Measuring Cr in high ferrous material

does anyone have an explanation for the fact, that I have a lower result for Cr (approx. 30%) with material with a high iron content, e.g. Millscale, with the measuring mode 'NoGas'? Measured with He mode, the results are correct. Measured with ICP-MS Agilent 7800, digestion in HNO3, HBF4 and water.
Thank’s and regards

  • Hello

    It is most likely an Argon Carbon interference. Ar(mass 40) + C (mass 12) will be the same mass as Cr most abundant isotope at mass 52. 

    He mode is great for avoiding polyatomic interferences. Since polyatomic species (ArC) are larger in size than individual atoms (Cr), the polyatomic species are slowed down in He mode by kinetic energy discrimination. 

    Hope that helps

  • Hi and thanks for the answer, but that would only be an explanation if the result was too high. But this is not the case, my Cr result is 30% too low...

  • Hello

    I am not an applications expert,  but if I had to guess it is because ArC would be present through your calibration - from blank to all standards. ArC present in no gas mode would artificially increases counts in blank and standards, thus potentially giving you a lower check standard concentration

    I found this great Agilent applications note further explain Cr52 interference. Hope this answers your question

  • Hi, thanks for the good input, I hadn't thought in this direction. The effect only occurs with materials that contain a lot of iron, in the middle of a batch that also contains other materials, so I thought it was an influence of Fe. No such effect occurs with other materials.

    I will have another look at this next week, best regards best regards

  • You can always use the semi-quant where you can check the isotopic ratio. This will give you some idea about the origin of the interference. 

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