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M. Alcudia-Leon, B. Lendl, P. Lucena, M. Cárdenas Gaudry, M. Valcárcel:
"Sensitive in-surface infrared monitoring coupled to stir membrane extraction for the selective determination of total hydrocarbon index in waters";
Analytical and Bioanalytical Chemistry, 398 (2010), 1427 - 1433.

In this paper, the direct coupling between stir
membrane extraction and infrared spectroscopy working
under transmission mode is presented for the sensitive
and selective determination of the total hydrocarbon
index in waters. For this purpose, a new extraction unit
was built using stainless steel in order to maximize the
adsorption of the target analytes in the 40-μm-thick
polytetrafluoroethylene membrane. The method allows
the determination of hydrocarbons in the presence of
grease, using hexadecane and stearic acid as model
compounds, respectively. The proposal is optimized in
depth, taking into account the main experimental variables
such as membrane thickness, extraction time, and
stirring and sample volume. Later on, the method was
characterized on the basis of its linearity, precision, and
limits of detection. The combination allows the determination
of the hydrocarbon index with a limit of detection
of 18 μgL−1, the precision being (expressed as relative
standard deviation) better than 4.3%. The analytical
method provides a high sample throughput since some
extractions can be performed in parallel, the relative
standard deviation between devices being better than 8%.
The proposed analytical method is finally compared in
terms of analytical figures with counterpart ASTM
method, recently presented.

http://dx.doi.org/10.1007/s00216-010-4040-x