Hello,
I have PMMA polymer particles embedded with CuO nanoparticles.
I analysed two samples via ICP-MS and obtained the Cu wt% within the expected range.
I then analysed further samples via ICP-OES and have obtained Cu wt% that are far too low (like 1-2% when should be around 8-10 wt%).
I could visually see the increase in CuO across the samples so I know there was much more than what the results provided.
Does anyone have any suggestions as to why this would happen?
The samples were dry (around 8-20 mg provided) and contained only PMMA, CuO, PVA, NaHCO3, the lab then acid digested prior to analysis. The CuO completely dissolved and the PMMA formed a clump.
I have asked the lab to repeat the samples again on ICP-MS to see if this makes a difference though the lab did not seem hopeful that this would provide a different result as usually the error between the two techniques is less than 3%.
Thank you :)
My first thought was: How close to the limit of detection is the Cu concentration in the ICP-OES sample? If the final volume of the sample diluted the sample too much, you will approach the lower limits of the instrument's accuracy. Roughly calculating; 10mg x 10% Cu in 10 ml final volume would be around 100 ppm. Even if it was 50 ml final volume, that would bring it down to 20 ppm, which shouldn't be a problem.
- Could there be an interference from another element on your Cu wavelength? Maybe the sodium from the NaHCO3 is causing baseline issues?
- Could the sample have absorbed moisture prior to analysis?
- Might the clump of PMMA be preventing full dissolution of the Cu, physically holding the Cu inside? (I don't know what PMMA is.)
- Are you sure the conditions were the same for the second digestion?
- Have you double checked that the calculations and results from the ICP-MS analysis are correct? Maybe the ICP-OES results are good and you've missed something in the first analysis?
Maybe when you repeat the analysis, submit a dilute CuO solution as well and see if the two instruments give you similar results. If they differ, then you can investigate the instruments as the source of difference. If the same, then it was your preparation(s) of nano-particles that seems to be the problem.
Thank you Matthew Wheal for such a thoughtful answer. I am certainly hoping it is the first point you mention as that makes the most sense.
I've thought through the other points and they are something to come back to if the first point isn't occurring.
- I am well above the limit of detection as that's stated in the report.
- It may have absorbed moisture but fairly unlikely as lid was on and the rooms where stored prior to analysis are temp controlled although I didn't wrap the lids with parafilm though I didn't wrap the previous samples either.
- I checked the clump visually and it was white so only if the Cu ions are embedded in that rather than in the surrounding liquid - ie. theres no undigested CuO by visual appearance.
- Lab double checked their results and used the same digestion protocol only change was MS OES to MS
Thank you again:)
Hi, I suggest that you compare OES Cu results obtained with different emission lines. Also such issue may be caused by false calibration solutions.
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