A solid-phase extraction (SPE) using multi-walled carbon nanotubes (MWCNTs) as adsorbent coupled with gas chromatography-mass spectrometry (GC-MS) method was developed for the determination of 16 polycyclic aromatic hydrocarbons (PAHs) in environmental water samples. Several condition parameters, such as extraction adsorbents, elution solvents and volumes, and sample loading flow rate and volume were optimized to obtain high SPE recoveries and extraction efficiency. 150 mg MWCNTs as sorbent presented high extraction efficiency of 16 PAHs due to the large specific surface area and high adsorption capacity of MWCNTs compared with the commercial C18 column (250 mg/2 mL). The calibration curves of 16 PAHs extracted were linear in the range of 20-5000 ng L-1, with the correlation coefficients (r(2)) between 0.9848 and 0.9991. The method attained good precisions (relative standard deviation, RSD) from 1.2% to 12.1% for standard PAHs aqueous solutions; method recoveries ranged in 76.0-125.5%, 74.5-127.0%, and 70.0-122.0% for real spiked samples from river water, tap water and seawater, respectively. Limits of detection (LODs, S/N = 3) of the method were determined from 2.0 to 8.5 ng L-1. The optimized method was successfully applied to the determination of 16 PAHs in real environmental water samples. (C) 2010 Elsevier B.V. All rights reserved.
An anion exchange solid phase extraction (SPE) procedure coupled with high-performance liquid chromatography was developed for the determination of sesamol in sesame oil. Sesamol was effectively extracted from sesame oil using a Cleanert PAX (500 mg per 6 mL) anion exchange SPE column. Conditions for the SPE procedure including the type, volume, and pH of the sample loading solvent, the volume and pH of washing solution, and the type, volume, and pH of the eluent were optimized for efficient sample cleanup with excellent sesamol recovery. The calibration curve of sesamol showed excellent linearity in the range of 10-500 mg L-1 with a correlation coefficient (r(2)) of 0.9996. The SPE-HPLC method demonstrated high reproducibility with precision values (relative standard deviations, RSDs) in the range of 1.9-8.2% and high recoveries in the range of 88.2-106.1% for spiked sesame oil samples. The limit of quantitation (S/N = 10) was found to be 5.0 mg kg(-1). The optimized method was successfully applied to the determination of sesamol in sesame oil samples from a local market.
A new polarization beam splitter is proposed based on a photonic crystal ring resonator (PCRR) composed of honeycomb-lattice cylindrical silicon rods in air. By shrinking the width of the bus waveguide and adjusting the radii of two nearest-neighbor center rods of the PCRR, an unpolarized beam can be separated well into TE and TM polarization states, respectively, at the backward and forward output ports. Simulation results obtained by the two-dimensional finite-difference time-domain technique show that the insertion losses are 3.58 dB and 3.08 dB, and the polarization extinction ratios are 21.42 dB and 28.53 dB for TE and TM polarization, respectively, at a 1566.7 nm center wavelength. The excess loss is less than 0.34 dB and its dimensions are roughly 43.2 mu m x 27.52 mu m. These findings offer potential practical applications in high-density photonic integrated circuits.
A simple, fast, sensitive and cost-effective method based on headspace solid-phase microextraction (HS-SPME) with on-fiber derivatization coupled with gas chromatography-mass spectrometry was developed for the determination of six typical aldehydes, 2E-hexenal, heptanal, 2E-heptenal, 2E,4E-heptadienal, 2E-decenal and 2E,4E-decadienal in laboratory algae cultures. As derivatization reagent, O-2,3,4,5,6-(pentafluorobenzyl) hydroxylamine hydrochloride, was loaded onto the poly(dimethylsiloxane)/divinylbenzene fiber for aldehydes on-fiber derivatization prior to HS-SPME. Various influence factors of extraction efficiency were systematically investigated. Under optimized extraction conditions, excellent method performances for all the six aldehydes were attained, such as satisfactory extraction recoveries ranging from 67.1 to 117%, with the precision (relative standard deviation) within 5.3-11.1%, and low detection limits in the range of 0.026-0.044 mu g/L. The validated method was successfully applied for the analysis of the aldehydes in two diatoms (Skeletonema costatum and Chaetoceros muelleri), two pyrrophytas (Prorocentrum micans and Scrippsiella trochoidea) and Calanus sinicus eggs (feeding on the two diatoms above).
A rapid and effective method is developed for the determination of organophosphorus pesticides (dichlorovos, methyl parathion, malathion, and parathion) in underground water by solid-phase extraction (SPE)-gas chromatography-mass spectrometry. Some important extraction parameters including types of SPE adsorbents, elution solvents, and injection volume of water samples are optimized. The use of Cleanert-PEP polymer SPE column improved higher extraction efficiencies than the C18 SPE column commonly used. Water samples are extracted using Cleanert-PEP as SPE adsorbent and ethyl acetate as elution solvent. Precision values expressed as relative standard deviation for 1 µg/L of spiked water sample are in the range of 1.6-4.0%. Dichlorvos, methyl parathion, malathion, and parathion are linear in the range of 0.1-1.0 µg/L (r2 = 0.9976), 0.1-2.0 µg/L (r2 = 0.9883), 0.1-2.0 µg/L (r2 = 0.9798), and 0.055-1.1 µg/L (r2 = 0.9790), respectively. The limits of detection for spiked water samples are in the range of 4-10 ng/L. The optimized method is applied to the determination of underground water samples. Recoveries are between 59.5% and 94.6% for spiked underground water samples. The benefit of the method developed is rapid, simple, and has good repeatability.
Reactive unsaturated aldehydes produced by marine diatoms upon cell damaged interfere negatively with the reproduction success of their grazers. In this paper, a method based on headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography-mass spectrometry (GC-MS) was developed for analysis of six aldehydes: [(E)-2-hexenal, heptanal, (E)-2-heptenal, (E,E)-2,4-heptadienal, (E)-2-decenal, (E,E)-2,4-decadienal] in two laboratory cultured diatoms (Skeletonema costatum and Chaetoceros Muelleri). HS-SPME experimental conditions including SPME fiber types, extraction time and temperature, desorption time and temperature were optimized. Under the optimal experimental conditions, limits of detection for six aldehydes were both in the range of 0.1-2 µg/L. The relative standard deviations ranged from 7.2 to 13.9%. Recoveries were in the range of 60.6-85.7%. The concentrations of six aldehydes in Skeletonema costatum were 0.359, 0.038, 0.028, 0.183, 0.023, and 0.058 ng/106 cells respectively. The six aldehydes were not found in Chaetoceros Muelleri. The study shown here provided a simple, fast and sensitive method for the analysis of aldehydes in diatoms.
Flash-based devices internally provide multilevel parallelism, and parallelizing flash operations is the key to improving performance. Most of existing research works dispatch and schedule host requests so that the obtained sub-requests can be served in parallel, however, these works seldom parallelize the extra operations introduced by the internal garbage collection (GC) process. The costly operation sequence of GC is the main reason for I/O blocking, especially when the device is close to be full. In this paper, we propose a novel Subdivided Garbage Collector (SGC), which exploits both the system-level and the flash-level parallelism to parallelize garbage-collecting operations as well as garbage-collecting activities. SGC confines the GC process inside a flash chip, utilizing the system-level parallelism to overlapping garbage-collecting activities with I/O services among different chips. The flash-level parallelism is further exploited with a novel queue mechanism, which schedules and packs the reordered partial steps of cleaning sequence into parallel operations. To make more parallelization possible, a dynamic conflict-aware address allocator is proposed to eliminate the host writes and cleaning operations from contending for the critical components of the device. Trace-driven simulations demonstrate that the proposals can hide overheads of GC, resulting in a shorter response time.
Due to the unique erase-before-write characteristic of flash memories, flash-based solid-state disks (SSDs) use out-of-place update and require a garbage collection process to recycle invalid data space. This process brings extra operations and latencies, causing I/O blocking and performance degradation, especially when the device is close to be full. In this work, we use a parallel-unit-aware allocation policy for the internal migrating write and incoming requesting write, scheduling and packing all the operations together to utilize the micro-architecture parallelism of multi-channel SSDs. Trace-driven simulations reveal that the proposed design reduces 33.31% of response time, on average, thus improves the device performance.
Nanocrystals of high purity magnesium hydroxide (Mg(OH) 2 ) about 30nm in size were synthesized using magnesium chloride and sodium hydroxide as precursor via hydrothermal route. XRD and TEM were used to characterize the chemical composition, size and structure of the product. TG and DSC curves were performed to investigate the thermal stability of as-prepared nanocrystals, and the result indicated that nanocrystals of magnesium hydroxide, potentially used as flame retardant, are appropriate in thermal property. The influencing factors on nanocrystal purity and potential perspective of the as-prepared product used as flame retardant were modestly discussed.