714 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS for various vapour components and gases, as a result of which the per- meated vapour composition changes in comparison with its original composition. Equally, the odour of the packaged product can be changed by prefer- ential permeation of one or more components of the vapour which charac- terize the odour, not being substituted sufficiently by the packaged product. It is not intended to discuss the vapour components as such, nor to consider their typical function, but to furnish preliminary information on the vapour composition preceding, and following, permeation through a number of well known packaging films. METHOD AND INSTRUMENTATION The method to determine the changes in odour when permeating through a packaging film, consists of two separate procedures: 1. Sampling the odorant vapour prior to, and after, permeation, and 2. analysis of the odorant vapour. For sampling the odorant vapour preceding, and following, permeation through a film the method developed by Wientjes, Maarse and Van Straten (1) is applied. The intrinsic part of it is the specimen holder (Fig. 1). The holder consists of two glass half spheres, separated by the film specimen. To avoid stresses, strains, and consequently orientation of the material, as encountered in earlier stages of testing, the specimen is sup- ported by a filter plate. The glass filter plate of porosity 2, is also used to determine pinholes in the specimen, if present. For this purpose the specimen is placed on top of the filter plate, while the space in the sphere below is evacuated. One or more pinholes show up immediately by a rapid loss of vacuum. For testing, the product is placed on top of the specimen, inside the upper half sphere. A stream of nitrogen through the lower half sphere carries the permeated vapour along at such speed as is necessary to keep the partial pressure of the vapour components at practically zero. Fig. 2 shows the test arrangement. After passing the lower half sphere, the vapour-laden nitrogen flow can either be led through the pre-column or the pressure control. Using a pressure gauge the pressure needed to overcome the resistance in the leads can be measured, and the resistance in the less resistant lead can be regula- ted by means of the pressure control. The pressure in the upper half sphere

CHANGES iN COMPOSITION OF VAPOURS OVER ODOROUS PRODUCTS 715 1 Figure 1 Specimen holder for measuring the permeation of yapours over odorous products through plastic films (1) scavenging piece, (2) lower half sphere, ($) support plate, (4) specimen, (5) upper half sphere. can be equalized as well. A flowmeter shows the volume of gas passing through per unit of time this flow is normally set at 30ml min-1. The pre-column is a small packed gas chromatographic column, precooled at _ 80øC. To obtain sizable component peaks in the final chromatogram it may be necessary to collect as much as 300ml of the gas flow, laden with the