About the authors DR. B. V. IOFFE was born in 1921. He is professor and director of the Gas Chromatography Laboratory at Leningrad State University, in Leningrad, U.S.S.R. He is the author of more than 200 publications and of six monographs and textbooks. His research interests include: physical methods for the investigation of organic compounds; gas chromatography--particularly head-space analysis by GC; gas chromatography--mass spectrometry; chemistry of the derivatives of hydrazine and hydroxylamine; and chemistry of nitrogen-containing heterocyclic compounds and of reaction intermediates (nitrenes, carbonium ions). He is a member of the Editorial Boards of the Journal of Organic Chemistry and Chemistry of Heterocyclic Compounds, both journals being published in the U.S.S.R. DR. A.G. VITENBERG was born in 1935. He is a Senior Research Scientist in Organic Chemistry at Leningrad State University, in Leningrad, U.S.S.R. He is the author of more than 60 publications and of a textbook on gas chromatography. His research interests include chemistry of aliphatic diazo-compounds, kinetics of chemical reactions, and gas chromatography--particularly headspace analysis by GC--and various concentration methods for trace analysis.