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.     

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.     

Determination of column selectivity toward polycyclic aromatic hydrocarbons

An empirical test is described for the evaluation of column selectivity in reversed-phase liquid chromatography. Using a test mixture of three polycyclic aromatic hydrocarbons (PAH), overall column selectivity toward PAH was assessed for over 20 different commercial C₁₈ columns. Retention behavior was correlated to phase type (i.e., monomeric and polymeric surface modification chemistry) for custom synthesized phases. A classification scheme is proposed in which commercial C₁₈ columns are grouped into three classes based on retention behavior: monomeric-like, polymeric-like, and intermediate phase selectivity toward PAH. Correlation of retention behavior of the test mixture with the separation of PAH mixtures and with more general column properties (e.g., phase thickness) is discussed.     

Selectivity trends in packed column supercritical fluid chromatography with C18 stationary phases

The retention behavior of polycyclic aromatic hydrocarbons (PAHs) in packed-column supercritical fluid chromatography (SFC) is studied for monomeric and polymeric C₁₈ columns. Molecular shape discrimination (shape selectivity) is assessed through the use of Standard Reference Materials (SRMs), adn changes in selectivity are studied as a function of temperature, pressure, and mobile phase composition. Examples of separations of complex PAH isomer mixtures are presented, and guidelines are provided for modification and optimization of shape selectivity in SFC.     

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.     

Universal Calibration Method for the Determination of Polycyclic Aromatic Hydrocarbons by High Performance Liquid Chromatography with Broadband Diode-Array Detection

Abstract

The response of polycyclic aromatic hydrocarbons (PAH) at different UV wavelengths was measured using high performance liquid chromatography with spectrophotometric diode-array detection. By utilizing the total UV absorption bandwidth (200-400 nm), it was found that a narrow distribution of normalized response factors (area/g) could be obtained for 16 PAH in a reference mixture of frequently-occurring species, even though the PAH represented a wide variety of different chromophores.

Using the mean response factor for the 16 PAH, a universal calibration factor was obtained that formed the basis of a method for the determination of PAH for which calibration data cannot otherwise be obtained. It utilized normal phase high performance liquid chromatography (HPLC) with a cyanopropyl column and a hexane-dichloromethane mobile phase. The HPLC conditions were optimized for the separation of PAH according to their aromatic ring number. The method was developed for the characterization of complex mixtures of fossil fuels-derived PAH that cannot be analyzed by traditional methods. It is applicable to PAH having from 1 to 10 or more fused aromatic rings.     

Origin of Polycyclic Aromatic Hydrocarbons (PAH) in Recent Sediments from the Continental Shelf of the “Golfe de Gascogne” (Atlantic Ocean) and in the Gironde Estuary

Abstract

Several aromatic series have been analysed on sediment extracts by high performance liquid chromatography coupled (HPLC) and by high resolution Shpol'skii spectroscopy. HPLC coupled to a programmable spectrofluorometer as detector has been used for the detection of the sixteen PAH priority pollutants recommended by the US Environmental Protection Agency. Relative distribution in methylated phenanthrene, chrysene, and pyrene series have been examined by high resolution spectrofluorometry in Shpol'skii matrices for the determination of the sources of aromatic matter in the sediments. These complementary studies would provide useful information on the origin of PAH in marine sediments.     

Resolution of Polynuclear Aromatic Hydrocarbons by Packed Column GLC

Abstract

Specific GLC stationary phases have been identified which allow the resolution of certain polynuclear aromatic hydrocarbon (PAH) isomers with packed six foot columns. Phenanthrene and benz(a)anthracene can be measured in the PAH fraction of tobacco smoke condensate without significant interferences from anthracene and chrysene, respectively.     

Ceramic Alumina in The HPLC Determination of Benzo(a)Pyrene in Air Particulate Material

Abstract

A fast room-temperature extraction by mechanical shredding of airborne particulate material collected on Hi-Vol filters is described. The polar compounds in the extract are quickly removed by test-tube adsorption. A group separation of polynuclear aromatic hydrocarbons (PAH) is made on Corning controlled pore ceramic alumina in stainless steel columns with methylene chloride in cyclohexane as the solvent. The pentacyclic fraction is taken at the same elution time as BaP and is evaporated to dryness under a stream of nitrogen. BaP is determined fluorometrically in concentrated sulfuric acid at F 538/553. It can also be dissolved in a polar solvent and separated and quantitated by reverse phase HPLC or gas chromatography. Total analysis time is approximately 2 hours, much of which is waiting time.     

Photooxidation of Selected Polycyclic Aromatic Hydrocarbons in Aqueous Organic Media in The Presence of Ti(IV)Oxide

Abstract

We have studied the photooxidation of selected polycyclic aromatic hydrocarbons (PAH) in the presence of Ti(IV)oxide in a mixed solvent system consisting of N-methylpyrrolidinone (NMP) and water. Reaction rates for the photooxidation of acenaphthylene and pyrene were investigated by monitoring the disappearance of the PAH substrate from the reaction mixture as a function of time. For both compounds plots of In C_o/C_t, as a function of time yielded straight lines, indicating first order kinetics with respect to the substrate. With an initial acenaphthylene concentration of 1.0 gL^?1 the first order reaction rate constant was 0.19 hr^?1 and the half life was 3.7 hr. With an initial pyrene concentration of 0.2 gL^?1 the first order reaction rate constant was 0.0285 hr^?1 and the half life was 24 hr. The photoproducts were characterized by high performance liquid chromatography with diode-array detection (HPLC/DAD) and by liquid chromatography/atmospheric pressure chemical ionization mass spectrometry (APCI/LC-MS). Although a number of simple oxidation products were identified the bulk of the photoproducts consisted of the parent PAH substituted with one or more solvent (NMP) molecules. The product mixtures from the photooxidation of the non-mutagens acenaphthylene and pyrene were found to be also non-mutagenic in our Salmonella typhimurium forward mutation assay.     

Particle-size distribution of polycyclic aromatic hydrocarbons in urban air in southern Spain

The size distribution of polycyclic aromatic hydrocarbons (PAH) was determined for airborne particles from a large city with high vehicular traffic. The analytical method was optimised and validated using NIST standard reference material (SRM 1649a Urban Dust). The 16 priority PAH listed in the US-EPA were Soxhlet-extracted from filtered particulate matter and then fractionated using on-column chromatography. The aromatic fraction was quantified by gas chromatography-mass spectrometry. Real samples of particles collected in Seville (Spain) were analysed using the validated method. Values for the total concentration of PAH in the air, as well as the concentrations of each PAH in six particle-size ranges were obtained. Values of the PAH in TSP, PM₁₀, PM_2.5 and PM₁ were assessed.     

High-Performance Liquid Chromatography of 2′-5′Oligoadenylates and Related Oligonucleotides

Abstract

HPLC has been used for the analysis and separation of the components of p_x (A2′p)_n A (x = 1 to 3, n = 1 to ≥4). Weak anion exchange columns give excellent resolution, but their instability in phosphate buffers makes them impractical for routine use. Reverse phase chromatography using C18 columns provides a satisfactory alternative method. For preliminary analysis of crude material, ammonium phosphate pH7.0 with a linear 1:1 methanol/H₂O gradient gives a good basic separation of the individual oligomers. Resolution of the 5′ mono-, di-and triphosphorylated oligomers or of the nonphosphorylated components can be obtained using ammonium phosphate pH6.0 and potassium phosphate pH6.5 buffers respectively. The C18 columns are very stable and any one column will give retention times reproducible within 0.2%.     

Decomposition of Chlorobenzene by Thermal Plasma Processing

Decomposition of chlorobenzene as a model molecule of aromatic chlorinated compounds was studied in radiofrequency thermal plasma both in neutral and oxidative conditions. Optical emission spectroscopy was applied for the evaluation of the plasma excitation and molecular rotational-vibrational temperature. Atomic (C, H, O) and molecular (CH, OH, C₂) radicals were identified, while the morphology of the formed soot was characterized by electron microscopy. Organic compounds adsorbed on the surface of the soot after plasma processing were comprised of various polycyclic aromatic hydrocarbons (PAH) and chlorinated PAH molecules. Their amount was greatly affected by experimental conditions, especially the oxygen content and plate power. The higher input power reduced the ring number of the PAH molecules. Addition of oxygen significantly reduced the amount of both PAHs chlorinated PAH molecules but enhanced the formation of polychlorinated benzene compounds.     

A Routine Method for the Quantitative Determination of Polycyclic Aromatic Hydrocarbons (PAHs) in Urban Air

Abstract

We have developed a method for the quantitative determination of polycyclic aromatic hydrocarbons (PAHs) present in urban air, which can be performed rather quickly, and which uses a minimal amount of solvents.

Air samples were collected using a home-made low-volume air sampler equipped with glass fibre filter and polyurethane foam plugs. After Soxhlet extraction a liquid-liquid partition was carried out to isolate the PAH fraction. This liquid-liquid partition was performed in micro-scale, enabling us to use small quantities of the solvents and to separate the solution layers very rapidly using a centrifuge. Sample clean-up was accomplished on a high performance liquid chromatograph equipped with two normal phase silica columns. The losses of all investigated PAHs occurring during the various steps of sample clean-up have been determined. The qualitative and quantitative determination of the PAHs was carried out by capillary gas chromatography; the results were confirmed by GC/MS measurements.

The analytical procedure described was applied over a period of one year to measure the concentrations of 21 PAHs in the city of Vienna at a site with high traffic density. The concentrations of the four more volatile PAHs were determined on a semi-quantitative basis. The ratio of two selected PAHs was used to estimate the respective contribution of traffic and domestic heating to the total PAH level at the sampling site.     

A Study On Air Pollution by Asphalt Fumes

Abstract

A TLC/HPLC procedure for the determination of polycyclic aromatic hydrocarbons (PAH), occuring in asphalt fumes (adsorbed on particular matter), is described. The method is based on extraction of asphalt fume particles, collected on glass fibre filters, using CCK₄. Following a clean up step by the aid of a TLC procedure on Al₂ O₃ thinlayer plates, using a mixture of cyclohexane/acetone/ether as the mobile phase. Under UV-light, occuring PAH are indicated as fluorescent spots. A separation of the collected PAH into individual components and their identification is performed by the aid of a HPLC procedure. Futher-more, an approach was made to verify the separated PAH by their fluorescence spectra and their mass spectra.     

Separation of Substances in Rotating Coiled Columns: From Trace Elements to Microparticles

The potentialities of rotating coiled columns in countercurrent chromatography (CCC) and centrifugal field-flow fractionation (CFFF) are demonstrated. A rotating coiled column is a fluoroplastic or steel coil wound around a rigid cylindrical drum, which revolves about its axis and, at the same time, revolves around the central axis of the device called planet centrifuge. The stationary (liquid, solid, or heterogeneous) phase is retained in the column because of the centrifugal force field, and the mobile liquid phase is continuously pumped through the column. The methods for recovery, separation, and preconcentration of various trace elements in geological samples and high-purity substances with the use of two-phase liquid systems (CCC) are developed. Procedures are proposed for the continuous sequential extraction of various element species from soil and for the recovery of polycyclic aromatic hydrocarbons from sewage sludge with the use of natural suspensions or solid particulates as stationary phases. It is also shown that rotating coiled columns can be used in a new field, microparticle fractionation by CFFF.     

Cross‐linked Multilayer Polymer‐Clay Nanocomposites and Permeability Properties

Abstract

Electrostatically layered aluminosilicate nanocomposites have been prepared by the sequential deposition of poly(allylamine hydrochloride)/poly(acrylic acid)/poly(allylamine hydrochloride)/saponite (PAH/PAA/PAH/saponite)₁₀ on poly(ethylene terephtalate) (PET) film. Exfoliated saponite nanoplatelets were obtained by extensive shaking, sonication, and centrifugation of a water suspension. To minimize permeability and improve the mechanical integrity, cross‐linking of composite films was carried out at different temperatures. The formation of amide linkage induced through heating was observed by Fourier Transform Infrared (FT‐IR) and x‐ray photoelectron spectroscopy (XPS). The cross‐linking of nanocomposites (PAH/PAA/PAH/saponite)₁₀ showed 60% decrease in permeability of oxygen when compared with the pristine PET substrate film. In contrast, water permeability of the nanocomposite membrane was not affected by heating temperature and deposition cycles.     

Selective determination of substituted PAH in aerosols using liquid CO2-extraction,HPLC prefractionation on chemically activated silica,and HRGC combined with negative ion mass spectrometry

A method is described which allows the determination of different substituted polycyclic aromatic hydrocarbons (PAH) such as NO₂-PAH, carbazoles, keto-PAH, and aza-arenes in aerosol samples. Liquid CO₂-extraction is used to minimize the loss of reactive compounds. High performance liquid chromatography on chemically activated silica is employed to prefractionate the samples into subfractions with a minimum of overlap between different PAH compound classes. Both electron capture detection and negative ion chemical ionization combined with capillary gas chromatography are used for identification and quantification. The latter method also allows distinction between isomers with different toxic properties when N₂O/CH₄ reaction gas mixtures are used. Selectivity for tetrachlorodibenzo-p-dioxins as against pesticides and polychlorinated biphenyls can be improved by this technique. The applicability of the method is critically discussed and different examples are given.     

Solid-phase extraction clean-up procedure for the analysis of PAHs in lichens

A clean-up procedure based on a solid-phase extraction column was optimized for determination of polycyclic aromatic hydrocarbons (PAHs) in lichen extracts to remove co-extracted compounds from the matrix in the final extract. Several kinds of solid phases were evaluated: normal phase (-NH₂ and alumina), strong anion exchange and reversed phase. The -NH₂ columns were the most effective by using a packed solid bed of 500?mg. The lichen raw extract was loaded on the column previously conditioned with dichloromethane and hexane. Hexane (0.5?mL) was used as rinsing solvent, and PAHs were quantitatively eluted (80–97%) using 2?mL of hexane–dichloromethane (65–35) as eluting solvent. In these conditions, even the heaviest PAHs were quantitatively eluted. The optimized SPE method provides a short time and low-solvent-consumption sample clean-up compared with other conventional methods based on column chromatography. The analytical procedure, dynamic sonication-assisted extraction, followed by the optimized solid-phase extraction clean-up, was used to determine the 16 EPA priority PAHs from native lichens collected from the Aragon valley in central Pyrenees. The PAH concentrations in lichen samples ranged from 352 to 1654?ng?g^?1, and the minimum concentration value was established as the regional reference PAH levels in the area.     

New Principles of Ion-Exchange Techniques Suitable to Sample Preparation and Group Separation of Natural Products Prior to Liquid Chromatography

Abstract

A Gentle method of group separation of low molecular weight hydrophilic natural products is reported. The method is based on separation of the compounds according to their net charge at different pH values using different types of ion-exchange columns connected in series. Precolumns retaining interfering compounds are used in some cases. Elution of the compounds retained on the columns is performed by use of volatile eluents. The elution principle for two of the ion-exchangers in question is removal of the charges on the column materials while for the third column the positive net charge on the compounds retained is removed. Thereby, the total amount of ions retained on the different columns is released and eluted into small volumes, which after evaporation leaves the ions as well defined salts. The method is experimentally simple and efficient to separation of natural products into groups suitable to direct use in sensitive methods of analysis as e.g. high-performance liquid chromatography and gas chromatography. Combinations of these column chromatographic methods have been adpated for micro or semimicro determinations of naturally occurring compounds, e.g., aromatic choline esters, amines, amino acids and esters of phenolic carboxylic acids. The methods seem to be general practicable for group separation of low molecular weight hydrophilic compounds.