical Monthly》2001,132(4):499-508
Summary. The van der Pauw method has been applied to conductivity relaxation experiments on YBa2Cu3O6+δ at 600°C in order to determine the chemical diffusion coefficient as a function of the oxygen partial pressure in the surrounding
atmosphere (100 > p
O
2/bar > 10−3). It is shown that the van der Pauw technique is suitable for monitoring the conductivity relaxation when the oxygen diffusion is perpendicular to the direct
current flowing through the sample in accordance with the van der Pauw geometry using thin tablets as samples. The oxygen partial pressure is changed stepwise (generally Δlogp
O
2 ≤ 0.5) by employing appropriate gas mixtures as well as an electrochemical oxygen pump device. An evaluation formula is given
for the determination of the chemical diffusion coefficient neglecting slow surface processes. In addition, the electronic
conductivity of YBa2Cu3O6+δ has been measured at 600°C as a function of oxygen partial pressure of the ambient atmosphere (100 > p
O
2/bar > 10−5) by means of the van der Pauw method applying the same experimental set-up. Typical values of the chemical diffusion coefficient are in the range of 10−6 cm2·s−1; the results of the conductivity measurements are interpreted in terms of an appropriate defect model.
Received May 30, 2000. Accepted June 8, 2000 相似文献
9.
Summary. Two novel Er-Cr ion-pair complexes ([Er(DMA)3(H2O)4][Cr(CN)6] and [Er(MPL)4(H2O)3][Cr(CN)6]·2H2O; DMA = dimethylacetamide, MPL = 1-methyl-2-pyrrolidinone) have been synthesized. [Er(DMA)3(H2O)4][Cr(CN)6] crystallizes in the monoclinic system (space group P
c
) with a = 9.789(2), b = 11.263(2), c = 13.997(3)?, β = 105.66(3)°, V = 1485.9(5)?3, Z = 2; [Er(MPL)4(H2O)3][Cr(CN)6]·2H2O crystallizes in the monoclinic system (space group P21) with a = 9.447(2), b = 13.881(3), c = 14.673(3)?, β = 101.85(3), V = 1883.1(7)?3, Z = 2. X-Ray crystal diffraction analyses reveal that the two complexes form a hydrogen bonding network structure through the
CN group and H2O molecules. Variable temperature susceptibilities for the two complexes indicate that weak antiferromagnetic interactions
exist between cation and anion pairs through this hydrogen bonding network. 相似文献
10.
Al-Dirbashi OY Al-Hassnan ZN Rashed MS 《Analytical and bioanalytical chemistry》2006,386(7-8):2013-2017
A liquid chromatography tandem mass spectrometric method is described for the analysis of homocitrulline in human urine, a
key metabolite in the differential diagnosis of hyperammonemia, hyperornithinemia, homocitrullinuria (HHH) syndrome. Urine
samples were prepared by mere five-fold dilution with a mixture of internal standards (2H2-citrulline and 2H3-creatinine) used for the simultaneous quantification of creatinine. Analytes were separated on a cyano column and eluted
isocratically within seven min. Detection was achieved by monitoring transitions of 190 > 84 and 190 > 127 for homocitrulline,
178 > 115 for 2H2-citrulline, 114 > 44 for creatinine and 117 > 47 for 2H3-creatinine. Calibration curves were linear up to 100 micromol/L. Intraday (n = 7) and interday (n = 6) variations were less than 10%. In urine samples from three siblings confirmed to have HHH syndrome, homocitrulline levels
were at 13.3 (74), 21.1 (50) and 108.2 (103) mmol/mol creatinine (micromol/L). Control values were 0–9 mmol/mol creatinine
(n = 120). The current method solves specificity issues in homocitrulline determination often encountered with some ninhydrin-based
systems (coelution with methionine) and some o-phthalaldehyde-based ones (coelution with taurine), and presents an attractive alternative with a relatively high throughput. 相似文献
11.
Matthias Weil Franz Werner Frank Kubel 《Monatshefte für Chemie / Chemical Monthly》2002,133(3):267-275
Summary. Single crystals of MgAl2F8(H2O)2 have been obtained under hydrothermal conditions (250°C, 14 d) from a starting mixture of AlF3 and MgAlF5(H2O)2 in a 5% (w/w) HF solution. The crystal structure has been determined and refined from single crystal data (Fmmm (#69), Z = 4, a = 7.2691(7), b = 7.0954(16), c = 12.452(2) ?, 281 structure factors, 27 parameters, R(F
2 > 2σ (F
2)) = 0.0282, wR(F
2 all) = 0.0885). The obtained crystals were systematically twinned according to (010/100/001) as twinning matrix, reflecting
the pseudo-tetragonal metric. The crystal structure is composed of perowskite-type layers built of corner sharing AlF6 octahedra with an overall composition of AlF4
− which are connected via common fluorine atoms of [MgF4/2(H2O)2/1] octahedra. Group-subgroup relations of MgAl2F8(H2O)2 to WO3(H2O)0.33 and to other M(II)M(III)2 F8(H2O)2 structures are briefly discussed. Above 570°C, MgAl2F8(H2O)2 decomposes under elimination of water into α-AlF3, β-AlF3, and MgF2.
Received October 29, 2001. Accepted (revised) December 6, 2001 相似文献
12.
The structure of water solubilized by reverse aggregates of calcium bis(2-ethylhexyl) sulfosuccinate in deuterobenzene and
toluene has been probed by Fourier transform-IR and 1H NMR spectroscopies. The νOD band of solubilized HOD (4% D2O in H2O) has been recorded as a function of the [water]/[surfactant] molar ratio, W/S. Curve fitting of this band showed the presence
of a main peak at 2550 ± 13 cm−1 and a small one at 2405 ± 15 cm−1. As a function of increasing W/S, the frequency of the main peak decreases, its full width at half-height increases, and
its area increases linearly. The 1H NMR chemical shift of solubilized H2O–D2O mixtures at W/S = 18.1 has been measured as a function of the deuterium content of the aqueous nanodroplet. These data were
used to calculate the so-called “fractionation factor” of the aggregate-solubilized water, the value of which was found to
be unity. The results of both techniques show that reverse aggregate-solubilized water, although different from bulk water,
does not seem to coexist in “layers” of different degrees of structure, as suggested, for example by the two-state water-solubilization
model.
Received: 12 July 1999/Accepted: 30 August 1999 相似文献
13.
Günter Grampp Stephan Landgraf Tomasz Wesierski Beata Jankowska Ewa Kalisz Dana-Maria Sabou Boryana Mladenova 《Monatshefte für Chemie / Chemical Monthly》2002,212(4):1363-1372
The kinetics of the CrO(O2)2 formation by H2O2 and Cr2O7
2− in aqueous acidic media was measured at 293 ± 2 K in a pH range between 2.5 and 3.3. Using the stopped-flow method with rapid scan UV-VIS detection, the rate law of the formation
of CrO(O2)2 was determined. For the media HClO4, HNO3 and CH3COOH, the reaction order in the Cr2O7
2− concentration was found to be 0.5. For [H2O2] as well as for [H+], the reaction was first order in all acids used. In HCl and H2SO4 media the reaction was first order in Cr2O7
2−. At T = 293 ± 2 K the rate constant for the formation of Cr(O)(O2)2 was found to be (7.3 ± 1.9) · 102 M−3/2 s−1 in HClO4. 相似文献
14.
Heinz Gamsj?ger Wolfgang Preis Harald Wallner 《Monatshefte für Chemie / Chemical Monthly》2001,28(6):411-415
The solubility of hellyerite, NiCO3 · 6H2O, in water was studied at different temperatures. From the experimental data obtained, a preliminary set of the thermodynamic quantities Δf G ⊖, Δf H ⊖, and S ⊖ for hellyerite was derived using the ChemSage optimizer routine. 相似文献
15.
Summary. Single crystals of sodium dithiophosphate undecahydrate (Na3PO2S2 · 11H2O) and sodium trithiophosphate undecahydrate (Na3POS3 · 11H2O) were grown from aqueous solution. The crystal structures of Na3PO2S2 · 11H2O (P212121; a = 1248.1(1), b = 945.2(1), c = 1383.1(1) pm; R
1 = 0.0202, wR
2 = 0.0502) and Na3POS3 · 11H2O (Pna21; a = 1262.0(2), b = 947.6(2), c = 1431.5(2) pm; R
1 = 0.0720, wR
2 = 0.1371) are related to each other in a sense that all constituting units are arranged in similar positions and with similar
orientations. The geometries of the anions were determined with high accuracy; thus, the structural parameters of the POS3−
3 anion were measured for the first time.
Received September 25, 2001. Accepted January 21, 2002 相似文献
16.
Kumar S. Ashok Wang Sea-Fue Yeh Chun-Ting Lu His-Chuan Yang Jen-Chang Chang Yu-Tsern 《Journal of Solid State Electrochemistry》2010,14(11):2129-2135
In this study, stable and homogenous thin films of multiwalled carbon nanotubes (MWCNTs) were obtained on conducting surface
using ciprofloxacin (CF, fluoroquinolone antibiotic) as an effective-dispersing agent. Further, MWCNTs/CF film modified electrodes
(glassy carbon and indium tin oxide-coated glass electrode) are used successfully to study the direct electrochemistry of
proteins. Here, cytochrome C (Cyt-C) was used as a model protein for investigation. A MWCNTs/CF film modified electrode was
used as a biocompatible material for immobilization of Cyt-C from a neutral buffer solution (pH 7.2) using cyclic voltammetry
(CV). Interestingly, Cyt-C retained its native state on the MWCNTs/CF film. The Cyt-C adsorbed MWCNTs/CF film was characterized
by scanning electron microscopy (SEM), UV–visible spectrophotometry (UV-vis) and CV. SEM images showed the evidence for the
adsorption of Cyt-C on the MWCNTs/CF film, and UV–vis spectrum confirmed that Cyt-C was in its native state on MWCNTs/CF film.
Using CV, it was found that the electrochemical signal of Cyt-C was highly stable in the neutral buffer solution and its redox
peak potential was pH dependent. The formal potential (−0.27 V) and electron transfer rate constant (13 ± 1 s−1) were calculated for Cyt-C on MWCNTs/CF film modified electrode. A potential application of the Cyt-C/MWCNTs/CF electrode
as a biosensor to monitor H2O2 has been investigated. The steady-state current response increases linearly with H2O2 concentration from 2 × 10−6 to 7.8 × 10−5 M. The detection limit for determination of H2O2 has been found to be 1.0 × 10−6 M (S/N = 3). Thus, Cyt-C/MWCNTs/CF film modified electrode can be used as a biosensing material for sensor applications. 相似文献
17.
Günter Grampp Stephan Landgraf Tomasz Wesierski Beata Jankowska Ewa Kalisz Dana-Maria Sabou Boryana Mladenova 《Monatshefte für Chemie / Chemical Monthly》2002,133(10):1363-1372
Summary. The kinetics of the CrO(O2)2 formation by H2O2 and Cr2O7
2− in aqueous acidic media was measured at 293 ± 2 K in a pH range between 2.5 and 3.3. Using the stopped-flow method with rapid scan UV-VIS detection, the rate law of the formation
of CrO(O2)2 was determined. For the media HClO4, HNO3 and CH3COOH, the reaction order in the Cr2O7
2− concentration was found to be 0.5. For [H2O2] as well as for [H+], the reaction was first order in all acids used. In HCl and H2SO4 media the reaction was first order in Cr2O7
2−. At T = 293 ± 2 K the rate constant for the formation of Cr(O)(O2)2 was found to be (7.3 ± 1.9) · 102 M−3/2 s−1 in HClO4.
Corresponding author. E-mail: grampp@ptc.tu-graz.ac.at
Received January 30, 2002; accepted (revised) June 5, 2002 相似文献
18.
Roseli M. de Souza Bárbara M. Mathias Ieda S. Scarminio Carmem Lúcia P. da Silveira Ricardo Q. Aucélio 《Mikrochimica acta》2006,153(3-4):219-225
Inductively coupled plasma optical emission spectrometry (ICP OES) was used to determine Mo, Cr, V and Ti, in diesel and in
used fuel oil. Samples were introduced into the ICP as emulsions to reduce interferences and allow the use of inorganic standards
for quantification. A comparative study between one Triton X-100 emulsion and one detergentless emulsion was made. A 23 factorial design was applied to elucidate and establish the relationship between three experimental variables: presence of
HNO3, amount of diesel fuel oil (between 5 and 25%) and the presence or O2 into the Ar plasma gas flow rate. Results indicated that best performance were achieved using 10% sample (w/w) together with
concentrated HNO3 (0.5 mL) and using O2 as auxiliary gas (0.047 L min−1). The use of O2 minimized both carbon deposits at the injector tip and plasma background. The addition of HNO3 resulted in good correlation between inorganic standards used for calibration, and metallo-organic standards used for sample
enrichment. Analyte enriched diesel and SRM 1634b were analyzed using the optimized conditions. Recoveries from 90.1 to 106.5%
were achieved, with better results for detergent emulsions which enabled limits of detection at the ng g−1 range for Mo, Cr, V and Ti and at smaller background. 相似文献
19.
Ashraf A. Mohamed 《Monatshefte für Chemie / Chemical Monthly》2001,132(8):919-928
Summary. A new selective, sensitive, and simple kinetic method is developed for the determination of trace amounts of iodide. The
method is based on the catalytic effect of iodide on the reaction of triflupromazine (TFP) with H2O2. The reaction is followed spectrophotometrically by tracing the oxidation product at 498 nm within 1 min after addition of
H2O2. The optimum reaction conditions are TFP (0.4 × 10−3
M), H2SO4 (1.0M), H3PO4 (2.0M), and H2O2 (1.6M) at 30°C. Following this procedure, iodide can be determined with a linear calibration graph up to 4.5 ng ċ cm−3 and a detection limit of 0.04 ng ċ cm−3, based on the 3 Sb criterion. The method can also be applied to the determination of iodate and periodate ions. Determination of as little as
0.2, 1.0, 2.0, and 4.0 ng ċ cm−3 of I−, IO3
-, or IO4
- in aqueous solutions gave an average recovery of 98% with relative standard deviations below 1.6% (n = 5). The method was applied to the determination of iodide in Nile river water and ground waters as well as in various food
samples after alkaline ashing treatment. The method is compared with other catalytic spectrophotometric procedures for iodide
determination.
Received January 19, 2001. Accepted (revised) March 12, 2001 相似文献
20.
The fungicide triadimenol consists of a mixture of two diastereoisomers. Diastereoisomer A (1RS,2SR) could be obtained from the mixture by fractionated crystallization from ethanol/water and toluene, successively, whereas
diastereoisomer B (1RS,2RS) could be separated by column chromatography on a silica gel column using ethylacetate as eluent. Four different crystal
forms of diastereoisomer A could be derived. The modifications were characterized by means of thermal analysis (thermomicroscopy,
DSC), FTIR-spectroscopy, FT-Raman-spectroscopy and powder X-ray diffraction, as well as pycnometry. The thermodynamic relationships
are illustrated in a semischematic energy/temperature-diagram which provides information about the relative thermodynamic
stabilities and physical properties of the four crystal forms. Mod. II (m.p. 132 °C, ΔHf 33.1±0.2 kJ mol−1, density 1.271±0.001 g cm−3) was obtained from toluene after the separation of diastereoisomer A and is enantiotropically related to mod. I (m.p. 138 °C,
ΔHf 32.0 ± 0.2 kJ mol−1, density 1.243±0.001 g cm−3). The transition point of mod. II with mod. I was determined between 30 and 40 °C, which means that mod. II is thermodynamically
stable at ambient conditions. Mod. III (m.p. 112 °C, ΔHf 25.1±0.5 kJ mol−1) and mod. IV were obtained from the melt. Furthermore, the phase diagrams of the binary systems of diastereoisomer B and
the four modifications of diastereoisomer A were calculated by means of the experimentally obtained thermodynamical data.
Received September 30, 1999. Revision July 30, 2000. 相似文献