Using Indium as your internal standard

The bottles contain 500.00 ug/ml ea: K, Na, P as well as 50.00 ug/mL ea: B, Mo, Si in 5.0% HNO3 (v/v) / tr. HF. The other bottle is the same except it contains 100.00 ug/mL ea: B, K, Na, P and 10.00 ug/mL ea: Ag, Al Ca, Cu Fe, Mg, Pb, Sn, Zn. It is also in 5% HNO3 with trace HF. These standards are not diluted. However, we dilute our samples 20x. Our thought is that if we use an internal standard, then we would need to add it to the standards as well as the samples. It would make it easier on the technicians if everything was diluted the same. Thanks for your help.

I would like to suggest that you try In (indium) as your internal standard. The following are considerations in making this recommendation:

  • In is not likely to be found in your samples.
  • In has very few spectral interferences upon it or upon other analytes.
  • In is chemically stable in dilutions of the blends that you are using.
  • We believe it will be stable in you sample solutions for the short term at the recommended working level of between 1 and 10 mg/L
  • This approach requires little modification or expense in your current methodology.
  • The use of the more popular Sc and Y may suffer from fluoride insolubility problems in your standard solution working solutions.
  • In is stable in HF matrices and in fact the fluoride ion reduces the tendency for In to hydrolyze in basic media.
  • The long term stability of In in basic media (if this is found to be a problem) can be eliminated through the addition of H4EDTA (the hydrogen form of EDTA).

Please feel free to call me to discuss.

Serving you in chemistry,

Paul R. Gaines, Ph.D.
CEO of Inorganic Ventures & Fellow Chemist

DISCLAIMER: Advice offered by the chemists at Inorganic Ventures is intended for the individual posing the question. Feel free to contact us to verify whether these suggestions apply to your unique circumstances.