I'm trying to identify an organic compound from a 48-hour-old bacterial broth culture. To do this, I need to remove the sugar and then purify the sample using C18 cartridges. However, the C18 cartridges left my sample very sticky, so I used ethanol precipitation. Unfortunately, this method doesn't remove all the sugar effectively. Is there a better way to remove the sugar efficiently before using the C18 cartridges?