Tulonru. Vol. 30. No. 2, pp. I t I- I20. t983 ~~9-914~~83/~2~11~-~~3.~~~ Prmted m Great Br~tam Pergamon Press Ltd zyxwvut SHORT ~~MMUNI~ATIUNS DETERMINATION OF SILICON BY AN INDIRECT ATOMIC-ABSORPTION METHOD USING CARBON-ROD ELE~TRUTHERMAL ATQMIZATIUN J. F. TYSON and W. S. WAN NGAW Department of Chemistry, University of Technology. Loughboraugh, Leicestershire, England zyxwvutsrqponmlk (Received 5 April I982. Accepted 16 September 1982) Sumw ry - An indirect procedure has been developed for the determination of trace amounts of silicon by atomic-absorption with carbon-rod electrothermal atomization. After dissolution, the silicon IS extracted as silicomolybdic acid into a mixture of diethyl ether and pentan-l-01 (5 + 1). The co-extrac- tion of excess of molybdate reagent IS prevented by the addition of citrate, which also destroys phospho- molybdic and arsenomolybdic acids. The orgamc layer is washed with hydrochloric acid, pl quantities are transferred to the electrothermal atomizer and the molybdenum is measured. The method has been applied to analysis of several steels. In attempting to extend the sphere of application of atomic-absorption spectrometry (AAS) in analytical chemistry both in terms of sensitivity (and conse- quentfy detection limit) and range of elements or spe- cies determined, the chemistry of the heteropolymo- lybdates offers several attractive possibilities, particu- larly when combined with electrothermal atomization devices. The polymerization reaction which occurs when a solution of molybdate (Mo@~-) is acidified in the presence of a hereroelement has been used as the basis of analytical methods for about 10 of the poss- ible 35 hetero-elements, namely P, Si, As, Ge, V, Th, Ta, Ti, Nb and Ce, Most of the previously reported methods use solution spe~trophotometry or flame AAS as the final measuring stage in a procedure that almost always includes a solvent extraction stage to separate the heteropoly species, H,XMo,,O,, (where the value of n depends on the oxidation state of X) from the large excess of molybdate reagent, which polymerizes under the reaction conditions to give one or more of the ~sopolymoly~ates. The indirect determination of the hetero-element by determination of the molybdenum in the hetero- poly species gives a considerable enhancement of sensitivity because of the 12:l molar ratio of MO to x. Preliminary results for phosphorus and arsenic have already been reported’ and the problems of the high blank values (due to co-extracted isopolymolyb- date) and the difficulties in atomizing molybdenum from a carbon-rod electrothermal device outlined. In this paper the development of a method for silicon is described. The analysis of some standard steel samples, in which interference effects might be expected, is included to illustrate the application of the method. Silicon has been determined by solution’-’ and AAS amplification methods.3*“‘0 Ultraviolet spectro- photometric methods are based on the measurement of the absorbance of silicomolybdic acid 6*7 or its reduction product’,’ (“molybdenum blue”) or its de- composition product in a basic buffer.2v3 The atomic- absorption methods3*8*9 are based on the measure- ment of the molybdenum content of silicomolybdic acid. Concentration ranges of 0.1-0.4 and 0.1-1.2 ppm of silicon are covered by the indirect ultraviolet and atomic-absorption methods, respectively.’ The direct determination of silicon by atomic-absorption has also been described (e.g., Price and Roos’~), but the sensitivity is poor. Silicon in steel has been determined by atomic- absorption spectrophotometiic,4~11~1z colori- metric,4*5.‘3 gravimetric,‘39’4 titrimetric and electro- chemical methods.14 A differential pulse polaro- graphic method has also been used for levels down to 0.002~. ” The methods used by British Chemical Standards for the determination of silicon in steel are gravimetric and photometric. Several workers have found that the addition of complexing agents such as citric, lactic, tartar& oxalic and mafonic acids, glycerol, mannitol and ethylene glycol to phosphomolyb~~ and ars~omoiyb~c acids destroys both acids, but not silicomolybdic acid.“-Is Chalmers and Sinclair16 found that certain complex- ing agents (notably citric, tartaric and oxalic acids, and mannitol) shift the absorption spectrum of iso- ~lymolybdates by complexation, and have estab- li7