A new approach for the indirect determination of cell concentration in the
case of nonconstant metabolic rates has been developed. The specific glucos
e-uptake rate was shown to be nonconstant in batch cultures of free suspend
ed and immobilized CHO SSF3 cells. Time-independent models correlating the
specific rate to the limiting substrate concentration were established, thu
s providing a continuous determination of the specific rate through on-line
measurement of the limiting substrate. The method could be applied to dete
rmine online cell concentration in both free suspended and immobilized cell
cultures. Results were verified off-line by crystal violet nuclei counting
. The predicted cell concentration was in very good agreement with the off-
line reference during the whole exponential-growth phase, until the specifi
c glucose-uptake rate tended to zero. (C) 2001 John Wiley & Sons, Inc.