Solid Phase Microextraction for Quantitative Analysis in Nonequilibrium Situations

Abstract

Solid phase microextraction (SPME) is a convenient and efficient extraction method that involves using a thin polymer film coating on a fine silica fiber to adsorb analytes of interests from a sample matrix. A theoretical model is proposed to deal with the dynamic adsorption process of SPME. In this model, mass diffusion from the matrix to the SPME polymer film is considered as the rate-determining step in reaching an adsorption equilibrium, and a steady-state diffusion is assumed for SPME in an effectively agitated sampling medium. Mathematical treatment of the adsorption process generates an expression that can describe experimental adsorption time profiles of the SPME process. The expression also provides a directly proportional relationship between the amount of analyte adsorbed by the SPME fiber and its initial concentration in the sample matrix. This relationship indicates that SPME quantification is feasible before an adsorption equilibrium is reached, once the agitation condition and the sampling time are held constant. The theoretical model is fitted with experimental data, and there is a very good agreement between them. Data plots of the adsorbed amount vs the initial concentration showed excellent linearity, with a sampling time much shorter than that required for reaching an adsorption equilibrium.

The use of headspace solid phase microextraction for the characterization of volatile compounds in olive oil matrices

“…The adjusted curves according to Eqs. (1) and (2) of the model of Ai [4] are shown in the graphs of Fig. 1, for 2-methylbutan-1-ol for both fibres at the concentrations studied.…”

“…It is not practical to do so when equilibration times are excessively long. Ai [4] presented a mathematical model (Eq. (1)) to demonstrate that SPME quantification, in aqueous solution, using fibres coated with a polymeric liquid, is feasible before absorption equilibrium is reached, if the amount of analyte absorbed (n) is proportional to the initial concentration in the sample matrix (C 0 ):…”

“…The parameter a h is controlled by mass transfer coefficients, equilibrium constants and the physical dimensions of the sample matrix, headspace and the polymeric film. It has different magnitudes depending on the ratedetermining step of the mass transfer process: matrix/headspace and headspace/polymer, diffusion in the polymeric film and evaporation from the matrix phase as described by Ai [4,5]. However, in Eq.…”

Determination of atrazine, acetochlor, clomazone, pendimethalin and oxyfluorfen in soil by a solid phase microextraction method

“…Although extraction using equilibrium time is recommended, some proposed theoretical models for explanation of the SPME process have indicated that quantification is possible before a sorption equilibrium is reached (Ai, 1997(Ai, , 1998Đurović et al, 2007), so that a 30 min extraction time, for practical reasons, was chosen in the following experiments. The time period of 30 min has been found enough time to provide sufficient analytical sensitivity for all compounds studied.…”

A headspace solid-phase microextraction method of use in monitoring hexanal and pentane during storage: Application to liquid infant foods and powdered infant formulas

“…A much shorter sampling time can be used for quantitative analysis provided sensitivity is not the main concern (Ai, 1997). …”