You need to establish the time required for the sample to travel between the detector and the fractionation tube. You can do this by knowing the length of the tubing, its diameter, and your flow rate. If this is difficult you can always inject something that has color such that you can establish what tube has more coloration, then you can relate the time required for you to observe the maximum in absorbance (in your online detector) with the tube with the brightest coloration. For this use short fractionation times. Hope it is clear what I am trying to say. 

 Hola Omar, soy una compañera de trabajo de Le Nurie. La cuestión es que aunque establezcamos los tiempos de recogida en función del flujo, no conseguimos recolectar la fracción en los intervalos que indicamos en el editor del método. Siempre nos recoge muestra periódicamente independentemente de los tiempos que hayamos establecido al inicio. Si pudieras ayudarnos te estaríamos muy agradecidas :)