Chemical Forums
Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: HailoMan on January 03, 2012, 06:45:14 AM
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Hi,
I am using a short (1mm) path length quartz cuvette to obtain UV-Vis absorbance of carbon nanotubes (CNTs) dispersion in various organic solvents.
After filling the cell with the CNTs dispersed in acetylacetone and draining it, I noticed that the CNTs got stuck to the wall of the cuvette. I suspect whatever residue substance that is in the wall of the cuvette binds with the CNTs nicely.
I have tried a whole range of things from warm water + detergent, solvents (ethanol, acetone, NMP), 5M nitric acid, KOH + isopropanol (I know they will etch quartz, but I'm really running out of ideas), but I can't seem to remove the CNTs from the wall of the cuvette.
I am currently considering air annealing the cuvette at 600 - 700°C to remove the CNTs as a last resort. Would this be okay?
Even if the annealing works, I have quite a lot of samples and limited number of quartz cuvettes. High temperature annealing in between samples would be very impractical.
Does anyone have any suggestion for quick cleaning of quartz cuvettes with carbonaceous deposits on the wall?
The small cell size makes it hard for me to physically clean the cuvette. However, I am considering wrapping a lens wiper around a needle and using it to wipe the cuvette. Scratching is a concern of course, but it's better than dirty unusable cuvettes I guess.
Thank you in advanced.
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Hmmm ... tricky. OK, try to find a cuvette washer, for starters. They look something like this -- http://www.google.com/products?q=cuvette+washer&hl=en&output=nojs This allows you to really flush out the cuvette with the solvent and rinse of your choice, and the vacuum air drys the cuvette for the next use. Some are better than others -- the rubber gasket really varies on how it can seal, especially when empty and drying.
You're analyzing a suspension, does your instrument allow for a tiny magnetic stirr bar (called a flea) to be there? That may help if you can keep the suspension moving. You'll get better results as well.
You'll have to try some things to get the suspension to not stick to the walls. You've tried extremes of pH, maybe you can try ionic strength? What ever forces are binding the CNT to the glass may be broken by something as simple as high sodium chloride, or something like that. The important thing is, it doesn't have to be a clear liquid i you have the cuvette washer to really flush the surface.
You can check with vendors, and see what temperature the cuvettes can handle. But talking them to extremes regularly will cause wear and tear. They may come apart, or their optical characteristics may change. You want to minimize that, so that your analyses can be compared to each other.
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Try strong oxidizers in solutions like: aqua regia, alkaline permanganate solution, or a chromic acid. The chromic acid will work for sure, but it is carcinogenic. Talk to organic colleagues. They have this cleaning issue daily when they need to clean glassware after synthesis.
Do not use high temperature as most of cuvettes are glued. You will burn the glue.