Particle standards for reflected light scatter measurements from degenerate particle foci

A method of a standardization and/or a calibration of a flow cytometer having a first channel, the first channel having two or more particle focal points such that particles flowing through the first channel are focused at said two or more particle focal points, the method comprising:

• (a) for each particle type of two or more different particle types:
• (a1) for each particle focal point of the two or more particle focal points, determining, for a light beam directed at a particle of at least a first particle type or a second particle type at one of said two or more particle focal points from a first direction, a total intensity of scattered light along a second direction, wherein the first direction is a propagation direction of the light beam, and the second direction is within 90 degrees of the first direction, and
• (a2) determining, for the first particle type or the second particle type, a difference between a highest light intensity and a lowest light intensity of the light scattered along the second direction determined at the two or more particle focal points;
• and
• (b) selecting, based on the determined differences, as a standard particle type, the first particle type or the second particle type for which the difference between the highest light intensity and the lowest light intensity at the two or more particle focal points is below a predetermined threshold;
• and
• (c) using the selected standard particle type in the standardization and/or the calibration of the flow cytometer,
• wherein the scattered light along the second direction is reflected from the particle, refracted by the particle, and reflected from a lower surface of the first channel,
• wherein the flow cytometer comprises an inertial focuser upstream of the first channel, and
• wherein a lower surface of the first channel is opaque.