The effect of sample volume on quantitative analysis by solid phase microextraction -: Part 2.: Experimental verification

The sample volume plays a very important role in solid phase microextraction (SPME) analysis. Its effect on the results of analysis can be neglected only when it is much larger than the fibre capacity KVf (K = fibre/sample partition coefficient, V-f fibre volume). Good agreement was obtained between theoretical predictions and experimental results for analyte extraction from two- and three-phase systems. The effect of headspace capacity on SPME extraction results and kinetics was illustrated on an example of amphetamine and methamphetamine determination in water. A dramatic improvement in extraction speed was achieved by increasing the extraction temperature, and thus also the headspace-sample partition coefficients. Difficulties with the accurate determination of large partition coefficients are discussed on an example of the extraction of C-8-C-12 hydrocarbons from air. Analyte sorption on the container walls led to significant losses of less volatile compounds, especially when vials of large surface-to-volume ratio were used. A discussion of problems encountered when trying to determine accurately partition coefficients of semi-volatile compounds in water is also presented.