共查询到20条相似文献,搜索用时 15 毫秒
1.
A rapid and sensitive high-performance liquid chromatographic (HPLC) assay for the simultaneous determination and quantification
of cefpirome and cetirizine or cefpirome and levocetirizine in pharmaceutical formulations and human plasma without changing
the chromatographic conditions is described. Chromatographic separations were performed on a prepacked Nucleosil 120, C18 (5 μm, 12.5 ± 0.46 mm) column using CH3CN: H2O (75: 25, v/v) as a mobile phase at a flow rate of 1 mL/min while UV detection was performed at 232 nm for monitoring the
effluent. A number of other brands of C18 columns were also employed which had a significant effect on the separation. The method has been validated over the concentration
range of 0.5–50 μg/mL (r
2 > 0.999). The limit of detection (LOD) and quantification (LOQ) for cefpirome and levocetirzine in pharmaceutical formulations
and serum were in the range 0.24–1.31 μg/mL. Analytical recovery from human plasma was >98%, and the within and between-day
relative standard deviation was <3.1%. The small sample volume and simplicity of preparation make this method suitable for
use in pharmaceutical industries, drug research centers, clinical laboratories, and forensic medical centers.
The text was submitted by the authors in English. 相似文献
2.
Mohammed A. Abounassif Mohammed M. Hefnawy Gamal A. E. Mostafa 《Monatshefte für Chemie / Chemical Monthly》2012,73(Z1):365-371
Abstract
A stereoselective HPLC method has been developed for the simultaneous determination of oxprenolol enantiomers in urine and pharmaceutical products. Enantiomeric resolution of oxprenolol was achieved on cellulose tris(3,5-dichlorophenylcarbamate) immobilized onto a 5 μm spherical porous silica chiral stationary phase (CSP) known as Chiralpak IC with UV detection at 273 nm. The mobile phase consisted of n-hexane:isopropanol:triethylamine 70:30:0.1 (v/v/v) at a flow rate of 1.0 cm3/min. The method was validated for its linearity, accuracy, precision, and robustness. The calibration curves were linear over the range of 0.5–75 μg/cm3, with a detection limit of 0.1 μg/cm3 for each enantiomer. An average recovery of 99.0% and a mean relative standard deviation of 2.6% at 40.0 μg/cm3 for S-(−)- and R-(+)-enantiomers were obtained. The overall recoveries of oxprenolol enantiomers from pharmaceutical formulations were in the range 97.5–99.0%, with RSDs ranging from 0.6 to 0.8%. The mean extraction efficiency of oxprenolol from urine was in the range of 86.0–93.0% at 0.5–5 μg/cm3 for each enantiomer. The assay method proved to be suitable as a chiral quality control for oxprenolol formulations using HPLC and for therapeutic drug monitoring. 相似文献3.
M. A. Naushad M. Aqil F. J. Ahmad A. Ali M. S. Faisal M. Rizwan S. Faiyaz 《Journal of Analytical Chemistry》2008,63(10):965-970
A simple, economic, selective, precise, and accurate high-performance liquid chromatographic (HPLC) method for the analysis of trimetazidine hydrochloride in both bulk drug and pharmaceutical formulations was developed and
validated in the present study. The mobile phase consisted of water: methanol: triethylamine (75: 25: 0.1 v/v/v), and pH 3.3
was adjusted with orthophosphoric acid. This system was found to give a sharp peak of trimetazidine hydrochloride at a retention
time of 3.375 ± 0.04 min. HPLC analysis of trimetazidine hydrochloride was carried out at a wavelength of 232 nm with a flow
rate of 1.0 mL/min. The linear regression analysis data for the calibration curve showed a good linear relationship with a
regression coefficient of 0.997 in the concentration range of 5–90 μg/mL. The linear regression equation was y = 35362x −
8964.2. The limit of detection (LOD) and limit of quantification (LOQ) were found to be 3.6 and 10.9 μg/mL, respectively. The developed method was employed with a high degree of precision and
accuracy for the analysis of trimetazidine hydrochloride. The developed method was validated for accuracy, precision, robustness,
detection, and quantification limits as per the ICH guidelines. The wide linearity range, accuracy, sensitivity, short retention
time, and composition of the mobile phase indicated that this method is better for the quantification of trimetazidine hydrochloride.
The text was submitted by the authors in English. 相似文献
4.
G. A. Shabir 《Journal of Analytical Chemistry》2011,66(10):963-968
A new and simple isocratic high-performance liquid chromatographic method with ultraviolet detection is described for simultaneous
determination of active guaiphenesin and preservative sodium benzoate in Liqufruta garlic cough medicine formulation. The
chromatographic separation was achieved using a Zorbax CN; 150 mm × 4.6 mm and 5 μm particle size column employing acetonitrile
and water (20: 80, v/v) containing 0.1% formic acid (pH 3.5 ± 0.05) as the mobile phase. The method was validated with respect
to linearity, range, precision, accuracy, specificity, limit of detection and limit of quantitation. The both analytes were
detected by UV-Vis detector at 245 nm. The method was linear over the concentration range of 0.2–0.8 mg/mL and 0.02–0.06 mg/mL
for guaiphenesin and sodium benzoate, respectively. The limit of detection was found to be 0.14 μg/mL for GP and 0.06 μg/mL
for SB and the quantification limit was 0.54 μg/mL for GP and 0.22 for SB. Accuracy, evaluated as recovery, was in the range
of 97.8–100.0%. Intra-day precision and intermediate precision showed relative standard deviation <1% in each case. 相似文献
5.
Two spectrophotometric methods were applied to the simultaneous assay of chlorhexidine hydrochloride (CHL) and lidocaine hydrochloride (LIH) in pharmaceutical formulations. Using derivative spectrophotometry, CHL was determined by measurement of its first derivative
signal at 290 nm (peak to zero amplitude) in the concentration range 5–9 μg/mL, and LIH was analysed by measurement of its
second derivative signals at 272 and 276 nm (peak to peak amplitude) in the concentration range 160–480 μg/mL. With the partial
least-squares (PLS-2), the experimental calibration matrix was constructed using 9 samples. The concentration ranges considered
were 5–7 μg/mL for CHL and 220, 240, 260 μg/mL for LIH. The absorbances were recorded between 240 and 310 nm at every 5 nm. 相似文献
6.
G. S. Nikoli? I. Savi? V. Marinkovi? 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2009,83(9):1609-1611
A selective, precise and new high-performance liquid chromatographic method for the analysis of loperamid hydrochloride in
pharmaceutical formulations was developed and validated. The mobile phase consisting buffer (sodium-octansulphonate, triethylamine
and ammonium hydroxide) in water: acetonitriie (45: 55, v/v) (pH 3.2). The absorbance was monitored with a DAD detector at
226 nm. The flow rate was 1.5 cm3 min−1. The linearity (r = 0.9947) and the recovery (98.58–100.42%) were found to be satisfactory. The detection and quantitation limits were found
to be 0.95 and 3.12 μg cm−3. The results demonstrated that the procedure was accurate, precise and reproducible. It can be suitably applied for the estimation
of lopera-mid hydrochloride in pharmaceutical formulations.
The article is published in the original. 相似文献
7.
Juan Agüero José-Esteban Peris Eduardo San-Martín 《Fresenius' Journal of Analytical Chemistry》1999,363(3):289-293
An analytical method for detecting and quantifying cefotaxime in plasma and several tissues is described. The method was
developed and validated using plasma and tissues of rats. The samples were analyzed by reversed phase liquid chromatography
(HPLC) with UV detection (254 nm). Calibration graphs showed a linear correlation (r > 0.999) over the concentration ranges
of 0.5–200 μg/mL and 1.25–25 μg/g for plasma and tissues, respectively. The recovery of cefotaxime from plasma standards prepared
at the concentrations of 25 μg/mL and 100 μg/mL was 98.5 ± 3.5% and 101.8 ± 2.2%, respectively. The recovery of cefotaxime
from tissue standards of liver, fat and muscle, prepared at the concentration of 10 μg/g was: 89.8 ± 1.2% (liver), 103.9 ±
6.5% (fat) and 97.8 ± 2.1% (muscle). The detection (LOD) and quantitation (LOQ) limits for plasma samples were established
at 0.11 μg/mL and 0.49 μg/mL, respectively. The values of these limits for tissues samples were approximately 2.5 times higher:
0.3 μg/g (LOD) and 1.25 μg/g (LOQ). For plasma samples, the deviation of the observed concentration from the nominal concentration
was less than 5% and the coefficient of variation for within-day and between-day assays was less than 6% and 12%, respectively.
The method was used in a pharmacokinetic study of cefotaxime in the rat and the mean values of the pharmacokinetic parameters
are given.
Received: 25 May 1998 / Revised: 27 July 1998 / Accepted: 1 August 1998 相似文献
8.
A simple, selective, rapid, and economical reversed phase high performance liquid chromatography(RP-HPLC) method for the determination of doxofylline in the commercial dosage form has been developed and validated. The separation
and quantification were achieved on an HiQ Sil C 18 W column using a mobile phase of acetonitrile: buffer (50: 50), pH 3,
at a flow rate of 1 mL/min with detection of analyte at 272 nm. The separation was achieved within 3.1 ± 0.3 min for doxofylline
sample. The method showed good linearity in the range of 10–80 μg/mL. The intra and inter day RSD ranged from 0.37–0.53%.
The recovery (mean ± S.D.) of low, middle and high concentrations were 100.04 ± 0.80, 100.01 ± 0.20, 100.07 ± 0.30 respectively.
Limit of detection and limit of quantification were 0.03 and 0.1 μg/mL, respectively. 相似文献
9.
J. W. Bae C. S. Myung C. I. Choi S. M. Moon C. G. Jang S. Y. Lee 《Journal of Analytical Chemistry》2010,65(12):1261-1265
The purpose of this study was to validate a reliable analytical method for pharmacokinetic study of ceftibuten in human plasma
by high performance liquid chromatography (HPLC) system with UV detection. Ceftizoxime was used as the internal standard.
After plasma sample was precipitated with acetonitrile and dichloromethane, the supernatant was directly injected into the
HPLC system. Separation was performed on a Capcell Pak C18 UG120 column (4.6 mm × 250 mm, 5 μm particles) with a mobile phase of acetonitrile/50 mM ammonium acetate (5: 95, v/v) and
UV detection at a wavelength of 262 nm. The intra- and inter-day precision expressed as the relative standard deviation was
less than 15%. The lower limit of quantification was 0.5 hg/mL of ceftibuten using 0.5 mL of plasma. The calibration curve
was linear in concentration range of 0.5–30 μg/mL (r
2 = 0.9998). The mean accuracy was 96–102%. The coefficient of variation (precision) in the intra- and inter-day validation
was 0.9–3.9 and 0.9–2.4%, respectively. The pharmacokinetics of ceftibuten was evaluated after a single oral administration
of 400 mg to healthy volunteers. The AUC0–9 h, c
max, T
max, and T
1/2 were 86.6 ± 12.7 μg h/mL, 18.4 ± 1.5 μg/mL, 2.63 ± 0.83 and 2.65 ± 0.41 h, respectively. The method was demonstrated to be
highly reproducible and feasible for pharmacokinetic studies of ceftibuten in eight volunteers after oral administration (400
mg as ceftibuten). 相似文献
10.
S. S. Ranher S. V. Gandhi S. S. Kadukar P. N. Ranjane 《Journal of Analytical Chemistry》2010,65(5):507-510
The simple, accurate and precise HPLC method for determination of Artesunate in bulk and tablet dosage form has been developed.
Quantitation of drug was carried out on Jasco HPLC system with HiQ-SiL C8 column (250 mm × 4.6 mm i.d.), using acetonitrile: 1 M sodium acetate buffer (pH 3 adjusted with o-phosphoric acid) in the ratio 70: 30 as mobile phase. Method was developed using Artemether as internal standard and UV detector
set at 220 nm. Linear concentration range was found to be 250–2500 μg/mL. The method has been successfully applied to the
analysis of drugs in bulk and pharmaceutical formulation. The method was validated with respect to linearity, precision and
accuracy as per the International Conference on Harmonisation guidelines. 相似文献
11.
Summary A sensitive and rapid routine HPLC method is proposed for quantitative estimation of morphine hydrochloride and hydromorphone
hydrochloride in pharmaceutical dosage forms. The drugs were chromatographed on a C18 reversed-phase column; the mobile phase was acetonitrile-water, 35:65 (v/v), containing sodium dodecyl sulphate (0.5%, w/v),
as ion pairing reagent, and acetic acid (0.4% v/v). Detection was at 230 nm.
The optimized method was validated and linearity (r>0.999), precision, and accuracy were found to be acceptable within the concentration ranges 86–124 μg mL−1 for morphine hydroloride and 60–180 μg mL−1 for hydromorphone hydrochloride.
The method is being used to investigate the stability of morphine hydrochloride and hydromorphone hydrochloride in solution
used for intramuscular injection. 相似文献
12.
Samir Mohamed El‐Moghazy Mohamed Abd El‐Azem Mohamed Marwa Fadel Mohamed Nadia Fayek Youssef 《中国化学会会志》2009,56(2):360-367
Reversed phase‐high performance liquid chromatography (RP‐HPLC), thin layer chromatography (TLC) densitometry and first derivative spectrophotometry (1D) techniques are developed and validated as a stability‐indicating assay of ezetimibe in the presence of alkaline induced degradation products. RP‐HPLC method involves an isocratic elution on a Phenomenex Luna 5μ C18 column using acetonitrile: water: glacial acetic acid (50:50:0.1 v/v/v) as a mobile phase at a flow rate of 1.5 mL/min. and a UV detector at 235 nm. TLC densitometric method is based on the difference in Rf‐values between the intact drug and its degradation products on aluminum‐packed silica gel 60 F254 TLC plates as stationary phase with isopropanol: ammonia 33% (9:1 v/v) as a developing mobile phase. On the fluorescent plates, the spots were located by fluorescence quenching and the densitometric analysis was carried out at 250 nm. Derivative spectrophotometry, the zero‐crossing method, ezetimibe was determined using first derivative at 261 nm in the presence of its degradation products. Calibration graphs of the three suggested methods are linear in the concentration ranges 1–10 mcg/mL, 0.1–1 mg/mL and 1–16 mcg/mL with a mean percentage accuracy of 99.05 ± 0.54%, 99.46 ± 0.63% and 99.24 ± 0.82% of bulk powder, respectively. The three proposed methods were successfully applied for the determination of ezetimibe in raw material and pharmaceutical dosage form; the results were statistically analyzed and compared with those obtained by the reported method. Validation parameters were determined for linearity, accuracy and precision; selectivity and robustness and were assessed by applying the standard addition technique. 相似文献
13.
Alaa S. Amin 《Mikrochimica acta》2000,134(1-2):89-94
A simple, rapid, accurate and sensitive spectrophotometric method for the determination of norfloxacin (NRF), ofloxacin (OFL)
and ciprofloxacin (CPF) is described. This method is based on the formation of an ion pair with sudan III in aqueous-acetone
medium [40% (v/v) acetone]. The coloured products are measured at 567, 565 and 566 nm for NRF, OFL and CPF, respectively.
The optimization of various experimental conditions is described. Beer’s law is obeyed in the range 0.4–12.0, 0.4–8.8 and
0.4–10.4 ;μg mL−1 of NRF, OFL and CPF, respectively. For more accurate results, Ringbom optimum concentration ranges were 0.8–11.2, 0.6–8.5
and 0.8–10.0 μg mL−1, respectively. The results obtained showed good recoveries of ±1.2, ±1.5 and ±1.7% with relative standard deviations of 0.67,
0.83 and 1.08% for NRF, OFL, and CPF, respectively. The molar absorptivity and Sandell sensitivity were also calculated. Applications
of the proposed method to representative pharmaceutical formulations are successfully presented.
Received April 30, 1999. Revision November 25, 1999. 相似文献
14.
S. Sharif I. U. Khan M. Ashfaq M. S. Iqbal S. Ahmad 《Journal of Analytical Chemistry》2010,65(10):1029-1034
A simple, sensitive and rapid high performance liquid chromatographic method was developed and validated for the simultaneous
determination of potassium clavulanate and cefadroxil in synthetically prepared tablets. Chromatographic separation and detection
was carried out on a C-18 column using 0.05 M potassium dihydrogen phosphate buffer (pH 5.0) and acetonitrile in the ratio
of 94: 06 (v/v) as mobile phase at wavelength of 225 nm. The method was linear in the concentration range of 3.75–22.5 μg/mL
for potassium clavulanate and 15–90 μg/mL for cefadroxil. The flow rate was 1.0 mL/min and the total analysis time was less
than 10 min. The mean recoveries was found to be greater than 99% with RSD less than 1.0%. The proposed method was validated
by performing linearity, recovery, specificity, robustness, LOD/LOQ and within-day and between-day precision. The chromatographic
results obtained from the synthetically prepared tablets show that the method is highly precise and accurate for the simultaneous
quantitation of clavulanate potassium and cefadroxil. 相似文献
15.
A simple reversed-phase high-performance liquid chromatographic (HPLC) method has been developed for the simultaneous determination
of the antiepileptic drugs (AEDs) zonisamide (ZNS), primidone (PRI), lamotrigine (LTG), phenobarbital (PB), phenytoin (PHT),
oxcarbazepine (OXC), and carbamazepine (CBZ) and two of their active metabolites, monohydroxycarbamazepine (MHD) and carbamazepine
10,11-epoxide (CBZE) in human plasma. Plasma (100 μL) was pretreated by deproteinization with 300 μL methanol containing 20 μg mL−1 propranolol hydrochloride as internal standard. HPLC was performed on a C8 column (4.6 mm × 250 mm; particle size 5 μm) with methanol–acetonitrile–0.1% trifluoroacetic acid, 235:120:645 (v/v), as mobile phase at a flow rate of 1.5 mL min−1. ZNS, OXC, and CBZ were monitored by UV detection at 235 nm, and PRI, LTG, MHD, PB, PHT, and CBZE by UV detection at 215 nm.
Relationships between response and concentration were linear over the concentration ranges 1–80 μg mL−1 for ZNS, 5–50 μg mL−1 for PRI, 1–25 μg mL−1 for LTG, 1–50 μg mL−1 for MHD, 5–100 μg mL−1 for PB, 1–10 μg mL−1 for CBZE, 0.5–25 μg mL−1 for OXC, 1–50 μg mL−1 for PHT, and 1–25 μg mL−1 for CBZ. Intra-day and inter-day reproducibility were adequate (coefficients of variation were ≤11.6%) and absolute recovery
ranged from 95.2 ± 6.13 to 107.7 ± 7.76% for all the analytes; for the IS recovery was 98.69 ± 1.12%. The method was proved
to be accurate, reproducible, convenient, and suitable for therapeutic monitoring of the nine analytes. 相似文献
16.
Three simple and sensitive colorimetric methods (A–C) for the determination of melatonin in bulk samples and in pharmaceutical
formulations are described. They are based on the formation of coloured species by reaction of ninhydrin with the drug (method
A, λmax 397 nm) by oxidation of the indol moiety in melatonin with potassium persulphate (method B, λmax 450 nm) or by reduction of osmium (VIII) (method C, λmax 516 nm). Regression analysis of Beer-Lambert plots showed good correlations in concentration ranges between 0.8–14.2, 70.0–140.0
and 2.0–40.0 μg/mL for methods A, B and C, respectively. The molar absorptivity, Sandell sensitivity and detection limit were
calculated. For more accurate analysis, Ringbom optimum concentration ranges were calculated. The validity of the proposed
methods was tested by analysing pharmaceutical formulations containing melatonin. The relative standard deviations were ≤ 0.95%
with recoveries 99.0–101.33%.
Received October 20, 1999. Revision February 10, 1999. 相似文献
17.
S. Tatar Ulu 《Chromatographia》2006,64(3-4):169-173
A new, simple, rapid and specific reversed-phase high-performance liquid chromatography (HPLC) method was developed and validated for the determination of fluvoxamine in pharmaceutical dosage forms. The HPLC separation was achieved on a C18 μ-Bondapack column (250 mm × 4.6 mm) using a mobile phase of acetonitrile–water (80:20, v/v) at a flow rate of 1 mL min−1. Proposed method is based on the derivatization of fluvoxamine with 1,2-naphthoquinone-4-sulphonic acid sodium salt (NQS) in borate buffer of pH 8.5 to yield a orange product. The HPLC method is based on measurement of the derivatized product using UV-visible absorbance detection at 450 nm. The method was validated for specificity, linearity, precision, accuracy, robustness. The degree of linearity of the calibration curves, the percent recoveries of fluvoxamine, the limit of detection and quantification, for the HPLC method were determined. The assay was linear over the concentration range of 45–145 ng mL−1 (r = 0.9999). Limit of detection and quantification for fluvoxamine were 15 and 50 ng mL−1, respectively. The results of the developed procedure (proposed method) for fluvoxamine content in tablets were compared with those by the official method. The method was found to be simple, specific, precise, accurate, reproducible and robust. 相似文献
18.
《液相色谱法及相关技术杂志》2012,35(2):447-462
Abstract Prifinium bromide is an anti-cholinergic drug, available commercially in various pharmaceutical formulations such as tablets, suppositories, syrups, and ampoules. The present available analytical methods are time-consuming and range from non-aqueous titration to UV-spectrophotometry to ion-pair visible spectrophotometry. The method reported here is a fast, reliable, and stability-indicating reversed phase HPLC for prifinium bromide in its various pharmaceutical formulations. The mobile phase was 0.03 M ammonium acetate in acetonitrile: water (65:35); the pH was adjusted to 4.0 with glacial acetic acid. The column utilized was (250 mm × 4.6 mm i.d.) Supelcosil LC-8-DB (5μ) and detection was carried at 254 nm. Benzophenone was used as internal standard. The assay was applied to commercial products and the results expressed in (% label claim ± RSD) are (99-58 ± 0.36), (100.50 ± 0.40), (99-95 ± 0.70), (99. 94 ± 0.29), (100.28 ± 0.52), and (99-99 ± 0.57) for six commercial formulations. The method was tested for linearity, recovery, and specificity and was found fast, stability-indicating, and free from interferences. The method can be extended to separate 相似文献
19.
Kiran R. Patil Vipul P. Rane Jaiprakash N. Sangshetti Devanand B. Shinde 《Chromatographia》2008,67(7-8):575-582
A simple, rapid, and precise method is developed for the quantitative simultaneous estimation of telmisartan and ramipril
in combined pharmaceutical dosage form. A chromatographic separation of the two drugs was achieved with an ACE 5 C18, 25-cm analytical column using buffer–acetonitrile (55:45 v/v). The buffer used in mobile phase contains 0.1 M sodium perchlorate monohydrate in double distilled water pH adjusted 3.0
with trifluoroacetic acid. The instrumental settings are flow rate of 1.5 mL min−1, column temperature at 30 °C, and detector wavelength of 215 nm using a photodiode array detector. The resolution between
ramipril and telmisartan were found to be more than 5. Theoretical plates for ramipril and telmisartan were 13,022 and 6,629.
Tailing factor for ramipril and telmisartan was 0.94 and 0.98. Telmisartan, ramipril and their combination drug product were
exposed to thermal, photolytic, hydrolytic and oxidative stress conditions, and the stressed samples were analysed by the
proposed method. Peak homogeneity data of telmisartan and ramipril is obtained using photodiode array detector, in the stressed
sample chromatograms, demonstrated the specificity of the method for their estimation in presence of degradants. The described
method shows excellent linearity over a range of 20–400 μg mL−1 for telmisartan and 2.5–50 μg mL−1 for ramipril. The correlation coefficient for telmisartan and ramipril are 1. The relative standard deviation for six measurements
in two sets of each drug in tablets was always less than 2%. The proposed method was found to be suitable and accurate for
quantitative determination and the stability study of telmisartan and ramipril in pharmaceutical preparations. 相似文献
20.
A flow-injection UV spectrophotometric method was developed for the determination of ambroxol hydrochloride in tablets. The
quantitative determination of ambroxol was performed at 245 nm using distilled water as the carrier solvent. In this study,
the flow rate, loop volume, and the number of injections per hour were 15 mL/min, 193 μL, and 100, respectively. The analytical
signal of ambroxol was linear in the concentration range of 40–200 μg/mL. The detection limit and limit of quantification
were found as 11.55 and 38.49 μg/mL, respectively. The results for the determination of ambroxol in tablets, 29.99 ± 0.23
mg (mean ± SD), were in good agreement with the labeled quantities (30 mg/tablet). A relatively high recovery value (100.4%)
shows the accuracy of the proposed method. Furthermore, the results obtained were in accordance with those obtained by the
HPLC method, which were used as a comparison method for the determination of ambroxol HCl, as far as the Student’s t-test
and Fisher test results were concerned. It was concluded that the proposed flow-injection UV spectrophotometric method was
fast, accurate, precise, and suitable for automation in the determination of ambroxol.
The text was submitted by the authors in English. 相似文献