Until recently there has been very limited information concerning the molecular geometry and conformation of biogenic monoamines and this lack of knowledge has seriously hampered efforts to unravel the structure—function relationships at the molecular level. Nevertheless, several theories have been proposed regarding interaction between the monoamines and their receptor sites. This is especially true for the neurohumoral transmitters dopamine, noradrenaline (norepinephrine) and serotonin (5-hydroxytryptamine), the target areas of which seem to be specific not only in the sense of chemical structure but also from the steric point of view. The well-known differences in biological activity due to chiralty illustrate the importance of the three-dimensional architecture of the molecules and indicate also the presence of stereospecific receptor sites. A detailed knowledge of the conformation of the biogenic monoamines would not only elucidate the requirements upon a natural or synthetic monoamine for proper function but also give indirect information about the geometry of the receptor sites.

Mass spectrometric analysis of organic compounds was in the early 1950s done mostly for quantitative determination of petroleum products. The use of the mass spectrometer for qualitative analysis of solid organic material samples was shown by O'Neil & Wier (1951) and since then a continuous increase in mass spectrometric studies of different classes of organic compounds has been noted. After the gas chromatograph was developed by James & Martin (1952) the quantitative analysis of complex mixtures of organic compounds was possible and after a few years the gas chromatographic method was considered as routine. The first connection of a gas chromatograph (GC) to a mass spectrometer (MS) was made by Holmes & Morell (1957). They studied gases using a splitter system where only a small part or less than 1% of the effluent from a packed column was transferred to the ion source of the mass spectrometer. The next step in GC—MS development was made by Gohlke (1959), who studied compounds of low molecular weight using capillary column directly connected to a time-of-flight mass spectrometer. This was possible due to the fact that the carrier gas flow rate could be limited to about 1 ml/min. To avoid the sample loss resulting from using a packed column with the splitter system a jet molecular separator was constructed as an interphase between the packed column and a mass spectrometer with magnetic sector analyser (Ryhage, 1964). Mixtures of fatty acids and of hydrocarbons with a molecular weight of up to about 420 were studied. In this study spectra were taken at irregular intervals.