Octyl bonded phase, HPLC

Variations in retention and selectivity have been studied in cyano, phenyl, and octyl reversed bonded phase HPLC columns. The retention of toluene, phenol, aniline, and nitrobenzene in these columns has been measured using binary mixtures of water and methanol, acetonitrile, or tetrahydrofuran mobile phases in order to determine the relative contributions of proton donor-proton acceptor and dipole-dipole interactions in the retention process. Retention and selectivity in these columns were correlated with polar group selectivities of mobile-phase organic modifiers and the polarity of the bonded stationary phases. In spite of the prominent role of bonded phase volume and residual silanols in the retention process, each column exhibited some unique selectivities when used with different organic modifiers [84],... 

The nomenclature of the RP is not consequent. The RP most often used contains octyl (RP C8) or octadecyl (RP C18) groups. There is no differentiation even when two methyl groups are introduced additionally with the silane (as with monofunctional silanes) or only one (difunctional) or none (trifunctional silane). Some manufacturer use silanes with bulky side groups (e.g., isopropyl groups) to improve the hydrolytic stability of the bonded phases, but here also, only the longest alkyl group is used in nomenclature. RP C8 and RP C18 are the work horses in HPLC. Shorter chains (RP4) are used in protein separations, and special selectivity can be obtained with bonded phenyl, cyano, amino or fluoro groups. 

The advances in column and instrument technology have significantly enhanced HPLC performance in recent years. Results comparing the effects of various column packings on TG separation by RP-HPLC were presented by El-Hamdy and Perkins (87). Six commercially packed columns produced by different manufacturers were used PARTISIL ODS-1 and ODS-2 octadecyl-bonded silica of 10-/rm partical size, ZORBAK-ODS octadecyl-silica of 6-7-/rm diameter (250 X 4.6-mm ID), 5-/rm octyl-bonded spherical silica LC-8, 5-//m methyl-bonded spherical silica LC-1, and a 5-/rm octadecyl-bonded spherical silica LC-18 (150 X 4.6-mm ID). The mobile phase employed consisted of mixtures of methanol/acetone/isopropanol/acetonitrile ranging from l 0 3 4to 1 6 3 4. Triglycerides were solubilized in either THF or acetone at 100 mg/ml for each compound. 

El-Fizga (108) developed a simple, rapid method for the detection of oils high in linoleic acid in olive oil by RP-HPLC and a simple authenticity factor and a derived equation to determine the extent of adulteration with a one short chromatographic step, completed in less than 15 min. They used two 150 X 4.5-mm ID stainless steel columns packed with an octyl-bonded silica stationary phase (Supelcosil-LC 8) (Supelco. Bellefonte, PA, USA) and a differential reffactometric detector. The isocratic mobile phase was acetone-acetonitrile (70 30, v/v) (Table 5). 

The avidin content of the fractions eluted from the ion exchange column were determined by reverse phase HPLC analysis using an Alltech octyl-bonded silica column, a Perkin Elmer Series 410 quaternary solvent... 

The analysis of mycotoxins, toxic substances produced by some fungi, is essential to guaranteeing the safety of foods such as cereals, nuts, oilseeds, and spices since the discovery of their significance to human health. The main mycotoxins, like aflatoxins and ochratoxin A, are determined using HPLC with octyl-or octadecyl-bonded phases and polar solvents such as methanol, acetonitrile, and water. For detection with the required sensitivity and selectivity, spectrofluori-metric detection is the most common method, with increasing use of mass spectrometric interfaces. 

Near-critical pSFC applications can be described as those where the mobile phase is solvent-modified CO2, pressurized only enough to maintain a single phase, with temperatures near (typically less than) the critical temperature. Many commercially available HPLC bonded silica phases have been used with modified-C02 mobile phases to achieve normal-phase separations, the choice of stationary phase being dictated by sample polarity. The modifiers added to CO2 acceptably overcome the unwanted analyte-sUica interactions observed with neat CO2 mobile phases. For structural separation of polar compounds such as pharmaceuticals [typically weak acids or bases of molecular weight (MW) < 1000], polar phases such as diol-, amino-, and cyano-bonded silica (or bare sihca) are used. Numerous apphcations for pharmaceutical, natural product, environmental and other compound classes have been reported in the recent hteratiu e (reviewed in Refs. ). For structural separation of higher-molecular-weight, less polar compounds, octyl- or octadecyl silane (ODS)-bonded phases are used... 

Reversed-phase chromatoqraphy has most widely been used in HPLC alkaloid analysis - particularly on microparticulate silica qel with chemically bonded alkyl qroups, i.e. octyl and... 

In the area of cyclodextrin ethers the -compound has been converted into a set of five tris-Tbdms ethers, all substituted at their various 6-positions, which were separated by hplc and characterized by n.m.r. spectroscopy. Related work applied to y-cyclodextrin gave the various 6,6 -disubstituted ethers. 5-Bromo-l-pentene was used to produce the 2-0-mono-4-pentenyl ether of P-cyclodextrin which was then permethylated and the product was chemically bonded to silica gel to form an efficient hplc stationary phrase for the separation of enantiomers. Peroctyl a-cyclodextrin has been studied as a chiral receptor for the ephedrinium ion. Various octyl ethers of a-, P- and y-cyclodextrin ranging in their substitution from the diethers to completely alkylated products were characterized by electrospray mass spectrometry and n.m.r. methods applied to methylated derivatives. The 2,6-didodecyl derivative of p-cyclodextrin has been used as a potentiometric sensor. In the field of aromatic ethers, naphthyl carboxylate substituents have been bonded at the 6-positions and the products were able to transfer excitation energy to complexed merocyanine held in the cavities of those molecules. These phototransfer processes were extremely efficient.P-Substituted cyclodextrin derivatives with p-allyloxybenzoyl or various benzyl substituents at 0-2 or 0-3 were incorporated by hydrosilylation to give hydromethylpolysiloxane polymers used as chiral phases for chromatographic resolution of enantiomers. Cyclodextrins with complex benzyl-like eth are illustrated in 22 and 23. The latter were prepared as artificial redox enzymes. 

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