1. Aysula, P., Anderson, P. and Langford, C.H. (1987), Anal. Chem. 59, 1582.
2. Bajo, S. (1992), in Preconcentration Techniques for Trace Elements,eds Z.B. Alfassi and C.H. Wai, CRC Press, Boca Raton, FL, p. 1.
3. Bajo, S., Suter, U. and Aschliman, B. (1983), Anal Chim. Acta
149, 321.
4. Basset, J., Denny, R.C., Jeffery, G.H. and Mendham, J. (1978), Vogel’s Textbook of Quantitative Inorganic Analysis, 4th edn, Longman, London, p. 115.
5. Bernas, B. (1968), Anal Chem. 40, 1682.