Separation, polycyclic aromatic

Poole, C. F., Butler, M. E., Coddens, M. E., Khatib, S., and Vandervennt, R. (1984). Comparison of methods for separating polycyclic aromatic hydrocarbons by high performance thin layer chromatography. J. Chromatogr. 302 149-158. 

One example of normal-phase liquid chromatography coupled to gas chromatography is the determination of alkylated, oxygenated and nitrated polycyclic aromatic compounds (PACs) in urban air particulate extracts (97). Since such extracts are very complex, LC-GC is the best possible separation technique. A quartz microfibre filter retains the particulate material and supercritical fluid extraction (SPE) with CO2 and a toluene modifier extracts the organic components from the dust particles. The final extract is then dissolved in -hexane and analysed by NPLC. The transfer at 100 p.1 min of different fractions to the GC system by an on-column interface enabled many PACs to be detected by an ion-trap detector. A flame ionization detector (PID) and a 350 p.1 loop interface was used to quantify the identified compounds. The experimental conditions employed are shown in Table 13.2. 

Figure 13.16 LC separation of urban air particulate exrtact (a), along with the GC/FID cliro-matogram (b) of an oxy-PAC fraction (transfeired via a loop-type interface). Reprinted from Environmental Science and Technology, 29, A. C. Lewis et al., On-line coupled LC-GC-ITD/MS for the identification of alkylated, oxygenated and nirtated polycyclic aromatic compounds in urban air particulate exti acts , pp. 1977-1981, copyright 1995, with permission from the American Chemical Society.

Coman et al. [82] used a new modeling of the chromatographic separation process of some polar (hydroxy benzo[a]pyrene derivatives) and nonpolar (benzo[a]pyrene, dibenz[a,/ ]anthracene, and chrysene) polycyclic aromatic compounds in the form of third-degree functions. For the selection of the optimum composition of the benzene-acetone-water mobile phase used in the separation of eight polycyclic aromatic compounds on RP-TLC layers, some computer programs in the GW-BASIC language were written. 

Bota et al. [84] used the PCA method to select the optimum solvent system for TLC separation of seven polycyclic aromatic hydrocarbons. Each solute is treated as a point in a space defined by its retention coordinates along the different solvent composition axes. The PCA method enables the selection of a restricted set of nine available mobile phase systems, and it is a useful graphical tool because scatterplots of loading on planes described by the most important axes will have the effect of separating solvent systems from one other most efficiently. 

Figure 4.4 Separation of SRM 1647 and SRH 869 polycyclic aromatic hydrocarbon test mixtures on a monomeric and polymeric reversed-phase octadecylsiloxane bonded phases by gradient elution. (Reproduced with permission from ref. 69. Copyright American Chemical Society).

Because process mixtures are complex, specialized detectors may substitute for separation efficiency. One specialized detector is the array amperometric detector, which allows selective detection of electrochemically active compounds.23 Electrochemical array detectors are discussed in greater detail in Chapter 5. Many pharmaceutical compounds are chiral, so a detector capable of determining optical purity would be extremely useful in monitoring synthetic reactions. A double-beam circular dichroism detector using a laser as the source was used for the selective detection of chiral cobalt compounds.24 The double-beam, single-source construction reduces the limitations of flicker noise. Chemiluminescence of an ozonized mixture was used as the principle for a sulfur-selective detector used to analyze pesticides, proteins, and blood thiols from rat plasma.25 Chemiluminescence using bis (2,4, 6-trichlorophenyl) oxalate was used for the selective detection of catalytically reduced nitrated polycyclic aromatic hydrocarbons from diesel exhaust.26... 

Yang, W.-H., Chen, I-L., and Wu, D.-H., Chemically bonded phenylsilicone stationary phases for the liquid chromatographic separation of polycyclic aromatic hydrocarbons and cyclosiloxanes, /. Chromatogr. A, 722, 97, 1996. 

Polycyclic aromatic hydrocarbons (PAH) are important air pollutants that have to be detected at very low concentrations. Fig. 2.4h shows the separation of a synthetic mixture of very low levels of PAH. They are barely detectable using uv absorption, but are easily monitored by fluorescence. 

Wise, S. A. and Sander, L. C. 1985. Factors affecting the reversed-phase liquid chromatographic separation of polycyclic aromatic hydrocarbon isomers. J. High Resolut. Chromatogr. Commun. 8 248-255. 

LC-MS has been used to study various aromatic fractions from coal derived liquids, and there are also a number of reports on its use in the analysis of porphyrin mixtures [601,602]. The early work by Dark et al. [601] using LC-MS for coal-derived liquids was mainly concerned with the separation and identification of polycyclic aromatic components. However, it is interesting to note that... 

Example 2 Separation of a polycyclic aromatic hydrocarbon and an alkyl benzoate. The logP values of fluorene and butyl benzoate are 3.91 and 3.74, respectively, from Table 4.1. The separation is poor in 50% aqueous aceto-... 

One component of the eluent should have properties similar to those of the analytes, and this solvent is diluted by another solvent to control the retention time. The basic idea can be understood from the chromatographic behaviour of phthalic acid esters and polycyclic aromatic hydrocarbons (PAH). This approach can be applied to the separation procedure for a variety of stationary phase materials, including silica gel, polystyrene gel, and ion-exchangers. 

---