Heated flow-cell for gas phase UV-visible detector in gas chromatography of polycyclic aromatic hydrocarbons

Summary A detection system for gas chromatography based on gas-phase, molecular absorption measurements is presented, in which the chromatographic column is directly joined to the spectrophotometer flow cell, without heated transfer lines. To maintain polyciclic aromatic hydrocarbons (PAHs) in the gas phase during detection an aluminium heater was constructed. A mixture of 13 PAHs was then separated and analyzed. Parameters affecting separation (temperature program and carrier gas flow) were studied and a program designed to modify the measurement wavelength during the chromatography. The analytical characteristics of each compound were calculated, obtaining detection limits 0.2–1.5 μg mL⁻. Given that some compounds overlaped, it was necessary to resolve their peaks mathematicaly. Finally, the method was applied to a certified synthetic mixture, with good results.     

Separation of mixtures of permanent gases and light hydrocarbons on spherical carbon molecular sieves by gas-solid chromatography

Summary Experimental results are presented on the application of Carbosieve S (Supelco) and Spherocarb (Analabs) spherical carbon molecular sieves for the gas chromatographic separation of mixtures of permanent gases and C₁–C₃ hydrocarbons using a single column or two columns in series. At a programmed temperature of 35–300°C, good separation of the sample components was obtained when using helium as the carrier gas. When hydrogen was used as the carrier gas and the analysis was carried out under isothermal conditions the elution sequence of oxygen and nitrogen reversed as the temperature was increased. This behaviour was observed within a temperature range of 35–225°C for Carbosieve S, and within a temperature range of 35–300°C for Spherocarb.     

An improved method for determination of light hydrocarbons in stabilized crude oil

Summary This paper reports a quick, and simple method for quantitative determination of C₂ to C₆ hydrocarbons in stabilized crude oil without using a back flush system. A mixture of crude oil and internal standard is injected into a GC equipped with a 6 meter length of fused silica capillary as a guard column. The light hydrocarbons are separated individually up to the last peak of the hexane group with the heavier components trapped in the guard column. The total analysis time for each sample is 15 minutes. The base line is table for up to 15 consecutive analyses. The guard column and the injector port are then reconditioned by simply heating them for one hour at 300 °C.     

Factors affecting the retention of polycyclic aromatic hydrocarbons in gas chromatography

Summary The retention index of a planar polynuclear aromatic hydrocarbon on the GC phases OV-101, SE-52, and OV-17 is strictly related only to the boiling point, and less closely to the relative molecular mass. The very approximates relation with connectivity index ins only a consequence of the latter. On a nematic lqiuid crystal phase, a variation of activity coefficient, expressed in terms of a shape factor, also influences the retention of PAH.     

Viscosities of carrier gases at gas chromatograph temperatures and pressures

Summary Equations are derived for viscosities of H₂, He, N₂ and Ar for use at chromatographic temperatures which are accurate to within 0.3% for H₂, and 0.1% for the other gases. The effect of pressure is usually negligible but may increase the viscosity of N₂ or Ar by as much as 0.5% at 25°C or lower and 5 atm or higher.     

Capillary complexation gas chromatography in analysis of cyclic and aromatic hydrocarbons

Summary Results of studies on stationary phases containing copper(II), nickel(II) and cobalt(II) chloride chemically bonded via cyano—or thiol groups are presented. The retention parameters—i.e. retention factor (k), retention index (I) and molecular retention index (ΔMe) and specific retention volume (Vg)-enabled the characteristics of specific interaction between aromatic and cyclic hydrocarbons and metal complexes chemically bonded to stationary phases to be determined. Presented at Balaton Symposium on High Performance Separation Methods, Siófok, Hungary, September 1–3, 1999     

Chromatographic determination of total hydrocarbons in ethanolamine employed in sweetening process of natural gas

Summary A rapid and easy gas chromatographic method is proposed for the determination of condensate content in monoethanolamine employed in the sweetening process of natural gas in the petroleum industry. This method covers a wide range of heavy hydrocarbons (condensate) content by using a short conventational column. A comparative study has been carried out and the advantages of the gas chromatographic technique have been demonstrated.     

Reaction gas chromatography: Study of the photodecomposition of halogenated hydrocarbons

Summary Photodecomposition of chloro- and bromoderivatives of saturated, unsaturated and aromatic hydrocarbons has been studied under flow conditions using reaction gas chromatography. The photodegradation products were separated on a column coated with squalane and identified by comparing the measured retention data with those of standards and published retention indices, The results can be used to clarify the decomposition of such compounds.     

Simultaneous determination of aliphatic hydrocarbons,PCBs and PCTs in pork liver by gas chromatography

Summary A multicomponent extraction/concentration procedure has been developed for the enrichment of PCBs, PCTs and aliphatic hydrocarbons (pristane, C₁₈, C₁₉, C₂₀, C₂₂, C₂₄, C₂₈, C₃₂ and C₃₆) in pork liver. These components of the enriched extract were then simultaneously determined by gas chromatography. Mean recoveries ranged from 81.5% for pristane to 93% for PCBs;CV% (0.9–6.7) indicated the method to be both precise and reproducible.     

Evaluation of solid-phase microextraction conditions for the determination of polycyclic aromatic hydrocarbons in aquatic species using gas chromatography

This paper describes a headspace solid-phase microextraction (HS-SPME) procedure coupled to gas chromatography with mass spectrometric detection (GC–MS) for the determination of eight PAHs in aquatic species. The influence of various parameters on the PAH extraction efficiency was carefully examined. At 75 °C and for an extraction time of 60 min, a polydimethylsiloxane–divinylbenzene (PDMS/DVB) fiber coating was found to be most suitable. Under the optimized conditions, detection limits ranged from 8 to 450 pg g⁻¹, depending on the compound and the sample matrix. The repeatability varied between 7 and 15% (RSD). Accuracy was tested using the NIST SRM 1974b reference material. The method was successfully applied to different samples, and the studied PAHs were detected in several of the samples. Figure Headspace SPME sampling followed by GC–MS facilitates routine monitoring of PAHs in aquatic species     

Analysis of gases containing inorganic compounds and light hydrocarbons on fused-silica open-tubular columns prepared with a thick liquid phase film

Capillary columns having a thick liquid phase film and a low phase ratio permit the separation of low molecular mass compounds which would have a very small capacity factor on columns with a classical thin film. At the same time, the increased sample capacity allows conventional hot-wire thermal conductivity detectors to be used with such columns. The analysis of natural and refinery gases, containing both inorganic compounds and light (C₁? C₇) hydrocarbons, utilizing a combination of hot-wire and flame ionization detectors, is demonstrated.     

Analysis of trace components in gases by gas chromatography

Summary Relationships are derived describing how the detection limit of a chromatographic system depends on the minimum detectable limit of the detector and the chromatographic parameters such as column length, efficiency, carrier gas flow rate and the capacity factor. Performance data of detectors developed in the last 25 years at the Dalian Institute of Chemical Physics of the Chinese Academy of Sciences are given and a few selected application examples are listed. These include trace analysis by preconcentration and by direct analysis and the utilization of multidimensional gas chromatography with two columns, two detectors, a 12-port valve, and a catalytic conversion reactor.     

Analysis of light hydrocarbons (C2?C6) at PPT levels by high resolution gas chromatography

An analytical technique is described which allows the determination of C₂? C₆ hydrocarbons in the ppt-range from up to 21 air samples after removal of air humidity. Preconcentration is carried out on a two stage cryotrap system. The compounds are separ ated on a temperature-programmed capillary coated with Al₂ O₃. Detection limits (S/N 2:1) of 1.5 to 5 ppt were obtained for air samples from the Arctic. The reproducibility of the method was about 3% at the 50–100 ppt level. Practical problems are discussed in detail.     

Rapid on-line analysis of low molecular weight hydrocarbons using glass capillary gas chromatography

Rapid analysis is important for on-line chromatography. Gaseous or vaporized samples have been injected via heated gas sampling valves of less than 500 μl dead volume. The critical sampling and split problems could be solved by temperature programming. The general analysis described could be successfully used inter alia in scouting reactions.     

Analysis of nitrated polycyclic aromatic hydrocarbons by glass capillary gas chromatography using different detectors

Glass capillary gas chromatography has been investigated as a method for the analysis of nitrated polycyclic aromatic hydrocarbons (nitro-PAH) using both splitless and on-column injection techniques. The nitro-PAH showed good chromatographic performance and thermal stability under the GC conditions used. Retention times and response factors of several nitro-PAH were compared to those of conventional PAH. Simultaneous flame ionization and thermionic nitrogen selective detection was used to facilitate identification of nitro-PAH in complex samples. The feasibility of the method is demonstrated on two samples of commercial carbon black. Besides 1-nitropyrene several isomeric dinitropyrenes have been identified.     

Rapid analysis of hydrocarbons and inert gases by a multidimensional gas chromatograph

A combination of a pressure switching system with multiple columns and photoionization detectors makes possible rapid analysis of a mixture of inorganic gases and hydrocarbons. Hydrocarbons are separated by a narrow bore capillary column. An alumina PLOT column is used for the separation of lower molecular weight hydrocarbons, especially C4 isomers, while a combination of a micro-packed column with Porapak N and a PLOT capillary column with Molecular Sieve 5A is used for the fast separation of inorganic gases. A photoionization detector is a powerful additional tool for organic gas analysis.     

Headspace gas chromatographic determination of aromatic hydrocarbons in natural and waste water

Summary The possibilities of using headspace analysis of aromatic hydrocarbon traces in aqueous solutions with changing values of the partition coefficients are discussed. A variant of headspace analysis of the simplest aromatic hydrocarbon in natural and waste water is described. It involves two-step gaseous extraction of a sample in vessels of varying volume before and after the equilibrium phase is replaced with a pure gas (air or nitrogen). This method permits to analyse 5–50 ml water samples with benzene and toluene contents varying from the ppb to the ppm range within an error not exceeding 155. The analysis time is about 1.5 h. The presence of non-volatile organic or mineral substances does not influence the determination. This method is unsuitable to heterogeneous systems (aqueous oil emulsions): before carrying out the analysis for the hydrocarbon content these systems have to be homogenized first.Presented at the Scientific Seminar on Headspace Gas Chromatography organized in cooperation with the Perkin-Elmer Corporation (Norwalk, CO, USA) in Leningrad, December 4–5, 1979.     

Viscosity of gases used as the mobile phase in gas chromatography

The vicosity-temperature relationship of the three gases (helium, nitrogen and hydrogen) most frequenly used as the carrier gas in gas chromatography is studied. Based on available data, equaitions are derived to describe this relationship. Using these equations viscosity data are tabulated for the chromatographically important temperature range.Dedicated to Professor A. Zlatkis on the occasion of his 60th birthday.