Evaluation of polycyclic aromatic hydrocarbons in gasoline by HPLC and GC-MS

Summary In this paper the evaluation of polycyclic aromatic hydrocarbons (PAHs) in gasoline is described. A procedure involving a double extraction of samples with N-methylpirrolidone-water-phosphoric acid and with cyclohexane has been used followed by HPLC-DAD and GC-MS. The results obtained show that all gasoline samples contain PAHs with two to six rings and no substantial difference was noticed between leaded and unleaded gasoline. The benzo(a)-pyrene content ranged between 1.0–2.0 mg L⁻¹, a comparatively high concentration for a dangerous compound.     

HPLC determination of the aromatic fraction of gasoline

Summary This work reports a rapid and easy procedure for the analysis of the aromatic fraction in gasoline. No sample pretreatment is required, since the gasoline is diluted in methanol and directly injected into a liquid chromatograph. A spectrophotometer detector and a spectrofluorimeter detector are used in series. The procedure has been applied to a large number of Italian and European refined gasoline samples.Dedicated to Prof. Dr. A. Liberti on the occasion of his 70th birthday.     

Retention characteristics of chlorinated polycyclic aromatic hydrocarbons in normal phase HPLC. I. Chloro-added PAHs

Summary Retention characteristics in normal phase HPLC of highly biologically active chloro-added polycyclic aromatic hydrocarbons (PAHs) were studied. Silica, cyanopropyldimethylsilyl- and aminopropylsilyl- modified stationary phases were investigated. Retention properties of chloroadded PAHs on these phases were shown to be strongly influenced by the number of chloro-additions. This is due to the strong polarity of the methylene carbon at the chloro-addition site. Active silica had a strongly degrading effect on the unstable chloro-added PAHs during separation. Aminopropylsilica did not exhibit sufficient selectivity towards chloro-added PAHs when compared to chlorosubstituted PAHs. Cyanopropyldimethylsilica was shown to be applicable to a group separation of chloro-added and chloro-substituted PAHs. A fast clean-up procedure for chloro-added PAHs in complex samplesis outlined. It involves an initial elimination of more polar substances on a short open column with strongly deactivated silica and a subsequent separation on a cyanopropyldimethylsilyl HPLC column in normal phase mode.     

HPLC analysis of the large polycyclic aromatic hydrocarbons in a diesel particulate

Summary High performace liquid chromatography (HPLC) was used to separate the large polycyclic aromatic hydrocarbons in a diesel particulate extract. Identification of individual peaks was made using a photodiode array UV/visible detector to collect their absorbance spectra. Comparisons between standard compounds and the peaks were made using both retention times and spectra. Compounds of up to 10 rings were identified.     

Use of a keeper to enhance the recovery of volatile polycyclic aromatic hydrocarbons in HPLC analysis

Summary The recorveries of volatile polycyclic aromatic hydrocarbons in HPLC analysis may be enhanced if a long-chain alcohol, e.g. 1-hexanol or 1-octanol, is used as keeper in the solvent-evaporation step. Even under the harsh conditions of the vacuum-concentrator centrifuge, recoveries of more than 90% were achieved for 14 of the 15 PAH tested. The use of liquid-liquid extraction (LLE) eliminates the problem of adsorption of highly condensed aromatics by the wall of the sampling bottle. The combination of LLE with vacuum-controlled rotary evaporation and use of a keeper yielded overall recoveries between 50 and 130%, for most substances close to 100%, from tap water spiked with trace concentrations. Presented at the 21^st ISC held in Stuttgart, Germany, 15^th–20^th September, 1996     

The use of large polycyclic aromatic hydrocarbons to study retention in non-aqueous reversed-phase HPLC

Summary Elution strengths of 11 common HPLC solvents on a polymeric C₁₈ phase were compared using a marker set of polycyclic aromatic hydrocarbons. Naphthalene, pyrene, benzo[ghi]perylene, and three larger naphthologues of 8, 10, and 12 rings (constituting a naphthalene zigzag series) were chosen because they span the solvent strength range up to and including the strongest solvents, tetrahydrofuran (THF) and chlorobenzene. Four pairs of similarly shaped isomers were used to probe solvent selectivity. With the exception of THF, HPLC solvent strength correlated with observed red shifts of fluorescence band maxima in each solvent. For THF, the pure solvent and blended mixtures behaved quite differently.     

Microcolumn liquid chromatography of polycyclic aromatic hydrocarbons and some isomeric compounds on cyclodextrin stationary phases

Preparative-grade bonded β- and γ-cyclodextrin stationary phases were used as the packing material of liquid chromato-graphic analytical microcolumns. Although the resulting columns are characterized by relatively low efficiency, the high selectivity of the cyclodextrin phases nevertheless allows their successful use for the separation of different classes of isomeric compounds that are difficult to resolve on conventional LC stationary phases. Examples of baseline (or almost baseline) separations of a number of isomeric compounds, including isomeric polycyclic aromatic hydrocarbons, are presented to demonstrate the analytical potential of such columns. Retention behavior of the separated isomers is discussed based on the structure of the solute molecule and the possibility of its inclusion into the molecular cavity of cyclodextrin stationary phases.     

Polycyclic aromatic hydrocarbons in waste waters and sewage sludge: Extraction and clean-up for HPLC analysis with fluorescence detection

Summary A modified solid-phase extraction technique using sonication of the adsorbent material instead of the elution normally applied has been compared with two conventional liquid-liquid extraction procedures for the determination of the 16 EPA PAHs in municipal waste waters by means of HPLC coupled with fluorescence detection. Liquid-liquid extraction with cyclohexane proved to be the most efficient and simplest procedure. Clean-up of the waste-water extracts was not considered necessary, because of the high chromatographic resolution of the column and the selectivity of the fluorescence detector. Different organic solvents were also compared for ultrasonic extraction of PAHs from sewage sludge. The best results were obtained by use of acetonitrile. Clean-up of sewage-sludge extracts was not found necessary for accurate quantification of the major PAH components with fluorescence detection. The precision of the whole analytical procedure from extraction to the final determination of PAHs was satisfactory for both waste-water and sewage-sludge samples.     

Retention behavior of polycyclic aromatic hydrocarbons in supercritical fluid chromatography on a chemically bonded stationary phases based upon liquid-crystalline polymer

Summary The retention behavior of a set of polycyclic aromatic hydrocarbons in supercritical fluid chromatography have been studied on a chemically bonded stationary phase based upon a side chain liquid crystalline polymer (LCP) with carbon dioxide-based mobile phase. The effects of the mobile phase pressure, column temperature and amount of mobile phase organic modifier have been investigated in order to detect a possible structural change in the liquid crystal polymer linked to the silica support. The influence of these factors on the selectivity coefficients has also been studied. Two distinctive behaviors with temperature are noted at low pressure on the one hand and at higher pressure on the other. This change in behavior is based on the density of the supercritical CO₂ and the PAH volatility rather than on any specific stationary phase structural change. Both lower mobile phase pressure and amount of mobile phase modifier are required to obtain better selectivities. Better planarity recognition is observed in SFC than in HPLC with these new bonded liquid crystal stationary phases. The bonded liquid crystal phase is only weakly affected by the addition of organic modifier in the supercritical CO₂.     

Survey of concentration of polycyclic aromatic hydrocarbons in lake balaton by HPLC with fluorescence detection

Summary Concentrations of polycyclic aromatic hydrocarbons (PAHs) were determined in water and sediment samples at 15 sites in Lake Balaton during three sampling campaigns in 1996. PAHs were concentrated from water samples by solid phase extraction. Sediment samples were extracted with acetone in an ultrasonic bath then cleaned by solid phase extraction. The total concentration of PAHs ranged from 30–360 ng g⁻¹ and from 170–720 ng L⁻¹ in sediment and water samples, respectively. Spatial and temporal variations of the concentration of PAHs were also investigated. Presented at: Balaton Symposium on High-Performance Separation Methods, Siófok, Hungary, September 3–5, 1997.     

Modified polystyrene,stationary phases for the separation of different aromatic hydrocarbon types by HPLC

Summary One possible method of characterizing chemicall-modified stationary phases is to describe their chromatographic properties. In this study we investigated several chemically-modifiedpolystyrene-divinylbenzene packings for the separation of nitroarenes, polycyclic aromatic hydrocarbons and aminosubstituted aromatic hydrocarbons. Chromatography was carried out on commercially available polymer stationary phases, for example C-18 or vinylpyridine modified polystyrene. In addition, a chemically-immobilized polymer packing was prepared by introducing nitrogroups, which were established by elemental analysis and infrared spectroscopy.     

Separation of polycyclic aromatic hydrocarbons with a C60 bonded silica phase in microcolumn liquid chromatography

A chemically bonded C₆₀ silica phase was synthesized as a stationary phase for liquid chromatography (LC) and its retention behavior evaluated for various polycyclic aromatic hydrocarbons (PAHs) using microcolumn LC. The results indicate that the C₆₀ bonded phase offers selectivity different from that of octadecylsilica (ODS) bonded phases in the separation of isomeric PAHs. With the C₆₀ phase, PAH molecules having a partial structure similar to that of the C₆₀ molecule, e.g. triphenylene and perylene, were retained longer than with ordinary ODS stationary phases. The results also show that good correlation exists between the retention data with this C₆₀ bonded phase and with C₆₀ itself as the stationary phase.     

Relationship between the average molecular polarizabilities of polycyclic aromatic hydrocarbons and their retention indices determined on various stationary phases

The Kováts retention indices of 10 polycyclic aromatic hydrocarbons were determined on SE-30, OV-101, SE-52, OV-7 and OV-17 stationary phases. A significant correlation has been found between the retention indices and the average molecular polarizabilities of the analyzed substances. Equations were derived for the direct determination of the average molecular polarizabilities from the retention index values. The influence of the temperature on this relationship is also indicated.     

Laterally attached liquid-crystalline polymers as stationary phases. Effect of temperature in RP HPLC and comparison with a commercial C18 stationary phase

Summary Specific side-on-fixed liquid-crystalline polymers (SOLCP) have been synthesized for use in silica-modified stationary phases in high-performance liquid chromatography (HPLC). The mesogenic side group of the SOLCP is composed of three benzoate-type phenyl rings with terminal alkoxy chains and is laterally linked to a polysiloxane backbone via an alkyl ester spacer arm. The dependence of the logarithm of the retention factor on the reciprocal temperature showed that the liquid-crystalline anisotropic order was conserved in the small pores (200 ? diameter) of the silica gel. The first-order nematic-isotropic transition is lost and probably becomes second-order. Adsorption enthalpies for the liquid-crystalline stationary phases have been measurement for three polycyclic aromatic hydrocarbon isomers (ortho-terphenyl, triphenylene, and chrysene) and compared with those for a commercial C₁₈ phase. The adsorption enthalpies never exceeded 30 kJ mol⁻¹, i.e. ten times the thermal agitation energy,RT. They were always less on the SOLCP stationary phase than on the C₁₈ column, emphasizing the more rigid structure of the liquid crystalline phase and its mechanism based upon adsorption. Better separation of steroids, pesticides and amino acids were obtained with the LCP-coated silica than the commercial bonded C₁₈ column. Four small peptides were successfully separated by using pure water as mobile phase.     

The effect of the structure of bonded cyanoalkyl stationary phases on their selectivity in the liquid chromatographic separation of polynuclear aromatic hydrocarbons

Summary The paper discusses the effect of the length and structure of the hydrocarbon chain connecting the nitrile group to the silica gel surface on the chromatographic properties of cyanoalkyl phases.When using non-polar and polar mobile phases, the selectivity of the cyanodecyl phases toward PAHs is higher than of the cyanopropyl phase and of hydroxylated silica gel.Polar additives to the mobile phase drastically decrease the retention on silica gel and on the cyanopropyl phase while affect the properties of cyanodecyl phases only to a considerably less degree. Newly synthesized phases with different structures of the hydrocarbon chain are compared with the commerical cyano-and ODS-phases. The retention mechanism on the cyanoalkyl phases is discussed.     

Separation of polycyclic aromatic hydrocarbons under isocratic conditions by a column switching technique

Summary A simple and efficient method of separating a 20-component PAH-mixture (RSM 1647 standard mixture +benzene, toluene, perylene and coronene) by RP-HPLC is described. Separation was by using two Superspher-100 RP-18 cartridges thermostatted at different temperatures under isocratic conditions with water-acetonitrile eluent. The analysis time with complete resolution of all components can be reduced to 15 min.     

Retention characteristics of chlorinated polycyclic aromatic hydrocarbons in normal phase HPLC. II. Chloro-substituted PAHs

Summary The retention behaviour of chloro-substituted PAHs on several commercial normal bonded phase HPLC columns has been investigated. Chloro-substitution was shown to generally decrease the retention on stationary phases like amino-, diol- and nitrophenylpropyl-modified silica. Dimethylaminosilica exhibited more complex retention characteristics towards chloro-substituted PAHs. On this stationary phase, the position of the chlorine substituents on the aromatic solute seemed to be of greater importance for retention than on the amino-, nitro- and diolsilica. For some chloro-PAHs, the retention was shown to increase with the number of chloro-substitutions, probably due to the large affinity of the electron-rich nitrogen in the stationary phase for the electron deficient -system of the chloro-PAHs. Chloro-substituted PAHs were strongly retarded on the electron donating 2-(1-pyrenyl)-ethylsilica (PYE) stationary phase. However, the molecular shape of the chloro-derivatives had a large influence on retention, which was considerably decreased for some nonplanar chloro-derivatives of chrysene and benz(a)anthracene. A two-dimensional back-flush HPLC method, consisting of a combination of a nitrophenylsilica column and a PYE column of matched lengths, was shown to be useful for clean-up of chloro-substituted PAHs in environmental samples.