Simplified ultrasonically- and microwave-assisted solvent extractions for the determination of ginsenosides in powdered Panax ginseng rhizomes using liquid chromatography with UV absorbance or electrospray mass spectrometric detection.

New approaches for the recovery of ginsenosides are presented that greatly simplify the liquid chromatographic (LC) determination of the total content of eight ginsenosides (Rb1, Rb2, Rc, Rd, Re, Rf, Rg1 and Rg2) in powdered Panax ginseng rhizomes. The extraction protocols not only recover the neutral ginsenosides, but also simultaneously incorporate base-catalyzed hydrolysis of the malonyl-ginsenosides using dilute potassium hydroxide added to the methanol-water extractant. This eliminates the need for an independent extraction step followed by acid- or base-catalyzed hydrolysis. Both ultrasonically-assisted and microwave-assisted extraction methods are developed. The optimization of these simplified methods to remove pendant malonate esters, while retaining the glycosidic linkages, was determined by LC through variation of the extraction/hydrolysis time, order of hydrolysis reagent addition, and evaluation of multiple extractions. A comparison of the ginsenoside profiles obtained with and without addition of base to the extractant solution was made using LCMS with positive-mode electrospray ionization (ESI(+)) detection. A number of malonyl-ginsenosides were tentatively identified by their mass spectral fragmentation spectra and indicating that they were converted to the free ginsenosides by the new extraction/hydrolysis procedure.

Application of capillary electrophoresis to predict crossover frequency of polystyrene particles in dielectrophoresis.

CE is used to calculate the zeta potential of polystyrene particles in order to estimate the surface conductivity of the particles. These values are used to predict the dielectrophoretic behavior, including the crossover frequency of particles under the influence of an AC electric field. Predictions for fluorescent polystyrene particles that are unmodified, carboxylate-modified, or streptavidin-modified are tested using miniaturized dielectrophoresis cells containing patterned gold quadrupole electrodes. The particle surface conductivities derived from CE separations differ from those derived from dielectrophoresis experiments by < or =0.003 S/m and serve as a guide to effectively select the suspending medium to generate a crossover frequency approximately 0.5 MHz. Prediction of dielectrophoresis crossover frequency is limited by several factors, especially the accuracy and precision of the conductivity measurements for the particle and suspending medium. A rapid analysis of particles by CE is a viable alternative to determine zeta potential.

Electrophoretic screening of ligands under suppressed EOF with an inert phospholipid coating.

The applicability of dual injection CE for affinity selection of biopolymers that contain multiple binding sites is demonstrated. The efficient analysis of biomolecules such as carbohydrates and proteins, as well as pharmaceuticals by CE requires the reduction or elimination of nonspecific interactions with the capillary surface. Phospholipids are integral components of cell membranes and aqueous phospholipid liquid crystals adopt a bilayer structure on fused-silica. This phospholipid surface does not interact significantly with the following biomolecules: serum albumin, the 96-110 heparin binding domain of amyloid precursor protein (APP), polydisperse glycosaminoglycans, and variable chain-length oligosaccharides. Pharmaceuticals including five anionic nonsteroidal anti-inflammatory drugs, three cationic analgesics, and two cationic beta-blockers, also show minimal interaction with the surface. In addition, the use of a phospholipid coating suppresses EOF, which enables reversed-polarity separations, dual opposite injection CE, affinity screening via CE by dual opposite injection, and serial target-ligand injections.