Transition metal complex stationary phases for the CGC analysis of ethers, thioethers and ketones

Summary The use of polysiloxanes with cyano or thiol groups as stationary phases for complexation gas chromatography is discussed. The polymers were obtained via polycondensation followed by polymerisation of the corresponding dichloro- or dimethoxy-silanes. Both the phases were modified by bonding transition metal chlorides with were modified by bonding transition metal chlorides with cyano (CuCl₂ or CoCl₂) and thiol groups (NiCl₂ or CoCl₂). The phases were examined in order to determine their application to the analysis of ethers, thioethers and ketones. Due to the presence of lone electron pairs on oxygen or sulphur atoms, the compounds should be capable of specific interacting with the electron-withdrawing centre of the liquid stationary phases. A number of retention parameters (retention indices, molecular retention indices and specific retention volume) were determined, which allowed characterisation of specific interactions between the bonded metal and the compound analysed. The results also enabled assessment of the influence of the structure of the compounds on their retention. The measurements were also carried out for the phases with free SH and CN groups as reference phases. The work demonstrates that the phases obtained may be useful for effective separations.     

A cold silanization method for preparation of medium polarity capillary columns

Silane-coupling agents, commonly used for fiberglass reinforced plastics (FRP), were applied for deactivation of silanol sites in glass capillary columns prior to coating with mediumpolarity phases such as Carbowax and Superox. The columns, prepared in a two-stage process in the case of glass (acidic leaching and drying, dynamic cold silanization followed by static coating with the phase) or a one stage process in the case of fused silica, gave the best results when deactivation and hence wettability were induced by glycidoxypropyltrimethoxy silane.     

PoraPLOT Q: A porous layer open tubular column coated with styrene-divinylbenzene copolymer

A porous polymer is deposited on the inner wall of fused silica capillary columns. The retention characteristics of this porous polymer were evaluated and found to be comparable with Porapak Q. The porous polymer has a high retention volume which enables the separation of permanent gases at ambient temperatures or higher. The hydrophobic character of the porous polymer allows the injection of water containing samples without changing retention due to adsorption of water. The inertness of the porous polymer allows the elution of a range of apolar and polar compounds. The maximum temperature of the porous polymer was estimated to be 250°C. With this new type of capillary column, high resolution separations are obtained in combination with short analysis times.     

On the influence of the solute sample size on temperature-programmed retention indices

The effect of the solute sample size on the measurement of temperature-programmed retention indices (I_TP) has been studied on glass capillary columns with different stationary phases, film thicknesses, and temperature programs. The sample capacity of a solute is little affected by the parameters of temperature program, i. e. initial temperature and heating rate. However, it has been found that in a temperature programmed run, allowable sample sizes for high I_TP values are lower than for low I_TP values. About 10 ng of each compound is recommended as the sample size for accurate measurement of I_TP values on commonly used capillary columns.     

Automatic simulated distillation of heavy petroleum fractions up to 800°C TBP by capillary gas chromatography. Part I: Possibilities and limits of the method

The characterization of heavy petroleum fractions is essential for the design and improvement of cracking plants converting heavy feedstock into valuable “white” products. Conventional simulated distillation methods using packed columns are unsuitable for this purposes, being limited to boiling points up to about 600°C. The method presented is able to cover a boiling points interval ranging from about 150°C up to around 800°C. It employs a short, nonpolar, highly thermostable capillary column routinely operated at temperatures around 430°C. The analytical system is based on a high temperature versions of a fully automatic, capillary dedicated gas chromatograph. The experimental data demonstrate that cold on-column injection is the sole sampling system suitable for such heavy compounds. The conversion of the retention times into boiling points, based on the use of low molecular weight polyethylenes, is extremely reliable, as demonstrated by the excellent retention time reproducibilities. The lower part (up to 550–600°C TBP) of the boiling point distribution curves of heavy petroleum fractions obtained on capillary columns fits well with the corresponding distribution curves based on packed column data. For the petroleum fractions fully eluted from the column the quantitative results obtained either using internal standards or by direct processing of the elution curves are in excellent agreement (less than 0.3 weight% differences). The method has been applied to the determination of the true boiling points corresponding to short path vacuum distillation (DISTACT) cut points over 300°C.     

Large sample injection method (≥ 100 μL) for capillary GC using a commercial thermodesorption unit as injection device

A commercial thermodesorption and cold trap unit can be used as a large sample volume injection device in high resolution gas chromatography. Volumes of more than 100 μl can be injected. More than 97% of solvents, such as hexane, can be removed by a Tenax TA precolumn without any loss of compounds with volatilities comparable to naphthalene. Experimental conditions, recovery rates of polycyclic aromatic hydrocarbons, and the reproducibility of the method are described in detail. The method was successfully applied for the determination of PAH in air particulate matter extracts.     

New stationary phase polarity parameters considering the electric intermolecular interactions in gas chromatographic column

Summary The possibility of evaluation of the parameters representing the dispersive solute-solvent interactions is presented. B_N and B_s values can be used to describe the liquid phase polarity and to predict the retention indices of alcohols when the model polyxyethylene glycol dialkyl ethers and their sulphur analogs are used as stationary phases. The possibility of the first ionization potentials estimation is also presented.     

Dicyclopentadiene dissociation in a chromatographic reactor. Effect of the liquid phase polarity on the reaction rate

Summary The gas chromatographic reactor technique was used to study the kinetics of dicyclopentadiene dissociation in several liquid phases (Versamid 900, neopentyl glycol sebacate, Triton X-305, Carbowax 6000, ethylene glycol phthalate and diethylene glycol succinate). Reaction rates and Arrhenius parameters are reported in the temperature range of 170–200°C. Kinetic data for the lower polarity liquid phases are in good agreement with literature values for liquid phases of the same nature reported previously. Reaction rates are higher when polar liquid phases are used. This behavior can be explained as a result of side reactions which lead to high molecular weight compounds which can be observed in the reaction chromatogram.     

Application of chemometrics to the classification of orange essence oil varieties by GLC

Orange essence oils of the Navel and Valencia variety were analyzed by GC and GC/MS using two parallel capillary columns of different selectivity. Data were normalized, converted into a computer compatible format, and transferred via an asynchronous communications interface to a mainframe computer for statistical treatment, using the chemometrics software package ARTHUR. After suitable preprocessing of the raw data, reliable classification was possible. It appears that four substances which are present in both varieties can be used for that purpose.     

On the efficiency of capillary columns coated with medium polarity thick films

The efficiency of FSOT columns coated with thick films of polyphenylmethylsiloxane was theoretically and experimentally compared to thin apolar and medium polar coatings and to thick apolar coatings. Experimental hū and TZū plots clearly demonstrate the enormous loss in chromatographic efficiency of thick films of medium polar siloxane stationary phases. The low diffusion coefficient in the liquid phaese is responsible for this behavior. The influence of the temperature and the nature of the solute on the efficiency was also studied.     

An improved method for steroid profile analysis using capillary gas chromatography

Summary Steroid conjugates are hydrolysed enzymatically using β-glucuronidase after extraction from urine using a solid phase extraction cartridge. After hydrolysis the free steroids are removed from the matrix, again utilising solid phase extraction. Derivatisation of the free hydroxyl groups using Hydrox-Sil AQ produces the respective TMS ethers which are extracted into hexane, in which solvent they are stable for many days. Capillary GC analysis with flame ionisation detection produces a profile of the steroids present in the sample. This technique is suitable for following changes in the urinary excretion profiles of patients undergoing investigation for a variety of steroid production-related diseases.     

A new method for in situ crosslinking of stationary phases on fused silica capillary columns

A new mixed crosslinking agent composed of dicumyl peroxide and tetra(methylvinyl)cyclotetrasiloxane was used to prepare fused silica capillary columns with in situ crosslinked stationary phases including PEG-20M, SE-54, and OV-1. These columns proved to have good thermostability and inertness. As examples of potential applications a mixture of isomers of nitrotoluene and dinitrotoluene, and pyrolyzates of polystyrene were separated by using these columns.     

A study of chromatographic properties of liquid crystalline polyacrylates using WCOT columns in gas chromatography

Liquid crystalline polyacrylates (LCPAs) are evaluated as stationary phases for capillary gas chromatography (CGC). Aromatic hydrocarbons as well as polar isomeric compounds are used as test solutes to compare the polarity of the LCPAs with a conventional polysiloxane column and a Carbowax 20M column. The relative polarity of the columns with respect to change in the lateral and terminal substituents is also discussed. Lateral substitution, polarity of the terminal group, together with the solute size, affect the LCPA selectivity.     

Capillary columns in series for the gas chromatographic analysis of essential oils

Summary By connecting capillary columns of different polarity in series and by changing the temperature program gradient, a system of variable polarity is obtained. The working conditions can be adjusted to optimize separations of complex mixtures. Application to the analysis of essential oils of: lavender, thyme, lemon petit grain, bergamot, and tangerine, are reported.Dedicated to Prof. Dr. A. Liberti on the occasion of his 70th birthday.