170135_inorganicventures_flipping

16.8 ICP-MS Measurement

Polyatomic (Molecular) Interferences:

• Molecular interferences are due to the recombina3on 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. • Star3ng with 39 K, polyatomic interferences becomes a significant issue. (For example, 39 K is interfered with by 38 Ar 1 H and 23 Na 16 O.) • Some polyatomic interferences can be avoided by elimina3ng certain matrix elements. (For example the classic 40 Ar 35 Cl interference upon the monoisotopic element 75 As can be avoided by elimina3ng HCl in the sample prepara3on.) • Elimina3ng HF, HCl, H 2 SO 4 , and H 3 PO 4 from sample prepara3ons helps but does not avoid the problem completely. (The isotopes 56 Fe, 39 K, and 44 Ca or 40 Ca are all interfered with by combina3ons of the Ar, O, and N isotopes.)

16.9 ICP-MS Measurement

Polyatomic (Molecular) Interferences:

• 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 formaAon.The severity of the MO interference can be reduced through reducAon of the sample argon gas flow rate. • The use of cool plasma techniques, reacAon / collision cells, desolvaAon, and chromatographic separaAons -- to name a few approaches -- have resulted in reducAon and, in some cases, complete eliminaAon of many polyatomic interferences. Mass correcAons may be an opAon in cases where the use of an alternate isotope is not an opAon. • Polyatomic interferences are parAcularly troublesome in the determinaAon of first row periodic table elements (K thru Se) due to the vast number of combinaAons of Ar with matrix components.