Polyaromatic hydrocarbons separation

Another technique reported for polyaromatic hydrocarbons separation uses ODS-filled (with frits) or entrapped (without frits) columns with 80% acetonitrile-20% 0.1 M acetate buffer (v/v) at pH 3 (30 kV per 17-25 cm - long capillary, i.d. 100 pm) [10], The results are seen in Fig. 10.2. The technique of using entrapped sorbents can also be used for materials other than ODS (typically, imprinted polymers for chiral separations). 

This publication provides several examples of the use of solid-phase extractions for separating analytes from their matrices. Some of the examples included are caffeine from coffee, polyaromatic hydrocarbons from water, parabens from cosmetics, chlorinated pesticides from water, and steroids from hydrocortisone creams. Extracted analytes maybe determined quantitatively by gas (GC) or liquid chromatography (LG). 

The analysis of cigarette smoke for 16 different polyaromatic hydrocarbons is described in this experiment. Separations are carried out using a polymeric bonded silica column with a mobile phase of 50% v/v water, 40% v/v acetonitrile, and 10% v/v tetrahydrofuran. A notable feature of this experiment is the evaluation of two means of detection. The ability to improve sensitivity by selecting the optimum excitation and emission wavelengths when using a fluorescence detector is demonstrated. A comparison of fluorescence detection with absorbance detection shows that better detection limits are obtained when using fluorescence. 

Funk et al. [128a] dipped silica gel plates in a 4% solution of caffeine in order to separate six polyaromatic hydrocarbons relevant in monitoring the quality of potable water (Fig. 42). 

The TLC plates prepared in a similar maimer may be used to separate monoar-omatie hydrocarbon fractions with Rj values in the range 0.29 to 0.78 from polyaromatic hydrocarbon fractions (Rj = 0.06 to 0.29) [84]. 

Adsorption chromatography on silica is well suited to the separation of less polar compounds such as polyaromatic hydrocarbons, fats and oils, and for the separation of isomers or compounds with differing functional groups. 

As yet, the number of applications is limited but is likely to grow as instrumentation, mostly based on existing CE systems, and columns are improved and the theory of CEC develops. Current examples include mixtures of polyaromatic hydrocarbons, peptides, proteins, DNA fragments, pharmaceuticals and dyes. Chiral separations are possible using chiral stationary phases or by the addition of cyclodextrins to the buffer (p. 179). In theory, the very high efficiencies attainable in CEC mean high peak capacities and therefore the possibility of separating complex mixtures of hundreds of... 

A spectrofluorimeter has been used as a detector in the high-performance liquid chromatographic separation of polyaromatic hydrocarbons in water samples [12-17], A great improvement in sensitivity and specificity can be obtained by the correct wavelengths. 

Lopez-Avila et al. [59] have described a microwave assisted extraction procedure for the separation of polyaromatic hydrocarbons from sediments. Tan [71] described a rapid sample preparation technique for analysing polyaromatic hydrocarbons in sediments. Polyaromatic hydrocarbons are removed from the sediment by ultrasonic extraction and isolated by solvent partition and silica gel column chromatography. The sulphur removal step is combined into the ultrasonic extraction procedure. Identification of polyaromatic hydrocarbon is carried out by gas chromatography alone and in conjunction with mass spectrometry. Quantitative determination is achieved by addition of known amounts of standard compounds using flame ionization and multiple ion detectors. 

Fig. 8. Separation of polyaromatic hydrocarbons using commercial stationary phases. (Reprinted with permission from [56]. Copyright 1997 VCH-Wiley). Conditions voltage 20 kV,capillary column 100 pm i. d., total length 33.5 cm, active length 25 cm, isocratic separation using 80 20 acetonitrile-50 mmol/1 TRIS buffer pH=8. Peaks thiourea (1), naphthalene (2), and flu-oranthrene (3)...

Stationary phases with a high density of bonded alkyl groups can differentiate between two molecules of identical size where one is planar and the other twisted out of plane. This shape selectivity has been described by Sander and Wise [53] for polymeric stationary phases, where in the preparation, water has been added on purpose and trichloro alkyl silanes have been used. The selectivity for the retention of tetrabenzonaphthalene (TEN) and benzo[a]pyrene (BaP) was taken as a measure to differentiate between polymeric and standard RP columns. With standard ( monomeric ) RP columns, the twisted TBN elutes after the planar BaP, which on the other hand is more strongly retarded as TBN on polymeric stationary phases. In these cases the relative retention of TBN/ BaP is smaller than 1, whereas with monomeric phases the value is >1.5. The separation of the standards on three different phases is shown in Figure 2.9. These stationary phases have superior selectivity for the separation of polyaromatic hydrocarbons in environmental analysis. Tanaka et al. [54] introduced the relative retention of triphenylene (planar) and o-terphenyl (twisted), which are more easily available, as tracers for shape selectivity. However, shape selectivity is not restricted to polymeric phases, monomeric ones can also exhibit shape selectivity when a high carbon content is achieved (e.g., with RP30) and silica with a pore diameter >15 nm is used [55]. Also, stationary phases with bonded cholestane moieties can exhibit shape selectivity. 

The Basic Extractive Sludge Treatment (B.E.S.T. ) process is an ex situ solvent extraction technology. The B.E.S.T. process uses one or more secondary or tertiary amines, such as diisopropylamine, to separate contaminants from soil, sediment, and sludge. This technology is applicable to most organics or oily contaminants, including polychlorinated biphenyls (PCBs), polyaromatic hydrocarbons (PAHs), pesticides, herbicides, dioxins, furans, and other organic compounds. 

Figure 24-12 Separation of two polyaromatic hydrocarbons on a wall-coated open tubular column with different carrier gases. Resolution. R. increases and analysis time decreases as we change from N2 to He to H2 carrier gas. [Courtesy J W Scientific, Folsom, CA.]...

Analytical Properties Separation of polyaromatic hydrocarbons and insect sex pheromones Reference 5... 

Felix, G. and Bertrand, C., Separation of polyaromatic hydrocarbons on caffeine-bonded silica gel, J. Chromatogr., 319, 432, 1985. 

Felix, G., Bertrand, C., and Van Gastel, F., A new caffeine bonded phase for separation of polyaromatic hydrocarbons and petroleum asphaltenes by high-performance liquid chromatography, Chro-matographia, 20, 155, 1985. 

Polyaromatic hydrocarbons and their nitro derivatives can be separated by capillary electrochromatography, as described in ref. [181]. Besides C18 phases, C8... 

Polyaromatic hydrocarbons (benzene, toluene, ethylbenzene, propylbenzene, butylbenzene, pentylbenzene) Separation segment ODS, 5 pm (200 mm), accelerating segment bare silica (0-280 mm) Acetonitrile-1.25 mM monobasic sodium phosphate pH 6.0 (75 25) 100 pm i.d., for length see stationary phase Two types of packing 12... 

At the same time calculations on the modified MEIS are possible without additional kinetic models and do not require extra experimental data for calculations, which makes it possible to use less initial information and obviously reduces the time and labor spent for computing experiment. Furthermore, there arise principally new possibilities for the analysis of methods to mitigate emissions from pulverized-coal boilers, since at separate modeling of different mechanisms of NO formation the measures taken can result in different consequences for each in terms of efficiency. Consideration of kinetic constraints in MEIS will substantially expand the sphere of their application to study other methods of coal combustion (fluidized bed, fixed bed, etc.) and to model processes of forming other pollutants such as polyaromatic hydrocarbons, CO, soot, etc. 

In [m] circulenes, a family of polyaromatic hydrocarbons so named in 1975 by Wynsberg, in which m refers to the number of aromatic rings arranged in a circle, the total number of n electrons does not indicate aromaticity or anti-aromaticity according to the Hiickel rule. This rule is strictly only applicable to monocyclic systems. It is adequate, however, to consider the inner and the outer n electrons separately whose numbers obey the An + 2 Hiickel criterion for aromaticity, since both these circuits are monocyclic [49]. Coronene, a flat graphite frag-... 

In addition to preserving structure, a soft ionization technique such as chemical ionization (Cl) has a further advantage in ms /ms. By minimizing the number of ions generated from each molecular species the complexity of the (ionic) mixture which has to be separated is minimized. It is for this reason that electron impact ionization is seldom a good choice for ms/ms, although for compounds such as the polyaromatic hydrocarbons which give predominantly one ion in their electron impact spectra this complication is minimized. 

The formation of novel membrane-like materials based on LDHs has also been established. These materials are of relevance to separation and membrane technologies. A LiAl-LDH containing myrisate or hexanoate anions, for example, has the ability to partition pyrene from a methanol/water solution containing the polycyclic aromatic [132], No sorption of pyrene was observed for a LiAl(succinate) LDH, however, and this was attributed to a sieving effect of this compound towards the pyrene molecule. The sorption of polyaromatic hydrocarbons, such as pyrene, is important from an environmental perspective. 

Certain fundamental characteristics of MECC that influence retention have been investigated (5). The technique has been used in the analysis of a variety of samples including phenolic compounds (1), phenylthiohydantoin—amino acids (6), and metabolites of vitamin Bg (7). In related electrokinetic separation techniques, substituted benzene compounds have been separated based on the formation of inclusion complexes with an ionic cyclodextrin derivative in the mobile phase (8) and polyaromatic hydrocarbons have been separated based on solvophobic interactions with a tetraakyl— ammonium ion in the mobile phase (9). The effects of injection procedures on efficiency have also been studied (10). 

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