SLM Unit and System Configurations

The heart of the SLM extraction procedure is the SLM unit, in which analyte extraction, preconcentration, and sample cleanup take place in one single step. The design of the SLM unit can be engineered according to the intended use of the unit. For instance, if an SLM unit is needed for an automated and flowing sample extraction, it can be manufactured from two blocks of polytetra-fluoroethylene (PTFE), poly vinylidine difluoride (PVDF), or titanium. However, for nonautomated, nonflowing SLM extraction, a short piece of porous HF membrane is used. 

Another format of the HF-SLM procedure was to employ a 15-20 cm long piece of HF as the extraction device. The HF lumen was then filled with acceptor solution using a microsyringe, and a loop made out of the HF. This loop was then soaked in an organic liquid before being added to the sample agitated on a shaker.71 

There are several review papers on SLM extraction that touch upon off-line or on-line SLM hyphenation to analytical instruments as well as the fields of SLM applications.6772 The following discussion will focus mainly on other aspects of SLM, such as transport mechanisms, selectivity, and equilibrium sampling with SLM. 

---