2.2.1. Volatiles in the headspace environment
Headspace environment refers to the techniques and devices used to manipulate the headspace, or air surrounding an odour source where volatiles are actively emitted. The volatile profile obtained from an odour source strongly depends on whether the headspace volatiles are contained (concentrated) or actively relayed to the collection device (via air flow) (for examples, see Heath and Manukian, 1994; Tholl et al., 2006; Carroll and Duehl, 2012). Volatiles can be collected from an open or closed air space. Open sampling schemes are simple to carry out but result in variable losses of target emissions and contamination by background odours. Partially or completely enclosed air systems surround the odour source with a containment system (containers built of glass, metal and other odourless materials) to concentrate volatile emissions and control the sampling rate. For longer collections in an enclosed system, an air flow system is required to ventilate the bees.
techniques can also be classified as dynamic or static. Dynamic flow systems
use active air flow (push), vacuum flow (pull), or combined air and vacuum flow
(push-pull) systems to move headspace volatiles through a filter containing an
adsorbent material volatile trap. The
benefit of dynamic collections is that quantification is easier because
volatiles are trapped at a known rate. Static flow systems have little or no
flow through the headspace. In a static airspace, there will be equilibrium
between volatile compounds present in the solid or liquid source and the same
volatiles in the gas phase. Changes in any volatile component will affect the
equilibrium for all other components in the airspace blend. The main benefit of
static technique is that it is very easy to use and does not require any
expensive equipment or instrument modifications.