Determination of J‐Type Centrifuge Extra‐Coil Volume Using Stationary Phase Retentions at Differing Flow Rates

Abstract

An alternative method for determining the extra‐coil volume (V _ext) of a J‐type centrifuge and its ancillary equipment is given based upon displaced volumes of stationary phase. The extra‐coil volume (V _ext) is determined by plotting the volume of stationary phase displaced from the coil and extra‐coil volume combined (V _E ), against the square root of the mobile phase flow rate. The extra‐coil volume is the intercept on the V _E axis for a zero flow rate of mobile phase. This extra‐coil volume is then used to produce a stationary phase retention characteristic where the intercept on the retention axis is 100% for a zero flow rate of mobile phase. Experimental evidence was gained for a heptane–ethyl acetate–methanol–water (1.4:0.1:0.5:1) v/v phase system, in normal phase mode using three helical stainless steel coils. The internal diameters of these coils were 3.73 mm, 5.33 mm, and 7.73 mm. Retention studies were conducted at rotational speeds between 600 and 1200 rpm. The same phase system was also tested in a multi‐layer PTFE coil in reverse phase mode at a rotational speed of 800 rpm. The internal diameter of the tubing for the PTFE coil was 1.6 mm. All of the coils used were fitted to a J‐type centrifuge with a rotor radius of 110 mm. These retention studies allowed the extra‐coil volume to be tested under conditions of different rotational speeds and coil tubing internal diameters. It was also tested using different tubing material, and in both normal and reverse phase modes.

Keywords:

• Countercurrent chromatography
• Extra‐column volume
• Fundamentals
• Liquid stationary phase retention

Acknowledgments

The authors of this paper would like to thank the following scientific funding bodies for financing this research: INTAS (Contract No. 000/00782) and EPSRC (Contract No. GR/R03143/01).

Notes

^aThe PTFE coil used with the syringe driver had a volume of 95.9 mL, a 1.59 mm bore, a length of approximately 48.5 m and a β-value range 0.816–0.845.

^bMicrosoft Excel was used to plot the results for extra-coil volume, fit linear trend lines and determine the equations of the fitted trend lines.

^cMicrosoft Excel was used to plot the results for retention, fit linear trend lines and determine the equations of the fitted trend lines.