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 microextractio n (SPME) analysis. Its effect on the results of analysis can be neglected o nly when it is much larger than the fibre capacity KVf (K = fibre/sample pa rtition coefficient, V-f fibre volume). Good agreement was obtained between theoretical predictions and experimental results for analyte extraction fr om two- and three-phase systems. The effect of headspace capacity on SPME e xtraction results and kinetics was illustrated on an example of amphetamine and methamphetamine determination in water. A dramatic improvement in extr action speed was achieved by increasing the extraction temperature, and thu s also the headspace-sample partition coefficients. Difficulties with the a ccurate determination of large partition coefficients are discussed on an e xample of the extraction of C-8-C-12 hydrocarbons from air. Analyte sorptio n on the container walls led to significant losses of less volatile compoun ds, especially when vials of large surface-to-volume ratio were used. A dis cussion of problems encountered when trying to determine accurately partiti on coefficients of semi-volatile compounds in water is also presented.