I am trying to do a UV-Vis diffuse reflectance measurement using a Perkin Elmer Lambda 750 instrument. Do you have experience with the instrument set up, where and how to put the sample in the holders, what should be used for back ground correction.
I try but could not contact Perkin Elmer for a training.
I attached a photo of the sample compartment for your reference. Please advise!
Hi,
In my understanding, you need to make a circular pallets of ur sample. So, mix the sample in the matrix powder (i think normally BaSO4 is used). Mix it well, and place it in pallette maker. Apply pressure to mak a nice citrcular pallette. This pallette can then be placed in the sample holder. and the sample holder can then be placed in such a way that the sample is facing towards the light in/out side.
This is what I uknow about Diffuse UV-Vis. I apologize in advance if this is not what you asked. Last time I used Diff. UV-Vis was 14 years ago! And definitely not on this perkin instrument.
By the way, for back ground correction, you would use a similar pallette made ONLY of BaSO4 (or any other matix powder you choose). So ur background or reference measurement will be the BaSO4 pallete WITHOUT sample.
Hi,
You need to use a special accessory for Lambda 750 - integrating sphere.
http://www.perkinelmer.com/Catalog/Category/ID/Integrating%20Spheres
http://www.perkinelmer.com/CMSResources/Images/44-74449BRO_LAMBDA-750-UV-Brochure.pdf
It is much easier life =)
To Sandeep: Thank you very much for your suggestion. I will read about the sample preparation with BaSO4.
To Victor: Currently we have the 60 mm intergrating sphere as in attached photo. But we have not get any training about how to set up and use it. Could you please suggest me how to prepare sample and how sample is place into that 60 mm intergrating sphere.
Thank you all, very much!
Hi,
If you want to use the integrating sphere, you might not need to do sample prep with BaSo4.
I have worked a lot with integrating and double-integrating spheres in general, and this is how it works.
In integrating sphere, one places a thin layer of sample in a glass/quartz cuvette such that it covers the sample entry port of the integrating sphere completely. Integrating sphere offers the option of measuring DIFFUSE reflectance/transmittance. For diffuse reflectance measurement, you allow the light beam to enter from the port almost at 180 degree to the sample port, such that the collimated light travels in a straight line in the integrating sphere and then falls onto the sample. As one can imagine, a portion of light falling onto the sample will get reflected back through refraction within the sample. And this will be the DIFFUSE back scattered light. This will fall onto the walls of integrating sphere and will homogeneously diffused by multiple reflections within the integrating sphere. And you will find a detector port in the integrating sphere so that you can collect the diffuse light in the integrating sphere onto the detector.
It is worth to look at some work published by Prof. Scott Prahl (father/inventor of this tech). http://omlc.org/software/iad/
One good reference to start with: http://omlc.org/~prahl/pubs/pdfx/pickering93a.pdf
Hi Sandeep and Victor,
Thank you for your comments and advice. Could you please help me with more practical detail on instrument set up. Below is the plot of my instrument set up. I just wonder where to place my sample and reference sample for baseline correction. Could you please advise!
The accessories available are: 1%, 10% attenuators; 8 degree wedges, 2 piece SRS 99% standards and a accessory for variable angle dissuse reflectance.
Hi Sandeep,
Thank you for your advice. I will try that set up and revert to you.
Thank you!
-Mer-
Hi,
I tried to measure by following approach:
- Use two spectralon standards for 100% bright baseline.
- Sample preparation: load a few drops of saturated solution on filter paper, let solvent evaporate, then measure.
The spectrum is as attached (first graph). It appears to be inverted (with respect to solution absorption).
In reported paper, i often see people present diffuse reflectance in graph of Absorption-Wavelength (second graph). May i ask how to convert the %R to kind of absorption? Is there anything to do with the Kubelka equation? Thank you very much!
I read some materials, they say take Abs = log(1/reflectance of sample*reflectance of standart). Please advise!
By the way, All we need is to observe the lowest energy UV-vis absorption band in solid state, so that we can conclude about the possibility of low energy electronic transition induced by solid-state packing such as pi-pi interaction or metal-metal interaction.
Thank you!
I am not sure if i understood completely how you got the spectra shown in the figure. But this is what is the standard procedure:
1. In the beginning, you measure dark current (physically obstruting the detectors so tht no light falls onto them. This is ur electronic noise. Lets call it Dark.
2. u measure the reflectance of the standard. Lets call it R_std.
3. u measure ur sample in refletance mode.Lets call it R_sam.
4. now ur net reflectance (R_net) from the sample is calculated as:
R_net= (R_sam - Dark)/(R_std - Dark)
5. this is similar procedure either from a transmittance or a reflectance measurement.
6. Now absorbance (A) can then be calculated as:
A = -log(R_net)
OR
A = log(1/R_net)
Both are the same formulas.
7. Once you have calculated A, plot it against wavelength (x-axis).
Good luck!
By the way, I am a bit surprised that you use integrating spheres for the application you just mentioned. I would think that there should be a simple reflectance measurement setup. But may be this is how it is in ur instrument. May be ask Victor who suggested using integrating sphere. He might comment on it better.
Thank you very much Sandeep. Yes, the instrument is just like that and you two helped me with sample/blank configuration so i follow to measure.
Thank you. I will try with both 100% and 0% baseline tomorrow.
Dark correction should not be necessary as you use a reflectance standard such as BaSO4. We always just measure reflectance of sample and of standard and divide the former by the latter.
An integrating sphere is not a must, but more reliable/precise as it minimizes the influence of sample preparation and morphology.
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