Solid-phase extraction INDEX

Ginkgolide A, B, C, and bilobalide in G. biloba leaves were determined simultaneously by RP-HPLC-ELSD. Methanolic extracts (10%) of the leaves were cleaned up by solid phase extraction via polyamide cartridge and silica gel cartridge, successively. RP-HPLC was carried out on a Cl 8 column with Me0H-H20 as mobile phase, eluted in gradient mode, and detected by ELSD. The poor linear response of ELSD could be compensated by multilevel calibration and logarithmic calculation. Meth-anol-water-orthophosphoric acid mobile phase was used in conjunction with refractive index (RI) detection. 

The relative PLMA MW was determined by using nonaqueous SEC with THF as solvent and an HP1037A refractive index detector from Hewlett-Packard. A solid-phase extraction cartridge (Waters Sep-Pak) was used to take the PLMA and surfactants from the water phase to THF and to adjust the concentration for SEC. Sodium sulfate was used to dry the THF extract before injection into the SEC columns. For some samples there was too much surfactant present, and it overloaded the cartridge in such cases ion-exchange beads were used to reduce the concentration of the ionic surfactants in the aqueous phase before extraction. The advantage of this extraction procedure is its simplicity. The overall separation scheme is shown in Scheme I. 

The sensitivity of a GC/FTIR system depends on the type of interface and the molar absorbance index of the analyte. Comparative studies of the three interfaces have shown that the highest sensitivity is achieved with the DD interface. In general, the limit of detection (LOD) of the hght-pipe GC/FTIR is about 10 ng on-column, while, the LODs of the DD/FTIR and MI/FTIR are 35 and 100 pg, respectively. In practice, the LODs of analytes in real samples are of the order of 0.5-25 ng on-column. To enhance the sensitivity of detection, additional clean-up and preconcentration methods are applied, such as head-space sampling, purge and trap, solid-phase extraction, and solid-phase micro-extraction. It would also be possible to achieve improved sensitivity by modifications of other parts of the analytical procedure, such as the use of large-volume sampling methods. 

Analytical conditions A solid-phase extraction silica cartridge is used to separate the nonpolar components by elution with petroleum ether diethyl ether (90 10) and the polar components with diethyl ether. The polar components are resolved by HPSEC on 2 columns in series of highly cross-hnked styrenedivinylbenzene copolymers, using tetrahydrofuran as mobile phase and a refractive index detector. 

More specific and sophisticated methodology has been developed recently to elucidate how lipid oxidation products and other bioactive compounds act in the complex mechanism of LDL oxidation. A large amount of work has been published recently on the GC-MS or LC-MS analyses of cyclic oxidation products of arachidonate described as isoprostanes in biological samples as an index of oxidative status. Because the level of arachidonate in LDL and blood is relatively small (Table 13.2), much effort has been made to use instrumental means to improve the sensitivity required to analyse isoprostanes. This instrumental approach is still beyond the capability of many laboratories, however. LC-MS has the advantage of direct measurements of isoprostanes in contrast to GC-MS (see Chapter 6), which requires the use of two or three thermally stable derivatives. On the one hand, LC-MS still requires purification by reversed-phase solid-phase extraction, followed by TLC to remove impurities, but this step can also be avoided if one can invest in a highly selective MS/MS system. On the other hand, the well-established methodology to measure oxidation products of linoleate, which is present in LDL at levels about seven fold higher than that of arachidonate (Table 13.2), is much more within the capability of many laboratories than the more expensive LC-MS and GC-MS and MS/MS approaches required for isoprostanes. 

MSFIA exploiting solid-phase extraction for the determination of the total phenolic index. Detector spectrophotometer HC holding coil IV injection valve R reagent RC reaction coil V solenoid valve. 

The refractive index responses of various sugars (NeuAc, Glc, Gal, Fuc, GlcNAc, maltose, maltotriose and maltotetraose) eluted from a cadon exchange resin colunm (H - form, acidic eluant) were shown to be proportional to the mass injected and their molecular mass. A method to rapidly monitor glucose, fructose, sucrose and maltose in fermentation broths involved solid-phase extraction of interfering substances and h.p.l.c. on a polyamine column with refractive index detection. ... 

SD standard deviation SDE simultaneous distillation extraction SDS sodium dodecyl sulfate SFC solid fat content SFI solid fat index SHAM salicylhydroxamic acid SIM selected ion monitoring SNIF-NMR site-specific natural isotope fractionation measured by nuclear magnetic resonance spectroscopy SP-HPLC straight-phase high-performance liquid chromatography... 

Extract the aqueous phase with six 250-m portions of methylene chloride wash the solid cake with three of the portions prior to their use on the solution. Dry the combined extracts over 40 g of anhydrous magnesium sulfate and inhibit with 0.5 g of hydroquinone. Remove the drying agent by filtration and strip the methylene chloride by distillation at atmospheric pressure remove final traces of this solvent by stripping at 20 mm pressure and room temperature. Then separate the mixture of crude vinyl isomers by distillation at reduced pressure. By heating to a pot temperature of 90°C, the 2-methyl-5-vinyltetrazole is conveniently and almost completely removed at 1.0 mm pressure. A well cooled condenser and a receiver chilled in an ice-water bath are needed to prevent loss of the condensate. The weight of once distilled 2-isomer is 89.9 g the index of refraction at 25°C is 1.4814, corresponding to a purity of 97.2 percent. The corrected yield amounts to... 

The general objective, principle, and scope of application of the pT-method are succinctly described in Section 1 and also reported elsewhere in this book (see Chapter 3 of this volume, Section 5.1), where readers will appreciate that this hazard assessment scheme is adaptable to both liquid and solid media. Briefly recalled here in the context of solid-media samples such as dredged material, the pT-value, which relates to a single bioassay, and the pT-index, derived from the most sensitive organism in a test battery, permit a numerical classification of environmental samples on the basis of ecotoxicological principles. Sediment from any aquatic ecosystem (freshwater, brackish, marine) and from any of its phases (whole sediment, porewaters, elutriates or organic extracts) can be appraised provided that the proper standardized toxicity tests are available. There are whole-sediment test protocols standardized for many agencies (e.g., Environment Canada, ASTM). 

---