[nextpauling]

I work in a petroleum lab where we analyze the composition of naturally occurring brine solutions.  I've heard that samples should not be acidified with hydrochloric acid before analysis so we used nitric acid.  Why can hydrochloric acid not be used with the ICP?  It seems that brine solutions which already contain chloride would be just as problematic...

[marquis]

My experience is with atomic absorption, not ICP.  However, the two techniques are closely related.

I think the issue is with the specific metal you are looking at.  There are some metal chlorides (not many) that are not acid soluble.  Almost all nitrate salts are acid soluble.

Having said that, we used hydrochloric acid for AA as long as we knew the metal salt would be acid soluble.

[Borek]

There are some metal chlorides (not many) that are not acid soluble.

Name four

[marquis]

Maybe I should have explained better.  The issue is whether the form of metal salt  you have dissolves in hydrochloric acid. 

The routine wet chemical test for chloride (cl-) is to take silver nitrate and mix it with the test solution.  Silver chloride is formed as a precipitate.  Not a soluble chloride.

Titanium is an issue.  The most common form of titanium is titanium dioxide.  If the titanium is in the form of titanium dioxide, it will not dissolve with hydrochloric acid.  The only acid that dissolves it is hot sulfuric acid. Not good for AA nebulizers.

There are a number of relatively heavy metals that cannot be quantitated because of low acid solubility.  The vendors will sell a high acid nebulizer to take care of these.  Even then, there can be issues.  Tin was the best example of this.

I had no problems with common metals such as zinc, calcium, magnesium, etc. with hydrochloric acid.

Hope this helps.

[marquis]

Sorry, got called away.

AA and ICP are good at measuring low levels of metals (ppm or ppb range).  If you are analyzing concentrated metal salts, better methods exist.  The samples submitted are usually organic. Some sort of digestion is required.  This is often done with mineral acids, such as HCl and HNO3.  A good working assumption is that the metals in the organic material went to the salt of the digesting acid.  If it is hydrochloric acid, you would suspect chlorides are formed.  And that is when you start checking chloride salt solubility for the metals you suspect are present.  It doesn't always work, but it is a good starting point.

Alternative- use a non-destructive test method such as Energy dispersive x-ray flourescence (EDXRF).  This has problems of its own, but can be used to ID elements present.

[kirsch]

I use ICP-MS from time-to-time to analyze arsenic. We use an argon-based plasma, and, if there are chlorides present, they can combine with argon and give an interference at the m/z for arsenic.  That's a pretty specfic case, I realize, but is one reason we don't want Cl around.

[kilroy]

I have a lot of experience of XRF technique, both energy dispersive x-ray flourescence and wavelength dispersive x-ray fluorescence and I might think you should consider using XRF as an alternative.

XRF has it´s own problems and issues for sure ( ) but it´s worth a try.

[mer-mer-mer-mer-mer]

I work in a petroleum lab where we analyze the composition of naturally occurring brine solutions.  I've heard that samples should not be acidified with hydrochloric acid before analysis so we used nitric acid.  Why can hydrochloric acid not be used with the ICP?  It seems that brine solutions which already contain chloride would be just as problematic...

I've used either conc. or 1:1 HCl in several EPA digestion methods for ICP analysis with very few problems. Method blanks and LCSs allow you to track any potential problems during sample prep.

[Fleaker]

I have a lot of experience of XRF technique, both energy dispersive x-ray flourescence and wavelength dispersive x-ray fluorescence and I might think you should consider using XRF as an alternative.

XRF has it´s own problems and issues for sure ( ) but it´s worth a try.

You can say that again.

 

[Lorax]

I use both ICP and XRF on a regular basis.  In my experience, the XRF is much faster and easier to use, but less accurate than the ICP.  We use nitric acid for our digests.  I believe the problem with HCl is the formation of insoluble salts, which can interfere with the analysis.