Miniaturization, Automation, and Hyphenation of MMLLE

As in the SLM systems, FS- and HF-MMLLE configurations can be run automatically in flowing modes and operated off-line or connected on-line to analytical instruments. Recently, a microfluidic chip-based FS-MMLLE system was reported.83 In addition, miniaturized, nonautomated, nonflowing, off-line MMLLE systems are usually used with HF membranes. The emphasis in this section will be placed on these latter modes of MMLLE operation. 

1 Off-Line Systems Flowing FS- and HF-MMLLE systems are usually operated by pumping the sample solution on the sample side of the membrane, which can be done with a peristaltic or syringe pump. The stagnant or flowing organic solvent is supplied by another similar pump to the acceptor channel and membrane pores. 

The impact of several factors on the MMLLE extraction yield of PAHs in water has been comprehensively studied using a flowing FS-MMLLE system and off-line analysis with GC-flame ionization detection (GC-FID).84 The flowing FS-MMLLE procedure combined with off-line GC-mass spectrometry (GC-MS) analysis has been utilized for the extraction of nonionic and derivatized ionic organotin compounds in river water.85 

2 On-Line Systems Flowing MMLLE systems have been established in different layouts with automation and on-line hyphenation to GC and HPLC analysis. An automated on-line FS-MMLLE-GC system with a loop-type interface compatible with LVI was used for the extraction of pesticides and PAHs in surface waters.86 In another study, pressurized hot water extraction (PH WE) was coupled on-line to a FS-MMLLE-GC-FID system and applied to the analysis of PAHs in soil, where MMLLE was used as a cleanup and concentration step of the PH WE extract prior to final GC analysis.87 In addition, an HF-MMLLE setup was incorporated in PHWE and GC, resulting in an online PHWE-HF-MMLLE-GC system, where the HF membrane module contained 10-100 HFs. The system served for the extraction and analysis of PAHs in soil and sediments  

Flowing FS-MMLLE with on-line hyphenation to FtPLC has also been investigated. Sandahl et al. were the first to interface FS-MMLLE with reversed-phase HPLC for the on-line extraction of methyl-thiophanate in natural water, obtaining an LOD of 0.5 pg L-1.89 Also, a parallel FS-SLM and FS-MMLLE design was coupled on-line to reverse-phase HPLC for the extraction of methyl-thiophanate (by MMLLE) and its metabolites (by SLM) in natural water.90 In addition, on-line coupling of FS-MMLLE and normal-phase HPLC has been successfully applied in the determination of vinclozolin (Ee =118 and LOD = 1 pg I. ) in surface water91 and of in-sample ion-paired cationic surfactants (Ee 250 and LOD = 0.7-5 ug L-1) in river water and wastewater samples.92 

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