Small sucrose density gradients: reproducible and automatic fractionation using a commercial fraction collector (Pharmacia). 
A simple, inexpensive modification of a programmable commercial fraction collector (Frac 100; Pharmacia, Sweden) was described.  This modification allowed reproducible automatic fractionation of small sucrose gradients by rinsing the hanging drop at the delivery head of the fraction collector into the sampling tube, using signals from the fraction collector to control this specialized function.  The described principle may also be useful whenever fraction size is near to drop volume and high resolution and reproducibility are desired.