Head Space Analysis

Another type of gas sampling technique is head–space analysis. This technique can be used to monitor trace organic components in air or some other permanent gas, which is in equilibrium with a sample matrix. It can be used to examine the condition of food 'stuffs' for deterioration. The deterioration of certain foods during storage is often accompanied by the generation of low molecular weight organic acids, alcohol's and ketones. The same sampling technique can also be used to identify essential oils from fruits or vegetables and the peak pattern can help identify their source.

Due to the nature of apparatus, the sample must be collected on site and then brought to the laboratory for extraction and analysis. It is important that no deterioration, or other change, takes place between sampling and the analysis. This is crucial if the sample is suspected of spoilage as the spoilage will continue between tissue collection and analysis and consequently the results will be false. Thus, after the sample of foodstuff has been taken, it should be placed in a sealed plastic bag (made from opaque material to prevent photochemical decomposition) and refrigerated at about 2°C. At this temperature bacterial action will be retarded and the sample will remain reasonably stable for several hours.

Figure 6 Head–Space Sampling

If the head space sampling and analysis cannot be completed in a few hours the sample should be frozen immediately after selection. The apparatus used is shown in figure 6, which demonstrates the simplicity of the technique: the apparatus can be fabricated in the laboratory if so desired.