43
Performing and Evaluating Measurements
Points to be Observed when Performing Measurements
Sample concentration
For correct measurement results, the concentration of the diluted cell suspension in the CASY cup
should not exceed certain maximum values. The concentration limit depends on the size of the
measuring capillary:
150 µm measuring capillary:
< 20 000 counts/ml
60 µm measuring capillary:
< 100,000 counts/ml
45 µm measuring capillary:
< 250,000 counts/ml
Higher concentrations than specified can result in
coincidence errors
, due to an increased
probability that two particles will be in the measuring pore at the same time. The CASY System will
evaluate two particles being in the measuring pore at the same time as if they are a single particle
with a correspondingly larger volume. The calculated particle count will therefore be too low and the
size distribution will shift towards the larger volumes.
Coincidence limits do not depend on the positions of your evaluation cursor settings. They are
always determined for the entire physical measuring range of the measuring capillary being used
(approx. 2% to 80% of the measuring pore diameter). In the case of cell samples, this includes
cell debris as well as cell aggregates with a diameter above the scaling range selected for the size
axis (X-axis). These coincidence limits guarantee that the cell counts and cell volumes are always
measured correctly.
You are not required to verify whether the concentration of your samples is too high. The CASY
TT displays the following warning message when the coincidence limit values indicated above are
exceeded.
ERROR SCREEN
TT-2AB-9999 15.04.2009 10:15
Concentration too high !
Please dilute your sample
Measured Counts/ml : 34345
Max Counts/ml allowed : 20000
Further information will be
Provided by your manual!
USE ENTER TO CONFIRM.
PRESS CLEAN TO FLUSH THE LIQUID SYSTEM.
You must confirm this message by pressing
ENTER
. The measuring result is displayed, but the
ConcRng
parameter is shown as
Too high
. To obtain valid measuring results for cell counts and cell
volumes, you must dilute your sample appropriately before repeating the measurements.
