Development and application of polymer-coated hollow fiber membrane microextraction to the determination of organochlorine pesticides in water

A novel extraction procedure coupled with gas chromatography-mass spectrometric detection for quantification of organochlorine pesticides (OCPs) in water is described. Amphiphilic polyhydroxylated polyparaphenylene (PH-PPP) was synthesized and coated on the surfaces of a porous polypropylene hollow fiber membrane (HFM). Due to the high porosity of the HFM, maximum active surface area to achieve high extraction efficiency is expected. The polymer-coated HFM was used for the extraction of 15 OCPs from water. The extraction efficiency was compared with emerging and established methods such as liquid-phase microextraction (LPME), solid-phase microextraction (SPME) and stir bar sorptive extraction (SBSE) techniques. We term the current procedure as polymer-coated hollow fiber microextraction (PC-HFME). PC-HFME showed good selectivity and sensitivity. Detection limits for OCPs were in the range of 0.001-0.008 microg l(-1). The sensitivity and selectivity of the coated HFM could be adjusted by changing the characteristics of the coated PH-PPP film.     

Size control of self-assembled nanoparticles by an emulsion/solvent evaporation method

A novel and simple method for size control of self-assembled nanoparticles is suggested in this paper. Polymeric nanoparticles were prepared from amphiphilic chitosan derivatives fluorescein isothiocyanate (FITC)-conjugated glycol chitosans (FGCs). The attachment of hydrophobic FITC onto hydrophilic glycol chitosan induced the amphiphilic conjugate to form self-assembled nanoparticles in aqueous media, depending on degree of substitution. The size of self-assembled nanoparticles was controlled by a novel emulsion/solvent evaporation method. Adding a small amount of an immiscible solvent with water (chloroform) to FGC nanoparticle suspensions in aqueous media followed by ultrasonification and solvent evaporation led to partial dissociation and subsequent reformation of nanoparticles. The evaporation of chloroform facilitated the hydrophobic association, which resulted in more dense and hardened hydrophobic cores. The size of nanoparticles was closely related with the FGC concentration in the emulsion. The mean diameters of self-assembled nanoparticles were 150–500 nm at the FGC concentrations of 0.3–2.5 mg/ml. Higher FGC concentration resulted in larger particles. The polydispersity factors (μ ₂/Γ ²) of the reformed nanoparticles were fairly low (0.001–0.094), indicating narrow size distribution. The FGC nanoparticles were stable in phosphate-buffered saline at 37°C up to 20 days. Lactose was a good excipient for maintaining the structural integrity of nanoparticles during freeze-drying. Without lactose, the freeze-dried nanoparticles were not homogeneously redispersed in aqueous media. However, the freeze-dried nanoparticles with lactose were spontaneously redispersed in aqueous milieu with their own sizes.     

Determination of triazines in soil by microwave-assisted extraction followed by solid-phase microextraction and gas chromatography-mass spectrometry

A method for determining triazine herbicides in soil samples that combines microwave-assisted extraction with solid-phase microextraction is described. Water containing 1% methanol was employed as extractant. The parameters of solid-phase microextraction and microwave-assisted extraction were investigated. In solid-phase microextraction, particular attention was paid to the negative effect of salt on fiber stability. Our experiments showed that this effect could be effectively reduced by simply washing the fiber with deionized water. The selected triazines could be efficiently extracted by the aqueous extractant at 105 degrees C for 3 min, with 80% output of maximum power (1,200 W). The extraction procedure provided good precision (<7%) and recoveries (76.1-87.2%). The limits of detection were in the range 2-4 microg/kg. Compared with conventional liquid extraction, microwave-assisted extraction-solid-phase microextraction was more efficient, accurate and faster, and used a very small amount of organic solvent (only 250 microL methanol). The extraction of aged spiked soil samples indicated that, although the recoveries were lower than those of freshly spiked samples, they were nevertheless satisfactory for the quantitative analysis of real-world samples.     

Arene-ruthenium complexes of an acyclic thiolate-thioether and tridentate thioether derivatives resulting from ring-closure reactions

The reaction of [(eta(6)-arene)RuCl(2)](2) (arene = C(6)Me(6), 1,4-MeC(6)H(4)CHMe(2)) with a large excess of the dianion of bis(2-mercaptoethyl) sulfide, (HSCH(2)CH(2))(2)S, obtained from deprotonation of the dithiol with freshly prepared NaOMe, gives the deep red, monomeric complexes [(eta(6)-arene)Ru(eta(3)-C(4)H(8)S(3))] (arene = C(6)Me(6) (5), 1,4-MeC(6)H(4)CHMe(2) (6)) in which the dianion is bound to the metal atom through one thioether and two thiolate sulfur atoms. Complex 5 reacts with [(eta(6)-C(6)Me(6))RuCl(2)](2) (4) in a 2:1 mole ratio to give a quantitative yield of the chloride salt of a binuclear cation [((eta(6)-C(6)Me(6))Ru)(2)Cl(mu(2)-eta(2):eta(3)-C(4)H(8)S(3))](+) (7) in which the thiolate sulfur atoms of the [(eta(6)-C(6)Me(6))Ru(eta(3)-C(4)H(8)S(3))] group bridge to a (eta(6)-C(6)Me(6))RuCl unit. This compound is also obtained directly from the reaction of 4 with the dithiolate, if the Ru dimer is used in large excess. The binuclear complex [((eta(6)-C(6)Me(6))Ru)(2)(MeCN)(mu(2)-eta(2):eta(3)-C(4)H(8)S(3))](PF(6))(2).MeCN, (9)(PF(6))(2).MeCN, is obtained by treatment of (7)Cl with NH(4)PF(6) in acetonitrile. Protonation of 5 with HCl gave the mono- and diprotonated derivatives viz. [(eta(6)-C(6)Me(6))Ru(eta(3)-C(4)H(9)S(3))]Cl, (8)Cl, and [(eta(6)-C(6)Me(6))Ru(eta(3)-C(4)H(10)S(3))]Cl(2), (10)Cl(2), respectively. The reaction of 5 with methyl iodide gives both the mono- and di-S-methylated derivatives. Treatment of 5 with dibromoalkanes, Br(CH(2))(n)Br (n = 1-5), effects ring closure to give the (eta(6)-C(6)Me(6))Ru dications containing the trithia mesocyclic zS3 (z = 8-12) ligands, isolated as their PF(6) salts. The X-ray crystal structures of 5, 6, the solvates of (7)Cl and (9)(PF(6))(2), and the trithia mesocyclic Ru complexes (eta(6)-C(6)Me(6))Ru(zS3)(PF(6))(2) (z = 8-11) are reported.     

Micro magnetic stir-bar mixer integrated with parylene microfluidic channels

Previously, we reported a micro magnetic stir-bar mixer driven by an external rotating magnetic field and its rapid mixing performance in polydimethyl-siloxane (PDMS) channels. The PDMS piece with embedded fluid channels were manually aligned to a glass substrate and assembled. In this paper, we report the fabrication and testing results of a micro magnetic stir-bar monolithically integrated in parylene surface-micromachined channels with improved design features, including small tolerance of the stir-bar to channel wall (10 microm). Using of parylene based microchannels with improved design not only provides improved mixing, but also eliminates certain problems associated with PDMS-based channels. For example, porosity of PDMS causes evaporation and absorption of chemicals and thus channels made of PDMS are prone to cross-contamination. We have also demonstrated that the magnetic stir-bar can be used to pump liquid in micro channels.     

CHARACTERIZATION OF RAD4 GENE REQUIRED FOR ULTRAVIOLET-INDUCED EXCISION REPAIR OF Saccharomyces cerevisiae PROPAGATED IN Escherichia coli WITHOUT INACTIVATION

The previously isolated RAD4 gene designated as pPC1 from the genomic library of Saccharomyces cerevisiae (Yoon et al., 1985, Korean J. Genetics 7, 97-104) appeared to propagate in Escherichia coli and yet retained its complementing activity to rad4 mutants without inactivation. The subcloned RAD4 gene was found to be localized within a 2.5 kb DNA fragment flanking Bg1II and BamHI sites in the insert DNA, and was shown to have the same restriction map as a yeast chromosomal DNA, as determined by Southern hybridization. Tetrad analysis and pulse-field chromosome mapping have revealed that the cloned RAD4 gene can be mapped and integrated into the yeast chromosome V, the actual site of this gene. DNA-tRNA hybridization has shown that the isolated RAD4 gene did not contain a suppressor tRNA gene. These results have indicated that the pPC1 is a functional RAD4 gene playing a unique role involved in the nucleotide excision repair of yeast without any genetic change during amplification in E. coli.     

Catalytic Hydrolysis of Phosphate Diesters by Lanthanide(III) Cryptate (2.2.1) Complexes

Lanthanide(III) Cryptate (2.2.1) chlorides (Ln(2.2.1)Cl(3); Ln = La (1a), Ce(1b), and Eu(1c); (2.2.1) = 4,7,13,16,21-pentaoxa-1,10-diazabicyclo[8.8.5]tricosane) are effective for the catalytic hydrolysis of bis(4-nitrophenyl) phosphate. Kinetic studies reveal that the europium(III) complex (1c) catalyzes the hydrolysis to produce 6 equiv of 4-nitrophenol with a significant rate (k(1) = 1.5 x 10(-)(4) s(-)(1) at 0.40 mM) at pH 8.5 and 50 degrees C. The catalytic activity of the complexes is increased with decreasing the ionic size, i.e, La < Ce < Eu. While the use of hydrogen peroxide further increase the activity of 1b (k(1) = 1.6 x 10(-)(3) s(-)(1) at 0.40 mM), the presence of molecular oxygen does not affect the activity at all. Crystal of 1a.CH(3)OH([La(2.2.1)(Cl)(2)](Cl)(CH(3)OH)) belongs to the space group Pnma with a = 17.072(3) ?, b = 19.037(3) ?, c = 14.725(2) ?, V = 4786(1) ?(3), Z = 8, D(x)() = 1.691 g cm(-)(3), &mgr; = 21.7 cm(-)(1). The encryptated metal ion is nine-coordinated, and all the heteroatoms of the cryptate (2.2.1) ligand coordinate the metal center to form a bowl-shaped structure. Two coordinating chloride anions are located on the open face with a cis geometry. The existence of coordinated water to the europium(III) complex 1c in the aqueous solution was confirmed by time-resolved Eu(III) luminescence spectroscopy. From the decay constants in H(2)O and D(2)O, the numbers of coordinated water molecules (q) are found to be 3.02 at pH of 5.0. The above kinetic and spectroscopic observation are supportive of mechanisms in which the metal complexes act as a center for binding and activation as well as a source of nucleophilic metal hydroxides.     

Enhancement of matrix-assisted laser desorption/ionization photodissociation tandem time-of-flight mass spectra; spectral reduction and cleanup of isotopomeric contamination

Weak signal intensity and poor precursor ion selection are the major difficulties in tandem time-of-flight (TOF) mass spectrometry of ions generated by matrix-assisted laser desorption/ionization (MALDI). Even though the latter can be overcome in photodissociation (PD) tandem TOF mass spectrometry via ion pulse-PD laser pulse synchronization, clean monoisotopic selection of precursor ions of high m/z can often be difficult for various reasons. A considerable enhancement of post-source decay (PSD) and PD tandem mass spectra has been achieved in this work via single-ion detection and post-acquisition reduction of the spectra. Also, an algorithm has been developed to clean up isotopomeric contamination when the resolution for precursor ion selection is less than adequate. A high-quality tandem TOF mass spectrum which results from PD of virtually monoisotopic precursor ions has been obtained.     

New on-line concentrator for LC-GC: Analysis of PAHs with LC-GC

A new, versatile, and low cost on-line LC-GC interface has been devloped for the fast and reliable introduction of large volume samples into a cappillary GC column without using the conventional retention gap. PAHs in soot were analyzed by on-line normal phase HPLC-capillary GC. A glass, vial-shaped on-line concentrator provides a zone for solvent evaporation and sample concentration. Large volumes of HPLC eluate can be concentrated with the on-line concentrator and then transferred directly into the cappillary column. Trace levels (< 10 ppb) of PAH compounds can be efficiently concentrated with the on-line concentrator and determined without loss or contamination.