Shi Zhiguo
Email Address
chmshiz@nus.edu.sg
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Publication Ferrofluid-based liquid-phase microextraction(2010-11-19) Shi, Z.-G.; Zhang, Y.; Lee, H.K.; CHEMISTRYA new mode of liquid-phase microextraction based on a ferrofluid has been developed. The ferrofluid was composed of silica-coated magnetic particles and 1-octanol as the extractant solvent. The 1-octanol was firmly confined within the silica-coated particles, preventing it from being lost during extraction. Sixteen polycyclic aromatic hydrocarbons (PAHs) were used as model compounds in the development and evaluation of the extraction procedure in combination with gas chromatography-mass spectrometry. Parameters affecting the extraction efficiency were investigated in detail. The optimal conditions were as follows: 20mL sample volume, 10mg of the silica-coated magnetic particles (28mg of ferrofluid), agitation at 20Hz, 20min extraction time, and 2min by sonication with 100μL acetonitrile as the final extraction solvent. Under optimal extraction conditions, enrichment factors ranging from 102- to 173-fold were obtained for the analytes. The limits of detection and the limits of quantification were in the range of 16.8 and 56.7pgmL-1 and 0.06 and 0.19ngmL-1, respectively. The linearities were between 0.5-100 and 1-100ngmL-1 for different PAHs. As the ferrofluid can respond to and be attracted by a magnet, the extraction can be easily achieved by reciprocating movement of an external magnet that served to agitate the sample. No other devices were needed in this new approach of extraction. This new technique is affordable, efficient and convenient for microextraction, and offers portability for potential onsite extraction. © 2010 Elsevier B.V.Publication Dispersive liquid-liquid microextraction coupled with dispersive μ-solid-phase extraction for the fast determination of polycyclic aromatic hydrocarbons in environmental water samples(2010-02-15) Shi, Z.-G.; Lee, H.K.; CHEMISTRYA new two-step microextraction technique, combining dispersive liquid-liquid microextraction (DLLME) and dispersive microsolid-phase extraction (D-μ -SPE), was developed for the fast gas chromatographic-mass spectrometric determination of polycyclic aromatic hydrocarbons (PAHs) in environmental samples. A feature of the new procedure lies in that any organic solvent immiscible with water can be used as extractant in DLLME. A special apparatus, such as conical-bottom test tubes, and tedious procedures of centrifugation, refrigeration of the solvent, and then thawing it, associated with classical DLLME or similar techniques are not necessary in the new procedure, which potentially lends itself to possible automation. In the present D-μ -SPE approach, hydrophobic magnetic nanoparticles were used to retrieve the extractant of 1-octanol in the DLLME step. It is noteworthy that the target of D-μ -SPE was the 1-octanol rather than the PAHs. Because of the rapid mass transfer associated with the DLLME and the D-μ -SPE steps, fast extraction could be achieved. Parameters affecting the extraction efficiency were investigated in detail. The optimal conditions were as follows: vortex at 3200 rpm in the DLLME step for 2 min and in D-μ -SPE for 1 min and then desorption by sonication for 4 min with acetonitrile as the solvent. The results demonstrated that enrichment factors ranging from 110-to 186-fold were obtained for the analytes. The limits of detection and the limits of quantification were in the range of 11.7-61.4 pg/mL and 0.04-0.21 ng/mL, respectively. The linearities were 0.5-50, 1-50, or 2-50 ng/mL for different PAHs. Finally, the two-step extraction method was successfully used for the fast determination of PAHs in river water samples. This two-step method, combining two different and efficient miniaturized techniques, provides a fast means of sample pretreatment for environmental water samples. © 2010 American Chemical Society.Publication Silica Monoliths in Solid - Phase Extraction and Solid - Phase Microextraction(2011-01-20) Shi, Z.-G.; Xu, L.; Lee, H.K.; CHEMISTRY