I have mixed some particles in oil. And have taken the UVis of the sample after regular intervals in three different positions. On x-axis is "absorbance" and y-axis is "wavelength". The absorbance level decrease initially but after some time the absorbance level increased. Does the increase in absorbance level indicate agglomeration of the particles?
Higher AU would in general imply bigger particles, but it depends on the wavelength range you are considering. At low wavelength there will a maximum for AU as a function of particle size. You might find this text helpful:
http://www.chem.agilent.com/Library/applications/5989-8805EN.pdf
Pieter
"The absorbance level decrease initially" what is the value? Is it negative?Hope you are measuring in double beam machine. If so what is your standard in each measurement! Please consider the wavelength also.
Hello Sir,
As far as I am aware of, UV-Visual Spectroscopy uses ultra violate rays to catch the ultra-violate spectral region. Thus wherever the particle quantity or particle size is greater, the graph will rise along the absorption axis representing the presence of higher volume of particles, thus the rate of absorption in that region is higher. This goes with the theory that absorption rate increases with the presence of higher quantity of particles and decreases with the decrease in particle quantity.
I hope this helps.
What you did is to obtained the UV-visible spectrum of your mixture, the wave of length has to be with how much energy was absorbed at this wave of length, it has to be with the electronic distribution of the compounds in your sample in specific the electrons of the outer shells, that are in the bonds of your sample, I do not know what was the composition of your sample or the type of oil employed, but you can see that the wave of length at which the absorbance was higher, is may be the color of your sample. This technique is useful to study the structure of the substances, and sometimes to characterize the products of a reaction qualitatively and quantitatively. Well I think it will give you an information, if you show me the spectrum I can give you more information.
have you considered - sedimentation of particles (initial reduction of absorbance) and dissolution (increase). We do not know your systems chemical composition.
Mr. Bhaumik,
There is not clear from the description where is the chromophore absorbing electromagnetic light within UV-VIS spectroscopic region - in the molecules of the particles (solute) or in the oil (solvent). Because due to different solute-solvent interactions your observations can originate due to different driving forces. Second very important aspect is about the solubility of your particles in the oil.
Despite those comments, let us assume that your chromophore is in particles. If yes, than decreasing in intensity of absorption maximum (A) means exactly aggregation. Have you well defined isosbestic points and how is their number? Please pay attention to the attachment, in spite of, described equilibria in solution.
If you have only decreasing in the intensity, without well defined isosbestic points, than we can further assume that it has a sedimentation of aggregates with increasing in their size. This would also agree with your results. If with time your aggregates start dissolve in oil, that this would explain why you have increasing in intensity finally.
Please bear in mind that you could have "aggregates" between the dissolved molecules, too, depending of the molecular scaffold and chromophore type of your solute molecule, having different UV - profile of an isolated molecule in diluted solution.
- Badges
- Science topic
- Similar topics
- Engineering
- Petroleum Engineering
- Oil