Equilibrium Sampling Through SLM

As mentioned in Section 4.2.3.2, nonexhaustive SPME at equilibrium can be used for speciation studies and the sampling of freely dissolved nonpolar compounds. However, speciation and sampling of polar compounds in aqueous samples is extremely difficult with SPME. As an alternative, the appropriateness of SLM extraction of polar species makes the SLM technique uniquely suitable for performing speciation studies of such compounds, when SLM operation is carried out at equilibrium and under nonexhaustive conditions. 

The operational performance of an HF-based ESTM technique was first described by Liu et al.71 A 15-cm piece of HF was filled with an acceptor buffer solution, after which the F1F was made into a loop. This loop-like F1F device was soaked in n-undecane, and then immersed in 1 L of a river or leachate water sample for extraction of freely dissolved chlorophenols. This FIF-loop device was also employed for selective ESTM sampling of freely available Cu+2 in leachate water.78 The selectivity stemmed from a selective liquid membrane (di-n-dihexyl ether) containing a carrier (crown ether/oleic acid) and a selective stripping agent in the acceptor solution. 

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