Silica derivatives, HPLC development

Nitrophenols in fog and atmospheric particles were determined by GC of the underiva-tized compounds and their corresponding acetate esters. Four fused-silica columns were used with three alternative detection modes, namely mass-selective detection, nitrogen-specific detection and ECD. GC-ECD of the acetate derivatives gave the best results501. A capillary GC-UVD method was developed for the determination of small amounts of nitrophenols present in the environment. The method was compared with HPLC-UVD from the point of view of selectivity and sensitivity. LOD for GC were about one-tenth of those for HPLC502. 

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). 

In RP-HPLC, the stationary phase is less polar than the mobile phase and is usually comprised of spherical silica particles (typically, 3-5 pm in diameter). The acidic functionalities on the silica material have been modified by deriv-atisation with alkyl (C2 to C18), phenyl, cyano and amino groups. Typical mobile phases used in RP-HPLC consist of mixtures of aqueous buffers mixed with water-miscible organic solvents, such as methanol and acetonitrile. In addition to modified silica stationary phases, other new developments in RP-HPLC are now available, e.g. porous polymeric, carbon and mixed modal phases. 

Analytical conditions Hydroperoxide isomeric mixtures from autoxidized methyl linoleate are reduced to hydroxydiene derivatives by sodium borohydride, and separated by preparative TLC on plates coated with silica gel treated with UV marker and developed with diethyl ether-hexane (6 4, v/v) and UV active hydroperoxides are eluted with diethyl ether. The dienol isomers are separated by HPLC on a preparative 6 m porous silica column with ethanol-hexane (0.5 99.5, v/v) as mobile phase with a UV detector set at 234 nm. The weight percent composition is based on the weight of each fraction collected. 

CDs are produced from starch by the action of Bacillus macerans amylase or the eitzyme cyclodextrin transglycosylate (CTG) [16-19]. The latter enzyme can be used to produce CDs of specific sizes by controlling the reaction conditions. In the past few years, enantiomers have been resolved using peralkylated a-, and y-CDs dissolved in polysiloxanes and coated within glass or fused silica capillary tubing [20, 21]. Subsequently, the CDs were linked to the solid supports. In 1979, Harada etal. [22] polymerized and crosslinked a CD with a gel support, and the CSP developed was tested for the chiral resolution of mandelic acid and its derivatives. Various workers have subsequently bonded all three CDs with different solid supports [23-33]. Of course, these CDs bonded to gel support have been used for the chiral resolution of different racemates, but they suffer from certain drawbacks because of their poor mechanical strength and efficiency in both GC and HPLC. An improvement to these... 

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