The selection of the alkylcarboxylic acid making up the SUPRAS
intended to extract PAH4 was based on criteria such as extraction
efficiency and no interference in the chromatographic resolution of
analytes. Three alkylcarboxylic acids, namely octanoic, decanoic
and dodecanoic acids were tested for this purpose. Extraction efficiency
for the target compounds was similar in the three types of
SUPRAS. Octanoic acid showed the lowest signal background at
retention times above 3.5 min (see Fig. 2), so it was selected as
extractant. As it has been detailed in Section 2.3, the volume of
SUPRAS produced was linearly dependent on the amount of octanoic
acid used for its synthesis. The water content for this SUPRAS
was 6.1 ± 0.1% (w/w).