According to the International Journal of Mass Spectrometry, knitted delay tubes KDT can be used in the following manner with mass directed prep chromatography:

Due to the low flow reaching the MS after the splitter relative to the high flow directed towards the collector or waste, a delay tube is placed between the prep UV and the fraction collector. The delay tube is designed to keep the eluent from reaching the collector valve too quickly, thus, allowing sufficient time for the flow directed to the MS to be analyzed and a determination to collect the sample or direct it to waste to be made.