Effect of ammonia carrier gas on the response of the flame ionization detector

The effect of using ammonia as a carrier gas on the response of the flame ionization detector (FID) has been investigated. It was found that the FID response, calculated as the effective carbon number (ECN), increased for all the compounds studied when ammonia, rather than helium, was used. The change was 0–0. 9 carbon atom for hydrocarbons, one carbon atom for alcohols and diphenyl ether, and 0.4–1 carbon atom for phenols and ketones. The increase in ECN was larger for amines (0. 8–5 carbon atoms), but these numbers also reflected an improvement in chromatographic performance as a result of reduced adsorption on the column. The largest change in signal-to-noise ratio, a six-fold increase, was obtained for octyl-amine; ratios for hexyl methyl ketone, diisobutyl ketone, dihexyl-amine, dibutylamine, and N-methyloctylamine increased by a factor of 2–3 when ammonia was used as carrier gas. To determine the extent to which the effect on detector response was solely attributable to ammonia, a mixture of 5 % ammonia in nitrogen was used as detector make-up gas with helium as carrier gas. Under these conditions the noise in the FID increased but for most of the compounds studied the signal-to-noise ratio also increased.     

Chromatographic efficiency of polar capillary columns applied for the analysis of fatty acid methyl esters by gas chromatography

The chromatographic efficiency that could be achieved in temperature‐programmed gas chromatography was compared for four capillary columns that are typically applied for analysis of fatty acid methyl esters (FAME). Three different carrier gases, hydrogen, helium and nitrogen, were applied. For each experiment, the carrier gas velocities and the temperature rates were varied with a full 9 × 3 design, with nine levels on the carrier gas velocity and temperature rates of 1, 2 or 3°C/min. Response surface methodology was used to create models of chromatographic efficiency as a function of temperature rate and carrier gas velocity. The chromatographic efficiency was defined as the inverse of peak widths measured in retention index units. The final results were standardized so that the efficiencies that could be achieved within a certain time frame, defined by the retention time of the last compound in the chromatogram, could be compared. The results show that there were clear differences in the efficiencies that could be achieved with the different columns and that the efficiency decreased with increasing polarity of the stationary phase. The differences can be explained by higher resistance to mass transfer in the stationary phase in the most polar columns.     

Factors influencing chromatographic data in fast gas chromatography with on‐column injection

The use of larger volume injection with on‐column injection and fast GC commercial instrumentation was evaluated with the model mixture of n‐alkanes of a broad range of volatility (C₁₀–C₂₈). The presented configuration allows introduction of 40–80‐fold larger sample volumes without any distortion of peak shapes compared to “usual” fast GC set‐ups using narrow‐bore columns. A normal‐bore retention gap (1–5 m×0.32 mm ID) was coupled to a narrow‐bore (5 m×0.1 mm ID×0.4 μm film thickness) analytical column using a standard press‐fit connector. The connection was tight and reliable, and hence suitable for hydrogen as carrier gas. The effect of pre‐column and analytical column connector, injection volume, pre‐column length, column inlet pressure, and analyte volatility on peak shape, peak broadening, and focusing are discussed. The precision of chromatographic data measurements and peak capacity under optimised temperature programmed conditions for fast separations with large volume injection were found to be very good. The presented fast GC set‐up with on‐column injection extends the applicability of the technique to trace analysis.     

Capillary gas chromatography of amines with ammonia as carrier gas

The use of ammonia as a carrier gas for the chromatography of aliphatic and aromatic amines has been investigated. As compared to nitrogen, ammonia gave drastically improved peak symmetry and lower capacity factors (k′) for primary and secondary amines on polar (Polyethylene glycol) and medium Polar (methylphenylcyanopropylsilicone) stationary Phases. The effect of ammonia was more Pronounced at low column temperatures. Considerably better detection limits of primary and secondary amines were obtained with ammonia as carrier gas than with nitrogen. No detrimental effects of using ammonia were observed on the gas chromatograph or on the columns over a period of about one year.     

气相色谱-质谱联用分析5种有机磷农药时氢气代替氦气作为载气的可行性考察

迄今为止,氦气几乎是气相色谱-质谱联用仪运行中唯一可选的载气.本文使用气相色谱-质谱联用仪考察了氢气和氦气分别作为载气时,对5种有机磷农药混合标准溶液的检测,以确定氢气代替氦气作为气相色谱-质谱联用仪载气用于有机磷农药分析的可行性.用工作站自带解卷积软件(自动质谱解卷积鉴定系统,AMDIS32),结合自建"有机农药质谱库"对结果进行了解析,而后用SPSS统计软件对数据进行了聚类分析.结果发现,以氢气为载气时虽然出峰稍快,但色谱峰分离度较低,解良度较低,且待测物信号不稳定,测定准确度较低,有些化合物甚至检测不到.因此以氢气为载气分析有机磷农药时应对测定准确度、信号稳定性、安全性等诸多因素进行慎重考虑.     

Capillary gas chromatographic separation of bile acid acyl glycosides without thermal decomposition and isomerization

A direct method for the capillary gas chromatographic (cGC) separation of the acyl glycosides of bile acids was successfully attained. The free acyl glycosides were derivatized to their complete trifluoroacetyl (TFA) derivatives with N-methyl-bis(trifluoroacetamide). The highly volatile TFA derivatives were chromatographed on a short-length (10 m), narrow-bore (0.1 mm) capillary column coated with a thin film (0.1 microm) of 5% phenyl polysilphenylene-siloxane at a column temperature below 280 degrees C. Each exhibited a single, well-separated peak of the theoretical shape without any accompanying peaks due to the thermal decomposition and isomerization. The bile acid 24alpha-glucosides were always eluted faster than the corresponding 24beta-glucosides, which eluted before the corresponding 24beta-galactosides. The method could be usefully applied to biosynthetic and metabolic studies of bile acid acyl glycosides in biological materials.     

Prediction of the separation number of capillary columns in programmed temperature gas chromatographic analysis

The efficiency of capillary columns in programmed temperature analysis can be evaluated by calculation of the separation number (“Trennzahl”). A procedure for the prediction of this parameter at various initial temperatures, carrier gas pressures and heating rates, by using as the starting data the retention times and the peak widths obtained in some isobaric and isothermal runs is described. An equation is proposed that permits to obtain the values of the peak width at half height in any isothermal and linearly programmed temperature gas chromatographic run and therefore to calculate the separation number value. The effect on this parameter of the column polarity was investigated by using polar and non-polar compounds (n-alkanes and 1-alcohols).     

Investigations of a new field in gas chromatography: capillary columns with a super-thick layer of stationary liquid phase

Basic characteristics (efficiency, selectivity, non-equilibrium) of capillary columns with a super-thick layer of stationary liquid phase are investigated. In contrast to traditionally used capillary columns with standard stationary phase thickness of 0.1-0.5 um, some new variables are now established. Firstly, the values of relative retention depend on carrier gas linear velocity. Secondly, the asymmetry of chromatographic peaks increased in accordance with the increase in carrier gas velocity. Thirdly, it was theoretically and experimentally shown that dependence of the height equivalent to a theoretical plate (HETP) on carrier gas velocity is linear. The above noted variables are evidences that the new type of GC is realized under these conditions. The use of capillary columns with super-thick layer of stationary liquid phase is practical when the following problems have to be solved: (1) Separation of highly volatile substances; (2) Preliminary concentration of trace compounds from strong diluted samples; (3) Improvements in measurement and accuracy due to the advantages of splitless injection into wide bore columns with super-thick films. Solutions to some analytical tasks while using super-thick stationary liquid phase are shown: (1) Large volume injection into capillary column with sample transfer speed up to 100 microL min(-1); (2) Isothermal splitless injection; (3) Separation of low boiling compounds; (4) Separation of polar substances (alcohols).     

Determination of anabolic steroids with gas chromatography-ion trap mass spectrometry using hydrogen as carrier gas.

Helium is considered to be the ideal carrier gas for gas chromatography/mass spectrometry (GC/MS) in general, and for use with an ion trap in particular. Helium is an inert gas, can be used without special precautions for security and, moreover, it is needed as a damping gas in the trap. A disadvantage of helium is the high viscosity resulting in long GC run times. In this work hydrogen was tested as an alternative carrier gas for GC in performing GC/MS analyses. A hydrogen generator was used as a safe source of hydrogen gas. It is demonstrated that hydrogen can be used as a carrier gas for the gas chromatograph in combination with helium as make-up gas for the trap. The analysis time was thus shortened and the chromatographic performance was optimized. Although hydrogen has proven useful as a carrier gas in gas chromatography coupled to standard detectors such as ECD or FID, its use is not mentioned extensively in the literature concerning gas chromatography-ion trap mass spectrometry. However, it is worth considering as a possibility because of its chromatographic advantages and its advantageous price when using a hydrogen generator.     

Separation of low-boiling hydrocarbons by capillary gas chromatography with glass columns treated with hot alkaline solution

Summary Soda-lime glass-capillary columns treated with 1M sodium hydroxide at 40–60°C for two days were employed for the gas chromatographic separation of low-boiling hydrocarbons. A 70.5 m×97 m I.D. column produced 780,000 to 930,000 theoretical plates for early-eluting components. Use of steam-doped carrier gas improved peak shape and column efficiency. The system was successfully applied to the separation of complex mixtures.     

Fabrication of a gas sensor using pentacene thin films as a detector

Highly sensitive gas sensors for both acidic and basic gases were fabricated based on conducting thin films of polyacene compounds. Gas sensors formed with pentacene thin films deposited on various kinds of substrates were found to exhibit high sensitivity in detecting subppm concentrations of NO₂ or Cl₂ by monitoring the conductivity of the thin film. Improvements in the conductance and duration period for detection were achieved by changing the shape of electrodes and substrate. The sensors with PEN thin films initially doped with iodine could detect ppm concentrations of ammonia gas, since iodine molecules were dedoped upon exposure to ammonia, causing the reduction of the conductivity.     

Ammonia as a carrier gas for acidic-basic chromatography

The influence of ammonia as a basic carrier gas on the retention of acidic and basic solutes was experimentally studied. Use of the basic carrier gas (ammonia) leads to an increase in retention of acidic solutes. A simplified theory on the influence of carrier gas basicity influence on the retention of acidic and basic solutes was developed. Contact of an inert gas with ammonia water at ambient temperature can be used to obtain basic humid carrier gas and to improve the chromatographic characteristics of amine's zones.     

Effect of the pressure of the carrier gas on the parameters of the Van Deemter equation for monolithic silica gel gas chromatography columns

The chromatographic properties of monolithic capillary silica gel columns for gas chromatography were examined with the use of four different variants of the Van Deemter model. The corresponding experimental curves were measured for the elution of light hydrocarbons with the helium carrier gas in the isothermal mode at 60°C. Despite the models tested are based on different mechanisms of the smearing of chromatographic peaks, the values of the Van Deemter equation parameters proved to be very close to each other for three of the four models. All models yielded negative values of the parameter A. Physically reasonable values of the parameters of the Van Deemter equation were obtained only for the Giddings model, which takes into account the pressure drop across the column. At the same time, this model overestimated the contribution from diffusional smearing (parameter B). It was concluded that none of the models tested adequately described the chromatographic properties of monolithic capillary columns for gas chromatography.     

Practical fast gas chromatography for contract laboratory program pesticide analyses

An approach to shortening the analysis time for practical fast gas chromatography (GC) by using Method Translator software, which can be downloaded free from the Internet, is presented. This software simplifies the process of optimizing temperature programming while changing column dimensions, carrier gas type, and flow. Basic chromatographic theory is employed in a practical manner for adjusting column dimensions for optimal performance. In addition, electronic pneumatic control and high oven ramp rates make it easier to achieve fast analysis times without reproducibility problems. This practical approach is demonstrated using Contract Laboratory Program pesticide analytes. The factors found to be most important in decreasing the analysis time without a loss of performance are utilization of GC columns having smaller diameters and substitution of hydrogen for helium as the carrier gas.     

Evaluation of a capillary gas chromatographic impurity test procedure for 4-hexylaniline

A capillary gas chromatographic test procedure for the detection and quantitation of impurities in the bulk intermediate, 4-hexylaniline, is evaluated and found to be accurate and precise. 4-Hexylaniline is dissolved in methanol and chromatographed isothermally at a temperature of 195 degrees C on a 60-m x 0.32-mm 85% polyethylene glycol-15% dimethylsilicone blend (DX-4) film column. A flame ionization detector is used, and the impurities in the parent compound are estimated from peak areas on a percent basis compared with the area of the parent peak in the chromatogram. Response factors are determined for the known impurities. Validation of this test method includes a recovery study of known impurity spiked samples fortified in the range of 0.1-1% (w/w). A repeatability study is performed, consisting of the analysis of two different synthetic batch lots of 4-hexylaniline analyzed over three experimental run days using two chromatographic columns of different manufacturing lots. These data and other aspects of this test procedure are discussed.     

Metal 3D‐printed catalytic jet and flame ionization detection for in situ trace carbon oxides analysis by gas chromatography

A gas chromatographic approach for the determination and quantification of trace levels of carbon oxides in gas phase matrices for in situ or near‐line/at‐line analysis has been successfully developed. Catalytic conversion of the target compounds to methane via the methanation process was conducted inside a metal 3D‐printed jet that also acted as a hydrogen burner for the flame ionization detector. Modifications made to a field transportable gas chromatograph enabled the leveraging of advantaged microfluidic‐enhanced chromatography capability for improved chromatographic performance and serviceability. The compatibility with adsorption chromatography technology was demonstrated with in‐house constructed columns. Sustained reliable conversion efficiencies of greater than 99% with respectable peak symmetries were attained at 400°C. Quantification of carbon monoxide and carbon dioxide at a parts‐per‐million level over a range from 0.2 ppm to 5% v/v for both compounds with a respectable precision of less than 3% relative standard deviation for peak area (n = 10) and a detection limit of 0.1 ppm v/v was achieved. Linearity with correlation coefficients of R² greater than 0.9995 and measured recoveries of >99% for spike tests were achieved. The 3D‐printed steel jet was found to be reliable and resilient against potential contamination from the matrices owing to the in situ backflushing capability.     

Higher mass loadability in comprehensive two-dimensional gas chromatography-mass spectrometry for improved analytical performance in metabolomics analysis

A major challenge in metabolomics analysis is the accurate quantification of metabolites in the presence of (extremely) high abundant metabolites. Quantification of metabolites at low concentrations can be complicated by co-elution and/or peak distortion when these metabolites elute close to high abundant metabolites. To increase the separation efficiency a comprehensive two-dimensional gas chromatographic-mass spectrometric method (GC x GC-MS) was set up, in which a polar first dimension column and an apolar second dimension column were used to maximize the peak capacity. The feasibility of using wider bore, thicker film columns in the second dimension to improve the mass loadability and inertness of the analytical system was investigated. Several column combinations with varying second dimension column dimensions were compared with a setup with a narrow bore column (0.1mm I.D.) in the second dimension. With a wider bore column (0.32 mm I.D.) in the second dimension the mass loadability was improved 10-fold, and the more inert column surface of the thicker film second dimension column resulted in a more accurate (automated) quantification and improved linearity in the presence of high concentrations of matrix compounds or metabolites. These benefits amply compensated the observed decrease in peak capacity of 40% compared to the narrow bore (0.1mm I.D.) thin film second dimension column. Compared to GC-MS and conventional GC x GC-MS, better performance for quantification of metabolites for typical metabolomics samples was achieved.     

Influence of carrier gas on the prediction of gas chromatographic retention times based on thermodynamic parameters

We present an investigation into the influence of carrier gas on the thermodynamics governing a capillary gas chromatographic separation. Thermodynamic parameters are estimated for a series of alkanes and alcohols on three common stationary phases using helium, hydrogen, and nitrogen carrier gases. It is shown that the substitution of carrier gases for one another results in a change in the thermodynamic parameters governing the separation. The effect of the carrier gas on the thermodynamic parameters is large enough to compromise the accuracy of the retention time calculations based on thermodynamic parameters collected in a carrier gas other than the one actually in use in a specific gas chromatographic system. A possible kinetic explanation for these observations is also investigated.     

Effect of injected sample amount on the shape of chromatographic peaks under condition of linear partition isotherm

In a previous paper a model function was tested in order to approximate the peak shape obtained on non-polar column by injecting different compounds. The simulation of the symmetrical or non-symmetrical shape of gas chromatographic peaks was satisfactory. In this paper, the influence of the amount of injected substance was investigated at different values of inlet pressure and carrier gas velocity, in order to evaluate the relative contribution to the total peak area and shape of the symmetrical distribution due to partition phenomena and of the non-symmetrical and tailing distribution due to adsorption-desorption kinetics. The effect of the molecular mass and of the chain length of compounds belonging to the homologous series of 1-alcohols and n-alkanes on the adsorption phenomena was evaluated.     

Dependence of the relative retention of organic compounds on the nature and pressure of the carrier gas and on the thickness of the PEG-20M film in the capillary column

The effects of the carrier gas nature and pressure on the relative retention values of organic compounds were studied using a series of capillary columns differing in the film thickness of the polar stationary phase (PEG-20M). Relative retention depends linearly on the carrier gas pressure. This dependence becomes more pronounced in the following order of carrier gases: helium < nitrogen < carbon dioxide. The limiting relative retention at a carrier gas pressure approaching zero rather than relative retention values measured experimentally (relative retention time, Kovats retention index,etc.) is an invariant characteristic of a compound subjected to chromatography. For the carrier gases studied, the limiting retention values almost does not depend on the nature of the carrier gas used. The limiting indicating the complex absorption-adsorption nature of these parameters. Dissolution of a carrier gas in the stationary liquid phase has an effect on the relative retention. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2177–2186, December, 1997.