, its
implementation requires the introduction of a highly selective
online GD [24–26] or pervaporation [27–29] separation step prior to
the analytical detection. In both membrane separation techniques
the sample is introduced into a donor stream where a volatile or
semi-volatile analyte or analyte that can be converted chemically
into volatile species is separated from the sample matrix containing
interferents by transferring it across a hydrophobic porous membrane into a static or flowing acceptor solution in direct contact with the membrane and containing suitable acid–base indicators [24]