Sensitive in-surface infrared monitoring coupled to stir membrane extraction for the selective determination of total hydrocarbon index in waters |
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Authors: | M C Alcudia-León B Lendl R Lucena S Cárdenas M Valcárcel |
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Institution: | 1. Department of Analytical Chemistry, Marie Curie Building (Annex), Campus de Rabanales, University of Cordoba, 14071, Córdoba, Spain 2. Institute of Chemical Technologies and Analytics, Vienna University of Technology, Getreidemarkt 9/164 AC, 1060, Vienna, Austria
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Abstract: | 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 μg L−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. |
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