Hello if your acid is pure and analytical grade the the molarity or pH influence in results will be negligible. The optimal concentration of acids in injecting solution is bout 2%.

Thank you for your prompt answer. So according to your answer we can aspirate 2% HCl into the flame. And 2 percent HCl has a density of 1.0082 which corresponds to approximately 0.568 M HCl. Am I right??

HCl normally 37% solution which is around 12Mol

2% HCL = 0.648 Mol.

If your HCL concentration is less than 37 recalculate.

Thank you Mr. Karen. Got it.

Ondřej Zvěřina thank you for your input. You mean 10% of HNO3 won't affect the nebulizer and spray chamber. And by matrix matching do you mean the molarity of acid is to be matched in samples, standards, and blank or any other metals present in analyte as matrix??

Dear Hafeez:

I wonder why you want to use the "highest possible" concentration of HCl or HNO3 in the first place. One uses acids for two main reasons:

A. To keep the analytes (cations) stable in solution (generally, 1-2% is more than sufficient),

OR/AND

B. As a byproduct of sample digestion/preparation step, usually high concentrated acids.

If it is for B, it is always good to dilute the samples to minimal acid concentration (optimally around 1-2%), unless you are really pushing the limit of detection and do not want to dilute the digested samples. However, higher acid concentration doesn't always mean it always gives you better, more precise and accurate results (it is a myth).

When you increase the acid concentration, you significantly deviate from the calibration standards, in terms of viscosity, surface tension, which affect the efficiency of the nebulizer and matrix effects in the atomizer, analyte signal, etc. You also increase the analyte blanks coming from the acids proportionately. As you increase the acid concentration, it becomes less and less user/instrument friendly.

So, by trying to increase the acid concentration beyond 1-2%, you don't gain much but asking for more and more trouble, with a higher signal but less accurate data.

Of course, it all depends on your analytical objectives.

Regards,

Nimal

Dear Nimal thank you for your valuable suggestion. I do know that increasing acid percentage doesn't necessarily mean that one will get accurate and precise results. And it is also obvious that in the long run this acid will create problems in nebulizer and burner head. My problem was the very low concentration of Ca and other metals and I wanted to do minimal possible dilutions. So I wanted to know the highest possible acid concentration that can be used in AAS. ANALYTE SIGNALS ARE effected by acid strength, therefore we have to match it in our standards and blank as well. Once again thank you

Too high a concentration of acid can also damage the burner. Usually, the burners are made of high-alloy steel or titanium. What are the approximate concentration ranges of the individual elements? Are they, rather, single micrograms per liter or much higher concentrations?

Zbigniew Jońca very low concentration. Below 2 ppm when I aspirate 2% HCl.

You mean Ca, up to 2 mg / L? It is not a very low concentration. It should be sufficient for quantitative AAS measurement in an acetylene-air flame. What other elements do you have to measure and in what concentrations are they? What spectrometer do you use (company, model)? Do you have the technical ability to use the so-called hot flame, ie acetylene-nitrous oxide? This requires a cylinder with this gas, a special single-slot burner, e.g. 50 mm x 0.4 mm, and a much greater intensity of the local exhaust over the flame of the spectrometer. Can you use another measurement technique, namely ICP-AES (ICP-OES)? Ideally, in the version with axial observation. Provide details, then I will be able to give you specific tips.

Yes, the difference in molarity may likely affect the result. It is better to maintain the same molarity across the test and standard.

@Zbigniew I do have the technical ability and facility of using nitrous oxide flame and I use it regularly. In this flame too, 0.2 to 0.5 molar HCl strongly affect the results for calcium specifically.

In flame measurements, the measurement sensitivity of calcium is very sensitive to the presence of other components in the measured solution. The calcium signal may be suppressed or enhanced, compared to the calcium signal of the calibration solution, despite the use of a hot flame. The situation is similar with other elements of this group (Mg, Sr, Ba), and also, but much weaker, are the interactions in the case of measurements of other elements. The easiest way is to equalize the concentration of acid or acids in the solutions. If, for some reason, you do not do this, you can dilute the solutions more, taking advantage of the sensitivity margin obtained with the use of a hot flame. If the above methods do not eliminate the differences in measuring sensitivity caused by differences in acid concentrations, try adding larger amounts (up to several grams per liter) of lanthanum chloride and cesium chloride (or Na, K, Rb) in an acidified solution to the solutions to be measured. The upper limit of the concentration of La and the other ingredients used depends on the resistance of the burner to clogging of its slot. For this La addition, it is best to use the so-called two capillary system. This method of reducing the differences in measurement sensitivity by adding La and Cs (Na, K, Rb, Sr,) is universal and should be used as the first and basic method when measuring low concentrations of calcium in the presence of other components of the solution, also when using a hot flame. The La and Na chloride preparations used for this purpose must be sufficiently pure with respect to their Ca content. Many useful tips on how to analyze a wide variety of metals and alloys can be found in older publications (articles and books) and in manuals and guides from manufacturers of flame spectrometers.