Calibration and analytical features

Calibration in headspace work is usually done by using one of four different techniques, namely external-standard, internal-standard, standard-addition and vapour-phase calibration. 

External-standard calibration can be implemented by using either a simulated matrix or a pure matrix, the similarity between both being a function of the ease of preparing a simulated matrix closely resembling the pure matrix. 

Solid sample treatments involving the removal of volatile species 

Single or multiple linear regression standard-addition calibration can be performed by using a single liquid or gas phase addition — the latter being more appropriate for solid samples however, it can also be implemented in conjunction with additional standards for normalization (see Fig. 4.15). 

Vapour-phase calibration (VPC) is based on the principle that the concentration of the volatile analyte in the gas phase can be determined by external-standard calibration. If the total amount present in the vial is known, the concentration in the sample phase at equilibrium is calculated from the difference. This technique, where the distribution of a volatile compound between two phases in a headspace vial is determined by using a pure vapour as reference, was originally implemented by Kolb using automated head-space equipment to determine distribution coefficients in gas-liquid [77] and gas-solid systems [78], and later by Schoene et al. [79] to determine solubility coefficients in vapours of both solid and liquid polymers. Although these investigations focused on 

---