[valdoraa]

Hi;

I am a new in this forum.

I would like to know why NaCl is used with AQUA REGIA (3 v HCl: 1 HNO3) in the analytical methods to determine gold concentration with Atomic Absorption Spectrometry.

If you have any idea about the chemical mecanism of this reaction, please give me a short answer.

Thank in advance

[Alpha-Omega]

You have to account for matrix effects...sodium chloride is used to correct for your background...

Ionization interferences occur when the flame temperature is sufficiently high to
generate the removal of an electron from a neutral atom, giving a positively charged ion. This
type of interference can generally be controlled by the addition, to both standard and sample
solutions, of a large excess (1,000 mg/L) of an easily ionized element such as K, Na, Li or Cs.
Each sample and standard should contain 2 mL KCl/100 mL of solution. Use 95 g of potassium
chloride in 1 L of reagent water for the KCl solution.

4.6 Spectral interference can occur when an absorbing wavelength of an element
present in the sample, but not being determined, falls within the width of the absorption line of
the element of interest. The results of the determination will then be erroneously high, due to
the contribution of the interfering element to the atomic absorption signal. Interference can also
occur when resonant energy from another element in a multielement lamp, or from a metal
impurity in the lamp cathode, falls within the bandpass of the slit setting when that other metal is
present in the sample. This type of interference may sometimes be reduced by narrowing the
slit width.

See this link:

http://www.epa.gov/sw-846/pdfs/7000b.pdf

[valdoraa]

Hi;

Thank you very much.

My problem that i have prepared standards Gold (Au) with aqua regia and NaCl but when i have tested them one by one the deviation is still 4% which is very big.

For example: standard 1 ppm, i have prepared it twice in the same conditions but the deviation is 4%.

So, why this difference. should i put the correction lamp off?

Thank you in advance

[Alpha-Omega]

Go to this site (VARIAN):  http://www.varianinc.com/cgi-bin/nav?applications/aa&cid=JQPONPINFO

Choose AA from the menu on the left.  This will bring you to the Varian Application notes.  In the center toward the bottom choose Application Nortes By element. Then on the next screen choose GOLD.

On the next page at the top you will see two Application notes for Gold Choose High purity GOLD.

I am also attaching the note.  This is a valuable site for AA application notes.

If you are using a deuterium lamp (separate source for background correction)-then read this it explains the accuracy compared to other methods: 

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

This is a guide published by Perkin Elmer for Inorganic Analyses by AA, ICP-OES, and ICP-MS-background correction methods are addressed (too big to attach-PDF file).

http://las.perkinelmer.co.uk/Content/Manuals/GDE_InorganicAnalysis.pdf


Here are two AA methods By THERMO using different background correction methods:

http://www.thermo.com/com/CMA/Files/articlesFile_20600.pdf

http://www.thermo.com/com/CMA/Files/articlesFile_20590.pdf

I hope this helps...

[valdoraa]

Thank you very much.

Very interesting papers. I hope finding a solution to my problem

Thanks

[geubrina]

Do you mixed the Aqua Regia with NaCl before dissolve the gold?

I think, the biggest impurity for gold is silver and copper. So, after you dissolved the gold with AR, the intention to put NaCl is to precipitate the Silver that dissolved.

So, the gold is left in the solution.

[Arkcon]

geubrina: The chemical reactions that occur with ionized Au atoms, either vaporized in a flame or in an argon plasma excited by an RF field, are likely very different from what happens in solution.