Large volume, low discrimination GC injection into a modified splitless injector

Summary A standard GC split/splitless injector was sealed with an airlock. The carrier gas and the sample were introduced through this valve. Such a configuration efficiently prevents an injector overflow. Injections up to 50 μL were made. An almost quantitative analyte and solvent transfer was observed, with only a minimal discrimination, of even volatile analytes. The use of an early vapor exit permitted a high initial liner flow and therefore a fast sample transfer.     

Development of a novel high volume band compression injector for the analysis of complex samples like toxaphene pesticide

A new type of injector has been developed for gas chromatographic analysis. The injector has high volume and band compression (HVBC) capabilities useful for the analysis of complex samples. The injector consists essentially of a packed liner operated at room temperature while a narrow heated zone is used to axially scan the liner selectively desorbing the compounds of interest. The scanning speed, distance and temperature of the zone are precisely controlled. The liner is connected to an interface which can vent the solvent or any undesirable compounds, and transfer the analytes to an analytical column for separation and quantification. The injector is designed to be compatible with injection volumes from 1 to more than 250microL. At a low sample volume of 1microL, the injector has competitive performances compared to those of the "on-column" and "split/splitless" injectors for the fatty acid methyl esters and toxaphene compounds tested. For higher volumes, the system produces a linear response according to the injected volume. In this explorative study, the maximum volume injected seems to be limited by the saturation of the chromatographic system instead of being defined by the design of the injector. The HVBC injector can also be used to conduct "in situ" pretreatment of the sample before its transfer to the analytical column. For instance, a toxaphene sample was successively fractionated, using the HVBC injector, in six sub-fractions characterized by simpler chromatograms than the chromatogram of the original mixture. Finally, the ability of the HVBC injector to "freeze" the separation in time allowing the analyst to complete the analysis at a later time is also discussed.     

Quantitative aspects of directly coupled supercritical fluid extraction–capillary gas chromatography with a conventional split/splitless injector as interface

The quantitative aspects of on-line supercritical fluid extractioncapillary gas chromatography (SFE-GC) with a split/splitless injector as interface were investigated. Special attention was paid to the discrimination behavior and the reproducibility of the split/splitless interface. A simple experimental set-up is proposed that allows accurate quantitation in on-line SFE-split GC. The results obtained in on-line SFE-GC compare favorably with those from conventional GC with split injection. Discrimination was found to be absent when working at sufficiently high interface temperatures. Finally, the effects of the carbon dioxide flow rate, interface temperature and split ratio on both discrimination and reproducibility were studied.     

Evaluating the impact of GC operating settings on GC-FID performance for total petroleum hydrocarbon (TPH) determination

Interlaboratory comparisons for the analysis of mineral oil have indicated that many laboratories have problems in producing data of acceptable quality, mainly because of variations in the gas chromatographic settings used in the determination. A D-optimal design was therefore utilized to study the effects of six different GC operating settings on the GC performance criterion proposed by ISO and CEN draft standards ISO/FDIS 16703:2004 and CEN prEN 14039:2004:E for total petroleum hydrocarbon (TPH) determination. Both qualitative and quantitative factors were investigated. The results indicate that the performance criterion can only be achieved if the splitless injection settings are carefully optimized. Otherwise mass discrimination readily affects the validity of the results. The most critical factors affecting GC performance were the inlet liner design, inlet temperature and injection volume. The methods, however, were robust with respect to small changes in split vent time, GC column flow and FID temperature. The results show that non-discriminating splitless injection can only be obtained by optimizing the injector settings with respect to the significant factors. The main conclusion that can be drawn is that, if no further standardization is to be given for TPH determination by GC-FID, then a proper estimate of the expanded uncertainty should be appended to the TPH results. Only then can the reliability of the TPH results be guaranteed and further justification thus gained to support the end-use of the data.     

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.     

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.     

Large volume splitless injection with concurrent solvent recondensation: keeping the sample in place in the hot vaporizing chamber

An injector liner packed with a plug of glass wool is compared with a laminar and a mini laminar liner for large volume (20-50 microL) splitless injection with concurrent solvent recondensation (CSR-LV splitless injection). Videos from experiments with perylene solutions injected into imitation injectors show that glass wool perfectly arrested the sample liquid and kept it in place until the solvent had evaporated. The sample must be transferred from the needle to the glass wool as a band, avoiding 'thermospraying' by partial solvent evaporation inside the needle. The liquid contacted the liner wall when the band was directed towards it, but from there it was largely diverted to the glass wool. In the laminar liners, part of the liquid remained and evaporated at the entrance of the obstacle, while the other proceeded to the center cavity. Vapors formed in the center cavity drove liquid from the entrance of the obstacle upwards, but the importance of such problems could not be verified in the real injector. Some liquid split into small droplets broke through the obstacle and entered the column. Breakthrough through the laminar liners was confirmed by a chromatographic experiment. An improved design of a laminar liner for large volume injection is discussed as a promising alternative if glass wool causes problems originating from insufficient inertness.     

A quick analytical method using direct solid sample introduction and GC-ECD for pesticide residues analysis in crops

In this work, an analytical method for GC using direct solid sample introduction was developed to tackle the problem regarding quick detection of pesticide residue in crops and large-scale screening of samples. 10 mg of the crop solid sample without sample pre-treatment was directly introduced into a modified split/splitless injector for GC analysis. A split/splitless injector was modified to quickly remove oxygen and low boiling-point matrices of the sample. The whole sampling procedure was simple and it required less than 5 min. The experimental parameters including injector-port temperature, removal of oxygen and low boiling point matrices, size and the amount of the solid sample, oven temperature program were studied. Satisfactory recoveries of 6 pesticides (methyl parathion, fenitrothion, aldrin, dieldrin, endosulfan, o,p′-DDT) were obtained in maize and rice sample. Relative standard deviation was less than 15%. Experimental results showed that the proposed method was quick and reliable for pesticide residues analysis in crops.     

Maximum transfer condition for spitless injection

Splitless injection conditions were optimized by the use of experimental designs (2-level factorial and central composite designs). Modified parameters were: Type of liner, injection volume, solvent, temperature, splitless time. A prolonged splitless time, considered to be an important parameter, proved to be statistically insignificant. This leads to the conclusion that analytes can penetrate the dead volume between column entrance and split valve. To prevent any penetration of solvents, a small reversed split flow was introduced. It could be shown that this auxiliary flow allows an almost complete transfer of solvents. To further speed up the transfer process, a liner modification was proposed.     

Fast Temperature Programming in Gas Chromatography using Resistive Heating

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.     

Headspace-programmed temperature vaporizer-fast gas chromatography-mass spectrometry coupling for the determination of trihalomethanes in water

A new method based on the use of a headspace autosampler in combination with a GC equipped with a programmable temperature vaporizer (PTV) and an MS detector has been developed for the screening and quantitative determination of trihalomethanes (THMs) in different aqueous matrices. The use of headspace generation to introduce the sample has the advantage that no prior sample treatment is required, thus minimizing the creation of analytical artifacts and the errors associated with this step of the analytical process. The PTV inlet used was packed with Tenax-TA. The injection mode was solvent vent, in which the analytes are retained in the hydrophobic insert packing by cold trapping, while the water vapour is eliminated through the split line. This allows rapid injection of the sample in splitless mode, very low detection limits being achieved without the critical problem of initial sample bandwidth. The capillary column used allowed rapid separations with half-height widths ranging from 1.68 s (chloroform) to 0.66 s (bromoform). The GC run time was 7.3 min. The use of mass spectrometry allows the identification and quantification of the analytes at the low ppt level. The S/N ratio was at least 10-fold higher when the SIM mode was used in data acquisition as compared to the scan mode. The proposed method is extremely sensitive, with detection limits ranging from 0.4 to 2.6 ppt.     

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.     

Application of the “cooled needle” technique to split and splitless sampling onto capillary columns

Cooled needle sampling using syringes was applied to splitless injection and to simulated distillation analyses. Slight changes of the construction of the previous device are also described. The changes concern the temperature profile within the injector and especially the vaporization insert. Even with the low carrier gas flow through the injector during splitless injection, discrimination by component volatility can be avoided. Precision and accuracy of simulated distillation data obtained with split sampling also can be improved by the cooled needle technique.     

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.     

Practical aspects of splitless injection of semivolatile compounds in fast gas chromatography

Possibilities and practical aspects of implementation of splitless injection of larger volumes for fast GC purposes utilizing narrow-bore column, hydrogen as carrier gas, fast temperature programming under programmed flow conditions and commercial instrumentation were searched. As a model sample semivolatile compounds of a broad range of volatility and polarity (7 n-alkanes and 19 pesticides) were chosen. Peak shapes, peak broadening and peak areas and its repeatability were evaluated under various experimental set-ups (liner/injection technique combinations). Various factors, such as liner design, injection technique, retention gap length, compound volatility and polarity, the solvent used, initial oven temperature influenced compound focusation and/or maximal injection volume. Combination of analytical column (CP-Sil 13 CB 25 m long, 0.15 mm i.d., film thickness 0.4 microm) with normal-bore retention gap (1 m long, 0.32 mm i.d.) allowed maximal injection volume 8 microl for 4 mm i.d. liner used without any peak distortion when solvent recondensation in the retention gap was employed.     

GC-14A气相色谱仪分流装置的故障排除

 介绍了日本岛津公司产GC-14A气相色谱仪中SPL- 14分流/不分流进样器的连接管引起的故障现象及排除方法。指出该公司产同类型带有分流/ 不分流装置的气相色谱仪,若长期分析高沸点油状化合物,则应定期清洗连接管,及时清除 堵塞物,以保证测试数据有较好的重现性。     

Performance of programmed temperature vaporizer, pulsed splitless and on-column injection techniques in analysis of pesticide residues in plant matrices.

A programmed temperature vaporizer (PTV) injection technique has been recently implemented in our laboratory. In present paper its performance is compared with other GC injection techniques commonly used in trace analysis of organic contaminants. Twenty-six pesticides representing different chemical classes were selected for the study. This group comprised compounds typically subjected to discrimination in the injection port of the gas chromatograph, e.g., polar organophosphorus pesticides and thermolabile carbamates. In the first set of experiments standards in pure solvent were injected into GC systems employing different types of injection, i.e., (i) on-column, (ii) pulsed splitless, (iii) PTV solvent split, (iv) PTV splitless, and the responses of analytes were compared. Discrimination of troublesome compounds was significantly decreased with the application of PTV solvent split injection. In the second set of experiments repetitive injections of purified wheat samples were performed, with aims to evaluate the long-term stability of responses, as well as matrix effects in different stages of system contamination for each injection technique. The tolerance of the GC system to co-injected matrix components was increased in the order: on-column相似文献   

Comparison of different injection modes in edible oil minor components analysis

Waxes and fatty acid alkyl esters are minor components used as official parameters to control the authenticity and quality of a high‐value olive oil product. A poor measurement can lead to a misleading classification of the oil. The official method requires their analysis together by capillary gas chromatography equipped with a flame ionization detector and an on‐column injector to avoid discrimination and thermal degradation. The degradation can occur to a different extent if different (and not properly optimized) injectors are used. However, other injection techniques, such as programmed‐temperature vaporizer, are much more versatile and more widespread. The aim of the present work was to compare the performance of a programmed‐temperature vaporizer injector, in on‐column and splitless mode, with the on‐column injector to analyze alkyl esters and waxes. Discrimination among high‐boiling compounds was evaluated, as well as the occurrence of thermal degradation, especially of sterols and diterpene alcohol (phytyl and geranylgeraniol) esters. A proper optimization of a programmed‐temperature vaporizer injection, with particular attention to the liner selection, was proven to provide comparable results to the traditional on‐column injection. A performance comparison was carried out both on standard mixtures and on real oil samples.     

Investigation of parameters affecting the on-line combination of supercritical fluid extraction with capillary gas chromatography

Two different injectors, a split/splitless injector and a programmed temperature vaporizer (PTV) injector were investigated as the interface in on-line supercritical fluid extraction (SFE)-capillary gas chromatography (cGC). The parameters affecting the chromatographic peak shapes as well as the quantitative performance of the interfaces in on-line SFE-cGC were identified and studied. Particular attention was paid to the case where modified extraction fluids were used. Experiments were performed on two different samples. The first sample consisted of PAHs spiked on sand at different concentration levels. The other sample was a polymeric material.