Contamination of the blank, possibly by pick up of Na from the vessels containing the blank. Your calibration curve is truly linear, showing great proportionality (0.4mg/l to 0.8mg/l).

But it is my continual problem and the source of solvent is the same as for STDs.

if your container has partially leachable Na, it will pass into solution , raising your zero. From your data, there is a pronounced gain on the blank which appears missing or negligible in the standards.

Hi Denisa,

I am in trouble with the same problem :) I am trying different methods to analyze Zinc and Iron.

I think you should prefer a glass flask especially amber for your solvents.

You can try solvent that is made in 2% HNO3 and KCl as blank.

We are working with ultrapure water as blank.

Also, I think your blank may contain Na. You should sure about that.

Maybe you can use a precipitative for Ca or Na. There are different chemicals and methods that you can find.

We are still working on Fe and Zn analysis. There is interference between Fe and Zn too.

By the way, are there Na and Ca in your samples together?

Well, Na can be added in high concentrations to increase Ca signal by oxidating and donating electrons to keep Ca as a neutral species in the flame. In this sense, the presence of Ca could have a decreasing effect in neutral Na in flames as well. However, Ca has to be in high concentrations to have a noticeable diminishing response in Na.

Dear Denisa

In the atomization stage, when the matrix could not be removed sufficiently in the pyrolysis stage, molecular absorption and radiation scattering, can result in artificially high absorption and an improperly high (erroneous) calculation for the concentration or mass of the analyte in the sample. Please look at the following below links which may help you in your analysis:

https://en.wikipedia.org/wiki/Atomic_absorption_spectroscopy

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=5304&context=rtd

Thanks