High‐throughput gas chromatography for volatile compounds analysis by fast temperature programming and adsorption chromatography

The synergy of combining fast temperature programming capability and adsorption chromatography using fused silica based porous layer open tubular columns to achieve high throughput chromatography for the separation of volatile compounds is presented. A gas chromatograph with built‐in fast temperature programming capability and having a fast cool down rate was used as a platform. When these performance features were combined with the high degree of selectivity and strong retention characteristic of porous layer open tubular column technology, volatile compounds such as light hydrocarbons of up to C₇, primary alcohols, and mercaptans can be well separated and analyzed in a matter of minutes. This analytical approach substantially improves sample throughput by at least a factor of ten times when compared to published methodologies. In addition, the use of porous layer open tubular columns advantageously eliminates the need for costly and time‐consuming cryogenic gas chromatography required for the separation of highly volatile compounds by partition chromatography with wall coated open tubular column technology. Relative standard deviations of retention time for model compounds such as alkanes from methane to hexane were found to be less than 0.3% (n = 10) and less than 0.5% for area counts for the compounds tested at two levels of concentration by manual injection, namely, 10 and 1000 ppm v/v (n = 10). Difficult separations were accomplished in one single analysis in less than 2 min such as the characterization of 17 components in cracked gas containing alkanes, alkenes, dienes, branched hydrocarbons, and cyclic hydrocarbons.     

Identification and quantitative analysis of nitrogen-containing polycyclic aromatic hydrocarbons in sediments

An integrated analytical methodology has been developed for determining nitrogen-containing polycyclic aromatic hydrocarbons, which enables quantitation of individual contaminants as low as 1 μg/kg in sediment samples. A cross-sectional profile from the Hamilton Harbour sediment samples was analyzed for azaarenes. These contaminants were separated by Soxhlet extraction, and pH adjustment allowed their isolation from different classes of neutral and acidic components. Separation and identification of the organic bases in each sample were achieved by using open tubular column gas chromatography with thermionic detection and HRGC-mass spectrometry. Organic bases present in the samples included mostly azaarenes such as acridines, benzacridines, azafluorene, benzoquinolines, azapyrenes, etc. Quantitation and environmental significance of these compounds are discussed. Recoveries of individual azaarenes at two different levels were evaluated. Data presented indicate that detection limits of this method are between 1 and 10 μg/kg. Recovery azaarenes from bottom sediment samples at concentration levels between 1 to 100 μg/kg is 81 ± 17%.     

Application of dicarbonyl-rhodium-trifluoroacetyl-d-camphorate to special problems of olefin analysis by gas-liquid chromatography

Summary The title compound, dissolved in squalane, has been used as stationary phase in g.l.c. for purity determinations of olefins. High resolution open tubular columns have been prepared with the same phase. C₂H₄, C₂D₄ and the isomeric butenes were efficiently separated.     

Behavior of fused silica capillaries subjected to gamma radiation. Part 1: Chromatographic performance

Fused silica capillaries deactivated with D₄ and coated with OV-1 were subjected to cobalt-60 gamma radiation in order to elucidate the effect of incident radiation on column performance. The chromatographic performance of these open tubular columns in which OV-1 was polymerized in situ was found to be dependent on the dosage of radiation and was evaluated before and after the irradiated columns were rinsed with solvent. Of the radiation dosages employed, 3 MRad produced superior chromatographic performance coupled with very favorable residual surface activity.     

Glass capillary gas chromatography of C1−C4 mononitroalkanes. Pre-calculation of the relative retention

Summary The separation of C₁–C₄ mononitroalkanes on four wall-coated glass open tubular (capillary) columns (liquid phases: OV-101, Ucon-LB-550X, NPGS and Carbowax 20M) was investigated. Retention indices were determined and the influence of the different factors (analysis temperature, method of determining the gas holdup time and the nature of the stationary phases) on their reproducibility were studied. Linear regression equations permit the pre-calculation of the retention indices of C₁–C₄ mononitroalkanes from their properties on all liquid phases studied.     

Simultaneous determination of C1−C8 n-alkyl acetates and corresponding mono-, di- and trichloroacetates on glass capillary columns with programmed temperature rise

Summary Gas chromatography of mixtures of aliphaticn-alkyl acetates (CH₃–COOR), chloroacetates (CHCl₂–COOR), dichloroacetates (CHCl₂–COOR) and trichloroacetates (CCl₃–COOR), where the alcohol chain length (R) varied between 1 and 8, has been studied on SE-30, Carbowax 20M and OV-351 glass capillary columns with programmed temperatures from 50°C at 2, 4, 6, 8 and 10°C/min. Compounds in the homologous series are eluted in the direct order from methyl ton-octyl acetate. The isomeric chloro esters are eluted on SE-30 according to their boiling points in the order: mono-, di- and trichloro isomer, whereas on polar columns di- and trichloro esters are eluted in the reverse order. The complete separation of all 32 individual components from the mixture could not be reached by any single column, the best separation occurred on SE-30. The mixture can, however, be separated by using columns with polar and non-polar stationary phases. The relative retention times for the compounds are given and the retention order discussed.     

Gas chromatographic and mass spectrometric characterization of isomeric alkylthiophenes (C20) and their occurrence in deep sea sediments

Six isomeric C₂₀ alkylthiophenes were synthesized in order to prove the occurrence of such compounds in various deep sea sediments. As expected from the analogy with the corresponding saturated hydrocarbons, 2- and 3-heptadecylthiophene have considerably longer relative retention times than the isomeric isoprenoid compounds, i.e. 2- and 3-(4,8,12-trimethyltridecyl)thiophene and 3- and 4-methyl-2-(3,7,11-trimethyldodecyl)thiophene. Covats retention indices for all compounds were determined by isothermal analysis at 190°C on two different silicone-coated capillary columns. The mass spectra of the monoalkylated thiophenes show a base peak at m/z 98 corresponding to a Mcafferty rearrangement product in the case of the 3-substituted isomers, whereas a simple benzylic cleavage dominates in the mass spectra of 2-alkylthiophenes. 4-Methyl-2-(3,7,11-trimethylodecy)thiophene is an exception from this simple rule because also shows the McLafferty rearrangement as dominant fragmentation. Two of the isoprenoid thiophenes are prominent compounds in various deep sea sediments.     

A new look at light hydrocarbon separations on commercial alumina PLOT columns: Column selectivity and separation

Alumina-coated porous layer open tubular (PLOT) columns are widely used for analyses of light hydrocarbons (C₁ to C₆). There is, however, a need for improved selectivity for complex analyses such as the determination of impurities in high purity petrochemical products. Some commercial alumina PLOT columns do not have sufficient selectivity for such analyses. The selectivity of four commercial alumina PLOT columns is evaluated for analyses of propylene and ethylene, and differences in column selectivity discussed. Requirements of column selectivity and retention are presented for several applications including the analysis of refinery gas, transformer oil gas, and fuel gas.     

Rapid gas chromatography of isomeric aromatic hydrocarbons

Summary A method is described for the gas-chromatographic separation of isomeric aromatic hydrocarbons up to C₉ using modified Bentone 34 short-capillary or high-efficiency small-bore packed columns. Properties of both column types are discussed. A mixture of ethylbenzene and isomeric xylenes can be separated within less than 3 min and the separation of a mixture of ethylbenzene, isomeric xylenes, ethyltoluenes, trimethylbenzenes and n-hydrocarbons C₆ to C₉ can be achieved within less than 5 min on a column 3 m×0.8 mm i. d. packed with Bentone 34 + dinonylphthalate on Chromosorb W.

---

Zusammenfassung Es wird eine Methode zur schnellen gas-chromatographischen Trennung isomerer aromatischer Kohlenwasserstoffe bis C₉ mit modifiziertem Bentone 34 an kurzen Capillarsäulen oder an gepackten Hochleistungs-Trennsäulen mit kleinem Innendurchmesser beschrieben. Die Eigenschaften der beiden Säulentypen werden diskutiert. Ein Gemisch von Äthylbenzol und Xylolisomeren kann in weniger als 3 min getrennt werden. Eine Trennung von Äthylbenzol, isomeren Xylolen, Äthyltoluolen, Trimethylbenzolen und Kohlenwasserstoffen C₆ bis C₉ kann innerhalb von 5 min an einer Säule von 3 m×0,8 mm i.D., gepackt mit Bentone 34 und Dinonylphthalat auf Chromosorb W, erreicht werden.

     

Elektronenstossinduzierte Fragmentierung von Acetylenverbindungen. XI—Energetische Betrachtungen zum Mas Senspektro-Metrischen Zerfall Einiger Offenkettinger und Isomerer Cyclischer Kohlenwasserstoffe

The enthalpy of formation of stable ions of some C₈H₆, C₁₀H₁₀ and C₁₂H₁₀ hydrocarbons have been calculated by means of AP/IP measurements and their correlation with thermochemical data. It has further been shown that under electron-impact-induced fragmentation aromatic and isomeric acetylenic compounds give open chain as well as cyclic ion structures.     

Chromatographic Properties of Monolithic Silica Capillary Columns for Polar and Nonpolar Compounds in Reversed-Phase HPLC

Retention properties of monolithic silica C₁₈ columns were examined for polar and nonpolar compounds. Monolithic silica columns were prepared from two kinds of starting materials, tetramethoxysilane (abbreviated as TMOS) or a mixture of TMOS and methyltrimethoxysilane (abbreviated as Hybrid), and modified with dimethyloctadecylchlorosilane (C₁₈). Retention factors of various compounds on Hybrid-C₁₈ are about twice as much as that on TMOS-C₁₈. The two types of columns showed very similar retention selectivity with few exceptions. TMOS-C₁₈ showed slight preference toward planar polynuclear aromatic hydrocarbons (PAHs) compared to bulky aromatic hydrocarbons, while Hybrid-C₁₈ showed opposite tendency. Some TMOS-C₁₈ columns showed peak tailing for PAHs, and also for basic compounds in an acidic mobile phase, while Hybrid-C₁₈ and majority of TMOS-C₁₈ columns resulted in good peak shape for these compounds.     

Simultaneous gas chromatographic determination of aliphatic C2−C20 n-carboxylic acids and their methyl esters using SE-30 and OV-351 quartz capillary columns

Summary Simultaneous determination of aliphatic C₂–C₂₀ carboxylic acids and their methyl esters was carried out using SE-30 and OV-351 quartz capillary columns with temperature programming. Complete resolution of all 36 components was achieved. On SE-30 the methyl ester and the corresponding free acid are eluted in turn, whereas on OV-351 acetic acid eluted after methyl octanoate, after which the C_n methyl ester and C_n-6 carboxylic acid (n>9) are eluted one after the other. A non-polar SE-30 column is better for long-chain acids giving sharp peaks without tailing, the analysis time of the mixture being less than 16 minutes. The weight response correction factors for compounds under optimum operating conditions are given.     

Gas chromatographic retention indices for alkenes on OV-101 and squalane capillary columns

Summary Gas chromatographic retention indices for 47 C₅ to C₈ alkenes on OV-101 dimethylsilicone at 50 and 70 °C were determined within a standard deviation of 0.3i.u. Data obtained on OV-101 are compared with those measured on squalane. The comparison of the retention index and dl/dT values from both columns is presented as linear regression equations with correlation coefficients greater than 0.98.     

Application of open tubular electrochromatography for acidic and basic analytes

Summary The separation of charged analytes by electrochromatography has been examined on porous-layer open tubular capillaries prepared using the sol gel method. An electroosmotic flow of about 2.10×10⁴ cm²V¹s¹ was obtained using between 10 and 30% acetonitrile in the mobile phase. Acidic diuretic drug compounds were successfully separated at high pH as were theN-alkylanilines in their basic and neutral forms. The limitation of open tubular columns was observed on separating some basic pharmaceutical drugs. These components showed severe peak tailing and were not resolved on a 20 μm i.d. porous silica layer open tubular column. Strongly acidic components could not be detected on these columns due to their higher counter electromobilities. The successful separation of neutral aryl alkyl ketones with an efficiency of 101,533 plates m¹ for butyrophenone was an indication of the improved phase ratio on this type of open tubular columns.     

Measurement of Henry coefficients by capillary columns coated with slightly polar solvents

Summary The specific retention volumes and Henry coefficients measured on packed columns are compared with those calculated via retention indices determined on wall coated open tubular capillary columns. The stationary phase liquids used were derivatives of a branched paraffin, C₇₈H₁₅₈, where a methyl or ethyl group of the paraffin was replaced by OH, CN, OCH₃ and SH groups. The retention indices of a series of molecular probes of varying polarity (aromatics, 1-chloroalkanes, 1-acetoxy-alkanes, 1-alkanols, 2-alkanones) were determined atT=403.15 K on fused-silica open tubular columns prepared by static coating that gave stable and uniform solvent films. After obtaining the absolute data on packed columns forn-alkanes, the specific retention volumes and Henry coefficients of the solutes were calculated. The retention data obtained on both columns showed good agreement. Presented at Balaton Symposium on High Performance Separation Methods, Siófok, Hungary, September 1–3, 1999     

Chemistry of the Higher Fullerenes: Preparative isolation of C76 by HPLC and synthesis,separation, and characterization of Diels-Alder monoadducts of C70 and C76

HPLC Separation of higher fullerenes was compared on two different stationary phases, and the preparative isolation of pure C₇₆ is described. Higher-fullerene derivatives 1 and 2 were prepared by Diels-Alder reaction of C₇₀ and C₇₆ with an ortho-quinodimethane intermediate generated in situ. Three out of four possible isomeric C₇₀ monoadducts, i.e. 1a – c , and, for the first time, one isomeric C₇₆ monoadduct, i.e. 2c , could be isolated in pure form and characterized by ¹H-NMR, ¹³C-NMR, UV/VIS, and mass spectrometry. Five other C₇₆ isomers i.e., 2a , b , d – f were obtained in partially separated product fractions. Coalescence temperatures and energy barriers were determined for the cyclohexene-ring inversion in two of the isomeric C₇₀ derivatives. The structure of the C₇₀ adducts could be deduced unambiguously from symmetry considerations based on high- and low-temperature ¹H-NMR spectroscopy. A simple model for the qualitative evaluation of the local curvature of fullerene surfaces is presented and used for the prediction of addition sites in higher fullerenes. These predictions are compared to the experimental results mentioned above as well as to predictions resulting from π-bond-order considerations and from calculated pyramidalization angles.     

Hydrogen‐bonding controls the solid‐state and enantiomeric comformations of the amino alcohol ligand 2‐[(2‐hydroxyethyl)amino]cyclohexanol

The crystal structure of the title compound, C₈H₁₇NO₂, consists of (R,R) and (S,S) enantiomeric pairs packed in adjacent double layers which are characterized by centrosymmetric hydrogen‐bonded dimers, generated via N—H...O and O—H...O interactions, respectively. Intermolecular interactions, related to acceptor and donor molecule chirality, link the achiral double layers into tubular columns, which consist of a staggered hydrophilic inner core surrounded by a hydrophobic cycloalkyl outer surface and extend in the [011] direction.     

Influence of the chemical nature of siloxanes on the thermodynamic characteristics of sorption for a series of linear and cyclic saturated hydrocarbons

The thermodynamic characteristics of sorption (Henry’s constants of sorption equilibrium K _sorp, heats of sorption q, and standard entropies of sorption ΔS°) were studied by gas chromatography to describe the behavior of linear and cyclic saturated hydrocarbons on phenylmethylsiloxane HP-5, fluoromethylsiloxane OV-210, and methylsiloxane OV-1. The K _sorp and q values and, correspondingly, the energy of dispersion interactions decrease in the series HP-5 > OV-1 > OV-210. The difference in structures of adamantane, trans-decalin, and decane molecules has almost no effect on the heats of sorption. Henry’s constants increase on going from decane to trans-decalin and, further, to adamantane. This effect becomes more pronounced with an increase in the sorbent polarity (OV-1 < HP-5 < OV-210). The entropy factor can play a key role in sorption processes on siloxanes.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 140–143, January, 2005.     

The effect of column characteristics on the minimum analyte concentration and the minimum detectable amount in capillary gas chromatography

The need for faster and more efficient separations of complex mixtures of organic compounds by gas chromatography has led to the development of small inner diameter open tubular columns. Owing to their decreased plate height, extremely narrow peaks are obtained. When differently sized columns with equal plate numbers are compared, injection of a fixed amount of a solute will give the highest detector signals for the smallest bore columns. When P is defined as the ratio of the column inlet and outlet pressures, it can be seen from theory that under normalized chromatographic conditions the minimum detectable amount (Q_º) for a mass flow sensitive detector increases proportionally to the square of the column diameter for P = 1. In the situation of greater interest in the practice of open tubular gas chromatography where P is large, a linear relationship is derived between Q_º and the column diameter. It is a widespread misunderstanding, however, that narrow bore capillary columns should be used for this reason in trace analysis. If a fixed relative contribution of the injection band width to the overall peak variance is allowed, a decreased plate height drastically restricts the maximum sample volume to be injected. It is shown that the minimum analyte concentration in the injected sample (C_º) is inversely proportional to the column inner diameter when a mass flow sensitive detector is used. For actual concentrations less than C_º, sample preconcentration is required. The effect of peak resolution and selectivity of the stationary phase in relation to C_º and Q_º will be discussed as well. The validity of the given theory is experimentally investigated. Minimum analyte concentrations and minimum detectable amounts are compared using columns with different inner diameter.