Rapid analysis of 2,4-D in soil samples by modified Soxhlet apparatus using HPLC with UV detection

The 2,4-dichlorophenoxy acetic acid (2,4-D) is used as a systemic herbicide to control broadleaf weeds in wheat, corn, range land/pasture land, sorghum, and barley. In this study, a fast and efficient method is developed by selection of modified extraction apparatus and high-performance liquid chromatography (HPLC)-UV conditions for the determination of 2,4-D in soil samples. The method is applied to the study of soil samples collected from the agricultural field. The herbicide is extracted from soil samples by acetonitrile in a modified Soxhlet apparatus. The advantages of the apparatus are that it uses small volume of organic solvent, reduced time of extraction, and better recovery of the analyte. The extract is filtered using a very fine microfiber paper. The total extract is concentrated in a rotatory evaporator, dried under ultrahigh pure N2, and finally reconstituted in 1 mL of acetonitrile. HPLC-UV at 228 nm is used for analysis. The herbicide is identified and quantitated using the HPLC system. The method is validated by the analysis of spiked soil samples. Recoveries obtained varied from 85% to 100% for spiked soil samples. The limit of quantitation (LOQ) and the limit of detection (LOD) are 0.010 and 0.005 parts per million (ppm), respectively, for spiked soil samples. The LOQ and LOD are 0.006 and 0.003 ppm for unspiked soil samples. The measured concentrations of 2,4-D in spiked soil samples are between 0.010 and 0.020 ppm with an average of 0.016 +/- 0.003 ppm. For unspiked soil samples it is between 0.006 ppm and 0.012 ppm with an average of 0.009 +/- 0.002 ppm. The measured concentrations of 2,4-D in soil samples are generally low and do not exceed the regulatory agencies guidelines.     

On the integration of data and mathematical modeling languages

This paper examines ways in which the addition of data modeling features can enhance the capabilities of mathematical modeling languages. It demonstrates how such integration is achieved as an application of the embedded languages technique proposed by Bhargava and Kimbrough [4]. Decision-making, and decision support systems, require the representation and manipulation of both data and mathematical models. Several data modeling languages as well as several mathematical modeling languages exist, but they have different sets of these capabilities. We motivate with a detailed example the need for the integration of these capabilities. We describe the benefits that might result, and claim that this could lead to a significant improvement in the functionality of model management systems. Then we present our approach for the integration of these languages, and specify how the claimed benefits can be realized.The author's work on this paper was performed in conjunction with research funded by the Naval Postgraduate School.     

The service system M/M R /∞ with impatient customers

An infinite server queue is considered where customers have a choice of individual service or batch service. Transient results have been obtained for the first two moments of the system size distribution. Waiting time distribution is important in system evaluation and steady state results are obtained.     

Design of a highly sensitive photonic crystal waveguide platform for refractive index based biosensing

In this paper, a photonic crystal waveguide platform on silicon-on-insulator substrate is proposed in order to realize a highly sensitive refractive index based biosensor. Following the design, the analysis of the sensor structure are made by using the three dimensional Finite Difference Time Domain method. The principle of sensing is based on the change in refractive index, which in turn changes the output spectrum of the waveguide. Results show that the sensitivity of the sensor depends mainly on the geometrical properties of the defect region of the photonic crystal structure. The phenomenon is verified for various samples having refractive index ranging from 1 (air) to 1.57 (Bovine serum albumin). Further, the structure is compared with few other conventional photonic crystal waveguide designs to analyze the sensing performance. The estimated value of sensitivity of the sensor is found to be 260 nm/RIU with a detection limit of 0.001 RIU. This high sensitivity can enhance the performance of low-concentration analytes detection.     

CTV Based Sensor for the Rapid Detection of Nitro Toluene With Computational Studies and Molecular Modelling

Journal of Fluorescence - A new tri-naphthoylated Cyclotriveratrylene molecule has been synthesized for the rapid and sensitive detection of 4-nitrotoluene (4-NT) among various nitro aromatic...     

Full potential calculation of electronic properties of rutile RO2 (R=Si, Ge, Sn and Pb) compounds via modified Becke Johnson potential

The electronic properties of RO₂ (R=Si, Ge, Sn and Pb; a group IVA element) compounds in rutile structure have been calculated using WIEN2k implementation of full potential linearized augmented plane wave (FPLAPW) method. The exchange and correlation (XC) effects are taken into account by an orbital independent modified Becke Johnson (MBJ) potential as coupled with Local Density Approximation (LDA) for all the compounds except for PbO₂ where only Generalized Gradient Approximation (GGA) is considered for the same. We predict a direct band gap in all these compounds with continuous decrease as the atomic size of IVA element increases such that there is an appearance of semimetallic band structure for the last compound, PbO₂. The largest band gap (7.66 eV) has been found for SiO₂, which governs its insulating nature. We observe that MBJLDA results for band gaps of these compounds are far better than those obtained using GGA and Engel-Vosko's GGA (EV-GGA). A very good agreement is observed between MBJLDA band gaps with corresponding experimental values as compared to other calculations. The electronic band structures are also analyzed in terms of contributions from various electrons.     

Coherent backscattering spectroscopy

Coherent backscattering (CBS) of light in random media has been previously investigated by use of coherent light sources. Here we report a novel method of CBS measurement that combines low spatial coherence, broadband illumination, and spectrally resolved detection. We show that low spatial coherence illumination leads to an anomalously broad CBS peak and a dramatic speckle reduction; the latter is further facilitated by low temporal coherence detection. Thus CBS can be observed in biological tissue and other media that previously were beyond the reach of conventional CBS measurements. We also demonstrate, for the first time to our knowledge, spectroscopic analysis of CBS. CBS spectroscopy may find important applications in probing random media such as biological tissue in which depth-selective measurements are crucial.     

Range‐independent background subtraction algorithm for recovery of Raman spectra of biological tissue

An important requirement for the use of Raman spectroscopy for tissue diagnostic applications is an appropriate algorithm that can faithfully retrieve weak tissue Raman signals from the measured raw Raman spectra. Although iterative modified polynomial‐fitting‐based automated algorithms are widely used, these are sensitive to the choice of the fitting range, thereby leading to significantly different Raman spectra for different start and stop wavenumber selection. We report here an algorithm for automated recovery of the weak Raman signal, which is range independent. Given a raw Raman spectrum and the choice of the start and the stop wavenumbers, the algorithm first truncates the spectrum to include the raw data within this wavenumber range, linearly extrapolates the truncated raw spectrum beyond the points of truncation on the two sides by using coefficients of linear least‐square fit, adds two Gaussian peaks of appropriate height and width on the extrapolated linear wings on either side and then iteratively smoothens the data with all these add‐ons such that the smaller of the ordinate values of the smoothed and the starting raw data serve as the input to each successive round of iterative smoothing until the added Gaussian peaks are fully recovered. The algorithm was compared with the modified polynomial‐based algorithms using mathematically simulated Raman spectrum as well as experimentally measured Raman spectra from various biological samples and was found to yield consistently range‐independent and artifact‐free Raman signal with zero baseline. Copyright © 2012 John Wiley & Sons, Ltd.     

Dielectric, magnetic and magnetoelectric properties of La and Nb codoped bismuth ferrite

Single-phase Bi(0.80)La(0.20)FeO(3) (BLFO) and Bi(0.80)La(0.20)Fe(1-x)Nb(x)O(3) (BLFNO) samples were prepared in order to study the dielectric, magnetic and magnetoelectric properties of La and Nb codoped BiFeO3. Rietveld refinement of x-ray diffraction patterns of La and Nb codoped samples has been performed using the R3c space group. Magnetic hysteresis loops revealed that codoping can effectively increase the spontaneous magnetization due to change in the bond angle of Fe-O-Fe as a result of distortion created by the Nb5+ doping. Magnetic field-induced relative change of the dielectric constant for BLFO and BLFNO samples is a signature of magnetoelectric coupling.