Packed column preparation coating methods

Bicchi and Bertolino [193] analyzed a variety of pharmaceuticals for residual solvents. Samples were equilibrated directly or dissolved in a suitable solvent with a boiling point higher than that of the residual solvent to be determined. Equilibration conditions were 90 or 100°C for 20 min. A Perkin-Elmer HS-6 headspace sampler was used. The chromatographic phase chosen was a 6 x Vs in. column packed with Carbopack coated with 0.1% SP 1000. Residual ethanol in phenobarbital sodium was determined by a direct desorption method. An internal standard, /-butanol, was used. Typically, 0.44% of ethanol was detected (compared to a detection limit of 0.02 ppm). The standard deviation of six determinations was 0.026. Pharmaceutical preparations which were analyzed by the solution method included lidocaine hydrochloride, calcium pantothenate, methyl nicotinate, sodium ascorbate, nicotinamide, and phenylbutazone. Acetone, ethanol, and isopropanol were determined with typical concentrations ranging from 14 ppm for ethanol to 0.27% for acetone. Detection limits were as low as 0.03 ppm (methanol in methyl nicotinate). 

However, it is still unclear how the efficiencies and resolutions of MIP monoliths compare to other methods of capillary fabrication using molecularly imprinted polymers. Future studies that directly compare the chromatographic results obtained using the same imprinting system under different preparation techniques (i.e., packed columns, coated thin films, immobilized particles, and monoliths) have... 

The stationary phase in LLC can be prepared in different ways, depending on the support particle size chosen. An often-applied preparation technique is the in situ coating method. In this case the stationary phase liquid is pumped through the dry packed (slurry packing) column. Later, the column is flushed with mobile phase to displace excess stationary phase liquid between the particles. 

Extensive experience of the preparation of bonded-silica columns for CEC has suggested to us that all packing methods have similar problems associated with the fragility of the fused-silica tubing material, especially at the Mt and detection window, where the polyimide coating had been removed. A less commonly met effect is the production of loosely packed silica particle beds with voids, giving rise to unstable currents. Approximately 70% of capillaries could be successfully packed by an experienced operator, with approximately 80% of packed and tested columns giving satisfactory CEC [23],... 

The methods of column packing preparation well known in gas chromatography practice [24] give the possibility to coat the silica gel surface with the monolayer of a given surface concentration or with the monolayer in SC state with a well-defined threedimensional excess if the specific surface area of adsorbent is known. On the other hand, inverse gas chromatography allows to determine the specific surface area of silica gel if aliphatic alcohol is used as a liquid stationary phase [25]. 

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