A variety of bonded phase parameters (endcapping, phase chemistry, ligand length, and substrate parameters) were studied for their effect on column retention and selectivity toward carotenoids. Decisions were made on how each of these variables should be optimized based on the separation of carotenoid and polycyclic aromatic hydrocarbon test probes. A column was designed with the following properties: high absolute retention, enhanced shape recognition of structured solutes, and moderate silanol activity. These qualities were achieved by triacontyl (C30) polymeric surface modification of a moderate pore size (approximately 20 nm), moderate surface area (approximately 200 m2/g) silica, without subsequent endcapping. The effectiveness of this "carotenoid phase" was demonstrated for the separation of a mixture of structurally similar carotenoid standards, an extract of a food matrix Standard Reference Material, and a beta-carotene dietary supplement under consideration as an agent for cancer intervention/prevention.

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Polycyclic aromatic hydrocarbons (PAHs) are frequently measured in the atmosphere for air quality assessment, in biological tissues for health-effects monitoring, in sediments and mollusks for environmental monitoring, and in foodstuffs for safety reasons. In contemporary analysis of these complex matrices, gas chromatography (GC), rather than liquid chromatography (LC), is often the preferred approach for separation, identification, and quantification of PAHs, largely because GC generally affords greater selectivity, resolution, and sensitivity than LC. This article reviews modern-day GC and state-of-the-art GC techniques used for the determination of PAHs in environmental samples. Standard test methods are discussed. GC separations of PAHs on a variety of capillary columns are examined, and the properties and uses of selected mass spectrometric (MS) techniques are presented. PAH literature on GC with MS techniques, including chemical ionization, ion-trap MS, time-of-flight MS (TOF-MS), and isotope-ratio mass spectrometry (IRMS), is reviewed. Enhancements to GC, for example large-volume injection, thermal desorption, fast GC, and coupling of GC to LC, are also discussed with regard to the determination of PAHs in an effort to demonstrate the vigor and robustness GC continues to achieve in the analytical sciences.

Molecular shape recognition is examined for a series of Ci8 columns prepared using a variety of synthetic approaches. Mono-, di-, and trifunctional silanes are used to prepare stationary phases through monomeric and polymeric surface modification procedures, including an approach employing self-assembled monolayer technology. Shape discrimination properties of the columns were investigated with various nonplanar, planar, and linear

C(18) phases prepared by different synthetic pathways are examined by solid-state NMR spectroscopy. Silane functionality is clearly indicated by (29)Si CP/MAS NMR spectroscopy. Order and mobility of the alkyl chains are investigated with high-speed (1)H MAS and (13)C CP/MAS NMR spectroscopy. Differences in coverage are monitored by (1)H line widths,( 13)C chemical shifts, (13)C cross-polarization constants, and (1)H relaxation times in the rotating frame. It is shown that C(18) phases prepared by the surface polymerization technique exhibit a more regular surface coverage than sorbents prepared by conventional polymeric synthesis. The findings from solid-state NMR investigations are discussed in the context of liquid chromatography (LC) separations of linear and bulky polycyclic aromatic hydrocarbon (PAH) solutes.