INDUCTIVELY COUPLED PLASMA-ATOMIC EMISSION-SPECTROMETRY IN EXPLORATION GEOCHEMISTRY

Inductively coupled plasma-atomic emission spectrometry (ICP-AES) is a well-established, cost-effective, multi-element technique which is routinely used for geochemical analysis in the mineral exploration industry. Systems available range from relatively expensive simultaneous instruments capable of precisely and accurately determining more than 35 major- and trace-elements in less than 2 minutes, down to much cheaper but slower sequential machines which compete directly with atomic absorption spectrometers. The practicalities of instrument design and operation are discussed in detail, to provide the geoanalyst with information on the selection, purchase and routine use of equipment and to help assess whether the method is suitable for particular analytical tasks. The advantages and disadvantages of different instrumental options and analytical protocols are stressed with specific reference to the routine analysis of exploration samples. It is demonstrated that all of the major elements and a wide range of trace elements can be determined by ICP-AES. The technique displays excellent sensitivity for many low atomic number elements (B, Be, Li, P. S), the alkali earths (Ba, Ca, Mg, Sr), refractories (Al, Ti, Zr), the rare-earth elements (REEs), Sc and Y. Performance for the first-row transition metals is also generally good. The number of elements determinable varies greatly depending on sample type and preparation procedures used. Spectral interferences commonly limit the range of trace elements which can be measured, but this can be usefully extended using simple chemical separation techniques such as cation-exchange chromatography prior to the determination of the REEs, hydride generation for As, Bi, Ge, Sb, Se, Te and Sn, OT solvent extraction for many trace metals. The precious metals may be determined at low levels following fire assay preconcentration. Comparisons with other instrumental methods indicate that ICP-AES is particularly versatile and compares very favourably with AAS, INAA and XRF for the determination of major and trace elements in a wide range of matrices. It is ideally complemented by ICP-MS which allows the determination of ultra-trace levels of heavier elements without the need for chemical separation procedures and can be employed on the same samples prepared for ICP-AES.