[The research on residual amplitude modulation characteristics in fiber frequency modulation spectroscopy].

Frequency modulation spectroscopy (FMS) not only can be used to simultaneously measure the absorption and dispersion of atoms and molecules, but is the key technology of the noise immunity cavity enhanced optical heterodyne molecular spectroscopy (NICE-OHMS). The optical devices or the instability of output light polarization of the laser source will induce the residual amplitude modulation (RAM) in the FMS. RAM greatly limits the FMS technology application in trace gas detection, so the research on the RAM characteristics in the FMS has very important significance. Firstly, the lineshape of FMS without absorption was analyzed, and the impact factors on the RAM were acquired, then the influence of input and output polarization direction and electro-optical modulation (EOM) temperature was measured, respectively. They all have linear relationship with the RAM. The results verify the theoretical analysis and provide the basis for reducing the RAM and other related working.

[Theoretical analysis of the residual amplitude modulation of frequency modulation strong absorption spectroscopy].

In the present paper a phase controllable waveplate model was applied to the analysis of polarization maintaining fiber. Under the temperatures of 24 degrees C and 26.8 degrees C there is no residual amplitude modulation (RAM) existing in frequency modulation spectroscopy (FMS) when performing the measurement of fiber temperature dependence on the RAM. However, the temperature setting can not reduce the background long term drift and a servo feedback suggested by N. C. Wong and J. L. Hall can be used to actively reduce the RAM. The error signal for feedback is from the dispersion background signal of FMS without gas sample. The variation of RAM induced by the temperature changing of PM fiber is the main reason for the long term background drift of dispersion signal of FMS.

[Experimental investigations of cavity ring-down spectroscopy under different threshold circuit design].

In the present paper, the authors simply describe the principle of cavity ring-down spectroscopy (CRDS) measurement technology and introduce a threshold circuit, based on 555 timer IC (integrated circuit), applied to CRDS. And we verify the feasibility of the circuit. By means of changing the input resistor and input capacity, we analyzee the influence of threshold circuit characteristics on single ring-down event, and found that the greater the input capacitance, and the smaller the input impedance of circuit, the more serious the distortion of measurement of ring-down curve, especially when the resistance is less than 50 omega the ring-down time produces very big change. Then we collected and analyzed the C2H2 absorption signal at 6 531.7805 cm(-1) with different input resistance and input capacitance, and fitted the absorption line with Voigt profile. We found that the change of the input capacitance and resistance caused the distortion of fitting curve. Finally We give the optimal design of threshold circuit: the input impedance of the threshold circuit should be great, minimum of 100 omega, the capacitive reactance should be as small as possible, preferably below 1 nf, at the same time it should be ensured that the threshold of the circuit time constant is much smaller than ring-down time. The experiment research on CRDS technique application has important reference value to threshold circuit design.

[Theoretical analysis of saturated spectral line shape of noise immune cavity enhanced optical heterodyne molecular spectroscopy].

In the present paper a theoretical description of the line shapes of frequency modulated noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) under saturated conditions is presented. Expressions for both Doppler broadened and Doppler free frequency modulated NICE-OHMS signals at their absorption and dispersion phases are given. The modulation frequency, saturation parameter and frequency modulation index are set to 384 MHz, 10 and 0.2, respectively in the simulation. Based on the simulated line shape curves, in the absorption detection phase there are four sub Doppler structures existing in the spectral envelope of absorption signals of two sidebands, and in the dispersion phase there are five sub-Doppler structures existing in the spectral envelope of dispersion signals of carrier and two sidebands. The sub-Doppler structure originates from the fact that two counter propagating waves interact with the same group of molecules and one can act as a detecting beam and the other can act as a pumping beam. Therefore the sub-Doppler structure can appear at laser carrier and sidebands frequency and their middle frequencies of carrier and sidebands. Since NICE-OHMS absorption signal is only related to the absorption of sidebands the small saturation parameters of two sidebands can not saturate the Doppler broadened signal too much Although the NICE-OHMS dispersion signal includes the dispersion of carrier and two sidebands, the amplitude of Doppler broadened signal does not have so much influence by saturation except for the Doppler free signal. Therefore NICE-OHMS technique is a good candidate for the high sensitive detection of gas medium but with high selectivity under the condition of low pressure. Finally the dependences of NICE-OHMS line shape on the detection phase and saturation parameter are simulated and analyzed, the results of which nicely agree with the existing experimental results. The researches on NICE-OHMS line shapes will help explain the phenomena of related experiment.

Three new naphthalenyl glycosides from the root bark of Juglans cathayensis.

Phytochemical investigations of the root bark of Juglans cathayensis DODE. led to the isolation of three new naphthalenyl glycosides, Jugnaphthalenoside A-C (1-3). Their structures were elucidated on the basis of extensive analysis of spectroscopic data. The cytotoxicities of the three new compounds were also evaluated.

Rapid and Sensitive Detection of Aflatoxin B1, B2, G1 and G2 in Vegetable Oils Using Bare Fe3O4 as Magnetic Sorbents Coupled with High-Performance Liquid Chromatography with Fluorescence Detection.

This paper reports a simple, sensitive and reliable method for the simultaneous detection of aflatoxin B1, B2, G1 and G2 in vegetable oils. Aflatoxins were extracted by magnetic solid phase extraction followed by high-performance liquid chromatography, then postcolumn photochemical derivatization and finally detected by fluorescence detector. Vegetable oil samples were first diluted with hexane and then commercial bare Fe3O4 nanoparticles were directly employed as sorbents to extract aflatoxins from complex vegetable oil samples, which significantly simplified the procedure of sample preparation and largely improved the sample analysis throughput. The effects of various parameters such as the amount of sorbent, loading, washing and eluting conditions were carefully optimized to improve the extraction efficiencies of aflatoxins. Under the optimal conditions, the limits of detection of four aflatoxins ranged from 0.01 µg/kg to 0.16 µg/kg, and squared regression coefficients (R2) >0.9990 were obtained within the linear range of 0.1-20 µg/kg (except for aflatoxin G2 with 0.5-20 µg/kg). Furthermore, the recoveries spiked at four concentration levels in a blank vegetable oil sample were from 82.6 to 106.2%, with inter- and intraday relative standard deviations <9.8%, indicating good accuracy and precision of the proposed method.

[Recent Distribution and Sources of Polycyclic Aromatic Hydrocarbons in Surface Soils from Yangtze River Delta].

A total of 243 surface soil samples collected from 11 cities in the Yangtze River Delta region were analyzed for the concentrations, spatial distribution, component profiles and emission sources of 29 PAH species. The analytical results indicated the total concentrations of PAHs in Yangtze River Delta fell in the range from 21. 0 ng x g(-1) to 3 578.5 ng x g(-1) with an arithmetic mean and standard deviation of 310.6 ng x g(-1) and 459.1 ng x g(-1), respectively. Our data showed spatial distribution of PAHs concentrations varied greatly in the region. In addition, the contents of PAHs were positively correlated with the total organic carbon fractions in topsoil. The sites with the highest levels of PAHs in the 11 cities studied were located in Suzhou with 759.0 ng x g(-1) +/- 132.9 ng x g(-1) ollowed by the areas of Wuxi and Shanghai, with the total PAHs concentrations of 565. 3 ng x g(-1) +/- 705.5 ng x g(-1) and 349.4 ng g(-1) 220. 1 ng-g(-1) respectively. The profiles of different components pointed to a predominant role of the species with 2-4 rings, and especially for the low molecular weight components with 2-3 rings. A preliminary identification on emission sources of local PAHs was performed by the specific ratios of isomeric species and principal component analysis (PCA). The results designated industrial coal and biomass combustion as the main mixed emission sources of PAHs in surface soils from Yangtze River Delta, and tail gas from transport as another major source in some areas.

[Concentrations and Component Profiles PAHs in Surface Soils and Wheat Grains from the Cornfields Close to the Steel Smelting Industry in Handan, Hebei Province].

In this study, paired surface soil and mature wheat grain samples were collected in the cornfields near the large Handan Steel Manufacturer; and the total concentrations and compositional profiles of the parent PAHs were measured, then the spatial distribution characteristics and correlation with total organic carbon fractions in soil were determined. Accordingly, a preliminary source identification was performed, and the association between PAHs in surface soil and wheat grain was briefly discussed. The median concentration of total PAHs in surface soils from the cornfields of Handan was 398.9 ng x g(-1) (ranged from 123.4 ng x g(-1) to 1626.4 ng x g(-1), where around 18% and 10% of all the studied soil samples were over the corresponding quality criteria for total PAHs and B [a] P in soils, respectively. The MMW and HMW species were the main components in the compositional profiles of surface soils. Based on the specific isomeric ratios of PAHs species, coal/biomass combustion and transportation fuel (tail gas) were the dominant mixed sources for the local PAHs emission. The fractions of surface soil TOC had significant positive correlations with the total PAHs and also with the individual components with different rings. In addition, the median concentration of total PAHs in wheat grains collected in the cornfields near the Handan Steel Manufacture was 27.0 ng x g(-1) (ranged from 19.0-34.0 ng x g(-1)). The levels in wheat grains were not high, and lower than the related hygienic standards of food proposed by EU and China. The LMW and MMW PAHs with 2 to 4 rings occupied a larger proportion, more than 84% of the total PAHs, which was largely different from the component profiles in surface soils. This situation suggested that the local sources of PAHs in wheat grains may originate not only from surface soil via root absorption and internal transportation, but also from ambient air through dry and wet deposition on the leaf surface (stoma).