[Jasim]

I am analyzing a couple of glass vials. I've crushed them, weighed them, and now I'm to the part where I need to add some HF to digest the glass for subsequent analysis via ICP-OES.

I'm working with someone else who is an ICP wizard and my mentor on the technique, but this is something he doesn't have much experience with. We've found quite a few resources on Google, but many of them use a mixture of HF, nitric, and HCl. I've used this mixture before for the digestion of coated pharmaceutical tablets. However, both of us agree that for this particular application the nitric and HCl doesn't seem that necessary.

We are planning (and hoping) that the glass particles will digest readily in HF only, left sitting capped in a hood overnight.

Here is the question:

Why so many papers used the mixture as opposed to just HF? Is this something that is really necessary? Our analytes include boron, silicon, aluminum, sodium, calcium, and potassium. Will just using HF without the nitric and HCl affect our recovery for any of these analytes, or is there any other reason we would want to use nitric and HCl?

We can get more sample and try this again if we don't get good results, so it's not a huge deal. But I would really like to better understand the methodologies I'm seeing.

[Arkcon]

HF is a weak acid.  I know it attacks glass, and most acids don't.  I know it will seriously damage human tissue right down to the bones.  But it is a weak proton donor.  And it forms many insoluble salts, particularly with calcium, which you are analyzing for.  So you will need the nitric and hydrochloric to insure you get good soluble salts for the ICP.

[Jasim]

Thanks Arkcon. I was aware that HF has a very low dissociation constant, making it pretty weak. I did let the crush glass sit in the vials overnight in Conc. HF...as would be expected from your explanation, they didn't digest. I'm going to add some aqua regia, cap tightly...and I'm guessing that will do the trick.

Also, I was not aware that HF formed insoluble salts....though that does make sense to me.

Thanks Arkcon!!

[Arkcon]

That's how HF kills.  Well, besides soft tissue trauma and bone loss, fluoride anion sequesters calcium as CaF, generally causing most organ systems to fail, because Ca is a common cellular communication ion.  I don't know how completely the vials need to be dissolved, before the nitric and hydrochloric reach entrained ions.  Like you, I'd assume the glass should be completely dissolved, but maybe if the HF makes it porous enough, you can get all the ions.  You may have to check your procedure further.  Or perhaps try some sort of standard -- glass with a known ionic contaminant level, to see if you're  getting it all.

[curiouscat]

That's how HF kills.  Well, besides soft tissue trauma and bone loss, fluoride anion sequesters calcium as CaF, generally causing most organ systems to fail, because Ca is a common cellular communication ion. 

Wouldn't you need a lot of HF to sequester all the Ca in the body? 

I suppose HF kills at concentrations waay below that quantum.

[Arkcon]

That's how HF kills.  Well, besides soft tissue trauma and bone loss, fluoride anion sequesters calcium as CaF, generally causing most organ systems to fail, because Ca is a common cellular communication ion. 

Wouldn't you need a lot of HF to sequester all the Ca in the body? 

I suppose HF kills at concentrations waay below that quantum.

Hydrofluoric acid-induced hypocalcemia.

http://www.ncbi.nlm.nih.gov/pubmed/3184225

I heard of a chip maker who got 350 ml that landed into his lap.  (And that's why there tend not to be chairs in labs anymore, you should stand and jump away from a spill.) They didn't get his pants off in the safety shower, and they didn't apply calcium gluconate gel.  Even after double amputation, he still died as each organ system shut down.  The localized depletion of calcium from some bones causes a systemic loss of Ca ion, which induces other bones to release their calcium, which depletes the reservoir needed for daily use.  See, human bones aren't dead rocks inside your body meant just to hold you up, they're dynamic, dissolving and rebuilding themselves constantly in response to serum Ca concentration.  All to insure that you have enough for your muscles to use to coordinate the twitch response.

[curiouscat]

Very interesting! Thanks!

[Jasim]

350mL is a lot of HF...I had to go through a ton of paperwork just to use a couple of mL's. And now I'm still restricted to using less than 25mL at a time...inside of a hood, with a full apron, two layers of gloves, and faceshield...Sounds like that guy wasn't really taking the proper precautions.

[osmium]

I am analyzing a couple of glass vials. I've crushed them, weighed them, and now I'm to the part where I need to add some HF to digest the glass for subsequent analysis via ICP-OES.

I'm working with someone else who is an ICP wizard and my mentor on the technique, but this is something he doesn't have much experience with. We've found quite a few resources on Google, but many of them use a mixture of HF, nitric, and HCl. I've used this mixture before for the digestion of coated pharmaceutical tablets. However, both of us agree that for this particular application the nitric and HCl doesn't seem that necessary.

We are planning (and hoping) that the glass particles will digest readily in HF only, left sitting capped in a hood overnight.

Here is the question:

Why so many papers used the mixture as opposed to just HF? Is this something that is really necessary? Our analytes include boron, silicon, aluminum, sodium, calcium, and potassium. Will just using HF without the nitric and HCl affect our recovery for any of these analytes, or is there any other reason we would want to use nitric and HCl?

We can get more sample and try this again if we don't get good results, so it's not a huge deal. But I would really like to better understand the methodologies I'm seeing.

You'll need an HF resistant sample introduction system to run this sample.  Standard quartz/glass sample intros can be ruined by running HF containing solution.  And your results for Si and B will be bad as the HF will leach them out of the sample intro components.

-os

[Jasim]

Thanks Osmium, I'm aware. We've done tablet digestions with HF. We have a special nebulizer, torch, and tubing that we use.

So, we found a good reference. We think part of the problem was our sample size, just too much. Going to try again this afternoon...20mg crushed glass, 600uL HF, 300uL HCl and 300uL nitric...capped tightly and maybe sonicate for ~60 mins. Thinking this should work.

From what I've found out, HF only or even just HF and nitric will produce insoluble flourides, as mentioned above...that's what the HCl is for. Just doing HF and HCl though doesn't lead to full digestion...so you do need all three. For glass digestion the references I've seen with best results report a ratio of approximately 2:1:1 of HF:HCl:nitric

[osmium]

Thanks Osmium, I'm aware. We've done tablet digestions with HF. We have a special nebulizer, torch, and tubing that we use.

So, we found a good reference. We think part of the problem was our sample size, just too much. Going to try again this afternoon...20mg crushed glass, 600uL HF, 300uL HCl and 300uL nitric...capped tightly and maybe sonicate for ~60 mins. Thinking this should work.

From what I've found out, HF only or even just HF and nitric will produce insoluble flourides, as mentioned above...that's what the HCl is for. Just doing HF and HCl though doesn't lead to full digestion...so you do need all three. For glass digestion the references I've seen with best results report a ratio of approximately 2:1:1 of HF:HCl:nitric

What kind of glass are you trying to digest?

[Jasim]

These are some small vials that apparently have been causing some kind of problem for some chemists...I never get details about these things. But we are looking at two different makers...one of them, Agilent, is causing some problems, the other isn't. They want to know what it is. I don't know what the vials are made of...I'm assuming they are a borosilicate or similar, lab-grade glass.

The main reference we are now utilizing was actually for sheet glass, windows.

[osmium]

These are some small vials that apparently have been causing some kind of problem for some chemists...I never get details about these things. But we are looking at two different makers...one of them, Agilent, is causing some problems, the other isn't. They want to know what it is. I don't know what the vials are made of...I'm assuming they are a borosilicate or similar, lab-grade glass.

The main reference we are now utilizing was actually for sheet glass, windows.

Thanks Osmium, I'm aware. We've done tablet digestions with HF. We have a special nebulizer, torch, and tubing that we use.

So, we found a good reference. We think part of the problem was our sample size, just too much. Going to try again this afternoon...20mg crushed glass, 600uL HF, 300uL HCl and 300uL nitric...capped tightly and maybe sonicate for ~60 mins. Thinking this should work.

From what I've found out, HF only or even just HF and nitric will produce insoluble flourides, as mentioned above...that's what the HCl is for. Just doing HF and HCl though doesn't lead to full digestion...so you do need all three. For glass digestion the references I've seen with best results report a ratio of approximately 2:1:1 of HF:HCl:nitric

I'd try heating that solution a bit.

Borosilicate glass shouldn't be a hassle to get into solution.

[curiouscat]

Wondering, what do you do your digestion in? What sort of material will a hot, sonicated HCl + HNO3 + HF cocktail not attack?

[osmium]

Wondering, what do you do your digestion in? What sort of material will a hot, sonicated HCl + HNO3 + HF cocktail not attack?

For HF digestions I'll usually use Teflon beakers, either on a hot plate or in a microwave.

I have also used polypropylene tubes in a block digester.