If flow rate is high, and we are studying minimal concentration particles, what should we do to detect it?

You balance the flow rate with the sample concentration. Both of these two factors affect the rate at which the particles pass into the flow cell. If the sample is very dilute, you raise the flow rate to balance it out. If it’s too dilute, concentrate your sample. Within this balance, the higher the flow rate needs to be, the higher the CVs.