Characterization of military fog oil by comprehensive two-dimensional gas chromatography

The most commonly used military fog oil is characterized by comprehensive two-dimensional gas chromatography (GC×GC) coupled to either Flame Ionization Detection (FID) or Time-of-Flight Mass Spectrometric Detection (TOFMS) to advance the knowledge regarding the complete chemical makeup of this complex matrix. Two different GC×GC column sets were investigated, one employing a non-polar column combined with a shape selective column and the other an inverse column set (medium-polar/non-polar). The inverse set maximizes the use of the two-dimensional separation space and segregates aliphatic from aromatic fractions. The shape selective column best separates individual polycyclic aromatic hydrocarbons (PAHs) from the bulk oil. The results reveal that fog oil (FO) is composed mainly of aliphatic compounds ranging from C₁₀ to C₃₀, where naphthenes comprise the major fraction. Although many different species of aromatics are present, they constitute only a minor fraction in this oil, and no conjugated PAHs are found. The composition of chemically similar aliphatic constituents limits the analytical power of silica gel fractionation and GC–MS analysis to characterize FO. Among the aliphatic compounds identified are alkanes, cyclohexanes, hexahydroindanes, decalins, adamantanes, and bicyclohexane. The aromatic fraction is composed of alkylbenzene compounds, indanes, tetrahydronaphthalenes, partially hydrogenated PAHs, biphenyls, dibenzofurans and dibenzothiophenes. This work represents the best characterization of military fog oil to date. As the characterization process shows, information on such complex samples can only be parsed using a combination of sample preprocessing steps, multiple detection schemes, and an intelligent selection of column chemistries.     

“Sock-Ball” Chromatographic Separation of Some Polycyclic Aromatic Hydrocarbons with C60-Fullerene Stationary Phase

Polycyclic aromatic hydrocarbons (PAHs) of different molecular shapes were tested and compared with a prepared C₆₀-fullerene-phase, and with the commercial Amino-phase or RP-18-phase in the mobile phase of methanol/dichloromethane (90/10 — 70/30) or n-hexane/dichloromethane (80/20). The chromatographic separation results indicate that C₆₀-fullerene-phase achieves the special selectivities and performances for the separation of PAHs. Based on the retention mechanism of “π-π” complex interaction or “Sock-Ball” shaped combination, PAHs undergo more pronounced interaction with C₆₀ ligand. For example, decacyclene, a sock-shaped PAH, the structure of which was calculated by means of semi-empirical molecular orbital methods, possesses stronger retention to give a “Sock-Ball” chromatographic separation with C₆₀-fullerene-phase. However, PAHs with bend, planar, or co-planar structures eluted on C₆₀-fullerene-phase undergo adsorption chromatography, but possess weaker retentions. The retention power of “Sock-Ball” chromatography can successfully recognize the different molecular shapes of PAHs.     

The Application of Perdeuterated Polycyclic Aromatic Hydrocarbons (PAH) as Internal Standards for the Liquid Chromatographic Determination of PAH in a Petroleum Crude Oil and Other Complex Mixtures

Abstract

A sequential liquid chromatographic (LC) procedure for the determination of polycyclic aromatic hydrocarbons (PAH) in a petroleum crude oil and other complex mixtures is described. The procedure includes normal-phase LC on an aminosilane column to isolate fractions containing isomeric PAH and reversed-phase LC on a polymeric C₁₈ column to separate the individual PAH isomers. Appropriate perdeuterated PAH are added to the sample so that each isomeric fraction will contain one internal standard. The perdeuterated PAH are excellent internal standards for this sequential LC procedure. Perdeuterated PAH have normal-phase and reversed-phase LC retention characteristics similar to those of the parent PAH. In the normal-phase LC separation, the perdeuterated PAH elute in the same fraction as the parent PAH. In the reversed-phase LC separation, the perdeuterated PAH elute first and are generally resolved from the parent PAH. The optimized spectrofluorometric detection of each PAH analyte is accomplished by programming appropriate sets of excitation and emission wavelengths to correspond with the elation time of each analyte on the polymeric C₁₈ column. The analytical results obtained from this procedure for the analysis of a shale oil sample [Standard Reference Material (SRM) 1580] and a petroleum crude oil (SRM 1582) are compared to values obtained by gas chromatography - mass spectrometry.     

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.     

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.     

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     

A Simple Liquid Chromatographic Method for Analysis and Isolation of the Unsaturated Components of Anacardic Acid

Abstract

Good analytical and preparative separation of the saturated, monoene, diene and triene components of anacardic acid have been achieved by reverse phase HPLC on a C₁₈ column by isocratic elution with methanol-aqueous acetic acid.     

The Purification of Xanthene Dyes by Reverse Phase High Performance Liquid Chromatography

Abstract

A reliable method for the separation of fluorescein dyes from their impurities was developed using high performance liquid chromatography and involved a μBondapak C₁₈ reverse phase column and mixtures of methanol and ammonium acetate buffer. This technique was used to verify the purity of commercial products as well as to aid in the development of an empirical theory related to retention of halogenated fluorescein dyes by reverse phase columns.     

Selectivity Factors for Several Pah Pairs on C18 Bonded Phase Columns

Abstract

The selectivity factors for four pairs of polycyclic aromatic hydrocarbons (PAHs) have been found to be very different on the HC-ODS column in comparison to most other C₁₈ bonded-phase columns. The selectivity factors for these PAH pairs varied slightly with different manufacturing lots of the HC-ODS material, the selectivity variations for each PAH pair being linearly correlated with those for the other pairs.     

Separation of Ethyl Anthranilate Azopigments from Germ-Free Rat Feces by Reversedphase High-perform Ance Liquid Chromatography

Abstract

A simple method was developed for the separation of ethyl anthranilate azopigments derived from conjugated bilirubins prepared from germfree (GF) rat feces. The Δ and α₀ azopigments were separated and these two azopigments were also separated into their endo-vinyl- and exo-vinyl isomers, respectively. The reverse-phase, high-performance liquid chromatographic (HPLC) separation was achieved by using a μBondapak C₁₈ column and a mixture of acetonitrile, distilled water and sodium acetate as the mobile phase.     

A review of: “HPLC of Biological Compounds-A Laboratory Guide,by William S. Hancock & James T. Sparrow, (Volume 26 of the Chromatographic Science Series,Jack Cazes,Editor), Marcel Dekker,Inc., New York,NY, 1984, 361 pp., £39.75 (US)”.

Abstract

The analytical and preparative separation of the saturated, monoene, diene and triene constituents of cardanol and cardol have been achieved by reverse phase HPLC on a C₁₈ column using gradient elution.     

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.     

Rapid Separation of Testosterone and its Microsomal Metabolites by Reverse-Phase High Performance Liquid Chromatography

Abstract

High performance liquid chromatography has been used to separate testosterone from its oxidative metabolites (7α-, 16α -and 6 β-hydroxytestosterone and androstenedione) following in vitro incubation with rat liver microsomes. The separation was accomplished in less than 18 minutes on a radially compressed C₁₈ reverse-phase column using isocratic elution with tetra-hydrofuran: water (24/76, v/v).     

High Pressure Liquid Chromatographic Determination of Parabens in Pharmaceutical Preparations Containing Hydroxyquinolines

Abstract

A high pressure liquid chromatographic (HPLC) procedure for the analysis of methyl paraben (MP) and propyl paraben (PP) in pharmaceutical preparations containing a halogenated hydroxyquinoline (HHQ) is described. The method involves a separation of the phenolic constituents, MP, PP and HHQ with a Bio-Rad AG 1–X8 anion exchange resin, elution of the phenols with methanol after acidification and a reverse phase HPLC separation of the parabens using methanol-pH 6.5 buffer (60/40) mobile phase, a 30 cm × 3.9 mm (i.d.) column packed with Waters μBondapak C₁₈ packing and a guard column packed with Waters Bondapak C₁₈/Corasil packing. Recovery, precision, specificity and interference data along with the application of the proposed method for some commercial formulations both with and without a hydroxyquinoline are described.     

“Sock-Ball” Chromatographic Separation of High Molecular Weight Fullerenes with Sock-Shaped Stationary Phase

A method for “Sock-Bail” chromatographic separation of high molecular weight fullerenes is described. A prepared sock-shaped stationary phase (Sock-SAF-phase) was used for HPLC separation of several polycyclic aromatic hydrocarbons (PAHs) and fullerenes. Fullerenes, as ball-shaped molecules, are much more strongly retained than PAHs on this stationary phase and have the eluted order C₅₀ < C₇₀ < C₇₆ < C₇₈ < C₈₄ in the mobile phase of n-hexane/dichloromethane (100/0 ～ 80/20). In contrast, chromatography on the corresponding unmodified silica phase or SC-3OH-phase (an intermediate phase of Sock-SAF-phase) gave no separation of fullerenes. This fact indicated that the separation of fullerenes on Sock-SAF-phase was related to the selective interaction with the sock moiety.     

Copolymer-grafted silica phase from a cation–anion monomer pair for enhanced separation in reversed-phase liquid chromatography

This work reports a new imidazolium and l-alanine derived copolymer-grafted silica stationary phase for ready separation of complex isomers using high-performance liquid chromatography (HPLC). For this purpose, 1-allyl-3-octadecylimidazolium bromide ([AyImC₁₈]Br) and N-acryloyl-l-alanine sodium salt ([AAL]Na) ionic liquids (IL) monomers were synthesized. Subsequently, the bromide counteranion was exchanged with the 2-(acrylamido)propanoate organic counteranion by reacting the [AyImC₁₈]Br with excess [AAL]Na in water. The obtained IL cation–anion monomer pair was then copolymerized on mercaptopropyl-modified silica (Sil-MPS) via a surface-initiated radical chain-transfer reaction. The selective retention behaviors of polycyclic aromatic hydrocarbons (PAHs), including some positional isomers, steroids, and nucleobases were investigated using the newly obtained Sil-poly(ImC₁₈-AAL), and octadecyl silylated silica (ODS) was used as the reference column. Interesting results were obtained for the separation of PAHs, steroids, and nucleobases with the new organic phase. The results showed that the Sil-poly(ImC₁₈-AAL) presented multiple noncovalent interactions, including hydrophobic, π–π, carbonyl–π, and ion–dipole interactions for the separation of PAHs and dipolar compounds. Only pure water was sufficient as the mobile phase for the separation of the nucleobases. Ten nucleosides and bases were separated, using only water as the mobile phase, within a very short time using the Sil-poly(ImC₁₈-AAL), which is otherwise difficult to achieve using conventional hydrophobic columns such as ODS. The combination of electrostatic and hydrophobic interactions are important for the effective separation of such basic compounds without the use of any organic additive as the eluent on the Sil-poly(ImC₁₈-AAL) column.

A Rapid Isolation of Human Chorionic Gonadotropin and Its Subunits by Reversed-Phase High Performance Liquid Chromatography

Abstract

A rapid isolation of human chorionic gonadotropin and its subunits from a commercially available concentrate of human urine has been achieved using reversed-phase high performance liquid chromatography. With μBondapak C₁₈ columns and a gradient employing aqueous trifluoroacetic acid as one solvent and dilute trifluoroacetic acid in acetonitrile as the other, complete separation can be accomplished in one day whereas standard column chromatographic procedures take about two weeks. Specific radioimmunoassays, polyacrylamide gel electrophoresis, and amino acid analyses were used to identify and characterize chromatographic peaks.     

Modification of Selectivity in Reversed-Phase Liquid Chromatography of Polycyclic Aromatic Hydrocarbons Using Mixed Stationary Phases

Abstract

Monomeric and polymeric C₁₈ materials provide significantly different selectivities for polycyclic aromatic hydrocarbons (PAH) in reversed-phase liquid chromatography. Selectivity factors vary in a regular manner with respect to surface concentration of C₁₈ groups on different C₁₈ columns. In this study, we investigated the feasibility of “customizing” a C₁₈ column to provide an intermediate selectivity by mixing 5-μm polymeric C₁₈ material from two different lots with high and low C₁₈ surface concentrations. Polymeric C₁₈ materials from different production lots were mixed in ratios of 30/70, 50/50, and 70/30 (w/w). Selectivity factors for these columns were found to be similar to those predicted by the linear addition of the selectivities of the two individual phases. The PAH selectivities on these mixed columns were also found to be comparable to data obtained from coupled short columns of appropriate lengths each containing one of these different C₁₈ materials. These studies indicate that columns of specific selectivity can be prepared by either mixing two different C₁₈ materials or by coupling columns containing each of these different phases. The use of mixed phase columns is illustrated for the analysis of a fraction containing five condensed ring PAH isomers (molecular weight 278) isolated from an air particulate sample.     

Atmospheric depositional fluxes of cosmogenic <Superscript>32</Superscript>P, <Superscript>33</Superscript>P and <Superscript>7</Superscript>Be in the Sevastopol region

⁹⁰Y was separated from ⁹⁰Sr using an extraction chromatographic resin consisting of 4, 4′(5′)-bis-t-butylcyclohexano-18-crown-6 (DtBuCH₁₈C₆), 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl) amide (C₂mimNTf₂), and a polymer (Amberlite XAD-7). Ionic liquid was introduced into the column to improve the separation efficiency. The column showed an excellent performance for the separation of Y from Sr. After the separation, the ratio of ⁹⁰Sr/⁹⁰Y was <2.0 × 10^?5; the column was recycled for >18 times. This study provides preliminary results on columns to produce ⁹⁰Y with a high purity in radiopharmaceuticals.     

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.