K. Weber, Concentration Curves
Hector Nolla (hector@soest.hawaii.edu)
Mon, 10 Apr 1995 10:48:42 -1000 (HST)
We have found that samples with a "high" count rate have lower
enumeration "correction" factors than samples with "lower" count rates.
Our best explanation for this phenomenom involves the electronic
processing of the various signals (from detection all the way to their
graphic display). This together with "dead volume" in your sample tubing
results in a non-specific loss of sample events. Our best solution for
dealing with this problem involves the use of bead(0.98um) and
bacteria(E.coli) standards. This known standards are diluted so that they
yield various count rates which are plotted against the
expected, theoretical, total yield of events, for
volume of sample analysed(Regression analysis). Interestingly enough, we
consistenly get different"correction factor" values for bacteria and bead
standards. (Bacteria correction factors are lower than beads which seems
to indicate that bacteria tend to "stick" to the sample tubing).
This difference can be pretty important if you are counting bacteria.
We routinly use the regression formula, from either of this to methods,to
individually correct each sample. We are open to comments or new insights
as to why for an equal volume of sample, total # of events displayed are
proportional to sample count rates. I hope this helps.
Hector Nolla
Dept. of Oceanography
University of Hawaii
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