Measurement of the distribution of time intervals between cell passages in flow cytometry as a method for the evaluation of sample preparation procedures

It is expected that the time sequence of cells passing through the sensing region of a flow cytometer should follow the statistics of a Poisson process. Thus, measurement of time intervals between passages of fluorescent microspheres and cells stained with mithramycin demonstrated the negative exponential distribution characteristic of such a process. However, analysis of cells stained with fluorescein-iso-thiocyanate showed marked deviations from a negative exponential distribution of time intervals. The distribution had an additional component due to time intervals with mean value about 60 times shorter than the population mean, and in certain cases more than 50% of the cells were registered with such short time intervals. This percentage could, however, be reduced to acceptable levels by modifications of the sample preparation procedures. Measurement of the distribution of time intervals between cell passages is proposed as a method for the evaluation of possible improvements in sample preparation procedures.