Try reduction and immobilisation of sulfur by copper (needs to be freshly precipitated, by adding Zn to a solution of CuSO4)

ICP-MS-wise maybe isotope correction may help (measure sulfur and correct the interfering isotope with that value according to the isotope ratio).

A collision cell could also help, because I think its molecular interference).

you may try EPA method. Here is the link:

http://www.epa.gov/osw/hazard/testmethods/sw846/pdfs/3660b.pdf

I have analyzed selenium using TXRF (Total Reflection X-Ray Fluorescence). In this case sulfur is not a problem as it emits x-rays in a different energy range.

Two possibilities for removing sulfur interference: (a) convert to sulfide and treat with silver nitrate to remove as silver sulfide; or (b) convert to sulfate and remove as barium sulfate with the addition of barium nitrate.

Thank you all, these are good paths. Se can substitute for S so I may remove some of it from the extract with the Cu or Ag precipitation.

After the extraction (HNO3/H2O2, or aqua regia/HClO4) S should be oxidized to sulfate. I do not have interference problem when analyzing sediment CRM with 1.9% S, presumably sulfide. The problem is when analyzing biological tissue.

I am getting the same value using multiple Se isotopes, so I think there is signal suppression to all of them. I am using Se 82 for the isotope dilution, but that does not correct.

I will try adding thiosulfate in the sediment CRM and see if that cause any problems, to verify that there is really a S interference.

mass spectrometric interfences ususally lead to an increased signal intensity and not to a decreased one. When you get the same result for different Se isotopes it is a hint that there is no problem with interferences. Also in hydride generation you have less interferences than in normal ICPMS.

potentail sources of errors could be incomplete extraction/digestion or strong matrix effects. I would try to completely digest the samples e.g. by a microwave assisted acid digestion. Another potential sourec is that you do have different yield in the hydride generation process for biological samples. A complete digestion could help here also.

I am performing Se speciation by means of HPLC-ICP-MS in fish muscle and I think that I have the same problem. I have monitored sulphur and some peaks appear at the same time that Se. Therefore, small peaks of Se could be sulphur interferences.

I cannot really follow this discussion with sulfur interference on selenium in ICP-MS. This would be quite unusual. First let us think what sulfur molecule could interfere. The sulfur isotope have the masses 32, 33, 34 and 36 and the selenium isotopes have the masses 74, 76, 77, 78, 80 and 82. So, there is no overlap. Looking at SO2 ions we will get masses from 64 to 68; even when taking S-36 and two time O-18, which both have very, very low abundances, we only get 72, which means the other selenium masses are free. Theoretically you can als have ArS, but it also ends at mass 76; 78, 80 and 82 are free of interference. With all this molecular ions you have to consider, that the formation rate is low and you need high sulfur concentrations. Beyond this it is required to measure selenium with medium to high mass resolution or with collision cell technology, because you have other interferences in ICP-MS disturbing selenium inferference such as Ar2 or Ar2H.

I have consider 32S216O but this would interfer in 80Se (or 82Se with 32S218O) but 78Se is still free of interference. Therefore, I do not understand very well. Could be a baseline instability due to high matrix effect when compounds from the matrix reach the plasma? I observe the same chromatograms for 78Se, 80Se and 82Se isotopes.

There is an interference workshop available from Thermo, where you can check for each mass individually and set some matrix compostions. This could be a good point to start. Typically molecular interference in ICPMS have formation rate in the low per cent range or below. Therefore the elements forming the interference need to be present at elveated concentration levels. The question is how much sulfur is in your sample? means what intensity or even better what concentration or mass fraction. Do you use sulfur containing buffers?

I am performing HPLC-ICP-MS speciation analysis and when I monitor SO signal it gives me high and broad peaks, even they saturate. I am analyzing fish muscle so it is expected a high concentration of sulfur coming from proteins, lipids and other aminoacids. There is no additional source of sulfur in the mobile phase, nor in the employed buffers and solutions.

Could be interferences coming from ArCa other possibility?

Thanks.

Hi dear all, I am having similar issues in the ICP-MS analysing Se and Ba in Brazil nuts. So Brazil nuts has a really complex matrix and presenting interferences possibily for the isotope Se80. So there is big difference between the concentrations provided by Se78 and Se80. and It doesn't happen with other samples such as CRMs and the quality control in general is ok. What I realized is that for the nuts with high Ba concentration, the gap is bigger. So probably the interference has some correlation with Ba, and then I am suspecting of sulphur, it might be associated with Ba in the nuts, also because Se80 has interference with sulphur oxide. Does anybody know how could I avoid this interference?