Samples Containing Lithium, Sodium, Potassium, Rubidium or Cesium

Hydrolytic Stability, Preferred Matrices and More

All of the alkali metals are soluble over the entire pH range. In addition the use of any mineral acid, water or caustic, is acceptable with the following exceptions. For K, Rb and Cs, avoid chloroplatinate, acid Tartrate, fluorosilicate, picrate, phosphomolybdate, perchlorate, periodate, fluorotitanate, fluorozirconate. For Na, avoid the fluorosilicate. All Li salts are soluble.

Attempt to use LDPE that has been pre-leached with dilute nitric acid as the container material whenever possible. Avoid glass due to the possibility of contamination with Na. The alkali metals are chemically compatible with all other elements and most inorganic molecular ions. In addition, spectral interferences upon other elements and from other elements are minimal with the Rare Earth elements presenting the worst interference issues when using ICP-OES.

When using axial view ICP-OES, be weary of ionization effects similar to that observed in flame AAS. Enhancements in the signal as large as a factor of three in matrices high in other elements, such as Cu for example, are possible. This ionization effect gets worse as the atomic number of the alkali element increases. Cs is often used as an ionization buffer with axial view ICP-OES for the determination of the lighter alkalis (usually Li, Na, and K). However it must be very pure, as in Inorganic Ventures' 1% Cesium Ionization Buffer.

ICP-MS is often the recommended technique for the determination of Rb and Cs where detection limits in the ppq region are common. The alkalis are also quite suited to measurement using ion chromatography because their tendency to form complex species is minimal at best.

Inorganic Ventures' QC laboratory uses axial view ICP-OES for trace Li, Na, and K determinations and ICP-MS for trace Rb and Cs determinations. Ion Chromatography or axial view ICP-OES are used for solutions where the alkalis are predominate and have the same order of magnitude in concentration to one another and/or other elemental components.

The following table contains suggested lines for ICP-OES and ICP-MS and typical detection limits:

Was this helpful?  Tell a Friend | Let us know