I started with 5 g stick lac and 100 ml DI water and with magnetic stirrer i stir it and take sample at some interval of time put in UV VIS to get the abs vs wavelength graph. I want to know the concentration of lac dye in water with respect to time. But after 30 min of stirring solution i got the absorbance value more than 2 . So i have to dilute the sample. But problem i am getting here is the concentration is increasing as volume of water is decreasing since the diluted sample cant be again putted back in solution.
So you want to measure the solubilisation of your dye in function of time right ? Can't you start with less dye or more water ? Or you can use smaller UV cell for example 0.5 or 0.1 cm to reduce absorbance.
Yes you are right Nicolas.... Can you please let me explain more about your second suggestion... Smaller UV cell
Of course, absorbance is define as A = ɛ x c x l, ( ɛ : molar attenuation coefficien, c : concentration, l pathlength). With typical UV cell of 1cm, the pathlength of the light in the solution is 1 cm. If you use cell of a smaller pathlength you will reduce the measured absorbance. For example : Starting from an absorbance of 2 with a cell of 1cm, you will obtain 0.2 with a cell of 0.1cm for the same solution. Those cells are aviable commercially.
Absorbance 1 means 90% of the light at that wavelength is absorbed.
Abs 2 = 1%T (means 99% of available light is being absorbed).
Abs of 3 = 0.1% T (99.9% of the available light is absorbed by sample).
Reading above 2 is outside the meaningful range of most spectrometers which are available in the market
Meaningful absorbance range for most instruments is from 0.1 to 1.
Whatever you are measuring it looks like you are missing to consider dilution ratios in order to make a right judgement of your reading.
You can also use smaller cuvette
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