Avoiding HF in preparation
I noticed that many of the REE standards suggest avoiding HF in preparation. Does this imply that use of EPA Method 3052 (HNO3 plus HF) should be avoided for sample digestion if the ICP-MS analysis is to include the REY group?
Actually, HF is OK at MS working levels of 1 to 10 ppb. The ppb stability study (published on our web site) showed good stability with REEs when mixed with the HF elements at ppb levels. I have also been able to dissolve zeolites containing % levels of REEs using a 95:5 ratio of HCl to HF. When the digestate is diluted to levels where the REEs are at the ppb level then HF is actually a good thing to have around. I do suggest spike recovery confirmation of this approach simply due to the fact that simple changes in order of addition/process can alter results. Confirmation of your procedure/approach is always a good idea. Please note that the 95:5 HCl HF digestion works because the amount of the F- (fluoride anion) is very low due to the high concentration of a strong acid – it is when you dilute the digestate the REEs will drop if their concentration is in the ppm rather than ppb level. Finally, if the digestate is high in REEs then dilution into an EDTA/Boric acid mixture will solve the fluoride precipitation problem. Please feel free to call me at the 1-800 number listed below if you would like to discuss and thanks for the great question.
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.