Zhongchen Wu

Differentiation of dried sea cucumber products from different geographical areas by surface desorption atmospheric pressure chemical ionization mass spectrometry.

Without any sample pretreatment, mass spectral fingerprints of 486 dried sea cucumber slices were rapidly recorded in the mass range of m/z 50-800 by using surface desorption atmospheric pressure chemical ionization mass spectrometry (DAPCI-MS). A set of 162 individual sea cucumbers (Apostichopus japonicus Selenka) grown up in 3 different geographical regions (Weihai: 59 individuals, 177 slices; Yantai: 53 individuals, 159 slices; Dalian: 50 individuals, 150 slices;) in north China sea were successfully differentiated according to their habitats both by Principal Components Analysis (PCA) and Soft Independent Modeling of Class Analogy (SIMCA) of the mass spectral raw data, demonstrating that DAPCI-MS is a practically convenient tool for high-throughput differentiation of sea cucumber products. It has been found that the difference between the body wall tissue and the epidermal tissue is heavily dependent on the habitats. The experimental data also show that the roughness of the sample surface contributes to the variance of the signal levels in a certain extent, but such variance does not fail the differentiation of the dried sea cucumber samples.

Dielectric barrier discharge non-thermal micro-plasma for the excitation and emission spectrometric detection of ammonia

Dielectric-barrier discharge (DBD) in argon as a cold source is used for the excitation of gaseous inorganic small molecules at atmospheric pressure. By choosing ammonia as a model molecule, the excitation process and the characteristics of the emission spectra are investigated. The emission spectra are recorded by designing either an open-end or an enclosed DBD excitation/emission source. The enclosed excitation mode effectively eliminates the background emissions arising from the ambient air components, especially those from nitrogen. Two emission lines attributed to the excitation of ammonia, i.e., 326.2 and 336.5 nm, are clearly isolated from the background emission spectra of argon, providing the basis for quantitative analysis. A detection limit of 0.37 ppm is achieved within a linear range of 1.2-35 ppm by monitoring at 326.2 nm. In practice, gaseous samples containing ammonia collected in a public toilet are excited in an enclosed excitation source and the emission at 326.2 nm is monitored for quantitative analysis. An ammonia concentration of 2.4 ppm is derived in the original atmospheric sample, and a spiking recovery of 94.7% is achieved at a 10 ppm ammonia level. This study shows that DBD cold excitation in combination with optical emission spectrometry (OES) offers a promising approach for the detection of ammonia pollution.

Coupling neutral desorption sampling to dielectric barrier discharge ionization mass spectrometry for direct oil analysis

Rapid analysis of viscous oil samples is of great interest in food science and the food industry. Herein, neutral desorption sampling in conjunction with dielectric barrier discharge ionization mass spectrometry (ND-DBDI-MS) has been established for the fast and accurate identification of various hogwash oil (HHO) and edible oil samples under ambient conditions. Mass spectra in the negative ion detection mode were recorded in the mass range of m/z 50–500 Da, and characteristic substances responsible for the classification were identified using MS/MS experiments. Particularly, free fatty acids (e.g., oleic acid, linoleic acid, palmitic acid, etc.), typical representatives of oil quality, were successfully measured and used as decisive markers to differentiate HHO from qualified edible oil samples with the help of principal component analysis (PCA). Methodological reproducibility was characterized in terms of statistical method such as cluster analysis (CA). The experimental results show that ND-DBDI-MS is an important tool for the rapid analysis of highly complex viscous samples such as oil samples, with potential applications in food safety analysis.

Sequential monitoring of elemental mercury in stack gas by dielectric barrier discharge micro-plasma emission spectrometry

A simple device was constructed for the on-site sequential monitoring of emitted elemental mercury (Hg0) in coal-fired stack gas. The device integrates on-line gold amalgam preconcentration, external thermal desorption and cold excitation in an enclosed atmospheric-pressure dielectric-barrier discharge (DBD) micro-plasma chamber. The emission was monitored by using a charge coupled device spectrometer. The Hg0 emission at 253.7 nm was well separated from the emission spectra of the Ar-DBD-plasma which eliminates the spectral interferences of ambient air and gaseous inorganic small molecular pollutants in the stack gas, e.g., NOx, SO2, H2S and HCl. Quantification was based on first derivative spectra. Among the three mercury species, Hg0 is efficiently and selectively trapped on the gold amalgam at <220 °C, the threshold temperature for thermal desorption of the trapped Hg0 is ca. 420 °C above which the gold amalgam releases the enriched Hg0 rapidly and gives rise to a high concentration of Hg0 in the flowing Ar stream in a very short period of time which significantly improves the detection sensitivity. A linear calibration graph was achieved within 8–256 ng (the mass of enriched Hg0 on the gold trapping micro-column) with a detection limit of 2.3 ng and an RSD of 4.0% at 32 ng. A spiking recovery of 96.1% was achieved at a spiking mass level of 50 ng Hg0. For real sample analysis (stack gas from a honeycomb briquette stove), a calibration range of 2.7–60.8 ppt was achieved after 5 min preconcentration with a 0.5 L min−1 sampling flow rate.

Portable Dielectric Barrier Discharge-Atomic Emission Spectrometer.

This paper describes the first demonstration of a portable dielectric barrier discharge-atomic emission spectrometer (DBD-AES). The instrument primarily consists of a miniature electro-thermal vaporizer (ETV), DBD, and optical signal acquisition units. It weighs only 4.5 kg and is powered by a 24 V DC battery with a maximum power consumption of 37 W. The accompanying software can be operated on a laptop computer. A specially designed quartz tube integrates the ETV unit with the DBD chamber. The effects of experimental parameters were investigated. The limit of detection (LOD) for mercury was 0.4 μg L-1 (1.2 pg) with a sampling volume of 3 μL. The instrument is applicable for multielement analysis, and the LODs ranged from 0.16 to 11.65 μg L-1 for Zn, Pb, Ag, Cd, Au, Cu, Mn, Fe, Cr, and As. The instrument was also validated by in-field analysis of seawater samples. The experimental results demonstrated the sensitivity, reliability, and practicality of the instrument.

Cold excitation and determination of hydrogen sulfide by dielectric barrier discharge molecular emission spectrometry.

A low-temperature microplasma generated in a dielectric barrier discharge (DBD) was used as a radiation source for the excitation of hydrogen sulfide and its determination by molecular emission spectrometry (MES). The excitation/emission chamber was enclosed to eliminate spectral interference from ambient air. The spectral emission lines of hydrogen sulfide were clearly discriminated from the background spectrum, and the emission line at 365.06 nm was selected for parameter optimization and quantitative analysis. The S(2-) ions in aqueous samples were reacted with acid to generate hydrogen sulfide and then determined. The experimental parameters affecting the determination of hydrogen sulfide and S(2-) were optimized. The limits of detection were 1.4 mg m(-3) for H2S and 11.2 mg L(-1) for S(2-). The repeatability of the method was satisfactory, as the RSD values were 2.3% for H2S and 1.8% for S(2-). The enclosed DBD-MES system was demonstrated to be a useful tool for the determination of hydrogen sulfide in gas samples and S(2-) in aqueous samples.

Extractive electrospray ionization mass spectrometry for sensitive detection of gaseous radioactive iodine-129

A rapid method based on extractive electrospray ionization mass spectrometry (EESI-MS) has been developed for quantitative detection of trace radioactive molecular iodine-129 (129I2) in negative ion detection mode in ambient air. For actual air samples, gaseous 129I2 was completely converted into iodine-129 ions (129I−) by an excess of Na2SO3 solution. By adding excess amounts of 127I2 into the solution, the 129I− ions formed triiodide ion complexes (i.e.129+127*2I3−) which were subjected to tandem mass spectrometry experiments to exclude false positives. Quantification of iodine-129 was achieved by quantitatively measuring the characteristic fragment (i.e., 129I−) of the triiodide ion complexes. The calibration curve showed a good linearity within an relatively wide concentration range of 0.01–1000 ppb (R2 = 0.991), a limit of detection (LOD) of 4.5 ppt and a relative standard deviation (RSD) of 4.0–13.1% (n = 5). The spiking recovery of this method was found to be 82.6–110.5%. The method had also been successfully applied to detecting the trace amount of gaseous 129I2 released in a simulated nuclear leakage accident, showing a satisfactory result for the tested gaseous samples. The experimental data demonstrated that EESI-MS was a useful tool for quantitative measurement of radioactive iodine in cases such as nuclear leakage, nuclear explosions and related scenarios.

Broad flattop transparent photonic band in truncated photonic crystals composed of the symmetric unit cell

We theoretically show that a one-dimensional finite all-dielectric periodic structure composed of symmetric unit cells can possess a broad flattop transparent photonic band. In contrast to the conventional viewpoint that the thickness of the truncated photonic crystals affects the transmission within the pass band, the transparent photonic band is insensitive to the change of the periodic number since the equivalent refractive indices of our structures can be nearly equal to that of the background in a wide frequency range. With easy fabrication, this broad flattop transparent photonic band will play an important role in the broadband filtering.