Dong-Qing Jiang

In Situ Hydrothermal Growth of Metal−Organic Framework 199 Films on Stainless Steel Fibers for Solid-Phase Microextraction of Gaseous Benzene Homologues

Metal-organic frameworks (MOFs) have received great attention due to their fascinating structures and intriguing potential applications in various fields. Herein, we report the first example of the utilization of MOFs for solid-phase microextraction (SPME). MOF-199 with unique pores and open metal sites (Lewis acid sites) was employed as the coating for SPME fiber to extract volatile and harmful benzene homologues. The SPME fiber was fabricated by in situ hydrothermal growth of thin MOF-199 films on etched stainless steel wire. The MOF-199-coated fiber not only offered large enhancement factors from 19,613 (benzene) to 110,860 (p-xylene), but also exhibited wide linearity with 3 orders of magnitude for the tested benzene homologues. The limits of detection for the benzene homologues were 8.3-23.3 ng L(-1). The relative standard deviation (RSD) for six replicate extractions using one SPME fiber ranged from 2.0% to 7.7%. The fiber-to-fiber reproducibility for three parallel prepared fibers was 3.5%-9.4% (RSD). Indoor air samples were analyzed for the benzene homologues using the SPME with the MOF-199-coated fiber in combination with gas chromatography-flame ionization detection. The recoveries for the spiked benzene homologues in the collected indoor air samples were in the range of 87%-106%. The high affinity of the MOF-199-coated fiber to benzene homologues resulted from the combined effects of the large surface area and the unique porous structure of the MOF-199, the pi-pi interactions of the aromatic rings of the analytes with the framework 1,3,5-benzenetricarboxylic acid molecules, and the pi-complexation of the electron-rich analytes to the Lewis acid sites in the pores of MOF-199.

Hydrofluoric Acid Etched Stainless Steel Wire for Solid-Phase Microextraction

Stainless steel wire has been widely used as the substrate of solid-phase microextraction (SPME) fibers to overcome the shortcomings of conventional silica fibers such as fragility, by many researchers. However, in previous reports various sorbent coatings are always required in conjunction with the stainless steel wire for SPME. In this work, we report the bare stainless steel wire for SPME without the need for any additional coatings taking advantage of its high mechanical and thermal stability. To evaluate the performance of stainless steel wire for SPME, polycyclic aromatic hydrocarbons (PAHs), benzene, toluene, ethylbenzene, chlorobenzene, n-propylbenzene, aniline, phenol, n-hexane, n-octane, n-decane, n-undecane, n-dodecane, chloroform, trichloroethylene, n-octanol, and butanol were tested as analytes. Although the stainless steel wire had almost no extraction capability toward the tested analytes before etching, it did exhibit high affinity to the tested PAHs after etching with hydrofluoric acid. The etched stainless steel wire gave a much bigger enhancement factor (2541-3981) for the PAHs than the other analytes studied (< or = 515). Etching with hydrofluoric acid produced a porous and flower-like structure with Fe(2)O(3), FeF(3), Cr(2)O(3), and CrF(2) on the surface of the stainless steel wire, giving high affinity to the PAHs due to cation-pi interaction. On the basis of the high selectivity of the etched stainless steel wire for PAHs, a new SPME method was developed for gas chromatography with flame ionization detection to determine PAHs with the detection limits of 0.24-0.63 microg L(-1). The precision for six replicate extractions using one SPME fiber ranged from 2.9% to 5.3%. The fiber-to-fiber reproducibility for three parallel prepared fibers was 4.3-8.8%. One etched stainless steel wire can stand over 250 cycles of SPME without significant loss of extraction efficiency. The developed etched stainless steel wire is very stable, highly selective, and reproducible for the SPME of PAHs.

Development of an ambient temperature post-column oxidation system for high-performance liquid chromatography on-line coupled with cold vapor atomic fluorescence spectrometry for mercury speciation in seafood

An efficient ambient temperature post-column oxidation system was developed for high-performance liquid chromatography online coupled with cold vapor atomic fluorescence spectrometry for mercury speciation analysis in seafood. The developed system does not require an external heat source, such as a hot water bath, microwave heating or UV irradiation, to decompose organomercury compounds into inorganic mercury ion (Hg(II)). Methylmercury (MeHg), ethylmercury (EtHg), phenylmercury (PhHg) and Hg(II) were baseline separated on an RP-C18 column with a mixture of methanol, acetonitrile and water (75 ∶ 5 ∶ 20) containing 0.01% m/v ammonium pyrrolidine dithiocarbamate (APDC) (pH 3.5) as the mobile phase. Online ambient temperature post-column oxidation of organomercury species eluted from the HPLC column was achieved by mixing the effluent with a 3% m/v K2S2O8 in 10% v/v HCl solution in a knotted reactor made of a 0.5 mm id × 200 cm long PTFE tube. The developed oxidation approach enhanced sensitivity for organomercury by a factor of 4 for MeHg, 3 for EtHg and 6 for PhHg, compared with that obtained without post-column oxidation. The detection limits for 100 μl injection were 0.19–0.27 μg l−1 (as Hg) in extract, corresponding to 4.75–6.75 μg kg−1 (as Hg) in fish tissue for a 50 ml final extract of 2 g tissue. The precision (RSD, n = 5) ranged from 1.8 to 2.8% for peak area, and from 1.7% to 2.9% for peak height at the 1 μg l−1 (as Hg) level. The method was validated by determination of methylmercury in a certified reference material (DORM-2, dogfish muscle) and applied to the speciation analysis of mercury in local seafood samples.

Determination of substituted benzenes in water samples by fiber-in-tube liquid phase microextraction coupled with gas chromatography

A method for determination of toluene, ethylbenzene, p-xylene, o-xylene, 1,3,5-trimethylbenzene and 1,2,4-trimethylbenzene in water samples was developed by a fiber-in-tube liquid phase microextraction technique (fiber-in-tube LPME) coupled with GC-flame ionization detector (FID). The method used a tube packed with polytetrafluoroethylene (PTFE) fibers as an extraction medium, improving the stableness of the solvent and the performance of extraction. Certain amounts of curled PTFE fibers were packed into a section of PTFE tube. Because the fibers were curled, they formed network structure in the tube. The fiber packed tube was firstly immersed into organic solvent to be filled with organic solvent and then was exposing to an aqueous solution to extract the target compounds. The extract was then retracted by a conventional GC microsyringe and analyzed by GC-FID. Extraction of the analytes in 8 ml aqueous solution for 15 min yielded enrichment factors of 224-361. The precision (R.S.D., n=5) was 3.6-8.1% for peak area. The limit of detection (LOD, S/N=3) for the six substituted benzenes were in the range of 0.3-5.0 microgl(-1).

A strong inorganic acid‐initiated methacrylate polymerization strategy for room temperature preparation of monolithic columns for capillary electrochromatography

A facile strong inorganic acid‐initiated methacrylate polymerization strategy was developed for fabricating monolithic columns at room temperature. The prepared monoliths were characterized by FTIR spectrometry, mercury intrusion porosimeter and SEM, while their performance was evaluated by CEC for the separation of various types of compounds including alkyl benzenes, polycyclic aromatic hydrocarbons, nonsteroidal anti‐inflammatory drugs, anilines, and nitrophenol isomers. The column‐to‐column and batch‐to‐batch reproducibility for the prepared monoliths in terms of the RSD of EOF flow velocity, retention factor, and the minimum plate height of naphthalene ranged from 3.4 to 12.4%. The fabricated monoliths gave excellent performance for the separation of the test neutral compounds with the theoretical plates of 170 000–232 000 plates per meter for thiourea, and 77 400–112 300 plates per meter for naphthalene. The proposed strong inorganic acid‐initiated methacrylate polymerization strategy is a promising alternative for fabricating organic polymer‐based monoliths.

Gas Chromatography-Inductively Coupled Plasma-Mass Spectrometry for Mercury Speciation in Seafood

Abstract A method for mercury speciation in seafood was designed by on-line coupling gas chromatography (GC) to inductively coupled plasma mass spectrometry (ICP-MS) with an improved interface. The detection limits (S/N = 3) of methylmercury (MeHg(I)) and ethylmercury (EtHg(I)) were 0.5 pg and 1.0 pg (as Hg), respectively. The quantitative limits (S/N = 8) were 1.5 pg and 2.8 pg for MeHg(I) and EtHg(I), respectively. The linear range of MeHg(I) and EtHg(I) determination was 1–1000 pg. The hybrid technique was applied for the speciation analysis of mercury in three certified reference materials, 14 fish, and shellfish samples collected from local markets. The measured MeHg(I) concentrations was 3.7–236.6 ng g−1 (as Hg), and no EtHg(I) was detected. The recovery of MeHg(I) in real samples was in the range of 91%–102%.