Aromatic HPLC separation

Another useful standard Is SRM 1647, priority pollutant polynuclear aromatic hydrocarbons (in acetonitrile). It can be used to calibrate liquid chromatographic Instruments (retention times. Instrument response), to determine percent recoveries, and to fortify aqueous samples with known PAH concentrations. Figure 8 Illustrates the HPLC separation and UV detection (fluorescence is also used extensively) for the 16 priority pollutants. 

Figure 8. Reversed-phase HPLC separation of SRM 1647, priority pollutant polynuclear aromatic hydrocarbons (In acetonitrile), using UV detection.

Successful combination of a chromatographic procedure for separating and isolating additive components with an on-line method for obtaining the IR spectrum enables detailed compositional and structural information to be obtained in a relatively short time frame, as shown in the case of additives in PP [501], and of a plasticiser (DEHP) and an aromatic phenyl phosphate flame retardant in a PVC fabric [502], RPLC-TSP-FTIR with diffuse reflectance detection has been used for dye analysis [512], The HPLC-separated components were deposited as a series of concentrated spots on a moving tape. HPLC-TSP-FTIR has analysed polystyrene samples [513,514], The LC Transform has also been employed for the identification of a stain in carpet yarn [515] and a contaminant in a multiwire cable [516], HPLC-FTIR can be used to maintain consistency of raw materials or to characterise a performance difference. 

Fig. 3.107. Comparison of micro-HPLC separations of aromatic sulphonic acids in different mobile phases (a) 0.005 M tetrabutylammonium hydrogensulphate (TBAS) in 15 per cent (v/v) methanol in water (1) Laurent acid, (2) amino-F-acid, (3) Cleve-1,6- and Peri acids, (4) unidentified impurity, (5) Cleve-1,7-acid and (6) unidentified impurity, (b) 0.005 M tetrabutylammonium hydrogensulphate (TBAS) in 15 per cent (v/v) methanol in water with 0.01 M /Lcyclodextrin (CD) (1) Laurent acid, (2) amino-F-acid, (3) Cleve-1,6-acid, (4) Peri acids, (5) unidentified impurity, (6) Cleve-1,7-acid and (7) unidentified impurity. Column, Biosphere Si C18, 162 X 0.32 mm i.d. flow rate 5 pl/min, column temperature ambient, detection, UV, 220-230 nm. Reprinted with permission from P. Jandera et al. [164].

An alternative method for fractionating and purifying petroleum hydrocarbons prior to GC or HPLC separation has been developed (Theobald 1988). The method uses small, prepacked, silica or Cjg columns that offer the advantage of rapid separation (approximately 15 minutes for a run) good recovery of hydrocarbons (85% for the Cjg column and 92% for the silica column) reusability of the columns and for the silica column in particular, good separation of hydrocarbon from non-hydrocarbon matrices as may occur with environmental samples. Infrared analysis and ultraviolet spectroscopy were used to analyze the aromatic content in diesel fuels these methods are relatively inexpensive and faster than other available methods, such as mass spectrometry, supercritical fluid chromotography, and nuclear magnetic resonance (Bailey and Kohl 1991). 

Figure 25-12 Isocratic HPLC separation of a mixture of aromatic compounds at 1.0 mL/min on a 0.46 x 25 cm Hypersil ODS column (C,8 on 5-jxm silica) at ambient temperature ( 22 C) (1) benzyl alcohol (2) phenol (3) 3, 4 -dimethoxyacetophenone (4) benzoin (5) ethyl benzoate (6) toluene (7) 2,6-dimethoxytoluene (8) o-methoxybiphenyl. Eluent consisted ot aqueous buffer (designated A) and acetonitrile (designated B). The notation 90% B in the first chromatogram means 10 vol% A and 90 vol% B. The buffer contained 25 mM KH2P04 plus 0.1 g/L sodium azide adjusted to pH 3.5 with HCI.

Because methylene-interrupted polyunsaturates do not have strongly absorbing chromo-phores in the UV region, detection by refractive index or far-UV detection (205-214 nm) has been utilized in RP-HPLC separations of free fatty acids and their aliphatic esters. Refractive index detection is less sensitive than UV detection. However, with far-UV detection, solvents absorbing UV below 210 cannot be used. The RP-HPLC separations reported to date have generally involved derivatization designed to incorporate aromatic chromophores allowing detection by fluorescence or UV detection. 

Takeoka et al. (5) also reported methods for derivatizing both aliphatic and aromatic Amadori compounds as -nitrobenzyloxy-amine (PNBO) derivatives to allow facile UV detection in the pico-molar range for HPLC separations. They reported in the same paper a simple method for derivatizing the Amadori compounds to allow gas chromatographic/mass spectrometric (GC/MS) separation and identification of highly purified Amadori compounds. 

Among more complex macrocycles, Li et al. [47-52] reported the preparation and characterization of stationary phases incorporating calixarenes or calix-crowns bonded to silica. With individual columns, high selectivity was observed in the separation of alkylated aromatics, aromatic carboxylic acids, sulfonamides, nucleosides, and water-soluble vitamins. In other work, Sokoliess et al. [53] have characterized calixarene- and resorcinarene-bonded stationary phases similar to those described in the previous section of this chapter. And Huai et al. [54] used an end-capped p-tert-butyl-calix[4]arene-bonded silica phase for HPLC separation of a number of organic compounds. Resorcinarenes have also found application in GC. [55-57] Recently, exotic macrocycles have been used in capillary electrochromatography, as reported by Gong et al. [58]... 

An optoelectronic image device has been used as an HPLC detector to obtain UV absorption spectra of shale oil aromatic hydrocarbons separated isocratically (10). Since isocratic separations maintain a constant mobile phase composition, the... 

The majority of CEC separations reported to date have been carried out on silica stationary phases that were originally developed for HPLC. Large differences have been observed [30] in using these HPLC phases in CEC. The differences seen in the separations of polycyclic aromatic hydrocarbon mixtures are far greater in CEC than would be expected for the corresponding HPLC separation. Two main reasons for this have been put forward (a) the differences in the packing of the capillary columns for CEC and (b) the particle size distribution of the materials, although all were nominally defined as 3 pm. 

Later, Klemm and co-workers [86,87] achieved partial resolution of aromatic compounds by low-pressure chromatography on silica gel impregnated with TAPA. The separation was attributed to n-n complexation between TAPA and the enantiomers. Mikes et al. [88] used a column packed with an (i )-(-)-TAPA aminopropyl-bonded silica support to accomplish the full resolution of helicenes. The authors extended their study to other homologues of TAPA (Figure 22-19). These compounds were coated on silica gel or ion-paired to an aminopropyl-bonded phase, and they were used in the HPLC separation of helicenes. To describe the selective interactions that occur between the stationary phase and the helicenes, the authors assumed that the 2,4,5,7-tetranitro-9-fluorenylidene moieties of the selector are laying down on the silica surface, while the X groups point away from the surface and above the plane of the fluorenyl ring. 

Typical Response Peaks. Figure 2 shows some typical response peaks for the HPLC separation of the saturates and aromatics in a typical vacuum gas oil. The curve in the upper portion of the figure is the response for the sample using the RI detector. After the saturates peak appeared, the backflush valve was switched and the attenuation changed as indicated in the figure. The peaks were very sharp and symmetrical and appeared in less than 10-min lapsed time from the point of injection. Base line drift was minimal and the areas of the response peaks were obtained with a ball and disc integrator on the strip chart recorder. 

Figure 2. Typical response peaks for HPLC separation of saturates and aromatics. Column, 1-ft /i-PorasU soU vent, n-heptane (1 mL/min) sample, 10 fiL of vacuum gas oil in n-heptane detectors, refractive index, and Pye Unicam moving wire.

Miguel AH, De Andrade JB. 1989. Rapid quantitation of ten polycyclic aromatic hydrocarbons in atmospheric aerosols by direct HPLC separation after ultrasonic acetonitrile extraction. Int J Environ Anal Chem 35(1) 35-41. 

Chlorinated insecticides The analysis of chlorinated pesticides in residue samples in complicated by the fact that they usually occur along with polychlorinated biphenyls (PCBs). The latter compounds occur widely in the environment due to their use as plasticizers, dye stuff additives and hydraulic oils, and both chlorinated pesticides and polychlorinated biphenyls are persistent in the environment. Since both compound classes include non-polar aromatic molecules, adsorption chromatography has been the mode of choice for the HPLC separation of these compounds. 

Relatively few molecular separations have been studied from the utilitarian standpoint. One of these, the purification of fullerenes via 8 , is discussed on p. 170. In a reciprocal experiment the separation of 4 " , 6 , and 8 with a column using a chemically-bonded C o silica stationary phase has been re-ported. Chromatographic selectivity has been achieved for amino acid esters and alkali metal cations on silica-bonded calix[4]arene tetraesters, the structure of which has been explored by and Si-CP-MAS NMR. Silica-bonded calixarenes have also been used as packing materials for HPLC columns that are capable of separating disubstituted aromatics, peptides, and nucleosides. The HPLC separation of phenols using 6 ° as a constituent of the eluent has been described. ... 

Figure 7.15 HPLC-UV diode array instrument and chromatograms, (a) HPLC diode array UV detector system (b) UV spectra recorded at three points on an HPLC peak to enable peak purity to be determined (c) Isometric map obtained by plotting successive spectra from an HPLC separation of polynuclear aromatics. A, naphthalene B, fluorene C, anthracene D, chrysene.

Figure 13.8 HPLC separation of seven aromatic compounds under quasi-normal phase conditions. Column Chromalite 5HGN (250 x 4.6 mm). Mobile phase pentane/CH2Cl2/isopropanol (75 5 20), flow rate, I.OmL/min. (Reprinted from [196] with permission of Elsevier.)...

The area of hyphenated techniques is so active that any researcher who wishes to stay abreast of the use of new appHcations and techniques must read the Hterature constantly. Each new issue of any of the major analytical chemistry journals contains one or two or more articles in this field. Conversely, by the nature of hyphenated techniques, an article on one particular technique can appear in many possible places. For example, an article on an HPLC separation with fuU spectrum UV absorbance detection of polycyclic aromatic hydrocarbons (PAHs) could appear in any of the journals that deal with analytical chemistry, chromatography, spectrometry, the chemistry of the PAHs, or materials containing PAHs. This author s own publications list shows several examples of papers appearing in each type of journal, even though each could have appeared in a different one than the one it did. 

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