5100 ICP-OES Internal Standard Enhancement During Calibration

I'm afraid that IS ratio drop means a drop in IS signal, not an enhancement.

High concentration of other elements is inducing a matrix effect.

To overcome this, robust conditions should be used, and reading in Radial mode is worth to check

Thanks for your opinion.

The IS stability plot is a little misleading because the IS intensities are actually increasing progressively as you go from Standard 1 (Blank) to Standard 7 but because the IS is ratioed with the IS Blank /IS Cal Stds it appears as a decrease on the ratioed stability plot but in reality it is actually a IS enhancement effect. The measurement conditions used are the default in terms of RF power so I don't suspect its the robustness of the plasma in question. Possibly the use of Cs and the reading of the IS's in Radial mode will offer a remedy. 

This is how the IS is being treated by the instrument software: 

Analyte SignalCORR = Analyte SignalMEAS x ISINIT/ISMEAS

Where Analyte SignalCORR = Corrected Analyte Emission Intensity

Analyte SignalMEAS= Measured Analyte Emission Intensity

ISINIT = Initial Internal Standard Emission Intensity

ISMEAS = Measured Internal Standard Emission Intensity

Thanks for your opinion.

The IS stability plot is a little misleading because the IS intensities are actually increasing progressively as you go from Standard 1 (Blank) to Standard 7 but because the IS is ratioed with the IS Blank /IS Cal Stds it appears as a decrease on the ratioed stability plot but in reality it is actually a IS enhancement effect. The measurement conditions used are the default in terms of RF power so I don't suspect its the robustness of the plasma in question. Possibly the use of Cs and the reading of the IS's in Radial mode will offer a remedy. 

This is how the IS is being treated by the instrument software: 

Analyte SignalCORR = Analyte SignalMEAS x ISINIT/ISMEAS

Where Analyte SignalCORR = Corrected Analyte Emission Intensity

Analyte SignalMEAS= Measured Analyte Emission Intensity

ISINIT = Initial Internal Standard Emission Intensity

ISMEAS = Measured Internal Standard Emission Intensity

 Hi Agricult,

The IS ratio trend follows the intensity trend. Is Ratio is ISMEAS/ISINIT

Some data from ICP Expert:

Luc

Thanks Luc, you are right. My understanding of the internal standard process was a bit backwards so your example helped a lot. 

I know its definitely the Na & K in my cal standards that's causing this depression so I'm just working on reducing that a bit.   Thanks again for you help 

Hi Luc, just a follow up question. If your method is reading come elements in Axial mode and some in Radial mode should you also be matching that for the internal standard readings too? E.g. Na is read in Radial, so should I also read its matching IS in Radial also and Zn in Axial with matching IS in Axial?