ICP Multi-Element Solution Incompatibilities
Karen's department was having some difficulty with their ICP-OES getting a full list of elements to pass at 1 mg/L for their criteria of ± 10% recovery. When they prepared their lab mix at 1 ppm using a stock standard of 23 elements (Ag, Al As, Ba, Be, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Mo, Na, Ni, Pb, Sb, Se, Tl, V, and Zn all at 100 ug/mL), the addition of other elements such as P, S, Si, Sn, Li, and Ti yielded many inaccurate readings. Karen wondered if there might be interference.
When you add the P, S, Si, Sn, Li, and Ti, there is a lot of chemistry that may take place. The list is as follows:
- The S will react with the Ba and Pb causing a precipitate, assuming that the manufacturer uses sulfate. At Inorganic Ventures, we use a different sulfur compound that does not precipitate with any of these elements.
- Sn and Ti can partially hydrolyze out of solution depending upon how these elements are chemically "fixed" (i.e., whether they are fluorides or chlorides).
- If Cl is present, Ag will precipitate or photoreduce depending upon the Cl and Ag concentrations.
- If too much Fluoride is present then Ba and Ca can partially precipitate.
- The viscosity of the solution may be altered sufficiently to cause a bias in the readings. The use of internal standardization is often used to compensate for this type of interference.
We have designed solutions and identified spectral lines that will give accurate readings for all of the elements in the periodic table. The only potential problem could be that the instrument you're using MAY not have the spectral range or sensitivity.
Please let me know if I can be of further help.
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.