Sulfur Assay

[redzilla]

Hi Everyone,

I have been asked to develop a method for assaying colloidal sulfur in cosmetic products. I saw somewhere (can't recall where) that HPLC can be used for such testing. I have no idea where to start on this one, as I can't seem to find any literature on colloidal sulfur assays in cosmetics.

Does anyone have any experience with this one at all? Any info would be greatly appreciated!

Redzilla

[tom jupille]

I'm not aware of anything, and my guess is that HPLC wouldn't be a first choice technique for colloidal anything. Assuming none of the other components contain sulfur, I would think that a simple elemental analyis would give the answer.

[Kostas Petritis]

I think that the reference below might help:

Detection of some sulphur anions and colloidal sulphur by flame molecular emission spectrometry
Analytica Chimica Acta, Volume 251, Issues 1-2, 21 October 1991, Pages 197-203
Sverre Hauge and Kjartan MarøyArngrímur Thorlacius

[JM]

If sulphur can be converted to sulphate by oxidative treatment, this can be analyse by Ion-Chromatography.

JM

[redzilla]

Yep, my first impression is that you wouldn't analyze via HPLC. But I found out that the company that we send our samples to assays the sulfur using HPLC. And of course since we pay them to do it, they are tight lipped about any methods they use.

I don't have any of the instruments generally used for elemental analysis, so I was trying to find a method via wet chem, HPLC or even UV-VIS. Thanks for the input.

[ljc]

If you are trying to determine elemental sulfur, HPLC can be used in combination with the right sample prep. Elemental sulfur is an octagonal molecule (S8 ), and there are also the hepta- and hexa- isomers (S7 and S6), which form on exposure of a solution containing elemental S8 to UV light. All three forms are hydrophobic and can be chromatographed on an alkyl bonded phase column in reverse phase mode. For example, on a Zorbax C8 column, the k' for elemental sulfur is around 4 using 75% methanol:25% water. It can be detected by UV at 250 nm or so (I forget the lambda max) with pretty good sensitivity. It does tail quite a bit, but tolerably.

[tom jupille]

Explained that way, it makes sense. Thanks!