IN a recent communication given by Amos and Hurrell1, the authors stated that it was difficult to obtain high efficiencies or adequate resolving power, when packed 0.25-in. external diameter (4 mm internal diameter) analytical chromatographic columns were used in association with thermal conductivity detectors. It was suggested that by using narrower bore columns and capillary restrictions at the end of the column the efficiency could be improved, an effect that had been demonstrated by Scott2 some time earlier.