Fraction Collector

Overview

A fraction collector parks at the outlet of a chromatography column and catches the eluate, splitting one continuous stream into a sequence of separate tubes. As a sample runs through the column its components leave at different times, and the collector's job is to capture each band in its own tube so it can be analyzed or pooled later. It is a fixture of protein purification, peptide and small-molecule chromatography, and any prep run where the separated fractions are the product.

The collector decides when to switch tubes by one of several rules. It can change on a fixed time interval, after a set number of drops or volume, or, wired to the detector, exactly at the start and end of each absorbance peak, so each tube holds one component and the gaps go to waste.

How it works

The tubes sit in the Rack Drive, a carousel a geared stepper indexes one row at a time under the arm, registered by a home sensor so every position is addressed by count. Over it the Dispensing Arm places the nozzle on the target tube: ball-screw X and Y axes carry the dispense head across the rack on linear guides, dropping the eluate stream precisely into each tube in turn.

Clean fraction boundaries need two things working together. The Drop Sensing & Diverter group reads an optical drop sensor that confirms flow and counts drops, and switches a diverter valve that sends the stream to waste during a tube change so nothing spills between positions. The eluate itself travels through inert Eluate Tubing from the column to the nozzle.

The collection rule lives in the Control Electronics, a microcontroller board that sequences the rack and arm to each position and times the diverter by clock, drop, volume or peak signal. The operator picks the rack, mode and parameters on the Operator Display, and the Enclosure encloses the mechanism over a drip tray that catches overflow and diverted waste.