Published:Journal of Chromatographic Science,
ISSN 0021-9665Volume 37, Number
8, August 1999, pp. 277-282
Extracted
Amounts by Solid-Phase Microextraction: A Realistic Approach to the Partition
Coefficient K
Louise
Urruty and Michel MonturyBecause
of its numerous advantages, the solventless solid-phase microextraction (SPME)
sampling method coupled with an efficient chromatographic technique is used more
and more to develop new analytical methods pertaining to organic molecules at
low concentration in aqueous solutions, especially in the field of environmental
chemistry. In a usual analytical procedure, the amount of analyte extracted by
the fiber need not be determined, because the quantitation step of the analysis
is mainly achieved using SPME external calibration. For some purposes, however,
the determination of the partition coefficient K relative to a particular fiber
for a specific analyte (for example) has to be calculated with accuracy. The traditional
method consists of determining the response coefficient of the detector used for
the analyte through a direct-injection calibration curve made from standard solutions
in organic solvents and reporting it with the signal observed for the analytical
sample. For the same goal, a depletion experiment method is suggested that consists
of running several SPMEs from the same standard sample with the same conditions
and then fitting the resulting data into an experimental regression curve, the
exponential coefficient of which affords an absorption coefficient characteristic
of the fiber/analyte system in a defined work-up. This self-calibrating method
is revealed to be much more accurate than the previous one. Four pesticides in
water solution were chosen to exemplify this study.
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