absorbance

Your assumption in the experiment is that the absorbance is directly proportional to the concentration of species of interest. This is true if the wavelength of light u used(by choosing suitable filter) is only absorbed by the interested species.
If you used a wrong filter, other chemical species would contribute to the absorbance, or that, your interested species would not absorb that wavelength, so your assumption is not valid, the absorbance then cannot reflect the concentration of ur interested species.

我諗呢...
如果你用錯filter ge話..
可能會量錯ga..
要小心d喎...
我就冇用錯過..
唔係好知...
但係我諗...
我冇估錯ge...
信我啦=]