For flow cytometry analysis, the minimal volume of sample required is 0.5 ml; the optimal concentration is between 0.5-1 x 106 cells per sample. Bring the resuspended cells in Falcon 5 ml 12 x 75mm polystyrene round-bottom tubes (BD Falcon cat. number 352054). Samples must be in a single cell suspension. If they are not, you run the risk of clogging the instrument since the tubing and nozzle through which the cells pass is very narrow.
Basically, if you see clumps or aggregates of cells and/or debris in your sample, it will not run properly. Adding 1mM EDTA should prevent the formation of cell clumps. In order to remove clumps or aggregates, the sample should be filtered prior to running. We recommend using Falcon 5 ml polystyrene round-bottom tubes with cell strainer cap (BD Falcon cat. number 352235).