1. Beitz, L. and Rönieke, G., Proceedings of the Third International Clean Air Congress, Düsseldorf, 1973, p. C32.
2. Luke, C. L., Anal. Chim. Acta, 41, 237 (1968).
3. Collin, R. L., Anal. Chem., 33, 605 (1961).
4. Van Nickerk, J. N., DeWet, J. F. and Wybenga, F. T., Anal. Chem., 33, 213 (1961).
5. Kashuba, A. T. and Hine, C. R., Anal. Chem., 43, 1758 (1971).