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1.
G. R. van der Hoff R. Hoogerbrugge R. A. Baumann U. A. Th. Brinkman P. van Zoonen 《Chromatographia》2000,52(7-8):433-438
Summary Normal-phase LC (NPLC) is a powerful method for the clean-up of fatty samples in the determination of organochlorine pesticides
(OCPs). The injected sample deactivates the stationary phase and the triglyceride matrix therefore serves as a polarity modifier
in the NPLC separation. Thus, the amount of sample injected is the key to both selectivity and sensitivity in matrixmodified
LC coupled to capillary GC.
In coupled LC-GC the NPLC separation becomes particularly critical because only a limited amount of the LC eluent can be transferred
to the GC and the triglyceride matrix must be prevented from entering the GC, because it degrades the performance of the injector
and the column. In previous applications method development was seriously hampered by these boundary conditions and tedious
and lengthy trial-and-error experiments were required to determine suitable experimental conditions. In this study an empirical
model was developed that describes the NPLC separation process in terms of column dimensions and fat loadability. The output
is given as the probability of achieving successful LC-GC analysis of a particular set of analytes, thus furnishing a useful
tool for the development of new applications in the field of exposure assessment and analysis of residues of apolar compounds
in fatty samples. The limitations of current procedures—maximum transfer volumes and minimal separation—are also discussed. 相似文献
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Summary A computer-assisted method is presented for mobile phase selection for the optimal separation of pesticides by HPTLC and HPLC. The system is based on a plot of solute retention value and separation criterion vs. binary mobile phase composition for graphic optimization. The result of HPTLC can be transposed to HPLC for optimal separation. The transposition equation is given. 相似文献
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全二维气相色谱技术及其进展 总被引:37,自引:2,他引:35
许多分析问题的解决需要得到比一维色谱技术能提供的更高的分辨率。分离能力可通过使用多种分离技术或机理的组合来增强。此时 ,样品被分散在不同的时间维 ,最终的分辨率强烈地依赖于这些维间分离特性的差异。当它们之间没有关联 ,也即相互间正交时 ,系统可获得最高的分辨率。全二维气相色谱 (GC×GC)提供了一个真正的正交分离系统。它把分离机理不同而又互相独立的两支色谱柱以串联方式结合组成二维气相色谱。在这两支色谱柱之间装有的一个调制器起捕集再传送的作用。全二维色谱的峰容量为组成它的两支色谱柱各自峰容量的乘积。 相似文献
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Effects of GC temperature and carrier gas flow rate on on‐line oxygen isotope measurement as studied by on‐column CO injection 下载免费PDF全文
Although deemed important to δ18O measurement by on‐line high‐temperature conversion techniques, how the GC conditions affect δ18O measurement is rarely examined adequately. We therefore directly injected different volumes of CO or CO–N2 mix onto the GC column by a six‐port valve and examined the CO yield, CO peak shape, CO–N2 separation, and δ18O value under different GC temperatures and carrier gas flow rates. The results show the CO peak area decreases when the carrier gas flow rate increases. The GC temperature has no effect on peak area. The peak width increases with the increase of CO injection volume but decreases with the increase of GC temperature and carrier gas flow rate. The peak intensity increases with the increase of GC temperature and CO injection volume but decreases with the increase of carrier gas flow rate. The peak separation time between N2 and CO decreases with an increase of GC temperature and carrier gas flow rate. δ18O value decreases with the increase of CO injection volume (when half m/z 28 intensity is <3 V) and GC temperature but is insensitive to carrier gas flow rate. On average, the δ18O value of the injected CO is about 1‰ higher than that of identical reference CO. The δ18O distribution pattern of the injected CO is probably a combined result of ion source nonlinearity and preferential loss of C16O or oxygen isotopic exchange between zeolite and CO. For practical application, a lower carrier gas flow rate is therefore recommended as it has the combined advantages of higher CO yield, better N2–CO separation, lower He consumption, and insignificant effect on δ18O value, while a higher‐than‐60 °C GC temperature and a larger‐than‐100 µl CO volume is also recommended. When no N2 peak is expected, a higher GC temperature is recommended, and vice versa. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
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薄层色谱综合分离程度的定量量度 总被引:1,自引:0,他引:1
薄层色谱对多元组分的分离程度,目前常用信息量~[1]来度量.但由于计算信息量时需人为地固定R_f值的分段,且认为同一区段内的R_f值等同,而不考虑每相邻两组分的R_f差值,也忽略了同一R_f区段内不同R_f值的细微差异.同时,由于薄层色谱分离的信息量并非连续函数,它只能取很有限的若干个分立值.因此,导致有时相同的信息量值却对应着相去甚远 相似文献
8.
Mir Ali Farajzadeh Seyed Esmaeil Seyedi Mohammad Safi Shalamzari Mehdi Bamorowat 《Journal of separation science》2009,32(18):3191-3200
For the first time a dispersive liquid–liquid microextraction method on the basis of an extraction solvent lighter than water was presented in this study. Three organophosphorus pesticides (OPPs) were selected as model compounds and the proposed method was carried out for their preconcentration from water samples. In this extraction method, a mixture of cyclohexane (extraction solvent) and acetone (disperser) is rapidly injected into the aqueous sample in a special vessel (see experimental section) by syringe. Thereby, a cloudy solution is formed. In this step, the OPPs are extracted into the fine droplets of cyclohexane dispersed into aqueous phase. After centrifuging the fine droplets of cyclohexane are collected on the upper of the extraction vessel. The upper phase (0.40 μL) is injected into the gas chromatograph (GC) for separation. Analytes were detected by a flame ionization detector (FID) (for high concentrations) or MS (for low concentrations). Some important parameters, such as the kind of extraction and dispersive solvents and volume of them, extraction time, temperature, and salt amount were investigated. Under the optimum conditions, the enrichment factors (EFs) ranged from 100 to 150 and extraction recoveries varied between 68 and 105%, both of which are relatively high over those of published methods. The linear ranges were wide (10–100 000 μg/L for GC‐FID and 0.01–1 μg/L for GC‐MS) and LODs were low (3–4 μg/L for GC‐FID and 0.003 μg/L for GC‐MS). The RSDs for 100.0 μg/L of each OPP in water were in the range of 5.3–7.8% (n = 5). 相似文献
9.
气相色谱柱是气相色谱仪的关键部件,主要用于混合气体组分的分离。与传统气相色谱柱相比,基于微机电系统(MEMS)技术设计制作的微型气相色谱柱具有重量轻、体积小、功耗低、分离快速等优点,便于集成到便携式气相色谱仪中,适应了目前气相色谱仪微型化的发展趋势。该文综述了MEMS微型气相色谱柱的研究进展,首先阐述了MEMS微型气相色谱柱理论基础,随后对MEMS微型气相色谱柱沟道布局及柱内结构、固定相支撑层及固定相制备等方面进行了综述,最后对其发展趋势进行了展望。 相似文献
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Soil fumigants, like 1,3-dichloropropene and metham-sodium (forming methyl isothiocyanate) diffuse into the atmosphere, thus presenting a hazard to people in the surroundings. A method is described in which a large volume (50 μl) of extractant, used to desorb the compounds from charcoal, is injected into a GC, equipped with two capillary columns. By way of Deans switching, the solvent is separated from the compounds of interest. Modification of a GC sampler makes unattended analyses possible. 相似文献
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Fernando M. Lanas Roseli A. Francelin Ailton J. de Souza 《Journal of separation science》1991,14(6):407-411
The modified simplex algorithm proposed by Nelder and Mead has been used to optimize the separation by temperature programmed capillary GC, of volatile compounds present in alcoholic beverages. An adequate objective function, CRF, based on the separation factor of Kaiser has been used for the optimization process. A factorial design was initially performed to verify the relationship between the several parameters of interest. Following this, the optimization was executed and a surface adjusted within the set of experimental data. 相似文献
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Jens Dallüge R. Ou-Aissa J. J. Vreuls Udo A. Th. Brinkman J. R. Veraart 《Journal of separation science》1999,22(8):459-464
The features of a resistive-heated capillary column for fast temperature-programmed gas chromatography (GC) have been evaluated. Experiments were carried out using a commercial available EZ Flash GC, an assembly which can be used to upgrade existing gas chromatographs. The capillary column is placed inside a metal tube which can be heated, and cooled, much more rapidly than any conventional GC oven. The EZ Flash assembly can generate temperature ramps up to 1200°/min and can be cooled down from 300 to 50°C in 30 s. Samples were injected via a conventional split/splitless injector and transferred to the GC column. The combination of a short column (5 m×0.25 mm i. d.), a high gas flow rate (up to 10 mL/min), and fast temperature programmes typically decreased analysis times from 30 min to about 2.5 min. Both the split and splitless injection mode could be used. With n-alkanes as test analytes, the standard deviations of the retention times with respect to the peak width were less than 15% (n = 7). First results on RSDs of peak areas of less than 3% for all but one n-alkane indicate that the technique can also be used for quantification. The combined use of a short GC column and fast temperature gradients does cause some loss of separation efficiency, but the approach is ideally suited for fast screening as illustrated for polycyclic aromatic hydrocarbons, organophosphorus pesticides, and triazine herbicides as test compounds. Total analysis times – which included injection, separation, and equilibration to initial conditions – were typically less than 3 min. 相似文献
14.
Philip L. Wylie Richard J. Phillips Kenneth J. Klein Michael Q. Thompson Bruce W. Hermann 《Journal of separation science》1991,14(10):649-655
An experimental injection port has been designed for split or splitless sample introduction in capillary gas chromatography; the inlet uses electronic pressure control, in order that the column head pressure may be set from the GC keyboard, and the inlet may be used in the constant flow or constant pressure modes. Alternatively, the column head pressure may be programmed up or down during a GC run in a manner analogous to even temperature programming. Using electronic pressure control, a method was developed which used high column head pressures (high column flow rates) at the time of injection, followed by rapid reduction of the pressure to that required for optimum GC separation. In this way, high flow rates could be used at the time of splitless injection to reduce sample discrimination, while lower flow rates could be used for the separation. Using this method, up to 5 μl of a test sample could be injected in the splitless mode with no discrimination; in another experiment, 2.3 times as much sample was introduced into the column by using electronic pressure programming. Some GC peak broadening was observed in the first experiment. 相似文献
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Mondello L Casilli A Tranchida PQ Lo Presti M Dugo P Dugo G 《Analytical and bioanalytical chemistry》2007,389(6):1755-1763
The present research is focused on the development of a comprehensive two-dimensional gas chromatography–rapid scanning quadrupole
mass spectrometric (GC x GC-qMS) methodology for the analysis of trace-amount pesticides contained in a complex real-world
sample. Reliable peak assignment was carried out by using a recently developed, dedicated pesticide MS library (for comprehensive
GC analysis), characterized by a twin-filter search procedure, the first based on a minimum degree of spectral similarity
and the second on the interactive use of linear retention indices (LRI). The library was constructed by subjecting mixtures
of commonly used pesticides to GC x GC-qMS analysis and then deriving their pure mass spectra and LRI values. In order to
verify the effectiveness of the approach, a pesticide-contaminated red grapefruit extract was analysed. The certainty of peak
assignment was attained by exploiting both the enhanced separation power of dual-oven GC x GC and the highly effective search
procedure. 相似文献
17.
Capillary electrophoresis (CE) is a high-resolution technique for the separation of complex biological and chemical mixtures. CE continues to emerge as a powerful tool in the determination of lipids. Here we review the analytical potential of CE for the determination of a wide range of lipids. The different classes of lipids are introduced, and the different modes of CE and optimization methods for the separation of lipids are described. The advantages and disadvantages of the different modes of CE compared to traditional methods like gas chromatography (GC) and liquid chromatography (LC) in the determination of lipids are discussed. Finally, the potential of CE in the determination of lipids in the future is illustrated. 相似文献
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改变相比/顶空气相色谱法测定变压器油中溶解气体的分配常数 总被引:3,自引:0,他引:3
采用改变相比/顶空气相色谱法测定了甲烷、乙炔、乙烯、乙烷和丙烷在变压器油中的分配常数。顶空瓶中的气体样品经石英毛细管送到气相色谱仪的六通进样阀样品管中,然后进行分离和定量。采用标准曲线法定量,通过测定5个不同相比时轻烃组分的顶空浓度,计算顶空浓度倒数与相比之间的线性回归方程,测定了20 ℃和50 ℃时烃类气体在变压器油中溶解气体的分配常数。除甲烷外,计算所得的分配常数与文献值基本吻合,油中溶解气体浓度的实验值与实际值之间的相对误差小于4.14%,表明用此方法可以测定不同温度下变压器油中溶解气体的分 相似文献
20.
Reaction liquid is continuously circulated between the reactor and an automated Bendix liquid injection valve. A well defined volume of liquid is injected into a hot zone. The liquid injected is then vaporized and the resulting sample gas is swept with a stream of helium into a series of dilution chambers. The analyte concentration-time profile at the exit of the last chamber was mathematically modelled. It was found that the degree of symmetry of the profile increases when the number of chambers increases. The design and performance of the system are discussed together with results of a kinetic study of a chemical reaction. 相似文献