On-line gas chromatographic analysis of light Fischer-Tropsch synthesis products

Summary A simple gas chromatographic system has been developed for the rapid on-line analysis of light Fischer-Tropsch products. This involves a single chromatography fitted with two columns, a porous-layer open-tubular column coated with KCl deactivated alumina and a packed Porapak-Q column. The capillary column separates the 16 most common C₁−C₄ hydrocarbons and permits a reasonable analysis of the hydrocarbons in the C₅−C₇ range. The packed column is used for the separation of methane, carbon monoxide, carbon dioxide, water and methanol. Retention characteristics for the analysis on the capillary column are presented. The total analysis cycle is 30 minutes.     

Separation of Fatty Acids as Their p-Bromophenacyl Esters on a C30-Bonded Silica Column by High Performance Liquid Chromatography

Abstract

A new C₃₀-bonded silica column was developed for high performance liquid chromatography. This column was tested for the fractionation of fatty acids as their p-bromophenacyl esters by the reverse-phase mode. Certain pairs of fatty acid esters that are very difficult to separate on a C₁₈-bonded silica column, i. e., arachidonic (C₂₀:4)-palmitoleic (C₁₆:1); elaidic (trans C₁₈:1)-vaccinic (cis C₁₈:1); behenic (C₂₂:0)-nervonic (C₂₄:1); and arachidonic (C₂₀:0)-erucic (C₂₂:1) esters, were completely resolved on the C₃₀-bonded column using solvent gradients of acetonitrile: water and acetonitrile: p-dioxane. A solvent system of methylene chloride: acetonitrile (2:1, v/v) was developed for this column to achieve good separation of a homologous series of extremely nonpolar C₇₆ to C₈₂ α-mycolic acid esters from Mycobacterium tuberculosis H37Ra.     

Protein separation on a polar-copolymerized C<Subscript>8</Subscript> stationary phase

A novel polar-copolymerized C₈ stationary phase composed of octyl and chloropropyl (C₈-C₃Cl)-bonded silica has been developed for protein separation. Separation of standard proteins on this homemade column was investigated and compared with separation on a Waters Symmetry 300 C₄ column. Results indicated that the chromatographic performance of the homemade column in the separation of proteins was excellent. The new polar copolymerized C₈ stationary phase enabled glycoprotein separation with good resolution and reproducibility. It was also used for purification of ovalbumin glycoprotein in order to improve identification of the protein.     

Comparison of a C30 Bonded Silica Column and Columns with Shorter Bonded Ligands in Reversed-Phase LC

The Carotenoid S is a new C₃₀ bonded silica stationary phase, intended for reversed-phase chromatographic applications, which is more hydrophobic and consequently shows stronger retention in comparison to conventionally used C₁₈ stationary phases. We compared the non-polar selectivities of the columns for homologous alkylbenzenes in acetonitrile—water and methanol–water mobile phases and polar reversed-phase selectivities employing the interaction indices and the Linear Free Energy Relationship models. Further, we investigated possibilities of separations of structurally closely related compounds in the groups of phenolic acids, flavones, phthalic acids and related compounds and of acylglycerols on the new C₃₀ column and with different types of columns for reversed-phase chromatography, including shorter alkyl C₄, C₈, C₁₈ and phenyl bonded stationary phases. The C₃₀ column has in some aspects properties similar to the non-endcapped Nova-Pak column for separation of some acylglycerols with equal equivalent carbon numbers, but enables separations of longer chain triacylglycerols in a single gradient run.

     

Comparison of various types of stationary phases in non-aqueous reversed-phase high-performance liquid chromatography–mass spectrometry of glycerolipids in blackcurrant oil and its enzymatic hydrolysis mixture

The selection of column packing during the development of high-performance liquid chromatography method is a crucial step to achieve sufficient chromatographic resolution of analyzed species in complex mixtures. Various stationary phases are tested in this paper for the analysis of complex mixture of triacylglycerols (TGs) in blackcurrant oil using non-aqueous reversed-phase (NARP) system with acetonitrile–2-propanol mobile phase. Conventional C₁₈ column in the total length of 45 cm is used for the separation of TGs according to their equivalent carbon number, the number and positions of double bonds and acyl chain lengths. The separation of TGs and their more polar hydrolysis products after the partial enzymatic hydrolysis of blackcurrant oil in one chromatographic run is achieved using conventional C₁₈ column. Retention times of TGs are reduced almost 10 times without the loss of the chromatographic resolution using ultra high-performance liquid chromatography with 1.7 μm C₁₈ particles. The separation in NARP system on C₃₀ column shows an unusual phenomenon, because the retention order of TGs changes depending on the column temperature, which is reported for the first time. The commercial monolithic column modified with C₁₈ is used for the fast analysis of TGs to increase the sample throughput but at cost of low resolution.     

High Performance Liquid Chromato-Graphy Separations of Nitrosamines. II. Acyclic Nitrosamines

Abstract

The separation of acyclic nitrosamines by HPLC using a β-cyclodextrin bonded silien gel column and a C₁₈ reversed phase column was evaluated. Four groups of nitrosamines were used to evaluate the utility of both columns: (1.) methylmethyl-, methylethyl-, methylpropyl and methylbutyl-; (2.) ethylmethyl-, ethylethyl-, and ethylpropyl-; (3.) propylmethyl-, propylpropyl-, and propylbutyl-; and (4.) butylmethyl-, butylethyl-, butylpropyl-, and butylbutyl nitrosamines.

The results show that both columns performed well in separating the nitrosamines in each group, with the C₁₈ column requiring a higher percentage of organic modifier (methanol) than the β-cyclodextrin column. The β-cyclodextrin column was superior in separating all the E to Z isomers of short chain alkyl nitrosamines, while the C₁₈ column was superior in separating long alkyl chain nitrosamines and their E and Z isomers.

It, was also found that, the longer the alkyl chain the longer the retention time, while nitrosamines having the same number of carbons, for example ethylbutyl-and propylpropyleluted at virtually the same time, using both columns.     

C18, C8, and perfluoro reversed phases on diamond for solid-phase extraction

In spite of advances in solid-phase extraction (SPE) technology there are certain disadvantages to current SPE silica-based, column packings. The pH range over which extraction can occur is limited and each column is generally only used once. New diamond-based reversed SPE phases (C₁₈, C₈, and perfluorinated) were developed in our laboratories. Studies were done which show that these phases do not have the same limitations as traditional silica-based stationary phases. The synthesis and properties of these diamond-based phases are presented, and the stability, percent recovery, and column capacity are given for the C₁₈ phase.     

Recycling HPLC of p-Bromophenacyl Esters of Saturated C35–56 Fatty Acids from Mycobacterium Tuberculosis H37Ra on a Silica Column

Abstract

The p-bromophenacyl esters of saturated C_35–56 fatty acids from Mycobacterium tuberculosis H37Ra were separated according to structural classes on a silica column by high performance liquid chromatography (HPLC). The sample was cycled five times during HPLC. Highly purified C_35–38 esters were obtained by this method. Further HPLC fractionation on a reverse-phase column (C₁₈-bonded silica) gave complete separation of most of the remaining fractions. By combining mass spectrometry with HPLC separations, many of the fatty acid esters were tentatively identified.     

Column Switching Technique for Group-Type Separation of Different Pah Classes by use of C18-Modified Silica and Polystyrene Packings

Abstract

A column switching technique was developed to realize a group-type separation of PAHs and nitrogen containing PAHs (N-PAHs) applying a C₁₈-immobilized polystyrene packing as well as a C₁₈-modified silica stationary phase. On the first column the group-type separation and also the separation of the N-PAH fraction in single compounds was performed. After backflush and transfer to a second column, the separation of the PAH fraction could be achieved.     

Hydrophilic interaction chromatography: A promising alternative to reversed‐phase liquid chromatography systems for the purification of small protonated bases

The overloaded band profiles of the protonated species of propranolol and amitriptyline were recorded under acidic conditions on four classes of stationary phases including a conventional silica/organic hybrid material in reversed‐phase liquid chromatography mode (BEH‐C₁₈), an electrostatic repulsion reversed‐phase liquid chromatography C₁₈ column (BEH‐C₁₈+), a poly(styrene‐divinylbenzene) monolithic column, and a hydrophilic interaction chromatography stationary phase (underivatized BEH). The same amounts of protonated bases per unit volume of stationary phase were injected in each column (16, 47, and 141 μg/cm³). The performance of the propranolol/amitriptyline purification was assessed on the basis of the asymmetry of the recorded band profiles and on the selectivity factor achieved. The results show that the separation performed under reversed‐phase liquid chromatography like conditions (with BEH‐C₁₈, BEH‐C₁₈+, and polymer monolith materials) provide the largest selectivity factors due to the difference in the hydrophobic character of the two compounds. However, they also provide the most distorted overloaded band profiles due to a too small loading capacity. Remarkably, symmetric band profiles were observed with the hydrophilic interaction chromatography column. The larger loading capacity of the hydrophilic interaction chromatography column is due to the accumulation of the protonated bases into the diffuse water layer formed at the surface of the polar adsorbent. This work encourages purifying ionizable compounds on hydrophilic interaction chromatography columns rather than on reversed‐phase liquid chromatography columns.     

Incarceration of Higher‐Order Fullerenes within Cyclotriveratrylene‐Based Hemicarcerands Allows Selective Isolation of C76, C78, and C84 from a Commercial Fullerene Mixture

Size‐complementary cyclotriveratrylene (CTV)‐based hosts can incarcerate C₇₆, C₇₈, and C₈₄, thus allowing the selective isolation of these higher‐order fullerenes from a commercially available mixture of fullerenes. The hemicarceplexes, formed after the encapsulation of the size‐complementary fullerenes within the hosts, are isolated by column chromatography and released at elevated temperature, thereby leading to the isolation of C₇₆/C₇₈ and C₈₄ in good purities (up to 95 and 88 %, respectively).     

Evaluation of capillary gas chromatography for the measurement of hydrocarbons by participating in an intercomparison experiment

Summary By participating in an International Hydrocarbons Intercomparison Experiment, a method for the determination of nonmethane hydrocarbons was evaluated. The method involves Tenax-TA sampling, thermal desorption and preconcentration combined with capillary gas chromatography with flame ionization detection. Sixty target compounds from C₂ to C₁₁ were separated by using a megabore capillary column with a thick film of bonded nonpolar siloxane stationary phase (5 μm, Rtx-1). The unusually thick film in the column was an advantage for resolving light hydrocarbons (C₂−C₃) at room temperature. The percent difference between the National Institute of Standards and Technology (NIST) and our laboratory in the intercomparison experiment is in the range of 0.99%–19.70%.     

Fast separation of light hydrocarbons by gas chromatography on monolithic capillary columns based on silica gel

Monolithic capillary columns based on silica gel were tested in the course of high-speed gas-chromatographic separations of a five-component mixture of C₁–C₄ hydrocarbons. It was found that short-length monolithic columns could be used because of their high specific efficiency; this allowed us to shorten the column dead time and the duration of analysis. The column performance of about 1000 theoretical plates per second was reached. The test sorbate mixture was completely separated on a 58.5-cm column with an efficiency of about 18 700 theoretical plates in a time shorter than 17 s. It was noted that CO₂ and N₂O should be predominantly used as carrier gases.     

The investigation and application of the packed glass capillary column with a core

A new type of packed glass capillary column (PGCC) with a core, and its potential usage in practice are described. The permeability of the column is considerably greater than that of conventional PGCC and its N/(P_i-P_o) value is also higher. This novel PGCC column has been successfully applied to the analysis of trace levels of ethyne, cyclopropane, propadiene, propyne, and other C₁? C₄ impurities in pure ethene, propene, 1,3-butadiene, and catalytic cracking gas samples as well as other petrochemical gases such as liquified petroleum gas.     

Poly(carboxyethyl acrylate-co-ethylene glycol dimethacrylate) precursor monolith with bonded octadecyl ligands for use in reversed-phase capillary electrochromatography

A carboxy precursor monolithic column, namely poly(carboxy ethyl acrylate-co-ethylene glycol dimethacrylate) was first produced in a 100 μm i.d. fused-silica capillary and subsequently surface bonded with n-octadecyl (C₁₈) ligands by a post-polymerization functionalization process with octadecylamine in the presence of N,N´-dicyclohexylcarbodiimide. The bonding of octadecyl ligands was achieved via an amide linkage between the carboxy functions of the precursor monolith and the amino group of the octadecylamine compound. The resulting C₁₈ monolith exhibited a very low electroosmotic flow (EOF), a fact that required the incorporation of small amounts of 2-acrylamido-2-methylpropane sulfonic acid (AMPS) in the polymerization solution to produce a precursor monolith with fixed negative charges of sulfonate groups. This may indicate that the conjugation of the carboxy functions with octadecylamine occurred to a large extent so that the amount of residual carboxy functions was sparsely dispersed and not enough to produce a desirable EOF. The EOF velocity of the C₁₈ column having fixed negative charges provided by the incorporated AMPS increased with increasing ACN content of the mobile phase signaling an increased binding of mobile phase ions to the polar amide linkages near the monolithic surface, and a decreased viscosity of the mobile phase, both of which would result in increased EOF velocity. The C₁₈ monolithic column constituted a novel nonpolar sorbent for reversed-phase capillary electrochromatography for nonpolar solutes, e.g., alkylbenzenes, alkylphenyl ketones, and polyaromatic hydrocarbons, and slightly polar compounds including phenol and chlorophenols. The C₁₈ monolithic column exhibited relatively high selectivity toward chlorophenols differing by one chloro substituent.     

Separation of a Homologous Series of Long-Chain Fatty Alcohols (C49-C58) From Mycobacterium Tuberculosis H37Ra by High Performance Liquid Chromatography

Abstract

Fatty alcohols were obtained from the saponified chloro-form-methanol extract of Mycobacterium tuberculosis H37Ra by extraction with diethyl ether and partially purified by silicic acid column chromatography. The long-chain fatty alcohols (C₄₉-C₅₈) were separated from the shorter-chain alcohols by Sephadex LH-20 column chromatography and further fractionated into saturated and unsaturated alcohols by argentation thin-layer chromatography. These two fractions were analyzed by proton nuclear magnetic resonance spectro-scopy, derivatized to the 3,5-dinitrobenzoyl esters, and fractionated on a C₁₈-bonded silica column by high performance liquid chromatography (HPLC). Complete separation of esters differing by two carbon units and partial separation     

Siliceous mesocellular foam for high-performance liquid chromatography: Effect of morphology and pore structure

Spherical siliceous mesocellular foam (MCF) particles with an average particle size of 4.8 μm have been successfully prepared. These spherical particles were tailored in pore sizes and surface areas. They were functionalized with C₈ or C₁₈ groups, and applied towards reversed phase high-performance liquid chromatography (HPLC) column separations. Their high surface areas gave rise to very good retention characteristics, as illustrated in the separation of a series of alkylbenzene solutes with increasing chain length. The highly interconnected porous structure and ultralarge pore size of MCF allowed the columns to be used at high flow rates without much loss in column efficiency. The column efficiency and peak symmetry were further improved by eliminating the micropores of the stationary phase. The reversed phase column packed with C₁₈-modified spherical MCF particles provided for excellent separation of different deoxynucleosides, illustrating the broad applicability of these materials due to their controlled pore size.     

Large Volume Injection in Fast Gas Chromatography with On‐Column Injector

In this work a fast gas chromatography set‐up with on‐column injection was optimized and evaluated with a model mixture of C₈–C₂₈ n‐alkanes. Usual injection volumes when using narrow‐bore (e. g., 0.1 mm i.d.) analytical columns are ca. 0.1 μL. The presented configuration allows introduction of 10–30‐fold larger sample volumes without any distortion of peak shapes. In the set‐up a normal‐bore retention gap (1 m×0.32 mm i. d.) was coupled to a narrow‐bore (4.8 m×0.1 mm i. d.×0.4 μm film thickness) analytical column using a low dead volume column connector. The effects of the experimental conditions such as inlet pressure, sample volume, initial injection temperature, and oven temperature on a peak focusing are discussed. H‐u curves for helium and hydrogen are used to compare their suitability for high speed gas chromatography and to show the dependence of separation efficiency on the carrier gas velocity at high inlet pressures. In the fast gas chromatography system a baseline separation of C₁₀–C₂₈ n‐alkanes was achieved in less than 3 minutes.     

Gas chromatographic separation of C4−C5 expoxides on a glass capillary colum coated with OV-101 methylsilicone

Summary The separation of C₄−C₅ epoxides on a glass capillary column coated with OV-101 methylsilicone liquid phase was investigated. Retention indices were determined at 70, 80 and 90°C.     

General model for precalculation of the retention indices of isoalkanes separated by gas or liquid chromatography

A general model consisting of two terms is proposed for precalculation of retention indices of isoalkanes separated by gas chromatography (GC) on a squalane column and by high-performance liquid chromatography (HPLC) on a column containing a bonded octadecyl phase. The first term (referred to as extensive) includes parameters which have the greatest correlation with the experimental value of the index; the second term (referred to as intenzive) includes parameters which can modify the value of the roughly calculated index in the direction of the experimental value. The equations derived have correlation coefficients better than 0.99. The maximum discrepancy between the experimental and calculated retention index for twenty C₆C₈ isoalcanes was less than ± 1 index unit in gas chromatography and less than 4 index units in HPLC. The retention indices of 23 other C₇C₉ isoalkanes, calculated in the extrapolation region of the equations, were sufficiently accurate.