Iron testing by USP <241>

[bdhedhy19]

Hi!
i am trying to do the Iron testing by USP <241> using 0.1g for Chloroxylenol sample, and the sample match with standard 100ppm in color comparision tube. we sent the sample out for Iron testing by ICP-MS and results was around 2.0 ppm. Is there is any way to use the USP method <241> or alter the method and i could see better results. I called vendor and they do their Iron testing by Flame AA and the results was <1.0 ppm. i used the procelain crucibles to digest the sample w/H2SO4 and ignite the sample at 600C to get rid off the carbon in the samples. Should i use different crucibles or should increase the sample amount or anything i can do to get the better results. please let me know at your convenience.
thanks

[Don_Hilton]

From memories of doing an analysis for iron, in school, years ago. I have a recollection of iron chloride being volitile under conditions for dry ashing a sample. If you are ashing a chloroxylenol sample, I would expect to have a lot of chloride ion available.

You may want to use a lower temperature ashing technique or wet ashing.

[krickos]

Hi

What Don says is true however if ashing is done properly, any Fe is converted to a more stable sulphate salt, you can always verify by running a spiked sample side by side.

So if I understand you correctly you want a more sensitive procedure than the USP limit test at 100ppm?

I have heard of people using a UV/VIS spectroscopic procedure when not having and AA or ICP around for more accurate measurements but do not know if it based on the same workup chemicals as in the USP test.

Occasionally we have had samples not working well for residue of ignition tests or similar with porcelain cups, switching to a Pt cup usually solves such issues.

[bdhedhy19]

Thanks Krickos and Don for your reply!
What do you mean by wet ash technique? And Krickos, Why procelain crucibles would be the problem? i don't get it.
I sent out the sample to other lab and they did in the platinum crucible and it shows high Fe like almost 100ppm than i asked them to do with ICP-MS and the results were like 2.0ppm. i think this USP method does not specify very clearly.
i will try wet ash technique if you explain me "how to do it" platinum crucibles would be very expensive"
And Krickos! I haven't try that Chinese pharmacopea for Arsenic Digestion yet! May be next week or week after. I will keep you posted.
thanks

[Don_Hilton]

On wet ashing - The sample is treated with sulfuric acid and heated. At some point the sample is transfered to the muffle oven. For a bit more description: http://inorganicventures.com/tech/trace ... procedures. And, if you look around on the web, I'm sure you will find more detail.

While looking to the web to be sure I was giving a reasonable answer, I noticed the following, which references losses to porcelain crucibles: http://www.ncbi.nlm.nih.gov/pubmed/18962980.

[krickos]

Hi

Thanks for the links Don, good summary.

bdgedhy, whats mention in Dons first link is what I hinted. Sometimes the sample or something in the sample may react with the porclaine. Have had a few cases with that when doing sulphated ash (wet ash technique) and switching to Pt cups sorted that problem.

[bdhedhy19]

Thanks Don for the links and Thank you Mr. Krickos for the explanation!!!
I will try these tips and wet ash technique after Thanksgiving holidays

Happy Holidays!