Chromatographic properties of a capillary column with the Aerosil modified with nematic 4-methoxy-4′-ethoxyazoxybenzene

The chromatographic properties of a SCOT capillary column with the Aerosil modified with a nematic liquid crystal of 4-methoxy-4′-ethoxyazoxybenzene were studied. The Rohrschneider constants and retention factors were determined for substances from various classes. The microheterogeneous adsorbent SCOT(SiO₂ + MEAB) belongs to medium-polarity stationary phases by its selectivity. It was shown that, in the temperature range 95–110°C, the studied column possessed high values of para-meta selectivity, efficiency, and capacity with respect to arenes and polar substances. Examples of rapid separations of mixtures containing isomers of different types are presented.     

Rapid RP-LC Method with Fluorescence Detection for Analysis of Fexofenadine in Human Plasma

A rapid and sensitive reversed-phase high-performance liquid chromatographic method for analysis of fexofenadine in human plasma has been developed and optimized. The analytes were extracted from biological samples by solid-phase extraction on hydrophilic–lipophilic balance cartridges. LC separation was performed on a C₁₈ analytical column (125 mm × 4 mm i.d., 5-μm particles) with 42:58 (v/v) acetonitrile–water adjusted to pH 2.7 with 85% orthophosphoric acid as mobile phase. Fluorescence detection was performed with excitation at 230 nm and emission at 290 nm. The total time for chromatographic separation was 7 min. The method was validated in accordance with EU guidelines by analysis of plasma samples fortified with fexofenadine at concentrations between 0.05 and 800 ng mL⁻¹. Calibration plots were linear in this range. Mean recovery was typically 94.03% and the detection limit was 0.05 ng mL⁻¹. The time required for quantitative analysis is shorter than that required by other methods.

     

Steroid analysis by gas chromatography with SCOT and wide-bore WCOT columns

Glass capillary columns are ideal for analysis of urinary steroid profiles (i.e. the total steroid neutral fraction without prior separation into sub-groups). In this paper performance of both SCOT and wide-bore WCOT columns has been compared, resulting in no significant quantitative difference on urine extracts run as trimethylsilyl ether derivatives. However, because of increased efficiency the WB-WCOT column exhibited more sensitivity in measurement of small amounts of 11-ox-aetiocholanolone. Sensitivity of other steroids was greatly enhanced by use of either SCOT or WB-WCOT, leading to an almost tenfold increase over conventional packed columns (e.g. androsterone and aetiocholanolone < 40 μg per 24 h urine sample). A simple splitless injection system (based on a design of Dr. W. Greenaway, Oxford University) is presented. Experiments were also carried out using a SCOT column in conjunction with an FM-electron capture detector. Whilst efficiency was impaired due to the design of the detector, use of He (carrier) and N₂ (make up gas) showed that several steroid derivatives could be easily measured at well below the 10^?10 g level with much more rapid retention times than with a 1½m packed column. Highly successful separation of 19 amino acids (as fluoro-acyl derivatives) was achieved in 35 minutes using a SCOT (30 m) SP2100 column.     

Dual column gas chromatographic system for use in mass spectral determination of nitrosamines.

A packed gas chromatographic column and a support coated open tubular (SCOT) column are connected in series. Between the columns are two micro-volume switching valves, one enabling solvent to be vented. Short retention nitrosamines are passed through both columns, whereas longer retention nitrosamines by-pass the SCOT column by means of the other switching valve.     

Quantitative Analysts of 5-Hydroxytryptamtne in Biological Material by High Perfornance Liquid Chromatography and Electrochmical Detection

Abstract

A quantitative method for the analysis of 5-hydroxytryptamine in biological material is described. The method is based on high performance liquid chromatography (HPLC) with electrochemical detection. A simple purification on a weakly acidic ion exchange resin prior to the analysis gives quite clean samples and permits concentration of diluted samples. The chromatographic separation is performed on a reverse phase column with organic modifier added to an aqueous eluent. With this analytical system 25 pg of 5-hydroxytryptamine can be detected.     

A Stability-Indicating LC Method for Lumefantrine

A simple, rapid, and precise method is developed for the quantitative determination of lumefantrine (Lume) in active pharmaceutical ingredient (API). A chromatographic separation of Lume and its degradants were achieved with an X-Terra RP18, 250 × 4.6 mm, and 5 μ analytical column using buffer–acetonitrile (30:70 v/v). The buffer used in mobile phase contains 0.1 M sodium perchlorate monohydrate in double distilled water pH adjusted to 2.1 with trifluoroacetic acid. The instrumental settings are flow rate of 0.5 mL (L), column temperature at 35 °C, and detector wavelength of 235 nm using a photodiode array detector. Lume was exposed to thermal, photolytic, hydrolytic and oxidative stress conditions, and the stressed samples were analysed by the proposed method. Peak homogeneity data of Lume obtained by photodiode array detection, in the stressed sample chromatograms, demonstrated the specificity of the method for estimation in the presence of degradants. The described method shows excellent linearity over a range of 10–200 μg L⁻¹ for Lume. The correlation coefficient is 1. The relative standard deviation of peak area for six measurements is always less than 2% between days. The proposed method was found to be suitable and accurate for quantitative determination and stability study of Lume in API.

     

A Simple Design to Realize Micro-column Separation by Conventional Analytical HPLC

The conventional analytical HPLC was successfully developed for micro‐column separation by using a simple eluate splitting system, self‐preparation of packing column and on‐capillary column detector in our laboratory. Porous inlet frit in fused silica capillary was rapidly prepared by sintering stainless steel powders under 500 meshes for about 20 s. The use of such frits or metal meshes in capillary to retain C₁₈ particles of chromatographic packing was demonstrated to be stable and specially robust with continuous packing and long chromatographic runs. Furthermore, the chromatographic behavior was detailedly evaluated by changing the flow rate and the percentage of mobile phase using the prepared capillary column. Under the optimal experimental conditions, baseline separation of the model analytes including thiourea, benzene, toluene, ethylbenzene was obtained with a high column efficiency near 70000N (plates/m) by the developed capillary‐HPLC.     

Increased productivity in quantitative bioanalysis using a monolithic column coupled with high-flow direct-injection liquid chromatography/tandem mass spectrometry

The feasibility of using a monolithic column as the analytical column in conjunction with high-flow direct-injection liquid chromatography/tandem mass spectrometry (LC/MS/MS) to increase productivity for quantitative bioanalysis has been investigated using plasma samples containing a drug and its epimer metabolite. Since the chosen drug and its epimer metabolite have the same selected reaction monitoring (SRM) transitions, chromatographic baseline separation of these two compounds was required. The results obtained from this monolithic column system were directly compared with the results obtained from a previously validated assay using a conventional C18 column as the analytical column. Both systems have the same sample preparation, mobile phases and MS conditions. The eluting flow rate for the monolithic column system was 3.2 mL/min (with 4:1 splitting) and for the C18 column system was 1.2 mL/min (with 3:1 splitting). The monolithic column system had a run time of 5 min and the conventional C18 column system had a run time of 10 min. The methods on the two systems were found to be equivalent in terms of accuracy, precision, sensitivity and chromatographic separation. Without sacrificing the chromatographic separation, sensitivity, accuracy and precision of the method, the reduced run time of the monolithic column method increased the sample throughput by a factor of two.     

Preparative separation of isoquinoline alkaloids from Corydalis impatiens using middle chromatogram isolated gel column coupled with positively charged reversed‐phase liquid chromatography

Positively charged reversed‐phase liquid chromatography was employed for the efficient preparative separation of isoquinoline alkaloids from Corydalis impatiens. Ten commercially available columns were compared for isoquinoline alkaloids analysis. While tailing, overloading, lower resolution, and buffer salts limited the application in purification of isoquinoline compounds of many of these columns, one positively charged reversed‐phase C18 column (XCharge C18) overcame these drawbacks, allowing for favorable separation resolution, even when loading isoquinoline compounds on a larger, preparative scale. The general separation process is as follows. First, isoquinoline alkaloids are enriched with Corydalis impatiens extract via a middle chromatogram isolated gel column. After column selection, separation is performed on an XCharge C18 analytical column, from which two evident chromatographic peaks are readily obtained. Finally, two isoquinoline alkaloids (protopine and corydamine) are selectively purified on the XCharge C18 preparative column. These results demonstrate that a middle chromatogram isolated gel column coupled with positively charged reversed‐phase liquid chromatography is effective for the preparative separation of isoquinoline alkaloids from Corydalis impatiens.     

两种轻烃分析方法(“PTV切割反吹”和“顶空”)的对比研究

 建立了“程序升温蒸发进样器 (PTV)切割反吹”和“顶空”两种有关原油中轻烃的分析方法 ,色谱柱的使用寿命长、分析周期短 ,原油中 < ,将原油直接注入汽化室所得的分析数据较可靠 ,并对引起误差的原因进行了探讨。指出用这两种方法所获得的数据是不能合在一起作地化研究的 ) % 5 2 1%～ ( 19个地化参数的相对误差范围约为± 10个油样用两种分析方法所得 6个油区的 ,还报道了采自我国 ,并有良好的重复性。。     

Analysis of polychlorodibenzo‐p‐dioxins and polychlorodibenzofurans in stationary source emissions in GC–MS/MS using hydrogen as the carrier gas

The European and American methods for the determination of polychlorodibenzo‐p‐dioxins and polychlorodibenzofurans in stationary source emissions require a high‐resolution mass spectrometer detector. At the same time, all of the 17 toxic 2,3,7,8‐chlorine‐substituted isomers have to be separated by an appropriate chromatographic method. The resulting analysis has long runtimes and sometimes a double‐column run is needed, which results in a huge waste of time, money and manual labor. To obtain a fast and cost‐effective but still reliable analytical system, a single‐column gas chromatography with hydrogen as carrier gas and tandem mass spectrometry detection is proposed. The use of hydrogen as the carrier gas is a good choice to shorten runtimes and improve the chromatographic resolution, while tandem mass spectrometry is a well‐known alternative for this analysis. All the chromatographic and mass spectrometric parameters fill the requirements of the reference methods with a 35% reduction of runtimes. The accuracy is tested with three fly ash samples of a proficiency interlaboratory test. A good correlation between the results is obtained (R ² = 0.992, slope = 0.9675), and no coelutions are noted. The system robustness is tested during 5 years of constant use and the maximal relative standard deviation of the relative response factor is 18.8%.     

RP-LC Determination of the cis-Isomer of Glimepiride in a Bulk Drug Substance

A rapid reversed-phase high-performance liquid chromatographic procedure is developed and validated for the resolution of the cis-isomer of 1-[[p-[2-(3-ethyl-4-methyl-2-oxo-3-pyrroline-1-carboxamido) ethyl] phenyl] sulfonyl]-3-(trans-4-methylcyclohexyl) urea, a dopamine agonist in bulk drugs. The cis-isomer and glimepiride were baseline resolved on a Waters Symmetry column (50 × 4.6 mm, 3.5 μm) using a mobile phase system containing water: tetrahydrofuran (75:25; v/v. The chromatographic resolutions between cis-isomer and glimepiride were found to be greater than two. The developed method was extensively validated and proved to be robust. The limit of detection and the limit of quantification of cis-isomer were 500 and 1,500 ng mL⁻¹, respectively, for 10 μL injection volume. The percentage recovery of the cis-isomer ranged from 97.3 to 102.0 in bulk drug samples of glimepiride. Glimepiride sample solution and mobile phase were found to be stable for at least 48 h. The proposed method was found to be suitable and accurate for the quantitative determination of the cis-isomer in bulk drugs.     

Quantitative Analysis of Terbutaline (Bricanyl®) in Human Plasma with Liquid Chromatography and Electrochemical Detection Using On-Line Enrichment

Abstract

A liquid chromatographic method with electrochemical detection (LC-EC) has been developed for the quantitative analysis of terbuta-line in the range 5–50 pmole ml^?1 of human plasma. Terbutaline is isolated from 2 ml of plasma on an ion-exchange column and the eluate is concentrated on a hydrophobic precolumn on-line in the chromatographic system. The precolumn is then back-flushed for further separation onto a hydrophobic analytical column. The mobile phase is a methanol-aqueous buffer to which sodium perchlorate is added to achieve resolution from interfering peaks. A glassy carbon electrode is used for detection. Comparison has been made with gas chromatography-mass spectrometry (GC-MS) to examine the accuracy of the method.     

Determination of amino acids in urine by gas chromatography

This report describes a convenient means of reducing the complex matrix which is responsible for interference during gas chromatographic determination of amino acids in urine. The pre-chromatographic clean-up employs the principle of solid phase extraction using bonded silica incorporating cation exchange groups. This approach avoids the detrimental effects on amino acid recoveries associated with resin-based cation exchangers. In spite of significant reduction in the complexity of chromatograms, only the high efficiency and resolving power offered by the analytical capillary column (e. g. fused silica open tubular, FSOT) is sufficient for quantitative and analysis of amino acids in urine. Reproducibility data from the complete procedure are determined, coefficients of variation (CV) for most amino acids being better than 5% with a mean recovery of 96%.     

Analysis of gases containing inorganic and organic compounds using a combination of a thick-film capillary column and a packed adsorption column

A gas chromatographic system consisting of one multiport valve, two (hot-wire and flame-ionization) detectors and two analytical columns (one thick-film capillary and one packed adsorption column) is used for the analysis of gas samples containing a number of inorganic compounds (hydrogen, argon, oxygen, nitrogen, carbon monoxide, and carbon dioxide) and organic compounds. Examples include samples containing hydrocarbons up to n-nonane and benzene and toluene. The system also permits the analysis of more complicated samples containing, for example, alcohols, in addition to hydrocarbons.     

Zirconia-based column high-performance liquid chromatography/atmospheric pressure photoionization tandem mass spectrometric analyses of drug molecules in rat plasma

A method using zirconia-based column high-performance liquid chromatography (HPLC) interfaced with an atmospheric pressure photoionization (APPI) source and a tandem mass spectrometer (MS/MS) was developed for the quantitative determination of new chemical entities in rat plasma in support of pharmacokinetics studies. The ionization suppression resulting from endogenous components of the biological matrices on the quantitative zirconia-based column HPLC/APPI-MS/MS method was investigated using the post-column infusion technique. The analytical results for 'rapid rat pharmacokinetics' for 12 drug discovery compounds, obtained by both silica-based phase (S-phase) and zirconia-based phase (Z-phase) chromatographic separation, are in good agreement in terms of accuracy. The application of a Z-phase column for high-temperature fast HPLC/MS/MS methods was explored to reduce the analysis time from 3 min to 30 s for column temperatures of 25-110 degrees C, respectively. The chromatographic retention times and peak responses of all analytes were found to be reproducible under high-temperature conditions following 100 continuous injections, with %CV less than 0.4 and 5, respectively.     

Pre-Column Switching Techniques for the Determination of Drugs and Metabolites in Body Fluids in Research and Routine Analysis

Abstract

The use of a column switching system for direct injection of samples and of a sample clean-up on reversed phase pre-columns is described. The pre-columns were filled with spherical C-18 silica gel of particle size 30 μm.

Two applications are reported on: (1) the direct injection of serum samples for the simultaneous analysis of nine antiepileptic drugs and metabolites and (2) the determination of phenytoin and of carbamazepine in serum ultra-filtrates.

The purge liquid for the sample clean-up was diluted phosphoric acid, and the eluent mixture for the chromatographic separation was water/acetonitrile. The analytical column (length 12.5 cm) was filled with C-18 silica gel of particle size 5 μm. A gradient elution was chosen for the first application, while the second application was carried out using isocratic chromatographic conditions.     

Ion chromatographic determination of iodide in urine and serum using a tubular ion-selective electrode based on a homogeneous crystalline membrane

The use of a laboratory-made iodide ion-selective electrode with tubular configuration and based on a crystalline membrane (AgI/Ag₂S) as the detector for ion chromatographic determination of iodide in urine and serum is described. A CIS reversed-phase column was coated withN-cetylpyridinium chloride to prepare a low-exchange-capacity analytical column and with hexadecyltrimethylammonium bromide to prepare a concentrator pre-column. A 2.0 ml min^–1 flow rate of deionized water and 0.1 mol 1^–1 KNO₃ solution was used for the pre-concentration and for the chromatographic separation, respectively. For optimum performance of the detector a background level of iodide was added into the column effluent. A linear relationship (r = 0.9997) between tubular electrode potential (as peak height) and iodide concentration in the range 5–400 g 1^–1 and a detection limit of 1.47 g 1^–1 were obtained. The method shows good reproducibility for both peak height (2.2% RSD) and retention time (1.3% RSD). Recoveries on its application to the samples were 93.0–100.9% for urine and 91.4–106.0% for serum.     

Determination of rifampicin in rat plasma by modified large‐volume direct injection RAM‐HPLC and its application to a pharmcokinetic study

A direct large volume injection high‐performance liquid chromatography (HPLC) method with homemade restricted‐access media (RAM) pre‐column and combined with a column‐switching valve was established and developed for determination rifampicin (RIP) in rat plasma. The rat plasma samples (100 μL) were injected directly onto pre‐column, where RIP was retained and pre‐concentrated, while proteins were washed to waste using a methanol–water (5:95) as the mobile phase at a flow rate of 1 mL/min. Then, by rotation of the switching valve at 5 min, the RIP were eluted from the pre‐column and transferred to an Luna C₁₈ analytical column by the chromatographic mobile phase consisting of methanol–acetonitrile–10 mm ammonium format (60:5:35) at a flow rate of 1 mL/min. The total analytical run time was 15 min with UV detection wavelength at 254 nm. Carbamazepine was used as the internal standard. Excellent linear correlation (r = 0.9993) was obtained in the range of 0.25–8 µg/mL for rat plasma. The intra‐day and inter‐day precisions of RIP were all <5.0%. The recoveries were in the range of from 99.98–113.66% for plasma. This on‐line RAM‐HPLC method was successfully applied to the pharmacokinetic study of RIP in rat plasma. Copyright © 2014 John Wiley & Sons, Ltd.     

Rapid RP-LC Method with Fluorescence Detection for Analysis of Fexofenadine in Human Plasma

A rapid and sensitive reversed-phase high-performance liquid chromatographic method for analysis of fexofenadine in human plasma has been developed and optimized. The analytes were extracted from biological samples by solid-phase extraction on hydrophilic–lipophilic balance cartridges. LC separation was performed on a C₁₈ analytical column (125 mm × 4 mm i.d., 5-μm particles) with 42:58 (v/v) acetonitrile–water adjusted to pH 2.7 with 85% orthophosphoric acid as mobile phase. Fluorescence detection was performed with excitation at 230 nm and emission at 290 nm. The total time for chromatographic separation was 7 min. The method was validated in accordance with EU guidelines by analysis of plasma samples fortified with fexofenadine at concentrations between 0.05 and 800 ng mL^?1. Calibration plots were linear in this range. Mean recovery was typically 94.03% and the detection limit was 0.05 ng mL^?1. The time required for quantitative analysis is shorter than that required by other methods.