The Use of Various Chromatographic Techniques for the Determination of Phenylurea Herbicides and Their Corresponding Anilines in Environmental Samples,II. Applications

Abstract

In earlier work, various strategies have been developed for the trace-level determination of phenylurea herbicides and the anilines which are their main degradation products. They include catalytic hydrolysis of the phenylureas on silica, liquid chromatographic fractionation of complex mixtures of herbicides and anilines, derivatization of anilines and herbicides with electron-capture-sensitive reagents, and final analysis by means of capillary gas chromatography. In the present paper, the application of these principles to trace-level analysis of surface water, soil and crop samples is demonstrated.     

Determination of zinc in marine/lacustrine sediments by graphite furnace atomic absorption spectrometry using Pd/Mg chemical modifier and slurry sampling

Effectiveness of Pd/Mg chemical modifier for the accurate direct determination of zinc in marine/lacustrine sediments by graphite furnace atomic absorption spectrometry (GF-AAS) using slurry samples was evaluated. A calibration curve prepared by aqueous zinc standard solution with addition of Pd/Mg chemical modifier is used to determine the zinc concentration in the sediment. The accuracy of the proposed method was confirmed using Certified Reference Materials, NMIJ CRM 7303-a (lacustrine sediment) from National Metrology Institute of Japan, National Institute of Advanced Industrial Science and Technology, Japan, and MESS-3 (marine sediment) and PACS-2 (marine sediment) from National Research Council, Canada. The analytical results obtained by employing Pd/Mg modifier are in good agreement with the certified values of all the reference sediment materials. Although for NRC MESS-3 an accurate determination of zinc is achieved even without the chemical modifier, the use of Pd/Mg chemical modifier is recommended as it leads to establishment of a reliable and accurate direct analytical method. One quantitative analysis takes less than 15 minutes after we obtain dried sediment samples, which is several tens of times faster than conventional analytical methods using acid digested sample solutions. The detection limits are 0.13?µg?g^?1 (213.9?nm) and 16?µg?g^?1 (307.6?nm), respectively, in sediment samples, when 40?mg of dried powdered samples are suspended in 20?mL of 0.1?mol?L^?1 nitric acid and a 10?µl portion of the slurry sample is measured. The precision of the proposed method is 8–15% (RSD).     

Volatile organic compounds in an urban environment: a comparison among Belgium,Vietnam and Ethiopia

The effects of urban and indoor air pollution on human health are a major environmental concern for all, but not much has been researched in the developing world. Specifically, quantitative data on the occurrence of volatile organic compounds (VOCs) – main contributors to air pollution – in Asia and Africa are scarce compared to the availability of data in the developed world. This paper presents one of the first studies focusing on the analysis and occurrence of VOCs in Vietnam and Ethiopia, which constitutes part of the novelty of this work. A spectrum of 34 VOCs was measured at eight different urban sites in Ghent (Belgium), Hanoi (Vietnam), Jimma and Addis Ababa (Ethiopia) during three sampling campaigns from September 2008 to September 2010. Sampling was done in an active way by means of sorbent tubes filled with Tenax TA. The analysis was done by TD-GC-MS using internal standard calibration. Data were interpreted and compared in terms of (i) individual, subgroup and total VOCs concentration (TVOCs), (ii) indoor-to-outdoor (I/O) concentration ratios, (iii) source identification by diagnostic ratio and/or correlation coefficients, and (iv) ozone formation potential (OFP) at outdoor sites based on up-to-date maximum incremental reactivity (MIR). I/O concentration ratios varied between 0.2 and 30, with big differences noticed with respect to the type of VOC(s) considered and the type of outdoor sampling location. The highest TVOC concentrations were measured in street samples with maximum values of 54?µg/m³ in Ghent, 507?µg/m³ in Hanoi and 318?µg/m³ in Addis Ababa illustrating the large difference in ambient air quality levels. This is also reflected in the arithmetic mean OFP values (µg/m³) of 82, 1308 and 596 in Ghent, Hanoi and Addis Ababa, respectively. Results of this study could be helpful to support formulation of national policy with regard to ambient air quality.     

Fitting formula for the injection volume of a gas chromatograph for radio‐xenon sampling in the lower troposphere

GC is usually used for xenon concentration and radon removal in the International Monitoring System of the Comprehensive Nuclear‐Test‐Ban Treaty. In a gas chromatograph, the injection volume is defined to calculate the column capacity. In this paper, the injection volume was investigated and a fitting formula for the injection volume was derived and discussed subsequently. As a consequence, the xenon injection volume exponentially decreased with the column temperature increased, but exponentially increased as the flow rate increased.     

Optimization of sampling frequency for routine river water quality monitoring

Sampling frequency is an important factor to be considered during the design of a water monitoring network,and the cost-effective selection of possible ways and means for the optimization of sampling frequency is still needed.This paper introduces water pollution index deviation ratio comparison(WPI DRC),a procedure for the optimization of sampling frequency for a routine river water quality monitoring system.Sampling frequency optimized using WPI DRC at monitoring station X5 in the mainstream of Xiangjiang River is compared with that established using the traditional Statistical Algorithm method.The result of comparison indicates that WPI DRC is more feasible than the traditional one.And then,the sampling frequencies for other 16 monitoring stations also have been optimized,and the results show the sampling frequencies of all the stations except that X4 are reduced,and there is no unacceptable difference between water quality evaluation results at 17 stations before and after the optimization.Therefore,it is concluded that WPI DRC is an effective optimization process with operable results,which can be used to fulfill the requirement of practical monitoring work.     

Generation of sub‐terahertz repetition rates from a monolithic self‐mode‐locked laser coupled with an external Fabry‐Perot cavity

A novel scheme to multiply the repetition rate of a monolithic self‐mode‐locked laser for generating sub‐terahertz pulse sources is successfully demonstrated. A coated Yb:KGW crystal is designed to achieve a self‐mode‐locked operation at a repetition rate of 24 GHz with an average output power exceeding 1.0 W at a pump power of 4.8 W. A partially reflective mirror is utilized to combine with the output surface of the gain medium to constitute an external Fabry‐Perot cavity. It is theoretically and experimentally verified that adjusting the external cavity length to satisfy the commensurate condition can lead to the frequency spacing to be various order harmonics of the mode spacing of the monolithic cavity. The maximum pulse repetition rate of the laser output can be up to 216 GHz and the pulse duration is as short as 330 fs. More importantly, the overall characteristics of the first‐order temporal autocorrelation traces obtained by sequentially scanning the external cavity.length display an intriguing phenomenon of temporally fractional revivals, similar to the feature of spatial Talbot revivals.

     

Application of accelerated heteronuclear single quantum coherence experiments to the rapid quantification of monosaccharides and disaccharides in dairy products

Monosaccharides and disaccharides are important dietary components, but if insufficiently metabolized by some population subgroups, they are also linked to disease patterns. Thus, the correct analytical identification, quantification, and labeling of these food components are crucial to inform and potentially protect consumers. Enzymatic assays and high-performance anion-exchange chromatography with pulsed amperometric detection are established methods for the quantification of monosaccharides and disaccharides that, however, require long measuring times (60–180 min). Accelerated methods for the identification and quantification of the nutritionally relevant monosaccharides and disaccharides d -glucose, d -galactose, d -fructose, sucrose, lactose, and maltose were therefore developed. To realize this goal, the NMR experiments HSQC (heteronuclear single quantum coherence) and acceleration by sharing adjacent polarization (ASAP)-HSQC were applied. Measurement times were reduced to 27 and 6 min, respectively, by optimizing the interscan delay and applying non-uniform sampling. The optimized methods were used to quantify d -glucose, d -galactose, d -fructose, sucrose, and lactose in various dairy products. Results of the HSQC and ASAP-HSQC methods are equivalent to the results of the reference methods in terms of both precision and accuracy, demonstrating that these methods can be used to correctly analyze nutritionally relevant monosaccharides and disaccharides in short times.     

Magnetic Hyperthermia Enhancement in Iron-based Materials Driven by Carbon Support Interactions

Magnetic hyperthermia (MH) shows great potential in clinical applications because of its very localized action and minimal side effects. Because of their high saturation magnetization values, reduced forms of iron are promising candidates for MH. However, they must be protected in order to overcome their toxicity and instability (i. e., oxidation) under biological conditions. In this work, a novel methodology for the protection of iron nanoparticles through confinement within graphitic carbon layers after thermal treatment of preformed nanoparticles supported on carbon is reported. We demonstrate that the size and composition of the nascent confined iron nanoparticles, as well as the thickness of their protective carbon layer can be controlled by selecting the nature of the carbon support. Our findings reveal that a higher nanoparticle–carbon interaction, mediated by the presence of oxygen-containing groups, induces the formation of small and well-protected α-Fe-based nanoparticles that exhibit promising results towards MH based on their enhanced specific absorption rate values.     

Siloxanes in Biogas: Approaches of Sampling Procedure and GC-MS Method Determination

A new approach of siloxane sampling based on impinger, micro-impinger, adsorption on active carbon, and direct TedlarBag methods followed by gas chromatography-mass spectrometry (GC-MS) was developed for the analysis of three linear (L2–L4) and four cyclic (D3–D5) volatile methyl siloxanes (VMSs). Three kinds of organic liquid-medium characterized by different polarities, namely acetone, methanol, and d-decane as siloxanes trap were arranged in the experiment which is widely discussed below. Thus, the GC-MS equipped with SUPELCOWAX-10 capillary column was employed to perform monitoring of VMS content in the analyzed biogas samples originating from landfill, wastewater treatment plants, and agriculture biogas plants. In all samples that have undergone the analysis, cyclic and linear VMSs were found in quantities exceeding 107.9 and 3.8 mg/m³, respectively. Significant differences between siloxanes concentrations depending on biogas origin were observed. Moreover, the high range of linearity (0.1 to 70.06 mg/m³), low LoD (0.01 mg/m³), low LoQ (0.04 mg/m³), and high recovery (244.1%) indicate that the procedure and can be applied in sensitive analyses of silica biogas contaminants. In addition to the above, the impinger method of sampling performed better than active-carbon Tube and TedlarBag, particularly for quantifying low concentrations of siloxanes. Overall, the evaluation of sampling methods for biogas collection simplified the analytical procedure by reducing the procedural steps, avoiding the use of solvents, as well as demonstrated its applicability for the testing of biogas quality.     

Nonuniform sampling and maximum entropy reconstruction applied to the accurate measurement of residual dipolar couplings

Residual dipolar couplings (RDC) provide important global restraints for accurate structure determination by NMR. We show that nonuniform sampling in combination with maximum entropy reconstruction (MaxEnt) is a promising strategy for accelerating and potentially enhancing the acquisition of RDC spectra. Using MaxEnt-processed spectra of nonuniformly sampled data sets that are reduced up to one fifth relative to uniform sampling, accurate 13C'-13Calpha RDCs can be obtained that agree with an RMS of 0.67 Hz with those derived from uniformly sampled, Fourier transformed spectra. While confirming that frequency errors in MaxEnt spectra are very slight, an unexpected class of systematic errors was found to occur in the 6th significant figure of 13C' chemical shifts of doublets obtained by MaxEnt reconstruction. We show that this error stems from slight line shape perturbations and predict it should be encountered in other nonlinear spectral estimation algorithms. In the case of MaxEnt reconstruction, the error can easily be rendered systematic by straightforward optimization of MaxEnt reconstruction parameters and self-cancels in obtaining RDCs from nonuniformly sampled, MaxEnt reconstructed spectra.