I've been running an analysis for Pb with 5 standards, blank and a CRM; the results have had extremely poor linearity (i.e. standard 1 is a positive, standard 2 is a low negative number, and so forth), but also high responses from the blanks. The blank response makes me consider contamination, although I am sure the standards were prepared adequately. Contamination related to the instrument itself?
The poor linearity occurred across all wavelenghts selected for analysis; only one line gave a somewhat promising linear result with R2 of approx. 0.8. This makes me believe there's something affecting all lines selected, not just poor choice in method.
What issues do you believe to be behind the poor results/what recommendation would you have for optimisation?
Hi,
This indeed brings contamination to mind : have you tried changing the whole sampling line (nebulizer, chamber, injector, torch and tubings) ? That'd be my first reaction, just to check if Lead hasn't adsorbed onto the whole line, which could lead to high noise and unpredictable leaching or desorption.
Check this by regularly measuring a well homogenized blank and/or standard over one hour : il the RSD of your repetitions is way too high, you probably have to envisage "spring cleaning" or replacement of your sampling line.
Hi,
This indeed brings contamination to mind : have you tried changing the whole sampling line (nebulizer, chamber, injector, torch and tubings) ? That'd be my first reaction, just to check if Lead hasn't adsorbed onto the whole line, which could lead to high noise and unpredictable leaching or desorption.
Check this by regularly measuring a well homogenized blank and/or standard over one hour : il the RSD of your repetitions is way too high, you probably have to envisage "spring cleaning" or replacement of your sampling line.
Hi Pierre,
Thank you for your quick answer!
Blockage in the nebulizer does sound like the likely issue here, I will have a look at the sampling line and experimental results after a clean up (once our labs re-open! Which sadly might be a while now).
Hi Andreea
I agree with Pierre Caulet that using a clean system is a reasonable first attempt.
In general it seems as if the signal/backgound ratio is insufficient for some reason.
Apart from contamination there are other possibilities:
-ICP operating conditions. Eventually the Rf-power, gas flow or observation settings are not optimized in this case. Did you verify that the instrument itself is working to specs?
-Fault in standards preparation. Could it be that the standards in fact are 10 (100, 1000) times lower due to incorrect dilution?
-Loss of Pb during sample prep. Could Pb have precipitated (sulfate, halides...) at one point during the preparation of the standards/CRM?
If you would provide some more information (instrument, concentrations, sample prep, matrix, solvents, wavelength,...) it could be easier to figure it out.
Glad having been of help and good luck with confinement (same here in France).
I actually had some of my equipment on TeamViewer in order to work from home, but ... you still need to get there frome time to time in order to prepare new samples and get them on the spectrometer or the microscope !
It is possible that you are not getting sufficient sensitivity in the first place, due to a clogged nebulizer, un-optimzed conditions, etc.. A quick look at the peak shape for each wavelength, and each standard will tell you how good the signals are and if it is due to poor sensitivity. If you see good clean Gaussian peaks, also for the blanks, that will give you a good clue about where the problem is, without much effort. Best wishes.
Stay safe,
Nimal
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