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News from the Lab  Articles Online  Analytical Quick Tip  Joke of the Month  Polyatomic (Molecular) Interferences

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Try using HCl rather than HNO₃ as the matrix acid for Hg⁺² measurements using ICP-OES or ICP-MS. Stability of ppb level solutions is better and washout is faster.

Molecular interferences are due to the recombination of sample and matrix ions with Ar and other matrix components such as O, N, H, C, Cl, S, F, etc. The light elements (Li, Be, B) are not affected due to their small masses.

Starting with ³⁹K, this type of interference becomes a significant issue. For example, ³⁹K is interfered with by ³⁸ArH and ²³Na¹⁶O. Some polyatomic interferences can be avoided by eliminating certain matrix elements such as the classic ⁴⁰Ar³⁵Cl interference upon the monoisotopic element ⁷⁵As, where the use of HCl in the sample preparation is to be avoided. The isotopes ⁵⁶Fe, ³⁹K, and ⁴⁴Ca or ⁴⁰Ca are all interfered with by combinations of the Ar, O, and N isotopes.

As we go to the heavier elements, the major polyatomic interferences come from isotopes that are 16 atomic mass units lower than the analyte isotope through molecular oxide (MO) interference. The lanthanide element isotopes are especially prone to molecular oxide formation.

The use of cool plasma techniques, reaction / collision cells, desolvation, and chromatographic separations -- to name a few approaches -- have resulted in reduction and, in some cases, complete elimination of many polyatomic interferences. The severity of the MO interference can be reduced through reduction of the sample argon gas flow rate. Mass corrections may be an option in cases where the use of an alternate isotope is not an option. Polyatomic interferences are particularly troublesome in the determination of first row periodic table elements (K thru Se) due to the vast number of combinations of Ar with matrix components.

The above passage was taken from the 'ICP-MS Measurement' section of our Reliable Measurements guide. Read the full article here.

Articles Online  more articles

ICP-MS Measurement · Part II
This part of our Reliable Measurements guide continues our discussion of ICP-MS sample measurement procedures, touching on various interferences and measurement techniques.

New Evaporation Device Shows Promise
A new evaporation instrument shows significant promise for reducing environmental contamination in the lab.

Cleaning Quartware
Dr. Gaines shares his preferred method for cleaning quartz flasks, specifically glassware used to digest organic compounds.

Joke of the Month  more humor

A small piece of sodium that lived in a test tube fell in love with a Bunsen burner.

"Oh Bunsen, my flame. I melt whenever I see you," the sodium pined.
"It's just a phase you're going through," replied the Bunsen burner.