Fast temperature programming in routine analysis of multiple pesticide residues in food matrices

Flash gas chromatographic (GC) analysis of 15 organophosphorus pesticides commonly occurring in food crops was performed using the Thermedics Detection EZ Flash upgrade kit installed in the oven of a HP 5890 Series II Plus gas chromatograph. The temperature program and splitless time period were the main parameters to be optimized. In the first set of experiments wheat matrix-matched standards were analyzed both by: (i) the flash GC technique (resistive heating of a 5 m capillary column), and (ii) the conventional GC technique (moderate oven temperature programming of a 30 m capillary column). Using the flash GC technique, the analysis time was reduced by a factor of more than 10 compared to the conventional GC technique. Dramatically improved detectability of analytes was achieved due to much narrower peak widths. The flash GC technique was compared with another approach to faster GC analysis employing a 5 m column and fast temperature programming with a conventional GC oven. In comparison with this alternative, in the case of flash GC significantly better retention time repeatability was observed. The other superiority of resistive heating is very rapid cooling down (i.e., equilibration to the initial conditions) which contributes to the increased sample throughput.     

Improving splitless injection with electronic pressure programming

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.     

Quantitation in capillary gas chromatography with emphasis on the problems of sample introduction

Sampling techniques for practical quantitative capillary GC have to meet certain principal requirements. Both the absolute and the relative peak areas (e.g. column loads) must be reproducible with high precision and at high accuracy; discrimination of certain constituents according to their volatility should not take place on sampling. On the basis of systematic studies, the three most reliable sampling techniques used for GC analyses with the aim of achieving precise and accurate quantitative data proved to be the following: On-column, injection, splitless PTV injection, and an optimized version of split sampling called “cooled needle split” injection. The on-column technique can be optimized by using precolumns with wider internal diameters and without stationary phase coatings to overcome the problems of large liquid sampling volumes and for automation. The PTV technique should only be used in the splitless mode because discrimination cannot be suppressed completely with the split mode. All three of the techniques can be operated automatically, either to avoid “human interference”, i.e. to improve precision or for unattended operation to save man-power.     

Analysis of headspace samples using off-line sorbent trapping coupled with automated thermal desorption and splitless injection onto a cryogenically cooled wide bore capillary column

Gas chromatographic equipment and procedures are described for automated splitless injection of pseudo-static headspace samples collected externally onto a sorbent trap. The GC microprocessor controls, in sequence, carrier gas backflushing of the sorbent trap for water removal, splitless thermal desorption into a cryogenically cooled wide bore (0.53 mm i. d.) capillary column and oven temperature programming. The method has been routinely applied for profiling the mid-to-high boiling compounds (bp 80–225°C) in the headspace of a variety of foods and beverages. Method criteria, advantages and limitations are discussed. FID and NPD chromatograms for brewed coffee and peanut butter volatiles are presented as typical examples.     

Sensitive determination of styrene and related compounds in human body fluids by headspace capillary gas chromatography with cryogenic oven trapping

Summary A simple and sensitive method is presented for determination of styrene, toluene, ethylbenzene, isopropylbenzene andn-propylbenzene in human body fluids by capillary gas chromatography (GC) with cryogenic oven trapping. After heating a blood or urine sample containing each compound andp-diethylbenzene (internal standard, IS) in a 7.0-mL vial at 60°C for 20 min, 5 mL of headspace vapor was drawn into a glass syringe and injected into a GC. All vapor was introduced into an Rtx-Volatile middle bore capillary column in splitless mode at oven temperature of 20°C to trap entire analytes, and the oven temperature then programmed to 280°C for GC measurements by flame ionization detection. The present conditions gave sharp peaks of each compound and IS, and low background noises for whole blood or urine samples.     

Rapid and quantitative extraction and analysis of trace organics using directly coupled SFE-GC

Supercritical fluid extraction can be coupled with capillary gas chromatography (SFE-GC) using commercially-available on-column or split/splitless injection ports. While liquid solvent extractions require several hours or even days to perform, SFC-GC analyses can be completed in ≤ 1 hour including extraction, analyte concentration, and GC separation. SFE-GC yields chromatographic peak shapes that compare favorably with those obtained using conventional liquid solvent injections. Quantitative extraction and recovery of analytes is usually achieved in 10 minutes, and maximum sensitivity is obtained since the extracted analytes can be quantitatively transferred into the GC column for cryogenic focusing prior to GC analysis. SFE-GC analysis of a variety of organic pollutants from environmental solids and sorbent resins, and flavor and fragrance compounds from food products will be discussed.     

Gas chromatography with ballistic heating and ultrafast cooling of column

An overview of the existing methods for minimization of the analysis time in gas chromatography (GC) is presented and a new system for fast temperature programming and very fast cooling down is evaluated. In this study, a system of coaxial tubes, a heating/cooling module (HC-M), was developed and studied with a capillary column placed inside the HC-M. The module itself was heated by a GC oven and cooled down by an external cooling medium. The HC-M was heated at rates of up to 330 °C min⁻¹ and cooled at the rate of 6000 °C min⁻¹. The GC system was prepared for the next run within a few seconds. The HC-M permits good separation reproducibility, comparable with that of a conventional GC, expressed in terms of relative retention times and peak areas of analytes reproducibilities. The HC-M can be used within any commercial gas chromatograph.     

The Use of Non-Splitting Injection Techniques for Trace Analysis in Narrow-Bore Capillary Gas Chromatography

The use of hot splitless, cold splitless, and on-column injections for trace analysis in narrow-bore capillary GC is evaluated. Despite the low flow rates for the columns used, the required splitless times for splitless injections can be surprisingly short if liners with a small inside diameter are used. On-column injection can be applied by using an appropriate normal-bore precolumn coupled to the narrow-bore analytical column using a specially designed low dead volume column connector. The effects of the experimental conditions such as sample volume, injection temperature, and initial oven temperature on peak focusing and the discrimination and degradation behavior of the analytes are discussed. The possibilities to obtain sensitive and fast separations are illustrated by various applications.     

Construction and application of a cold on-column injection system for capillary gas chromatography

A cold on-column injection system for capillary gas chromatography (GC) applications was constructed. It was based upon a conventional split/splitless capillary GC inlet, which in turn was a modification of a conventional packed GC column inlet. The heart of the laboratory constructed cold on-column inlet design was a disposable pyrex micro-sampling pipet, which functioned as a needle guide for sample injection. The sample was injected through a traditional GC septum. Construction of the injection system is described and applications are illustrated by separations of a variety of complex mixtures.     

Large volume sample introduction using temperature programmable injectors: Implications of liner diameter

Temperature programmable injectors with liner diameters ranging from 1 to 3.5 mm are evaluated and compared for solvent split injection of large volumes in capillary gas chromatography. The liner dimensions determine whether a large sample volume can be introduced rapidly or has to be introduced in a speed controlled manner. The effect of the injection technique used on the recovery of n-alkanes is evaluated. Furthermore the influence of the liner diameter on the occurrence of thermal degradation during splitless transfer to the analytical column is studied. Guidelines are given for the selection of the PTV liner internal diameter best suited for specific applications.     

Fast Capillary Gas Chromatography: Comparison of Different Approaches

Savings in analysis time in capillary GC have always been an important issue for chromatographers since the introduction of capillary columns by Golay in 1958. In laboratories where gas chromatographic techniques are routinely applied as an analytical technique, every reduction of analysis time, without significant loss of resolution, can be translated into a higher sample throughput and hence reduce the laboratory operating costs. In this contribution, three different approaches for obtaining fast GC separations are investigated. First, a narrow-bore column is used under conventional GC operating conditions. Secondly, the same narrow-bore column is used under typical fast GC conditions. Here, a high oven temperature programming rate is used. The third approach uses a recent new development in GC instrumentation: Flash-2D-GC. Here the column is placed inside a metal tube, which is resistively heated. With this system, a temperature programming rate of 100°/s is possible. The results obtained with each of these three approaches are compared with results obtained on a column with conventional dimensions. This comparison takes retention times as well as plate numbers and resolution into consideration.     

快速气相色谱法分析石油饱和烃

提出了一种快速分析原油和岩石抽提物中饱和烃组分的毛细管气相色谱(GC)方法。由于在该方法中采用了细内径毛细管柱,故饱和烃的GC分析周期由原来的80~90 min缩短至15 min,分析速度加快约5倍,大大提高了工作效率和仪器通量,使石油饱和烃得到了很好的分离分析。该方法符合中华人民共和国石油天然气行业标准SY/T5120-1997的要求。20万理论塔板数的细径柱的应用,可供石油中异构烷烃,尤其是甾烷、萜烷类的气相色谱/质谱(GC/MS)快速分析方法及芳烃的GC快速分析方法借鉴。     

毛细管气相色谱法测定食品、中药中的有机氯农药

建立食品和中药中有机氯农药残留量的毛细管气相色谱检测方法。样品经有机溶剂超声提取,硫酸净化,采用OV-1701毛细管柱,不分流分流进样,程序升温分离,电子捕获检测器检测,外标法定量,平均回收率为84.3%~100.6%,RSD为1.28%~3.56%。该法操作简便,重复性及分离效果好。     

A new configuration for coupling purge-and-trap/cryogenic focusing/capillary column gas chromatography with splitless injection mode

A new configuration for coupling a purge-and-trap unit to a capillary column gas chromatograph via a cryogenic focusing interface has been developed. In this configuration, the precolumn of the cryogenic focusing interface was inserted through the septum of a split/splitless injection port where it served as both sample transfer and carrier gas supply lines. The injection port of the gas chromatograph was modified by plugging the carrier gas and the septum purge lines. This configuration allowed for the desorption of analytes at high flow rates while maintaining low, analytical-column flow rates which are necessary for optimum capillary column operation. The capillary column flow rate is still controlled by the column backpressure regulator. Chromatograms of purgeable aromatics exhibited improved resolution, especially for early eluting components compared to those obtained by direct liquid injection using the normal splitless injection mode. Quantitative sample transfer to the analytical column afforded excellent linearity and reproducibility of compounds studied.     

Possibilities and limitations of fast GC with narrow-bore columns

In this work, two narrow-bore capillary columns with different internal diameters (I.D.) 0.15 mm (15 m length, 0.15 microm film thickness) and 0.10 mm (10 m length, 0.10 microm film thickness) with the same stationary phase (5% diphenyl 95% dimethylsiloxane), phase ratio and separation power were compared with regard to their advantages, practical limitations and applicability in fast GC on commercially available instrumentation. The column comparison concerns fast GC method development, speed and separation efficiency, the sample transfer into the column utilizing split and splitless inlet, sample capacity, detection (analysing compounds of a wide range of polarities and volatilities--even n-alkanes C16-C28 and selected pesticides) and ruggedness (in the field of ultratrace analysis of pesticide residues in real matrix). Under conditions corresponding to speed/separation efficiency trade-off 0.10 mm I.D. versus 0.15 mm I.D. column provides a speed gain of 1.74, but all other parameters investigated were better for the 0.15 mm I.D. column concerning more efficient sample transfer from inlet to the column using splitless injection, no discrimination with split injection. Better sample capacity (three times higher for the 0.15 mm than for the 0.10 mm I.D. column) resulted in improved ruggedness and simpler fast GC-MS method development.     

Evaluation of solid-phase microextraction desorption parameters for fast GC analysis of cocaine in coca leaves

By its simplicity and rapidity, solid-phase microextraction (SPME) appears as an interesting alternative for sample introduction in fast gas chromatography (fast GC). This combination depends on numerous parameters affecting the desorption step (i.e., the release of compounds from the SPME fiber coating to the GC column). In this study, different liner diameters, injection temperatures, and gas flow rates are evaluated to accelerate the thermal desorption process in the injection port. This process is followed with real-time direct coupling a split/splitless injector to a mass spectrometer by means of a short capillary. It is shown that an effective, quantitative, and rapid transfer of cocaine (COC) and cocaethylene (CE) is performed with a 0.75-mm i.d. liner, at 280 degrees C and 4 mL/min gas flow rate. The 7-microm polydimethylsiloxane (PDMS) coating is selected for combination with fast GC because the 100-microm PDMS fiber presents some limitations caused by fiber bleeding. Finally, the developed SPME-fast GC method is applied to perform in less than 5 min, the quantitation of COC extracted from coca leaves by focused microwave-assisted extraction. An amount of 7.6 +/- 0.5 mg of COC per gram of dry mass is found, which is in good agreement with previously published results.     

GC/MS和NMR分析5-氟-2-硝基苯乙醚还原反应的副产物

采用GC-MS分析5-氟-2-硝基苯乙醚的还原反应产物．在30．0m×250μmZB-5MS毛细管柱上,载气为He气,流量为0．8mL／min,起始柱温120℃维持3min,以20℃／min的速率升至260℃并维持10min,气化室温度270℃的条件下,5-氟-2-硝基苯乙醚还原的多种产物获得良好分离．通过对相应质谱图的解析,共鉴定出包括主产物在内的6种主要反应产物．经柱色谱分离提纯得到其中主要副产物,结合^1H-NMR确证该产物为未见报道过的副产物4-氟-2-氯-6-乙氧基苯胺．     

Analysis of triglycerides by capillary gas chromatography with programmed-temperature injection

The capillary gas chromatographic analysis of complex naturally occurring and food-product triglyceride mixtures is accomplished qualitatively and quantitatively on columns coated with methyl and methyl-phenyl (65%) silicones using programmed-temperature split/splitless and on-column injection. Faster analysis times are achieved using elevated initial column oven temperatures with cold initial injector temperatures.     

Design and Implementation of Comprehensive Gas Chromatography with Cryogenic Modulation

Comprehensive gas chromatography is the realization of true continuous multidimensional (dual column) gas chromatography. The key requirement in the comprehensive GC experiment is that the second dimension analysis is completed in a rapid time‐frame compared to the elution of components in the first dimension, and that the two coupled dimensions represent ‘orthogonal’ analyses towards the analytes to be separated. The former normally necessitates pulsing of contiguous segments of each chromatographic band from the first to the second dimensions. The two dimensions should be in fluid communication. The comprehensive GC×GC experiment passes all the column flow from the first column to the second column, leading to no sample loss, but this also requires a suitable method for time‐ or zone‐compression of the band to be pulsed to the second column. The final pulse should be narrow, and should be delivered to the second column quickly. A simple procedure can achieve this using the cryogenic modulator that has been recently described by this group. The system uses a cryogenic trap which can be moved away from the cooled zone of the column faster than 10 ms. A fast‐acting pneumatic ram achieves this performance. The cooled column heats up to the prevailing oven temperature within 10–15 ms. Molecules as volatile as C5 alkanes or small aromatics will be fully retained by the trap within the period of modulation used for GC×GC. The technique is simple to implement and requires no special column connections. Using a gas chromatograph which allows control of external events and can acquire from a detector at 50 Hz or faster, and a timing controller for modulation, the comprehensive result can easily and effectively be achieved.     

气相色谱近年的发展

简要阐述了近几年气相色谱(GC)的发展和特点。GC是一个成熟的技术,广泛地应用于各个领域,近几年GC的发展除了继续研究新的固定相和高性能的毛细管色谱柱之外,主要在全二维气相色谱(GC×GC)、快速GC、便携式GC仪和微型GC仪几个方面。近几年新研究的GC固定相主要集中在常温离子液体和各种环糊精的衍生物。现在GC研究者趋向于使用商品化的GC毛细管柱,而商品化的GC毛细管柱应用最多的是以含5%苯基的聚甲基硅氧烷为固定相的色谱柱。GC×GC发展迅猛,特别是关于调制器的研究,已开发出十多种调制模式,并广泛地应用于各个领域。为了适应大量样品的分析和现场分析,研究和开发了多种快速GC方法和仪器以及便携式GC仪。为了仪器的小型化和专属性检测,μGC仪的研究也稳步地发展起来。