Characterization of a microelectromechanical systems-based counter-current flame ionization detector

This work is concerned with the influence of different operating parameters on the response of a counter-current micro flame ionization detector (cc-μFID) with low gas consumption for mobile applications. At cc-μFID flow rates (<10ml/min hydrogen), the response depends mainly on the oxygen flow. At 7.5ml/min hydrogen flow, highest sensitivity (13.7mC/gC) is obtained with the smallest flame chamber and nozzle size, moderate sample gas flow (2.0ml/min), and an oxygen flow above stoichiometry (9.4ml/min, λ=2.5). The largest absolute signal is obtained at increased sample gas flow (8.0ml/min). However, to prevent parting of the micro-flame by the sample gas stream, largest nozzles (smallest outflow velocity) give the best result (4.37nA). Whereas cc-μFID sensitivity is comparable with conventional FID sensitivity, peak-to-peak noise of 1pA is relatively large. Therefore, the minimum detectable carbon mass flow of 1.46×10(-10)gC/s and the minimum detectable methane concentration of 3.43ppm are larger than typical FID detection limits. μGC-μFID experiments show the difference between premixing the sample with the hydrogen or with the oxygen with respect to sensitivity and response factors. Sensitivity is decreased considerably when the column effluent is added to the oxygen instead of to the hydrogen. For hydrogen premixed samples the response factor to butane can be increased up to 0.81 (methane=1), whereas for oxygen premixed samples it is maximally 0.31. This smaller sensitivity to oxygen premixed samples and the larger variation of response factors shows the importance of the hydrogen atom during breakdown of organic molecules to single-carbon fragments before ionization.     

Carbon response characteristics of a micro-flame ionization detector

The carbon response characteristics of a recently noted micro-flame ionization detector (μFID) mode are examined in detail. The μFID supports an extremely small (30 nL) “upside-down” flame that is generated from a low counter-current flow of oxygen immersed in hydrogen. Ionization measurements made in the μFID are directly compared to those obtained from a conventional FID. In terms of reproducibility of response and relative sensitivity towards different types of hydrocarbons, the μFID and a conventional FID produce no major differences with respect to either of these characteristics for a variety of compounds examined. Of note, for replicate measurements made in each detector, the average %R.S.D. of response typically differs by less than 2% between the two devices, while the average normalized sensitivity differs by less than 4%. In contrast to this, regarding absolute sensitivity, the analyte signal from the conventional air-rich FID is found to be three times larger than that of the hydrogen-rich μFID mode explored here. This discrepancy is ascribed directly to the difference in flame stoichiometry between the two detectors.     

烟用香精的气相色谱法质量控制研究

采用配有氢焰检测器或催燃检测器的气相色谱仪,对烟用香精进行了快速分析。方法操作简便,结果可靠,可作为烟用香精原料、产品质量监控的有效手段。     

Stability of the FID sensitivity during an analysis in capillary GC

The sensitivity of an FID may change when the carrier gas flow rate changes during a chromatographic run. Sample parts which are eluted at reduced FID sensitivity produce a reduced peak area, hence are discriminated as compared to other components. Sensitivity changes were studied for hydrogen as carrier gas. For the detector tested, differences in the carrier gas flow rates of 1 ml/min shifted the FID sensitivity by 1 to 5% (depending on the fuel gas supply). Thus the stability of the sensitivity is no longer ensured as soon as the carrier gas flow rate is changed manually or by an automatic programmer during an analysis. Sensitivity drifts may also occur during temperature programmed runs with a pressure regulated carrier gas supply since the gas flow through the capillary drops with increasing temperature. Such shifts in the response became noticeable as soon as relatively high carrier gas flow rates combined with long range temperature programmes were used. The typical patterns of such discriminations are shown, closing with a discussion on the possibilities for minimizing such undesired effects.     

Dispersive liquid–liquid microextraction using extraction solvent lighter than water

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).     

Use of small diameter WCOT columns for ultra-high resolution GC/MS

For clinical and environmental analyses utilizing capillary gas chromatography/mass spectrometry (GC/MS), increased sensitivity and speed of analysis are highly desirable. These performance advantages are realized using a WCOT column of 100 μm i.d. as compared to the more conventional 200 μm i.d. capillary columns. The improved sensitivity of capillary direct GC/MS with the 100 μm i.d. column for the confirmation of drugs of abuse will be demonstrated. For environmental analysis, the superior efficiency and resolution of the 100 μm i.d. column can be employed for the separation of priority pollutants. This approach is more amenable to capillary direct GC/MS providing a more effective interface to the mass spectrometer. As a result improved sensitivity and a considerable decrease in analysis time is achieved over that obtained with the larger diameter environmental specialty phase columns.     

Micro-flame ionization detector with a novel structure for portable gas chromatograph

A micro-flame ionization detector (μ-FID) for portable gas chromatograph (GC) based on conventional mechanical fabrication techniques was developed and evaluated. Structure was redesigned and dimensions were optimized for best performance. Air is introduced from upper part of the detector, flowing downwards into the burning chamber along a narrow round gap between the collection electrode and the inner wall of the detector body, forming a uniform flow field around the burning jet. The lowest detection limit of the μ-FID was 5 × 10⁻¹³ g/s for n-decane, with a linear response range of five orders of magnitude. The consumption of gases is only 10 ml/min for hydrogen, and 120 ml/min for air, that is about 1/3 of the gases required for conventional FIDs. A comparative study between the μ-FID and commercial FID was also performed that proved the advantages of the μ-FID. The μ-FID is simple in structure, low heating power, and low consumption of gases that not only decrease the cost of running, but also increase the portability of GC for filed applications.     

PID—100C型光离子化气相色谱仪的研制与应用

作者研制一种微机化光离子化气相色谱仪，其灵敏度和检出限优于ＦＩＤ两个数量级（苯）可用于有机挥发物痕量分析。     

Coupling stir bar sorptive extraction‐dispersive liquid–liquid microextraction for preconcentration of triazole pesticides from aqueous samples followed by GC‐FID and GC‐MS determinations

Stir bar sorptive extraction (SBSE) combined with dispersive liquid–liquid microextraction (DLLME) has been developed as a new approach for the extraction of six triazole pesticides (penconazole, hexaconazole, diniconazole, tebuconazole, triticonazole and difenconazole) in aqueous samples prior to GC‐flame ionization detection (GC‐FID). A series of parameters that affect the performance of both steps were thoroughly investigated. Under optimized conditions, aqueous sample was stirred using a stir bar coated with octadecylsilane (ODS) and then target compounds on the sorbent (stir bar) were desorbed with methanol. The extract was mixed with 25 μL of 1,1,2,2‐tetrachloroethane and the mixture was rapidly injected into sodium chloride solution 30% w/v. After centrifugation, an aliquot of the settled organic phase was analyzed by GC‐FID. The methodology showed broad linear ranges for the six triazole pesticides studied, with correlation coefficients higher than 0.993, lower LODs and LOQs between 0.53–24.0 and 1.08–80.0 ng/mL, respectively, and suitable precision (RSD < 5.2%). Moreover, the developed methodology was applied for the determination of target analytes in several samples, including tap, river and well waters, wastewater (before and after purification), and grape and apple juices. Also, the presented SBSE‐DLLME procedure followed by GC‐MS determination was performed on purified wastewater. Penconazole, hexaconazole and diniconazole were detected in the purified wastewater that confirmed the obtained results by GC‐FID determination. In short, by coupling SBSE with DLLME, advantages of two methods are combined to enhance the selectivity and sensitivity of the method. This method showed higher enrichment factors (282–1792) when compared with conventional methods of sample preparation to screen pesticides in aqueous samples.     

Charcoal open tubular traps for the analysis of air and headspace samples

5 cm × 0.3 mm i.d. glass capillary tubes coated with fine charcoal particles are used for the analysis of organic compounds, particularly tri- and tetrachloroethylene, benzene, and toluene, in air and headspace samples. Due to their small size, these traps are easy to use with capillary GC. As, e.g. 20 ml of gas can be sucked through this trap in 20 s, it is a simple technique providing high sensitivity; compared to headspace with split injection, sensitivity is increased by a factor exceeding 100. The column effluent is split into FID and ECD in such a way that small as well as large amounts of the chlorinated compounds can be detected.     

Analytical bias among different gas chromatographic approaches using standard BTX gases and exhaust samples

In this study, the analytical compatibility of the gas chromatographic (GC) approach was evaluated through a cross‐calibration exercise. To this end, three aromatic volatile organic compounds (VOCs: benzene, toluene, and p‐xylene (BTX)) were simultaneously analyzed with four individual instrumental setups (type I = GC with MS plus solid phase microextraction (SPME) method, II = GC with flame ionization detection (FID) plus SPME, III = fast GC‐FID plus SPME, and IV = GC‐FID plus air server/thermal desorption (AS/TD) method). A comparison of basic quality assurance (QA) data revealed considerable differences in DL values among the methods with moderate variabilities in the intercompound sensitivity. In light of the differences in detection properties, the analytical bias involved for each methodological approach was assessed by the relative relationship between analytes and basic operating conditions. The results suggest that the analysis of environmental samples at ultra‐low concentration levels (at or below ppb level) can be subject to diverse sources of bias. Although detection properties of target compounds seem to be affected by the combined effects of various factors, changes in the sample concentration levels were seen to be the most consistent under the experimental setups analyzed in this study.     

tability Indicating Method for the Analysis of Nicotine in Transdermal Drug Delivery Systems by Means of Gas Chromatography

The delivery of drugs through human skin using transdermal drug delivery (TDD) systems has become an established technology. A popular drug with that dosage form is nicotine for smoking cessation. A stability indicating method for the analysis of nicotine TDDs using gas chromatography (GC) with post-column effluent splitting to a flame ionization detector (FID) and a nitrogen-phosphorus detector (NPD) is described. FID detection gave reliable results with low day-to-day variability. The detector is relatively simple to operate. NPD detection offered enhanced sensitivity and specificity. The combination of both detectors resulted in a rugged method for content analysis with high sensitivity for detection of degradation products at low concentration levels. Despite a relatively simple sample preparation procedure no matrix interferences were observed.     

导数测量技术在气相色谱信号处理中的应用

介绍了导数测量技术在气相色谱信号处理中的应用。导数-气相色谱的热导检测器对苯的灵敏度和敏感度分别达到270kV·L/kg和0.3μg／L。与可分辨导数色谱峰相对应的常规色谱峰最小分离度为2．8。在被测组分质量浓度为8．1～810g／L的范围内,导数峰上峰高、下峰高、总峰高、峰面积均与质量浓度呈线性关系,其线性相关系数分别为0．9911,0．9982,0．9960和0.9991。     

Determination of curcumol in rat plasma by capillary gas chromatography with a hydrogen flame ionization detector

A simple and sensitive capillary gas chromatography with a hydrogen flame ionization detector (GC‐FID) method was developed for the determination of curcumol in rat plasma. From a variety of compounds and solvents tested, buagafuran was selected as the internal standard (IS) and acetonitrile was found to be the best protein precipitation agent and solvent for extracting curcumol from plasma and tissues samples. (Buagafuran was used as an internal standard. Curcumol was extracted by a protein precipitation with acetonitrile.) The samples were determined by GC on an HP‐5 column (30.0 m × 0.32 mm, 0.25 μm); inlet volume 2 μL; split ratio 10 : 1; inlet temperature 250°C; oven temperature 180°C; flow 1.0 mL/·min; FID 250°C; carrier gas N₂. The resulting retention times of curcumol and IS were 6.0 and 9.5 min. There was good linearity over the range 0.133–133.3 μg/mL (r = 0.9999) in plasma samples. The method recoveries were 97.7–102.0% in plasma, and the intra‐ and inter‐day variances (RSD) were less than 15% in all cases. The GC method was applied to develop a pharmacokinetics study in which experimental rats received a single administration of curcumol by intravenous injection. Copyright © 2009 John Wiley & Sons, Ltd.     

衍生化气相色谱法测定早强剂中三乙醇胺含量

建立了衍生化气相色谱法定量分析水泥早强剂中三乙醇胺含量的方法。以丙三醇作为内标,采用HP-5毛细管柱分离样品,氢火焰离子化检测器(FID)测定三乙醇胺含量。三乙醇胺在0.2～5.0mg/mL范围内与三乙醇胺/内标的乙酰化物色谱峰面积的比值呈线性关系,相关系数r=0.9996。方法检出限为42.6μg/mL,平均回收率为96.6%,相对标准偏差(RSD)为0.759%。该方法具有操作简便、快速、准确等优点,可用于测定水泥早强剂中三乙醇胺的含量。     

Novel on-column and inverted operating modes of a microcounter-current flame ionization detector

Improved operating modes of a microcounter-current flame ionization detector (microFID) are demonstrated. By operating the flame inside the end of a capillary gas chromatography (GC) column, the effective cell volume enclosing the flame is considerably reduced and results in significantly lower gas flows being required to produce optimal sensitivity from the stable flame. For instance, in this mode the tiny counter-current flame is situated "upside down" inside the column on the end of a stainless steel capillary delivering 4mL/min of oxygen and is stabilized by a counter flow of only 10mL/min of hydrogen carrier gas. Under these approximately fourfold reduced gas flow conditions, the microFID carbon response is linear over almost 5 orders of magnitude and yields a detection limit of 6x10(-10)gC/s. These figures agree well with those reported for the original microFID, which also similarly operated under hydrogen-rich conditions. To better simulate the oxygen-rich environment of a conventional FID flame, a novel "inverted" counter-current flow mode was also investigated. In this post-column microFID arrangement, a very lean flame is now situated on the end of a stainless steel capillary delivering 10mL/min of hydrogen, which is opposed by a counter-current flow of only 20mL/min of oxygen. The microFID detection limit obtained in this stable, oxygen-rich counter-current flame mode is 7x10(-11)gC/s with a response that is linear over almost 6 orders of magnitude. These findings are more comparable to those of a conventional FID. Overall, the low-flow sensitive microFID operating modes presented demonstrate that this detector may be potentially useful for adaptation to portable devices and related GC applications.     

Comparison of thick film capillaries with packed columns from the point of view of loadability in combination with high resolving power

The present paper compares the potential of high pressure packed column gas chromatography, with a particle size in the range of 30–80 μm and conventional packed column GC. with that of thick film capillaries for obtaining the maximum loadability at a given performance in efficiency and speed of separation. An alternative treatment, discussing the maximum efficiency of the three column types at normalized loadability and speed of separation is given. Known and established relationships describing plate height, loadability, and linear velocity are used to arrive at the said comparisons. The conclusion of the paper indicates a reconsideration of packed column GC for particular types of analyses where large amounts or high concentrations are required in the detection step.     

Improved determination of flavour compounds in butter by solid-phase (micro)extraction and comprehensive two-dimensional gas chromatography

The practicability and potential of comprehensive two-dimensional gas chromatography (GC x GC) coupled to both conventional flame ionisation (FID) and time-of-flight mass spectrometric (TOF-MS) detection, were compared with those of conventional one-dimensional (1D) GC, with the determination of flavour compounds in butter as an application. For polar flavour compounds, which were collected from the aqueous fraction of butter by means of solid-phase extraction (SPE), it was found that GC x GC dramatically improves the overall separation. Consequently, quantification and preliminary identification based on the use of ordered structures, can be performed more reliably. The improvement effected by replacing 1D-GC by GC x GC is considerable also in the case of TOF-MS detection, as illustrated by the high match factors generally obtained during identification. GC x GC was also used successfully for the characterisation of volatile flavour compounds in the headspace of butter collected by solid-phase microextraction (SPME) and to study the effect of heat treatment on the composition of butter samples in more detail.     

Can gas chromatography combustion isotope ratio mass spectrometry be used to quantify organic compound abundance?

Quantifying the concentrations of organics such as phospholipid fatty acids (PLFAs) and n‐alkanes and measuring their corresponding ¹³ C/¹² C isotope ratios often involves two separate analyses; (1) quantification by gas chromatography flame ionisation detection (GC‐FID) or gas chromatography/mass spectrometry (GC/MS), and (2) ¹³ C‐isotope abundance analysis by gas chromatography/combustion/isotope ratio mass spectrometry (GC‐C‐IRMS). This requirement for two separate analyses has obvious disadvantages in terms of cost and time. However, there is a history of using the data output of isotope ratio mass spectrometers to quantify various components; including the N and C concentrations of solid materials and CO₂ concentrations in gaseous samples. Here we explore the possibility of quantifying n‐alkanes extracted from sheeps' faeces and fatty acid methyl esters (FAMEs) derivatised from PLFAs extracted from grassland soil, using GC‐C‐IRMS. The results were compared with those from GC‐FID analysis of the same extracts. For GC‐C‐IRMS the combined area of the masses for all the ions (m/z 44, 45 and 46) was collected, referred to as 'area all', while for the GC‐FID analysis the peak area data were collected. Following normalisation to a common value for added internal standards, the GC‐C‐IRMS 'area all' values and the GC‐FID peak area data were directly compared. Strong linear relationships were found for both n‐alkanes and FAMEs. For the n‐alkanes the relationships were 1:1 while, for the FAMEs, GC‐C‐IRMS overestimated the areas relative to the GC‐FID results. However, with suitable reference material 1:1 relationships were established. The output of a GC‐C‐IRMS system can form the basis for the quantification of certain organics including FAMEs and n‐alkanes. Copyright © 2011 John Wiley & Sons, Ltd.     

Determination of Atenolol in Pharmaceutical Preparations by Gas Chromatography with Flame Ionization and Mass Spectrometric Detection

The present work describes the methodology and validation of gas chromatography with flame ionization (FID) and mass spectrometric (MS) detection after derivatization with N-Methyl-N-(trimethylsilyl)trifluoroacetamide (MSTFA) for determination of atenolol with an internal standard (metoprolol) in pharmaceutical preparations. The linearity was established over the concentration range of 0.5–20 μg/mL for GC/FID and 12.5–500 ng/mL for GC/MS method. The intra- and inter-day relative standard deviation was less than 4.72 and 5.80%, respectively. Limit of quantification was determined as 500 ng/mL and 12.5 ng/mL for GC/FID and GC/MS, respectively. No interference was found from tablet excipients at the selected assay conditions. Developed GC/FID and GC/MS methods in this study are accurate, sensitive, and precise and can be easily applied to Tensinor tablet as pharmaceutical preparation.