Column efficiency high-speed

Development of short monolithic silica columns with high efficiencies (up to 200.000 plates per meter) and high-speed separations, performance parameters that can be obtained with column packed with sub-2 pm particles, but achieved with monolithic silica columns at very lower system back-pressure. 

High efficiency columns currently available for gel permeation chromatography of small molecules and oligomers provide high speed separations. The use of multiple detectors provides additional information which facilitates characterization and determination of the separated species. 

ELEVATED TEMPERATURE HPLC FOR HIGH-SPEED SEPARATION-EFFECTS ON VISCOSITY AND COLUMN EFFICIENCY... 

The situation described in Equation 9.1 is reversed at a reduced temperature. The overall column efficiency decreases rather dramatically for most samples, but successful separations are still practical with the correct choice of parameters. The reduced longitudinal diffusion in the first term means that the optimal flow rate shifts to lower flow rates. The increased viscosity of the mobile phase requires lower flow rates as well. While at high temperatures one often operates the HPLC at flow rates many times the optimal value, in subambient work, it is best to sacrifice speed and work close to the optimal flow rate. 

Improved separation of natural oil TGs using short columns packed with 3-//m alkyl bonded-phase particles was reported by Dong and DiCesare (88). The HPLC columns used were HS-3 high-speed columns packed with 3-/um C18 bonded-phase particle (100 X 4.6-mm ID) with a column void volume of ca. 0.8 ml and efficiencies in the range of 13,000-15,000 theoretical plates (measured under optimized conditions) and HS5 C,8 columns (125 X 4.6-mm ID packed with 5-yttm particles). Two detectors were used a modified refractive index detector having an 8-/rl flow cell and 0.007-in. ID inlet tubing and a variable-wavelength UV/visible detector. 

Modern HPLC techniques have resulted in a spectacular improvement in speed, resolution, and sensitivity. Separation times in HPLC are usually short, mostly in the interval of 10 - 20 min, with simpler separation problems being carried out in less than 10 min. This is due generally to the use of stationary phase that consists of very small and uniform porous particles with high ligand density. These conditions lead to better mass transfer and higher column efficiency. Consequently, high-performance separations can be obtained in short times (5). 

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