Modes Of Liquid-phase Microextraction Research Articles

Emulsion-based liquid-phase microextraction: a review

In the past decade, liquid-phase microextraction (LPME), which can also be called solvent microextraction, has emerged as a minimal organic solvent-based sample preparation approach. The main advantages of this method include versatility, simplicity and effectiveness of its extraction procedures at reducing sample complexity, as well as the convenience of liquid sample concentration and injection techniques. LPME is based on the distribution of analytes between the organic solvent and the aqueous solution. Hitherto, several different LPME modes have been developed. Some of the described methodologies usually offer slow extraction kinetics due to the low contact surface between the sample and the extractant phase. Since the introduction of dispersive liquid–liquid microextraction, a number of studies have been focused on the features of emulsification in preconcentration techniques. Emulsification enhances the surface area between the extraction solvent and aqueous sample by the efficient dispersion (chemically assisted or by the use of an external energy source) of the extractant in the sample. In this paper we review the emulsification-based liquid-phase sample preparation techniques. A brief practical and theoretical description of each technique and some applications are given.

Hollow fiber liquid phase microextraction combined with electrothermal vaporization ICP-MS for the speciation of inorganic selenium in natural waters

A novel method for the speciation of Se(IV) and Se(VI) in environmental water samples based on liquid-phase microextraction (LPME) methods in conjunction with electrothermal vaporization (ETV) ICP-MS has been developed. Two modes of LPME: single drop microextraction (SDME) and hollow fiber liquid phase microextraction (HF-LPME) were studied comparatively. The organic chelating reagent ammonium pyrrolidine dithiocarbamate (APDC) was used as both the extractant for microextraction and the chemical modifier for ETV-ICP-MS determination. Under the optimal conditions, enrichment factors of 75 and 410 could be achieved for SDME and HF-LPME, respectively. The detection limit of Se in HF-LPME-ETV-ICP-MS and SDME-ETV-ICP-MS were 0.50, 0.56 pg mL−1 and 2.7, 3.0 pg mL−1 for Se(IV) and Se(VI), respectively. HF-LPME was finally selected for the analysis of Se(IV) and Se(VI) in lake water, river water and pool water samples due to its good analytical features and robustness. The proposed method was validated by the determination of total Se with PN-ICP-MS.

Application of static and dynamic liquid-phase microextraction in the determination of polycyclic aromatic hydrocarbons

Two modes of liquid-phase microextraction (LPME), static and semi-automated dynamic, have been developed for the HPLC analysis of polycyclic aromatic hydrocarbons. In static LPME, a small drop (3 μl) of organic solvent was held at the tip of a microsyringe needle and exposed to the sample containing the analytes, permitting extraction to occur. In semi-automated dynamic LPME, a syringe pump was used to automate the repetitive procedure of filling a microsyringe barrel that functioned as a microseparatory funnel, with fresh aliquots of sample, and expelling them after extraction. The factors influential to both techniques such as the type of organic solvent, extraction time, sampling volume, number of samplings, salt concentration and temperature were investigated. Static LPME provided high enrichment (60- to 180-fold) and simplicity. The analytical data exhibited a relative standard deviation range of 4.7–9.0%. Dynamic LPME provided higher (>280-fold) enrichment within nearly the same extraction time (≈20 min) and better precision (≤6.0%). Both methods allow the detection of polycyclic aromatic hydrocarbons at μg/l levels in water by HPLC. Water samples collected from two rivers were analyzed using the methods, respectively. The results demonstrated that both modes of LPME were fast, simple and accurate.

Liquid-phase microextraction combined with hollow fiber as a sample preparation technique prior to gas chromatography/mass spectrometry.

Two modes of liquid-phase microextraction (LPME) combined with hollow fiber (HF) were developed for gas chromatography/mass spectrometry (GC/MS). Both methodologies, that is, static LPME with HF and dynamic LPME with HF, involved the use of a small volume of organic solvent impregnated in the hollow fiber, which was held by the needle of a conventional GC syringe. In static LPME/HF, the hollow fiber impregnated with solvent was immersed in the aqueous sample, and the extraction processed under stirring; in dynamic LPME/HF, the solvent was repeatedly withdrawn into and discharged from the hollow fiber by a syringe pump. This is believed to be the first reported instance of a semiautomated liquid microextraction procedure. The performance of the two techniques was demonstrated in the analysis of two PAH compounds in an aqueous sample. Static LPME/HF provided approximately 35-fold enrichment in 10 min and good reproducibility (approximately 4%). Dynamic LPME/HF could provide higher enrichment (approximately 75-fold) in 10 min and even better reproducibility (approximately 3%). Both methods allow the direct transfer of extracted analytes to a GC/MS system for analysis.

Liquid-Phase Microextraction in a Single Drop of Organic Solvent by Using a Conventional Microsyringe

Two modes of liquid-phase microextraction (LPME) were developed for capillary gas chromatography. Both methodologies, i.e., static LPME and dynamic LPME, involve the use of very small amounts of organic solvent (<2 μL) in a conventional microsyringe. The performance of the two techniques is demonstrated in the determination of two chlorobenzenes extracted into a single drop of toluene by the use of a 10-μL syringe. Static LPME provided some enrichment (∼12-fold), good reproducibility (9.7%), and simplicity but suffered relatively long extraction time (15 min). Dynamic LPME provided higher (∼27-fold) enrichment within much shorter extraction time (∼3 min), and relatively poorer precision (12.8%), primarily due to repeated manual manipulation. Both methods allow the direct transfer of extracted analytes into a gas chromatograph.