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Topic: Atomic Absorption problem  (Read 4782 times)

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Offline sannewc

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Atomic Absorption problem
« on: May 13, 2011, 06:27:17 PM »
Hi I wonder if anyone can answer this.

 In the lab, we are having a problem where when sodium chloride is dissolved in an acidic solution we get a higher reading by AA than when it is dissolved in water.

 Surely if the Na+ ions are in solution, any acid in there will not affect the concentration or will it?

 Thanks all
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Offline enahs

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Re: Atomic Absorption problem
« Reply #1 on: May 13, 2011, 06:53:32 PM »
What acid? What concentration of acid?
What exactly is your solution?
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Offline sannewc

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Re: Atomic Absorption problem
« Reply #2 on: May 13, 2011, 07:20:33 PM »
Quote from: enahs on May 13, 2011, 06:53:32 PM
What acid? What concentration of acid?
What exactly is your solution?

HCl

works out about 0.003M HCl in the sample solution, which is 0.254g of Sodium chloride diluted 5ml>100ml in water then 20>1000ml in the acid solution
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Offline Stepan

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Re: Atomic Absorption problem
« Reply #3 on: May 14, 2011, 08:49:38 AM »
We do not work with Na, but have experienced similar problems with Zn and Cr, so the solution might be useful for you case.

Zn - we found that Zn is leached from some polymers by acid. Mostly from rubber and PVC parts of the standard storage containers. The effect was stronger at high dilutions (0.1-2 ppm of Zn); As a hypothesis: in your case, acid may extract Na from glass containers.

Cr - Recovery was different for samples with Cr(+3) and Cr (+6).   To resolve, we prepared two solutions of identical concentrations, one with Cr(+3) and another with Cr(+6). The flame conditions were tuned to get identical signal for both forms of Cr. In application to your project, you may want to see if signal of Na in Acid is the same as Na in water. If they are different and this is not due to contamination, try to adjust the flame.

If none of above helps, you will need to prepare the sample and standard in identical matrix.

Hope this helps
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Offline sannewc

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Re: Atomic Absorption problem
« Reply #4 on: May 14, 2011, 04:58:29 PM »
thanks stepan, how would i adjust the flame?

you mean adjust % of acetylene/air?
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Offline Stepan

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Re: Atomic Absorption problem
« Reply #5 on: May 15, 2011, 12:08:50 AM »
On my instrument I can adjust amount of acetylene (air is fixed). Yes, we adjust air/acetylene ratio. Also try different sections of the flame, by moving the torch up and down relative to the lamp beam. They have different temperature and different fuel/oxidizer ratio, and might give you quite different signal.   
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Offline Lohe

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Re: Atomic Absorption problem
« Reply #6 on: May 23, 2011, 09:02:17 AM »
May be it is due to ionization of Na, usually I use  CsCl for the supressing ionization as reccomended. Do you use absorption or emission mode?
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