My two cents: We did a comparison of integral vs peak measurements and integral vs width measurements --- to discriminate G2M cells from doublets on a FACSCalibur. I believe this instrument has a 20 micron beam width -- and the integral vs width comparison showed excellent discrimination between G2M cells and doublets, but the integral vs peak discrimination was poor (presumably because, if the doublet is entirely in the laser beam at some point in time, its peak height will be identical to that of a G2M cell when it is entirely in the laser beam). For comparison, we also looked at integral vs peak measurements on a Coulter bench top instrument --- and got good discrimination of G2M cells from doublets. The Coulter instrument has, I believe, a beam width of 10 microns and this makes, as Nick Terry says, a big difference in the value of the peak value for aggregate discrimination. Because the Coulter instrument that we were using did not display a width parameter, we had no way of comparing integral vs peak with integral vs width discrimination on this instrument. Alice Alice L. Givan Englert Cell Analysis Laboratory of the Norris Cotton Cancer Center Dartmouth Medical School Lebanon, New Hampshire NH 03756 tel 603-650-7661 fax 603-650-6130 givan@dartmouth.edu
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