To be clear, the initial focus of this community is on GC and GC/MS technologies and applications that rely on them. ICP-MS is on our roadmap for inclusion later. That said, we're not going to refuse your post, but please keep in mind we don't have a dedicated place to post your question, and we don't necessarily have materials in place to support an answer for you yet.
I have a technical question, which i'll ask separately.
Thanks. - Josh
I'd like some help understanding your question a little. Using the theoretical mass calculator here (http://www.chemcalc.org/), we find the following masses for the substances in which you're interested:
- MoO: MW = 111.936997, EM = 113.90032
- Cd: MW = 112.411552, EM = 113.90336
Comparing the theoretical spectra, it looks like you'd expect different peak distributions for each substance, even though you'd get highly similar accurate masses for the dominant isotopic compositions. The substantial peak at ~107.9 for MoO looks like it could be an easily identifiable distinguishing feature.
What do you think? I'm not at all experienced in ICP-MS personally, but it seems like this would be a reasonable way of distinguishing the two without an MS that had super-resolution. Maybe if you had a mix of MoO and Cd you you determine the relative concentrations based on the relative intensities of the ~114 and ~108 peaks?
Thanks. - Josh
Manoj, Have you tried looking at the Cd 105.9 line? It should not be interfered by the MoO
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The measurement of sub-ppb Cd in the presence of Mo is challenging given the isobaric interference of MoO on all isotopes of Cd, expect for cadmium-106 which is low abundance (1.25%). As you mentioned, the Agilent 8800 ICP-MS and oxygen addition to the Octopole Reaction System (ORS) eliminates this interference, but how do we evaluate this on single quadrupole ICP-MS?
First, I would recommend creating a Cd calibration curve with your MoO matrix, and measure the Cd background equivalent concentration (BEC) and detection limit (DL) in all available gas modes - nogas, He, high energy He, and hydrogen (if available). Recommended tuning parameters are attached for the 7900 ICP-MS with the x-lens configuration. Based on empirical comparison of Cd at 110-116 amu, we can then determine the relative impact of the MoO isobaric interference.
The DL and BEC results are shown in the information for each calibration curve in ICP-MS MassHunter Data Analysis, so you can get real time information on interference removal.
For example, it would be interesting to compare cadmium-116 in hydrogen mode since we're mass shifting MoO (116) to MoOH (117), but possibly complicated by the InH interference. This might be a good alternative, but the BEC/DL measurements are the best guide here. This also depends on your detection limit requirements and relative cadmium concentration. So for starters I would recommend BEC and DL measurements under the different available gas modes - let the results be your guide.
I went ahead and flagged the “Correct Answer” on this post. If you still need help though, please let us know and we would be happy to continue working with you.