Dispersive micro-solid phase extraction combined with gas chromatography-chemical ionization mass spectrometry for the determination of N-nitrosamines in swimming pool water samples.

A simple sample pretreatment technique, dispersive micro-solid phase extraction, was applied for the extraction of N-nitrosodimethylamine (NDMA) and other four N-nitrosamines (NAs) from samples of swimming pool water. The parameters affecting the extraction efficiency were systematically investigated. The best extraction conditions involved immersing 75 mg of carbon molecular sieve, Carboxen™ 1003 (as an adsorbent), in a 50-mL water sample (pH 7.0) containing 5% sodium chloride in a sample tube. After 20 min of extraction by vigorous shaking, the adsorbent was collected on a filter and the NAs desorbed by treatment with 150 µL of dichloromethane. A 10-µL aliquot was then directly determined by large-volume injection gas chromatography with chemical ionization mass spectrometry using the selected ion storage mode. The limits of quantitation were <0.9 ng/L. The precision for these analytes, as indicated by relative standard deviations, were <8% for both intra- and inter-day analyses. Accuracy, expressed as the mean extraction recovery, was between 62% and 109%. A preliminary analysis of swimming pool water samples revealed that NDMA was present in the highest concentration, in the range from n.d. to 100 ng/L.

Synthesis of Cisplatin(IV) Prodrug-Tethered CuFeS2 Nanoparticles in Tumor-Targeted Chemotherapy and Photothermal Therapy.

In this study, for the first time, CuFeS2 nanocrystals were successfully prepared through a facile noninjection-based synthetic strategy, by reacting Cu and Fe precursors with dodecanethiol in a 1-octadecene solvent. This one-pot noninjection strategy features easy handling, large-scale production, and high synthetic reproducibility. Following hyaluronic acid (HA) encapsulation, CuFeS2 nanocrystals coated with HA (CuFeS2@HA) not only readily dispersed in water and showed improved biocompatibility but also possessed a tumor-specific targeting ability of cancer cells bearing the cluster determinant 44 (CD44) receptors. The encapsulated CuFeS2@HA showed broad optical absorbance from the visible to the near-infrared (NIR) region and high photothermal conversion efficiencies of about 74.2%. They can, therefore, be utilized for the photothermal ablation of cancer cells with NIR light irradiation. In addition, toxicity studies in vitro (B16F1 and HeLa) and in vivo (zebrafish embryos), as well as in vitro blood compatibility studies, indicated that CuFeS2@HA show low cytotoxicity at the doses required for photothermal therapy. More importantly, CuFeS2@HA can be used as delivery vehicles for chemotherapy cisplatin(IV) prodrug forming CuFeS2@HA-Pt(IV). Their release profile revealed pH- and glutathione-mediated drug release from CuFeS2@HA-Pt(IV), which may minimize the side effects of the drug to normal tissues during therapy. Subsequent in vitro experiments confirmed that the use of CuFeS2@HA-Pt(IV) provides an enhanced and synergistic therapeutic effect compared to that from the use of either chemotherapy or photothermal therapy alone.

On-line derivatization gas chromatography with furan chemical ionization tandem mass spectrometry for screening of amphetamines in urine.

A simple alternative method with minimal sample pretreatment is investigated for screening of amphetamines in small volume (using only 20 microL) of urine sample. The method is sensitive and selective. The method uses gas chromatography (GC) direct sample introduction (DSI) for on-line derivatization (acylation) of amphetamines to improve sensitivity. Furan as chemical ionization (CI) reagent in conjunction with tandem mass spectrometry (MS/MS) is used to improve selectivity. Low background with sharp protonated molecular ion peaks of analytes is the evidence of improvement in sensitivity and selectivity. Blank urine samples spiked with known amounts of amphetamine, methamphetamine, 3,4-methylenedioxyamphetamine, 3,4-methylenedioxymethamphetamine and 3,4-methylenedioxyethylamphetamine is analyzed. Selected ion monitoring of the characteristic product ions (m/z 119+136+150+163) using furan CI-MS/MS in positive ion mode is used for quantification. Limits of detection (LOD) between 0.4 and 1.0 ng mL(-1) and limits of quantitation (LOQ) between 1.0 and 2.0 ng mL(-1) are established. Linear response over the range of 1-1000 ng mL(-1) (r(2)>0.997) is observed for all analytes, except for methamphetamine (2.0-1000 ng mL(-1)). Good accuracy between 86 and 113% and precision ranging from 4 to 18% is obtained. The method is also tested on real samples of urine from suspected drug abusers. This method could be used for screening and determination of amphetamines in urine samples, however needs additional work for full validation.

Optimization of dispersive micro solid-phase extraction for the rapid determination of benzophenone-type ultraviolet absorbers in aqueous samples.

A solvent-free method for the rapid analysis of six benzophenone-type UV absorbers in water samples is described. The method involves the use of dispersive micro solid-phase extraction (DmSPE) followed by the simultaneous silylation and thermal desorption (SSTD) gas chromatography-mass spectrometry (GC-MS) operating in the selected-ion-storage (SIS) mode. A Plackett-Burman design was used for screening and a central composite design (CCD) for optimizing the significant factors was applied. The optimal experimental conditions involved immersing 1.5mg of the Oasis HLB adsorbent in a 10mL portion of water sample. After vigorous shaking for 1min, the adsorbents were transferred to a micro-vial, and were dried at 122°C for 3.5min, after cooling, 2µL of the BSTFA silylating reagent was added. For SSTD, the injection-port temperature was held at 70°C for 2.5min for derivatization, and the temperature was then rapidly increased to 340°C to allow the thermal desorption of the TMS-derivatives into the GC for 5.7min. The limits of quantitation (LOQs) were determined to be 1.5-5.0ng/L. Precision, as indicated by relative standard deviations (RSDs), was equal or less than 11% for both intra- and inter-day analysis. Accuracy, expressed as the mean extraction recovery, was between 87% and 95%. A preliminary analysis of the municipal wastewater treatment plant (MWTP) effluent and river water samples revealed that 2-hydroxy-4-methoxybenzophenone (BP-3) was the most common benzophenone-type UV absorber present. Using a standard addition method, the total concentrations of these compounds ranged from 5.1 to 74.8ng/L.

Rapid screening of haloacetamides in water using salt-assisted liquid-liquid extraction coupled injection-port silylation gas chromatography-mass spectrometry.

The rapid screening of trace amounts of the nitrogenous disinfection by-products, haloacetamides (HAcAms), in drinking and swimming pool water was performed by a simple and reliable procedure based on salt-assisted liquid-liquid extraction (SALLE) combined with injection-port silylation gas chromatography-mass spectrometry (IPS-GC-MS) method. The optimal SALLE conditions involved the injection of 4-mL of ethyl acetate into a 10-mL water sample (pH 7) containing 3-g of sodium sulfate. After vortex extraction for 1min and centrifugation, 10µL of the extract (mixed with 1µL of MTBSTFA) was directly determined by IPS-GC-MS. The limits of quantitation (LOQs) were determined to be 0.03-0.3µg/L. Precision, as indicated by relative standard deviations (RSDs), was less than 10% for both intra- and inter-day analysis. Accuracy, expressed as the mean extraction recovery, was between 76% and 94%. The SALLE plus IPS-GC-MS was successfully applied to quantitatively determine HAcAms from drinking and swimming pool water samples, and the total concentrations of the compounds ranged from 0.43 to 4.03µg/L.

Application of paramagnetic graphene quantum dots as a platform for simultaneous dual-modality bioimaging and tumor-targeted drug delivery.

Here, we report the development of a multifunctional nanocarrier consisting of paramagnetic graphene quantum dots (GQDs), folate, and doxorubicin (Dox), used as delivery vehicles, a targeting ligand, and a chemotherapeutic drug, respectively. The paramagnetic GQDs, named folate-GdGQDs, were successfully prepared by covalently conjugating diethylenetriaminepentaacetic acid gadolinium and folic acid onto the surface of GQDs. The resultant folate-GdGQDs, which showed a longitudinal relaxivity r1 of 11.49 mM-1 s-1, greatly enhanced the brightness of the T1-weighted magnetic resonance (MR) images, indicating their potential for use as positive contrast agents for MR imaging (MRI). The feasibility of utilizing the folate-GdGQDs with strong luminescence emissions for targeted imaging of HeLa cells was also evaluated. An in vitro cell (HeLa and HepG2 cells) viability assay and in vivo evaluation of toxicity to the embryonic development of zebrafish showed that these folate-GdGQDs exhibited negligible cytotoxicity and excellent biocompatibility within the given range of concentrations. More importantly, strong therapeutic activity was achieved by loading Dox onto the surfaces of folate-GdGQDs through π-π stacking and hydrophobic interactions, leading to the formation of folate-GdGQD/Dox multifunctional nanocarriers. Approximately 80% of the loaded Dox was released from the folate-GdGQD/Dox nanocarriers under mild acidic conditions (pH 5.0), whereas only 20% of Dox was released at pH 7.0 after 48 h. Furthermore, these multifunctional nanocarriers could efficiently induce an inhibitory effect on HeLa cells, as confirmed by an in vitro cytotoxicity assay. The combined flow cytometry analysis and confocal laser scanning microscopic observation showed that these nanocarriers were efficiently taken up by the cancer cells overexpressing folate receptors. Taken together, these results suggested that the multifunctional nanocarriers could be used as promising targeted drug delivery vehicles for the diagnosis and image-guided chemotherapy of various cancers.

Selective adduct formation by furan chemical ionization reagent in gas chromatography ion trap mass spectrometry.

The analytical potential of furan as a chemical ionization (CI) reagent was evaluated for selectivity with nine monosubstituted naphthalene compounds. The ion-molecule reactions of furan and tetrahydrofuran (THF) were compared with those of methane, methanol and acetonitrile (prominently producing [M + H](+) ion base peaks) with naphthalene compounds in chemical ionization mass spectrometry (CI-MS). Reactions with furan predominantly show M(+) and [M + 39](+) ions. Based on this phenomenon, investigations were carried out for some of the molecular factors such as proton affinity, substituent effects and the preferred site of [C(3)H(3)](+) ion attachment that influence reactivity in furan CI. High selectivity with different substituents is observed in the formation of [M + 39](+) adduct ion, suggesting its usefulness as selective ionization reagent liquid. The selectivity and sensitivity are illustrated in the analysis of mixture of amino acids. Furthermore, the structure determination and reaction mechanism study is characterized by collision-activated dissociation experiments in CI-MS/MS and CI-MS/MS/MS.

Transportation of silver nanopaticles in nanochannels of carbon nanotubes with supercritical water.

Supercritical water (SCW) as a highly destructive environment has been utilized to open multiwall carbon nanotubes (MWNTs) and to break silver aggregates into nanoparticles (diameter 2-20 nm). Water was drawn into open-ended MWNTs by capillary suction, pulling Ag nanoparticles into the MWNTs. The Ag nanoparticles (solid), presumably transported in the nanochannels of MWNTs by the fluidity of SCW, stacked, and fused to form nanorods, suggesting SCW associated with MWNTs (hollow interior) might be exploited as a nanoreactor.

Development of nonstoichiometric CuInS2 as a light-harvesting photoanode and catalytic photocathode in a sensitized solar cell.

A simple one-pot approach was developed to obtain nonstoichiometric CuInS2 nanocrystals. Using this approach, both In-rich and Cu-rich CuInS2 nanocrystals could be reliably synthesized by tuning stoichiometric combinations of [Cu]/[In] precursor constituents. By designing Cu-rich CuInS2 heteronanostructures to serve as counter electrodes, quantum-dot-sensitized solar cells (QDSSCs) equipped with In-rich CuInS2 and CdS cosensitizers delivered a power conversion efficiency of 2.37%, which is significantly more efficient than conventional Pt counter electrodes. To the best of our knowledge, this study represents the first report utilizing nonstoichiometric CuInS2 nanocrystals as a photon-harvesting sensitizer comprised of a photoanode and photocathode in QDSSCs; also unique to this report, these nonstoichiometric CuInS2 nanocrystals were formed by simply changing the cationic molar ratios without complicated precursor preparation. Impedance spectroscopy and Tafel polarization indicated that these Cu-rich CuInS2 heteronanostructures had electrocatalytic activities (used for reducing S(2-)/Sn(2-)) that were superior to a Pt catalyst. Moreover, we demonstrated that Cu-rich CuInS2 heteronanostructures were also useful counter electrodes in dye-sensitized solar cells, and this finding revealed a promising conversion efficiency of 6.11%, which was ∼96% of the efficiency in a cell with a Pt-based counter electrode (6.32%).

Dispersive micro solid-phase extraction for the rapid analysis of synthetic polycyclic musks using thermal desorption gas chromatography-mass spectrometry.

A simple and solvent-free method for the rapid analysis of five synthetic polycyclic musks in water samples is described. The method involves the use of dispersive micro solid-phase extraction (D-µ-SPE) coupled with direct thermal desorption (TD) gas chromatography-mass spectrometry (GC-MS) operating in the selected-ion-storage (SIS) mode. The parameters affecting the extraction efficiency of the target analytes from water sample and the thermal desorption conditions in the GC injection-port were optimized using a central composite design method. The optimal extraction conditions involved immersing 3.2mg of a typical octadecyl (C18) bonded silica adsorbent (i.e., ENVI-18) in a 10mL water sample. After extraction by vigorously shaking for 1.0min, the adsorbents were collected and dried on a filter. The adsorbents were transferred to a micro-vial, which was directly inserted into GC temperature-programmed injector, and the extracted target analytes were then thermally desorbed in the GC injection-port at 337°C for 3.8min. The limits of quantitation (LOQs) were determined to be 1.2-3.0ng/L. Precision, as indicated by relative standard deviations (RSDs), was less than 9% for both intra- and inter-day analysis. Accuracy, expressed as the mean extraction recovery, was between 74 and 90%. A preliminary analysis of the river water samples revealed that galaxolide (HHCB) and tonalide (AHTN) were the two most common synthetic polycyclic musks present. Using a standard addition method, their concentrations were determined to in the range from 11 to 140ng/L.

Determination of melamine and cyanuric acid in powdered milk using injection-port derivatization and gas chromatography-tandem mass spectrometry with furan chemical ionization.

A reliable, sensitive and eco-friendly injection-port trimethylsilylated (TMS) derivatization and gas chromatography-tandem mass spectrometry (GC-MS/MS) with furan chemical ionization (furan-CI) method was developed to determine melamine and cyanuric acid in powdered milk samples. The effects of several parameters related to the TMS-derivatization process (i.e., injection-port temperature, residence time and volume of silylating agent) and of various CI agents were investigated. Addition of a solution (3 µL) of bis(trimethyl)silyltrifluoroacetamide (BSTFA) containing 1% trimethylchlorosilane (TMCS) reagent to a 20-µL extract from the powdered milk sample gave an excellent yield of the tris-TMS-derivatives of melamine and cyanuric acid at an injection-port temperature of 90°C. Furthermore, using furan as the CI agent in conjunction with tandem mass spectrometry provided the greatest sensitivity and selectivity of detection. The limits of quantitation (LOQs) for melamine and cyanuric acid were 0.5 and 1.0 ng/g in 0.5-g of powdered milk samples, respectively. The recoveries from spiked samples--after simple ultra-sonication with 5% dimethyl sulfoxide in acetonitrile coupled with n-hexane liquid-liquid extraction--ranged from 72% to 93% with relative standard deviations of lower than or equal to 18%. In three of four real powdered milk samples, melamine was detected at concentrations ranging from 36 to 1460 ng/g; and cyanuric acid was detected in two of these samples at concentrations of 17 and 180 ng/g.

Chemical ionization of substituted naphthalenes using tetrahydrofuran as a reagent in gas chromatography with ion trap mass spectrometry.

The ion/molecule reactions of nine monosubstituted naphthalene compounds in chemical ionization mass spectrometry (CI-MS) were studied using tetrahydrofuran (THF) as CI reagent. Proton affinity factors, substituent effects and the preferred site of adduct ion attachment were examined. Good correlation was observed between proton affinity and the formation of [M](+*) and [M+H](+) ions. The influence of substituents on protonation and site-specific adduct [M+13](+) and [M+41](+) ion formation is also observed, with the cyano substituent showing the most stable [M+41](+) ion. Collision-activated dissociation experiments were used to characterize the variety of adducts formed under CI conditions, and provided insight into product ion structures and mechanisms of dissociation and condensation during CI-MS/MS.

A simple and rapid method for identifying the source of spilled oil using an electronic nose: confirmation by gas chromatography with mass spectrometry.

Two types of electronic nose (EN), different in operational principle, were used to identify the source of spilled oil in an accident. The suspected sources considered were petroleum oil reservoirs and pipelines located near the site of the accident. Gas chromatography/mass spectrometry (GC/MS), operated in both EI and CI modes, was employed to confirm the identified source. The advantage of multisensors in spatially resolved sensing for direct multicomponent analysis was explored to minimize tedious sample preparation procedures. Subsequent principal component analysis helped in identifying the source. The advantage of fast separation in temporally resolved sensing was explored to rapidly yield compositional information; the resulting graphical representations helped clarify the source. Traditional GC/MS not only confirms the identified spilled oil source, but also provides detailed diagnostic information such as total petroleum hydrocarbons, polycyclic aromatic hydrocarbons and their C1-C4 alkylated homologues, as well as the n-alkanes, which are essential for follow-up remedial and regulatory actions. The main use of the electronic nose was demonstrated to be as a simple and rapid screening method for identifying a spilled oil source.