Static (equilibrium) headspace injection is commonly used for GC determination of volatiles in solid and liquid samples. Quantitative analysis can be performed using standard techniques, such as external or internal standard methods and/or methods of standard addition.
If matrix effects adversely influence quantitation, a multiple headspace extraction (MHE) approach can be utilized to prove that equilibrium has been reached. The total amount of an analyte or standard in a sample can then be determined mathematically by extrapolating the peak areas from subsequent extractions of the same vial to calculate the total peak area. A key step to this technique is venting of the headspace between injections, followed by re-equilibration of the sample. Traditionally, pressure balanced and pressure loop type headspace samplers have offered automated MHE. For conventional syringe based systems this has not been possible, because they are limited in the amount of headspace which can be removed from the vial in each extraction step, usually equal to the volume injected. A 1.0 to 2.0 mL injection from a 20 mL headspace vial usually does not displace enough analyte to accurately extrapolate and calculate the total analyte amount.
A novel purge tool for the GERSTEL MultiPurpose Sampler (MPS 2) under MAESTRO software control allows the headspace of a sample vial to be purged with inert gas between injections. This new feature enables the syringe based MPS 2 to perform MHE quantitation. The tool also allows automated purging of headspace samples prior to extraction. A brief explanation of MHE methodology along with specific examples will be given.
