ICP Detection Limits
I have a question for you and seek your advice. We all know every ICP manufacturer will produce a specification for claiming the lowest detection their ICP can achieve, but as for the user, why we will never be able to achieve such lower detection as what the ICP manufacturer claims? What are we supposed to do?
Great question and this is one that I hope all analysts address. At IV we perform many TMI determinations on our products and thereby encounter lots of issues with DLs. We use a standard additions approach where we analyze the sample and then the sample plus a spike addition of typically 4 ppb of the analyte. If the matrix is lowering the sensitivity (high salt content and ion quenching) you will be able to determine this from the spike/net intensity. From these data (sample and sample + spike) you can estimate the DL of each mass/element. Basically, the question is (what concentration will give a signal that is 3 times the standard deviation of the blank. By measuring the standard deviation of your reagent blank along with the counts/ppb for the standard addition you can estimate the DL. The better your reagent blank matches the sample matrix then the better the estimation. Various types of interferences for given masses must be recognized and accounted for and for some masses the estimation is truncated to a simple decision to not use that mass for a given matrix. There is much more written about DL on InorganicVentures.com in the TECH center but I just want to first encourage you to keep asking this question and exploring ways of estimating the DL. Finally, remember that the DL is an estimate and our view is often clouded when looking at complicated matrices.
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.