Rare Earth Elements determination with Agilent 7800 Helium mode

Hi everyone, I work for an environmental analysis company and we are currently trying to assess the REE concentration in various wastes (mainly slag and ashes from waste incineration), I work with an ICP-MS 7800, has anyone tried to optimize the system for such analysis?
I've tried to make an acquire method from scratch, using high integration times, actually 200 sweeps/replica, 5 replica each point, 1 sec integration time in no gas and 2 sec integration in gas as you can see below

Tune was made using the "general purpose" preset as follows

No gas mode:

He Tune

Helium mode: (actually lowered He flow to 4.5 ml/min to achieve higher counts)

Any suggestion about optimizing the system? Higher or lower integration times, different tune setting and so on?

Also how to determine Sc Y & Tb as analytes when they are also used as ISTD? Is there any "functional" ISTD selection that doesn't contain such analytes? Using just In and Bi as internal standards seems a bit troublesome since In is often found in wastes (so the signal is not reliable as istd) and Bi is too heavy as mass to cover the whole spectrum

  • Rare earths are all very easy to ionize so I will generally use fairly short integration times (0.3-0.5s). Iridium is a very common internal standard for rare earth analysis. Using general purpose settings should give you good sensitivity for trace level work. You want to be careful if you decide to combine your rare earth standards with your other analyses because REEs will form doubly charged species that can interfere with elements like As and Se.

  • Thank you for the advice, I didn't check the ionization potential in advance so I clearly overextended the integration time, I'll fall back to a 0.5-ish sec integration as suggested, it will greatly reduce analysis time. Also I'll take a look into Iridium as ISTD, maybe Rhodium could be used too (despite its cost) in order to cover 100-ish mass levels? Any other reliable element closer to Y/Sc masses?

  • Yes. Rhodium is another option. Rhenium is also fairly common to use - anything that's very rare in nature and not in your samples. Sc is tricky since it is often the I.S. not the analyte so there really isn't something close in mass that isn't common in nature. Sometimes you just have to make do with what you can when assigning I.S even if it's not perfect. 

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