Hitachi CHROMASTER 5160, Instruction Manual

Page: 448 / 1022

2.3.2 Advantages of fluorometry
For verifying the advantage of fluorometry, the limitation of
absorbance measurement in its application to low-concentration
samples is explained first.
In this discussion, we will consider the detection of a sample that
has a transmittance of 99% (relative to the blank). If we
assume that the inaccuracy of the % transmittance measurement
is 0.1%, the reliability of the observed data is as follows:
Percent transmittance of blank
Percent transmittance of sample 100.0
±
0.1%
99.0
±
0.1%
Difference (proportional to concentration of sample) 1.0
±
0.2%
In this example, the uncertainty in the concentration
measurement is
±
20%. In contrast, in fluorometry, a difference
in the signal is directly proportional to the concentration of
sample.
An analysis of the error in the measurement is as follows:
Output signal level at measurement of sample
Value corresponding to blank 100
±
0.1
0
±
0.1
Difference (proportional to concentration of sample) 100
±
0.2
As is evident from this example, the error percentage by
fluorometry is not dependent on sample concentration
theoretically, so this method is very advantageous for low sample
concentrations.
In actuality, some error factors will increase relatively as sample
concentration falls extremely, but it can generally be said that
fluorometry is capable of detecting concentrations at least 3
digits lower than by absorptiometry.
2 - 8