Application Of Liquid-phase Microextraction Research Articles

A guide to recent trends in green applications of liquid phase microextraction for bioanalytical sample preparations

Liquid phase microextraction (LPME) techniques have become increasingly important components for bio-analytical sample preparation methods due to the versatility, adaptability, sensitivity, and conformity to green analytical chemistry (GAC) principles that they provide for the analyses of complex biological matrices. Despite having been used for sample preparations for some 25 years, LPME is not a static sample preparation field, but is continuously undergoing innovation and improvements and new research and applications for bio-analytical sample preparation are being published constantly. This review is meant to serve not only as a listing of recent literature, but as a guide to current trends in LPME. In order to fully understand the trends, advantages and limitations of this field in bio-analytical sample analyses, LPME based methods are compared with traditional sample preparation methods, the limitations and advantages of each LPME mode examined, and a variety of reviews and successful applications papers for LPME are included. To simplify searching for appropriate LPME methods these reviews and applications have been categorized to aid in searching for a needed application technique or publication. Following sections briefly cover the trends in LPME development, concentrating on bioanalytical sample preparation applications. The review continues with an examination of the trends for the use use of non-traditional green solvents for LPME based methods, and concludes with a discussion of recent innovations which have the potential for commercialization of high throughput automation for LPME based bio-analytical sample preparation and analysis methods.

Applications of liquid-phase microextraction in the sample preparation of environmental solid samples.

Solvent extraction remains one of the fundamental sample preparation techniques in the analysis of environmental solid samples, but organic solvents are toxic and environmentally harmful, therefore one of the possible greening directions is its miniaturization. The present review covers the relevant research from the field of application of microextraction to the sample preparation of environmental solid samples (soil, sediments, sewage sludge, dust etc.) published in the last decade. Several innovative liquid-phase microextraction (LPME) techniques that have emerged recently have also been applied as an aid in sample preparation of these samples: single-drop microextraction (SDME), hollow fiber-liquid phase microextraction (HF-LPME), dispersive liquid-liquid microextraction (DLLME). Besides the common organic solvents, surfactants and ionic liquids are also used. However, these techniques have to be combined with another technique to release the analytes from the solid sample into an aqueous solution. In the present review, the published methods were categorized into three groups: LPME in combination with a conventional solvent extraction; LPME in combination with an environmentally friendly extraction; LPME without previous extraction. The applicability of these approaches to the sample preparation for the determination of pollutants in solid environmental samples is discussed, with emphasis on their strengths, weak points and environmental impact.

Application of liquid phase microextraction based on solidification of floating organic drop for the determination of triazine herbicides in soil samples by gas chromatography with flame photometric detection

A simple and efficient liquid phase microextraction based on solidification of floating organic drop coupled with gas chromatography–flame photometric detection was developed for the extraction and determination of some triazine herbicides (metribuzin, simetryn, ametryn and prometryn) in soil samples. The type and volume of the extraction solvent, sample solution temperature, salt addition, stirring rate, and the extraction time were optimized. Under the optimal conditions, the linear response was observed over the range of 10–2000 µg kg−1 for metribuzin and 2–500 µg kg−1 for simetryn, ametryn, and prometryn, respectively, with the correlation coefficients (r) varying from 0.9990 to 0.9992. The limits of detection were in the range between 0.2 and 1.0 µg kg−1 (S/N = 3 : 1). The recoveries of the target analytes for the spiked soil samples ranged from 75.5% to 97.3%, with the relative standard deviation values less than 7.2% (n = 5). The enrichment factors were achieved ranging from 122 to 336. The developed method was applied for the preconcentration and determination of triazine herbicides in real soil samples and a satisfactory result was obtained.

Recent developments and applications of liquid phase microextraction in fruits and vegetables analysis

The sample preparation step has been identified as the bottleneck of analytical methodology in chemical analysis. Therefore, there is need for the development of cost-effective, easy to operate, and environmentally friendly miniaturized sample preparation technique. The microextraction techniques combine extraction, isolation, concentration, and introduction of analytes into analytical instrument, to a single and uninterrupted step, and improve sample throughput. The use of liquid-phase microextraction techniques for the analysis of pesticide residues in fruits and vegetables are discussed with the focus on the methodologies employed by different researchers and their analytical performances. Analytes are extracted using water-immiscible solvents and are desorbed into gas chromatography, liquid chromatography, or capillary electrophoresis for identification and quantitation.

Application of liquid-phase microextraction and gas chromatography to the determination of chlorfenapyr in water samples

A new method was developed for the determination of chlorfenapyr in water samples using liquid-phase microextraction (LPME) and gas chromatography coupled to micro-cell electron capture detection. The main factors influencing the extraction efficiency of LPME, such as extraction solvent, volume of extraction solvent, stirring rate, extraction time and ionic effects were studied. Analytical parameters such as linearity, repeatability and limits of detection were also evaluated. The method enables simple and rapid analysis of chlorfenapyr in water with limits of detection below 0.01 µg L−1 for tap water and river water. The relative recoveries ranged from 80 to 102%, with relative standard deviations varying from 9 to 12%.

Application of liquid-phase microextraction and on-column derivatization combined with gas chromatography–mass spectrometry to the determination of carbamate pesticides

A method has been established for the determination of five carbamate pesticides in water samples using liquid-phase microextraction (LPME) followed by on-column derivatization and gas chromatography–mass spectrometric (GC–MS) determination. Trimethylphenylammonium hydroxide (TMPAH) and trimethylsulfonium hydroxide (TMSH) were used as derivatization reagent for extracts prior to GC–MS analysis as carbamate pesticides are thermally labile compounds. Parameters that affect the extraction efficiency (selection of organic solvent and extraction time) and derivatization efficiency (choice of derivatization reagent and concentration of derivatization reagent) were investigated. The proposed method provided good enrichment factors up to 224, with reproducibility ranging from 4.86 to 7.81%, and good linearity from 1 to 400 μg/L. The limits of detection (LODs) ranged between 0.2 and 0.8 μg/L (S/N = 3) using GC–MS with selective ion monitoring. This method was applied to the determination of carbamate pesticides in tap water and waste water.

Application of Liquid-Phase Microextraction and Gas Chromatography-Mass Spectrometry for the Determination of Chloroform in Drinking Water

In this paper, a novel method for the determination of chloroform in drinking water has been described. It is based on liquid-phase microextraction (LPME) and gas chromatography-mass spectrometry (GC-MS). Extraction conditions such as solvent selection, organic solvent dropsize, stirring rate, content of NaCl and extraction time were found to have significant influence on extraction efficiency. The optimized conditions were 1.5 microl xylene, 20 min extraction time at 400 rpm stirring rate without NaCl addition. The linear range was 1.0 - 100 microg l(-1) for chloroform. The limit of detection (LOD) was 1.0 microg l(-1); and relative standard deviation (RSD) at the 30 microg l(-1) level was 2.9%. Tap water samples from a laboratory were successfully analyzed using the proposed method. The relative recovery of spiked water samples was 104%.

Application of liquid-phase microextraction and gas chromatography–mass spectrometry for the determination of polychlorinated biphenyls in blood plasma

This study investigated the feasibility of applying liquid-phase microextraction combined with gas chromatography–mass spectrometry (GC–MS) to determine polychlorinated biphenyls (PCBs) in blood plasma. An efficient and simple extraction technique has been developed for the enrichment of PCBs from human blood plasma samples using single-step liquid-phase microextraction (LPME) in conjunction with a hollow fibre membrane (HFM). An eight PCB congener mixture was spiked into 2.5 ml of blood plasma, and the solution was then adjusted to pH 10.5 with a salinity of 20% (w/v) prior to making the total volume to 5 ml with ultrapure water. The porous HFM, filled with 3 μl of organic solvent, was then immersed into the solution, which was continuously agitated at 700 rpm for 30 min. Extract (1 μl) containing the pre-concentrated analytes was then injected into a GC–MS without further pre-treatment. Using an optimised extraction procedure, a large enrichment factor of the analytes, i.e. up to 241-fold was achieved in 30 min. The procedure resulted in a relative standard deviation of <11% ( n=6), and a linear calibration range from 2.5 to 150 μg/l ( r>0.999), and detection limits between 0.07 and 0.94 μg/l, respectively. To demonstrate the feasibility of the procedure, PCB concentrations were determined in actual blood samples collected from the local population in Singapore using the optimised LPME technique.

Feasibility of a liquid-phase microextraction sample clean-up and liquid chromatographic/mass spectrometric screening method for selected anabolic steroid glucuronides in biological samples.

Anabolic androgenic steroids (AAS) are metabolized extensively in the human body, resulting mainly in the formation of glucuronide conjugates. Current detection methods for AAS are based on gas chromatographic/mass spectrometric (GC/MS) analysis of the hydrolyzed steroid aglycones. These analyses require laborious sample preparation steps and are therefore time consuming. Our interest was to develop a rapid and straightforward method for intact steroid glucuronides in biological samples, using liquid-phase microextraction (LPME) sample clean-up and concentration method combined with liquid chromatographic/tandem mass spectrometric (LC/MS/MS) analysis. The applicability of LPME was optimized for 13 steroid glucuronides, and compared with conventional liquid-liquid extraction (LLE) and solid-phase extraction (SPE) procedures. An LC/MS/MS method was developed for the quantitative detection of AAS glucuronides, using a deuterium-labeled steroid glucuronide as the internal standard. LPME, owing to its high specificity, was shown to be better suited than conventional LLE and SPE for the clean-up of urinary AAS glucuronides. The LPME/LC/MS/MS method was fast and reliable, offering acceptable reproducibility and linearity with detection limits in the range 2-20 ng ml(-1) for most of the selected AAS glucuronides. The method was successfully applied to in vitro metabolic studies, and also tested with an authentic forensic urine sample. For a urine matrix the method still has some unsolved problems with specificity, which should be overcome before the method can be reliably used for doping analysis, but still offering additional and complementary data for current GC/MS analyses.