An alternative is to saturate the plasma with a high concentration of another EIE such as cesium. Therefore, the effect of adding cesium as an ionization buffer to the standards and samples was also investigated.
Cesium was chosen as an ionization buffer as it has a low energy of ionization, is not very sensitive by ICP-AES and, therefore, spectral interference is generally not a problem. Cesium chloride is available in a very pure form and does not build up in the torch injector tube as readily as other alkali salts.
The accuracy and validity of the method was assessed by the use of Nycomed Pharma Seronorm Trace Elements Serum batch no. 311089.
A Varian Liberty Series II ICP-AES with the axiallyviewed plasma was used for the analysis. The Liberty Series II ICP features a 40 MHz free running RF generator, a 0.75 m Czerny-Turner monochromator with a 1800 grooves/mm holographic grating used in up to four orders. The resolution of the optical system ranges from 0.018 nm in the 1st order to 0.006 nm in the 4th order.
The instrument was controlled with a Digital Equipment Corporation (DEC) Venturis computer with an Intel Pentium processor and Varian Plasma 96 software running under Microsoft Windows 95 operating system.
The instrument operating conditions are listed in table 1.
For the determination of sulfur, an Auxiliary Gas Module-2 (AGM-2) is required. The AGM-2 provides a nitrogen purge for the monochromator to extend the working wavelength range from 189 nm down to 175 nm. The default grating order was used for all lines with the exception of the Al 396.152 nm line where the order was chan