AN ELECTRICALLY-HEATED COLD TRAP INLET FOR HIGH SPEED GC.

摘要

The development of an electrically-heated cold trap for WCOT columns is described. Two heating methods, one involving a high-current transformer and the other using a capacitive discharge system, are experimented with. While more efficient heating is demonstrated with the discharge method, good results are obtainable with the transformer. Either method can reinject bands 15 ms wide at half-maximum.;Arrival times and band widths of solutes reinjected directly from the cold trap to the FID are determined under a wide variety of conditions. The necessity for rapid heating of the trap is demonstrated. Efficient heating reduces boiling point discriminations, narrows the bandwidths of reinjected peaks (down to the limit set by diffusional broadening) and increases the precision of arrival time measurements. Choice of carrier gas (hydrogen or helium) does not greatly affect either arrival time or peak width. Heating the downstream electrode also reduces boiling point discrimination, but heating of the upstream electrode has very little effect. Measurement of the solute transit time between the trap and detector has an accuracy of about 10 ms (1 standard deviation).;A study of 5 different 0.5 mm i.d. column lengths (1, 2, 3, 5.6 & 11.6 m) shows identical values of H for flow rates ranging from 20 cm/s to over 200 cm/s. The short columns give same number of plates as the longer columns for fast (3-5 s) analysis times, but for slower analyses (20-50 s) the longer columns offer more effective theoretical plates even though the required flow rates are higher. Several examples of high speed separations are shown. Among these is a separation of pentane, hexane, heptane and octane in about 1 s and a separation of 9 aromatics and alkanes in under 7 s.;Detailed parametric studies of the cold trap are presented. Trapping efficiency is studied varying trap diameter, carrier gas, flow rate and the temperature of copper electrodes which connect the trap to the heating source. The best results are achieved for the narrower bore trap, 0.5 mm i.d., with hydrogen as the carrier gas. Trapping efficiency decreases with increasing flow rate, although at a helium flow rate of 200 cm/s 95% of the sample is trapped. Heating the upstream electrode has a detrimental effect on trapping efficiency, while heating the downstream electrode has no effect.