Measurement and Results - Tungsten (W) and Iridium (Ir) ICP-MS drift

I have a question regarding ICP-MS analysis of tungsten and iridium. We are using your standards as calibration and/or calibration verification solutions. During sample analysis, if the unknown samples contain tungsten or iridium, we are seeing a downward drift in concentrations. The ICP-MS instrument seems not to be the issue and all calibration checks are coming back within acceptance throughout the analysis. Your stock standard containing tungsten has HF at 1% and when we dilute down, the final standards contain ~0.0005%. However, our unknown samples we are running do not have any HF. Do you think this could be the issue for tungsten, maybe it is a sample stability issue? Our iridium stock solution we purchase is in 10% HCl, but we dilute these into ~2% HNO3, 0.5% HCl. The samples would be the same matrix. I do not understand the downward drift concentration of iridium for the unknown samples, and any insight regarding this issue would be greatly appreciated.

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admin Total posts: 529	The behavior you observe for tungsten in your samples could be instability due to lack of a complexing ligand like fluoride from HF. As your calibration standards appear stable, adding a proportional amount of HF to your sample preparations would be worth trying to correct the apparent W instability. Just be aware of the issues HF can cause for elements such as the Th and the rare earths, and if your samples contain significant amounts of alkaline earth elements (e.g., Ca, Mg), adding trace HF to them might not stabilize the W, but we think it’s a good first approach. As for the Ir instability, that is a bit more perplexing, as the dilution matrix is apparently appropriate for the standards, but again not the samples. As the sample matrix seems to be a factor, if you could please provide additional information about the exact nature of the samples (and any preparation procedures) we may be able to offer more specific suggestions. Posted: 09/05/18 21:16:17

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admin Total posts: 529

The behavior you observe for tungsten in your samples could be instability due to lack of a complexing ligand like fluoride from HF. As your calibration standards appear stable, adding a proportional amount of HF to your sample preparations would be worth trying to correct the apparent W instability. Just be aware of the issues HF can cause for elements such as the Th and the rare earths, and if your samples contain significant amounts of alkaline earth elements (e.g., Ca, Mg), adding trace HF to them might not stabilize the W, but we think it’s a good first approach. As for the Ir instability, that is a bit more perplexing, as the dilution matrix is apparently appropriate for the standards, but again not the samples. As the sample matrix seems to be a factor, if you could please provide additional information about the exact nature of the samples (and any preparation procedures) we may be able to offer more specific suggestions.

Posted: 09/05/18 21:16:17

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Measurement and Results - Tungsten (W) and Iridium (Ir) ICP-MS drift

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