Internal Standardisation query on ICP-OES 5100

I'm developing a method for detecting several elements in a biological fluid but have 2 questions relating to the use of internal standards with the 5100 OES instrument. 

1. I have a on-line IS set-up. How long should you have the IS solution running through the introduction system and plasma before starting your analysis? I know for ICP-MS the IS solution is normally run allowed 30 - 60 mins to stabilise in the plasma before beginning the analysis. Is there a similar recommendation for ICP-OES?

2. In ICP-Expert software when you select a IS on the 'Elements' tab and assign that IS to your analyte lines. Then in the 'conditions' tab your assign the measurement conditions to your analyte lines. For me I have 7 analytes with 2 wavelengths for each using both Axial and Radial in the same method. I then have 2 internal standards with 1 wavelength each. My question is is the IS stability plot formed from reading the analyte sample + IS together under the measurement condition you assigned to that analyte? See image 1 below. Or is the IS stability plot formed from the just the internal line by itself that was originally selected? See image 2 below. In the case of scenario 2 being correct, does that mean I should select the same IS line twice each IS i'm using and assign one to read axial and the other radial?

  • You do not have to wait a long time for IS stability as in ICPMS. After sample uptake delay, a typical stabilization time is 15-20 seconds. Look at the %RSD on your IS replicates for each solution and if the concentration of the IS  is sufficient to give a good Signal-to-background ratio, and you select a sensitive wavelength for the IS, then the %RSD should be less than 1% for the IS. This indicates excellent stability. 

    For your second question, since you are measuring analytes in both axial and radial views, you need to have both axial and radial IS wavelengths. Ratio an axial analyte wavelength to an axial IS wavelength, and ratio a radial analyte wavelength to a radial IS wavelength. 

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