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.     

Glass capillary column with nematogenic liquid crystals as stationary phases for separating polycyclic aromatic hydrocarbons

Summary Use of the homologues and analogues of nematogenic liquid crystals of the type N,N-bis(p-methoxylbenzylidene)-,-bi-p-toluidine (BMBT) as stationary phases in glass capillary columns is described. These stationary phases are very useful for resolving closely related, rigid solute isomers of three-, four- and five-ring PAH. With these columns it is possible to achieve faster and more complete separation of PAH compared with packed columns with a liquid crystalline stationary phase.     

Retention behavior of large polycyclic aromatic hydrocarbons on metalloprotoporphyrin-silica stationary phases

The retention behavior of large polycyclic aromatic hydrocarbons (LPAHs) (≥ 7 rings) on newly developed metalloprotoporphyrin (MProP)-silica stationary phases is examined and the results are compared to previously reported data for retention of the same solutes on commercially available phases. HPLC columns packed with FeProP-silica are shown to exhibit unique shape selectivity for LPAH retention, with the planar LPAHs always retained much longer than corresponding non-planar solutes. Solute planarity, length to breadth ratio (L/B value), and number of carbon atoms within the LPAHs are all demonstrated to contribute to the retention sequence observed. Further, the retention of LPAH solutes on FeProP-silica phases is shown to be more predictable than on other reversed-phase columns, with the elution sequence constant regardless of the mobile phase composition. Due to the extremely high planar selectivity of FeProP-silicas with respect to LPAH retention, it is envisioned that columns packed with these phases could be used in conjunction with existing commercial columns to devise methods for more efficient separation of complex mixtures of LPAHs in environmental and other samples.     

Retention behavior of large polycyclic aromatic hydrocarbons on metalloprotoporphyrin-silica stationary phases

The retention behavior of large polycyclic aromatic hydrocarbons (LPAHs) (> or = 7 rings) on newly developed metalloplotoporphyrin (MProP)-silica stationary phases is examined and the results are compared to previously reported data for retention of the same solutes on commercially available phases. HPLC columns packed with FeProP-silica are shown to exhibit unique shape selectivity for LPAH retention, with the planar LPAHs always retained much longer than corresponding non-planar solutes. Solute planarity, length to breadth ratio (L/B value), and number of carbon atoms within the LPAHs are all demonstrated to contribute to the retention sequence observed. Further, the retention of LPAH solutes on FeProP-silica phases is shown to be more predictable than on other reversed-phase columns, with the elution sequence constant regardless of the mobile phase composition. Due to the extremely high planar selectivity of FeProP-silicas with respect to LPAH retention, it is envisioned that columns packed with these phases could be used in conjunction with existing commercial columns to devise Inethods for more efficient separation of complex mixtures of LPAHs in environmental and other samples.     

Effect of column temperature on the retention of peropyrene-type polycyclic aromatic hydrocarbons on various chemically bonded stationary phases in reversed-phase liquid chromatography

The effect of column temperature on the reversed-phase retention of polycyclic aromatic hydrocarbons has been investigated using various chemically bonded phases. Four solutes, coronene, tetrabenzo[a,cd,j,lm]perylene, tetrabenzo[a,cd,f,lm]perylene and benzo[lm]phenanthro[4,5,6-abcd]perylene, were used as the test probes. The temperature dependences of the retention are almost linear (the logarithm of capacity factor is proportional to the reciprocal of the column absolute temperature) with monomeric C18, monomeric C18 with endcapping and diphenyl bonded phases, while non-linear behaviour was observed with polymeric C18 phases. These differences in behaviour of the stationary phases are interpreted in terms of their structural differences.     

Selective gas chromatographic separation of polycyclic aromatic hydrocarbons on Bentone 34

Summary Using modified Bentone 34 as a thin layer on glass beads in a short micropacked column at maximum working temperature reasonable retention times of polycyclic aromatic hydrocarbons were achieved up to perylene. Some differences in the elution order were observed as compared with other sorbents.     

Selectivity of stationary phases for the resolution of polycyclic aromatic hydrocarbons

Summary Relative retentions, heats and entropies of solution for 16 PAH in seven different stationary phases were measured under standard isobaric conditions using GC. The experimental conditions to obtain reproducible retention data at non-linear adsorption isotherms are discussed and standard conditions are recommended using the linear relationship between retention time and 1/log h (where h is the peak height). A linear relationship was established between the relative molar heats of solution and the number of carbon atoms in the PAH-molecule. This relationship is valid only for non-polar stationary phases. Certain effects of the isomeric structures of PAH are studied using the relative molar heats and entropies of solution. The latter function is very sensitive to the spherical form of a molecule. Different aspects of isomeric selectivity are discussed and it is concluded that the better way for resolving complex PAH-mixtures is rather an improvement in column efficiency than searching for new stationary phases.     

Evaluation of various collection phases for polycyclic aromatic hydrocarbons (PAH)

Summary Particle-bound and gaseous polycyclic aromatic hydrocarbons (PAH), some of which are strongly carcinogenic, can be detected as components of pyrolysis products of organic materials and are emitted at the place of work during certain manufacturing processes.An assessment of the risk to exposed workers depends on the determination of as wide a spectrum of PAH in the atmosphere as possible. Their quantitative collection on glass fibre filters causes problems because of the high volatility of PAH.A suitable collection system for air sampling of these substances has been sought on the basis of _n = 20 chosen PAH.Employing the phase equilibrium method and a simulated sampling process in a stream of nitrogen with PAH-coated collection phases it was possible to demonstrate a collection efficiency for volatile PAH of 82.7 to 105.7% on the adsorbing resin Tenax and of 82.9 to 103.9% on XAD-2 using toluene as eluent. Silica gel and Polygosil proved unsuitable as PAH adsorbents.An extremely effective sampling system suitable for the evaluation of the total PAH concentration at work places consists of the combination of a glass fibre filter as a collector for particulate PAH followed by an adsorption tube containing either Tenax or XAD-2 as back-up system for trapping the vapour-phase PAH.

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Bewertung verschiedener Sammelphasen für polycyclische aromatische Kohlenwasserstoffe (PAH)

Zusammenfassung Partikel-gebundene und gasförmige polycyclische aromatische Kohlenwasserstoffe (PAH) mit teilweise ausgeprägten carcinogenen Eigenschaften können als Bestandteile von Pyrolyseprodukten aus organischem Material bei bestimmten Fertigungsprozessen am Arbeitsplatz emittiert werden.Eine Risikoabschätzung exponierter Arbeitnehmer orientiert sich vorwiegend an Luftmessungen eines möglichst umfassenden PAH-Spektrums. Ihre quantitative Probenahme mittels Glasfaserfilter stößt wegen unterschiedlich ausgeprägter Flüchtigkeit der PAH auf Schwierigkeiten.Anhand von n = 20 ausgewählten Referenzsubstanzen wird ein geeignetes Sammelsystem im Probenahmeverfahren für PAH evaluiert.Durch Anwendung der sog. phase equilibrium method und des simulierten Probenahmeverfahrens mittels im Stickstoffstrom mit PAH beaufschlagter Sammelphasen konnten Überführungsraten für die gasförmigen PAH von 82,7 bis 105,7% an den Adsorberharzen Tenax und von 82,9 bis 103,9% an XAD-2 mit Toluol als Elutionsmittel erhalten werden. Nicht geeignet erwiesen sich Silicagel und Polygosil.Eine repräsentative Probenahme zur Abschätzung der PAH-Totalkonzentration ist bei einer kombinierten Anwendung von Glasfaserfilter als Sammelphase für partikuläre PAH und nachgeschaltetem Adsorptionsrohr mit wahlweise Tenax oder XAD-2 als Sorbens für gasförmige PAH als äußerst effektiv zu bezeichnen.

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Supported by the Bundesministerium für Forschung und Technologie of the Federal Republic of Germany, Project-No. 01 VD 093.     

Optimizing separation conditions for polycyclic aromatic hydrocarbons in micellar electrokinetic chromatography

We report the separation of polycyclic aromatic hydrocarbons (PAHs) using 0.1% poly(ethylene oxide) (PEO) in micellar electrokinetic chromatography (MEKC). In the presence of PEO, adsorption of PAHs on the capillary wall was reduced, leading to better resolution and reproducibility. Effects of tetrapentylammonium iodide (TPAI), dextran sulfate (DS), methanol, and sodium lauryl sulfate (SDS) on the separation of PAHs were elucidated. In terms of resolution and speed, DS, compared to TPAI, is a better additive for separation of PAHs. When using 0.1% PEO solution containing 45% methanol, 50 mM SDS, and 0.02% DS, separation of 10 PAHs containing 2 to 5 benzene rings was accomplished in less than 12 min at 15 kV in a commercial CE system. The method has also been tested for separating seven PAHs with high quantum yields when excited at 325 nm using a He-Cd laser. Unfortunately, separation of the seven PAHs was not achieved and sensitivity diminished under the same conditions. To optimize sensitivity, resolution and speed, a stepwise technique in MEKC has been proposed. The seven PAHs were resolved in 35 min at 15 kV when separation was performed in 0.1% PEO solution containing 35 mM SDS, 40% methanol and 0.02% DS for 2 min, and subsequently in 0.1% PEO solution containing 20 mM SDS, 50% methanol, and 0.02% DS.     

Laterally attached liquid-crystalline polymers as stationary phases in reversed-phase high-performance liquid chromatography. III. Effect of the local anisotropic order on the separation of polycyclic aromatic hydrocarbons

Specific stationary phases based upon non-liquid-crystalline polymers, liquid-crystalline molecules and side-on fixed liquid-crystalline polymers (SO-LCP) have been synthesized for use as silica modified stationary phases in high-performance liquid chromatography (HPLC). The mesogenic side group of the SO-LCP was composed of three phenyl ring benzoate type with terminal alkoxy chains and was laterally linked to a polysiloxane backbone via an alkyl ester spacer arm. This study demonstrated that the shape recognition of stationary phases based upon SO-LCP towards the length-to-breath ratio (L/B) was strongly connected to the existence of a local liquid-crystalline order into the pores of silica gel, warranting the interest of the collective organization of mesomorphic materials in liquid chromatography. Furthermore, the chromatographic performances depended on the kind of anisotropic order and it was more advantageous to use smectic side-on liquid-crystalline polymer than nematic and obviously non-liquid-crystalline ones. Finally, for a series of polymers having the same mesomorphism, the larger the temperature stability range of the mesophase, the more pronounced the local order effect and the higher the shape recognition.     

Comprehensive two-dimensional high-performance liquid chromatography for the separation of polycyclic aromatic hydrocarbons

A comprehensive two-dimensional HPLC system for the separation of polycyclic aromatic hydrocarbons was developed using a pentabromobenzyl column as the first dimension and two short monolithic C18 columns as the second dimension. The primary column and two secondary columns were coupled by a 10-port 2-position valve. The effluent from the first dimension was repetitively injected into the second dimension every 12 s. Due to its resolution, this technique is a powerful tool for the separation of polycyclic aromatic hydrocarbons in a complex matrix such as environmental samples.     

Partitioning study of polycyclic aromatic hydrocarbons between water and some selected water-insoluble phases

An investigation on the partitioning of naphthalene and phenanthrene between water and some water-insoluble phases has been carried out by Uv-vis-NIR spectrophotometry. The analysis of the experimental results emphasized the role of intermolecular interactions and structural features of the hosting phases as driving forces of the partitioning of these polycyclic aromatic hydrocarbons. The critical comparison of the resulting distribution constants allowed to evaluate the potentials of some extracting phases to set up sensitive analytical methods and/or effective environment remediation technologies.     

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.     

南充市表层土壤中多环芳烃的源解析研究

运用同分异构体比率、聚类分析法和主成分因子载荷法对南充市表层土壤多环芳烃(PAHs)污染源进行了定性和定量分析。研究表明:同分异构体比率分析揭示表层土壤中PAHs污染来源以燃烧源为主;聚类分析将土壤中13种PAHs组分分成3个主群,3个主群分别指示为交通类PAHs污染、煤燃烧类PAHs污染和混合类PAHs污染。主成分因子/多元线性回归分析显示,PAHs主要来源于3大污染源,并定量计算了3种源的贡献量,其中交通燃油污染的贡献率最大(占42.4%),而燃煤燃烧排放、混合污染所占比例分别为32.4%和25.2%。     

Retention of polycyclic aromatic hydrocarbons on propyl-phenyl stationary phases in reversed-phase high performance liquid chromatography

A study on the retention of PAHs on three Propyl-phenyl stationary phases was conducted, assessing absolute retention, selectivity, retention correlation and thermodynamic behaviour. The chromatographic retention data revealed that each of the three Propyl-phenyl columns exhibited differences in absolute retention, however, comparison of the compensation temperatures derived from enthalpy-entropy compensation plots showed that the underlying processes responsible for the retention on these columns were the same.     

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.     

Palladium-catalyzed pentannulation of polycyclic aromatic hydrocarbons

We present a new and versatile one-step synthesis of a series of small molecular chromophores based on cyclopentannulated polycyclic aromatic hydrocarbons (PAH). Easily available pyrene, anthracene, and perylene bromides serve as starting materials for the reactions. The formation of the five-membered ring is achieved by the straightforward palladium(0)-catalyzed carbannulation with various substituted acetylenes. This approach is applicable either to single or multiple annulation procedures leading to hitherto inaccessible PAH topologies. According to the resulting products of the diverse reactions, a mechanistic explanation is proposed. UV/Vis absorption as well as cyclovoltammetric measurements were performed for characterization demonstrating the value of this annulation technique. Optical absorptions of up to 780 nm and absorption coefficients ranging from 8000 to 34,000 M(-1) cm(-1) were detected.