EVALUATION OF ORAL ODOR 293 nose so that boiling characteristics of objectionable gases will be recorded from the flame (or ion detector) output and their objectionability noted on the proper recording. Through the use of secondary traps it is possible to concentrate particular gases for further analysis. This technique requires absolute temperature control throughout the range from the liquid tem- perature of the gas outside the trap up to 20øC. Because of the extensive temperature monitoring and control system needed, the method has never been useful beyond the preliminary collection of a few odors. If one has some idea of the chemical configuration of the gas in question, it is possible to capture the gas into a material which will selectively absorb or adsorb it. This capturing chemical is placed in a tubular column through which the gas is directed. These columns can then be heated slowly while flushing hydrogen or in some cases inert gases through them. Characteristic peaks will be recorded by ion or flame detectors for particular temperatures, and these can be compared with peaks for known chemicals which have been captured by the column. Columns are available for the analysis of polar compounds, some hydrocarbons, nonpolar materials of up to six carbons, some low boiling point hydrocarbons, some blood volatiles, some primary phenols and cresols, a few steroids, some fatty acid configurations and some other specific gases. More columns are becoming available weekly. Until more comprehensive atlases of the characteristic column capabilities are available, the use of column chrornatographic analysis for the study of oral odor producing compounds will be limited. Infrared Detection The energy of light of wavelengths from 1-8 u is not sufficient to break chemical bonds. It is sufficient to stretch and bend bonds so that changes due to the absorption of energy in chemical compounds may be detected and recorded. Because atlases are available for the interpretation of characteristic bond mobilization energies, the use of infrared gas analysis techniques offers more promise in the study of oral odors. The equipment and techniques are available but expensive. The results obtained require interpretation by experienced personnel. These interpretations require the availability of considerable data and confirmatory chemistry, thus render- ing them unsuitable for clinical evaluation programs. Two techniques have been developed in our laboratory which may offer some data for the general field of oral odor analysis. The first of these requires the use of an infrared gas detection apparatus. The method may be used for approximating the molecular weight of compounds of particular interest because of their odor producing properties. Air is exhaled through the mouth into a cell. This cell is attached to a tube filled with inert gas which has an infrared detector at its other end (as shown in Fig. 5). Both the cell and the tube are pressurized to the same pressure with inert gas.

294 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS By use of a magnet, a port is carefully opened between the cell and the tube, and the time taken for a particular gas to diffuse through the tube to the detector is recorded. By reference to calibration graphs comparing diffu- sion times with infrared detector outputs for known substances, it is pos- sible to estimate the various molecular weights of gases from the oral cavity, together with information upon some of their chemical configura- tion. A second method, one which is more applicable to clinical evaluation, has been developed for saliva samples. Infrared cells which are capable of withstanding dissolving by water are expensive. They further require complete cleaning between samples. This has limited the use of the in- C•• Sample and Pressure Inlet %•_•e Balance Inlet I Infrare d Cell 'Jl•. Diffusion Tube ,•o i Detecto r • Movable Seal l- I Odor Sampling Port Figure 5.--Schematic layout of apparatus for the study of the diffusion rates of odor containing gas mix- tures. The odor sampling port is used to extract samples of gases for odor analysis after their diffusion charac- teristics have been established. frared analysis of saliva, even in laboratory studies. We have developed infrared cells which are disposable using 0.5 ml. Teflon ©* FEP-fiuoro- carbon film for the windows and holding the layers of Teflon apart by use of shims. This plastic is transparent throughout the 1-Su range and is in- expensive enough to be thrown away after use. For clinical analysis, cells made of cardboard with Teflon windows could be prepared in advance and rapidly analyzed directly after the donation by a test subject. It has been possible with these cells to identify some dissolved gases in saliva. The same techniques could be used for the analysis of oral odor gases dissolved in one of several organic solvents since Teflon is inert to most organic sol- vents and oils. Micro-Dens ilometry By passing visible and ultraviolet light through pressurized quartz cuvettes containing gases dissolved in appropriate solvents, it is possible to record some absorption activity. However, the stability of gases from human breath exhaled through the oral cavity and bubbled into solvents other than water must be questioned. The method is suggested here