FAQ for colorimetry
Question - I have
two Model 254 colorimeters and when I put the same solution in each, even
after blanking, why do I get different results?
Answer - This
is because each instrument and particularly each filter have slight
differences in the way they pass the light through . You must therefore,
for quantitative work , not only blank the colorimeter, but a standard of
known concentration must be measured and the absorbance of the unknown
sample be measured and compared with that of the standard.
( When blanking ( zeroing), the cuvette ,which will be used for
measuring the standard and samples, should be filled with the solvent
(usually water)that is to be used for the sample and standards (including
all other reagents except the sample and standard substance). The cuvette
is placed in the cuvette holder and the absorbance is set to 0.00 (0.000
for the Model 257) by adjusting the coarse and fine controls
Question - How do I choose the correct wavelength filter for my
Answer - If you are using a commercial kit of
chemicals to perform an assay the kit manufacturer will give the
wavelength in the kit "insert" or instructions.
If you are developing a new method and want to measure the
concentration of a substance only at one wavelength then perform a
spectral scan of the susbstance under investigation on a spectrophotometer
to determine the wavelength of maximum absorbance.
Determine how broad the wavelength peak is at half peak height.
If it is less than 10nm then choose an interference filter with the
wavelength the same as the peak
If it is > 20nm then you could choose a gelatin filter with a
wavelength within 10nm of the peak wavelength.
If you have no spectrophotometer available then choose a filter of
For further information see our technical help
Question - How long does a bulb last
Answer - About