Analytical applications of liquid-liquid phase equilibria: analysis of binary mixtures of chemically similar components

A new, simple and rapid method based on the principle of liquid-liquid phase equilibria has been developed for the analysis of binary mixtures of chemically similar organic compounds. The method does not require elaborate instrumentation and can be used to analyse mixtures of members of homologous series. The application of the method has been illustrated by analysing binary mixtures of n-hexane and n-octane; the maximum uncertainty in this analysis is ~2%.     

Direct hapten coated immunoassay format for the detection of atrazine and 2,4-dichlorophenoxyacetic acid herbicides

A novel immunoassay format employing direct coating of small molecular hapten on microtiter plates is reported for the detection of atrazine and 2,4-dichlorophenoxyacetic (2,4-D). In this assay, the polystyrene surface of microtiter plates was first treated with an acid to generate -NO₂ groups on the surface. Acid treated plates were further treated with 3-aminoprpyltriethoxysilane (APTES) to functionalize the plate surface with amino groups for covalent linkage to small molecular hapten with carboxyl groups. The modified plates showed significantly high antibody binding in comparison to plates coated with hapten-carrier protein conjugates and presented excellent stability as a function of the buffer pH and reaction time. The developed assay employing direct hapten coated plates and using affinity purified atrazine and 2,4-D antibodies demonstrated very high sensitivity, IC₅₀ values for atrazine and 2,4-D equal to 0.8 ng mL⁻¹ and 7 ng mL⁻¹, respectively. The assay could detect atrazine and 2,4-D levels in standard water samples even at a very low concentration upto 0.02 and 0.7 ng mL⁻¹ respectively in the optimum working range between 0.01 and 1000 ng mL⁻¹ with good signal reproducibility (p values: 0.091 and 0.224 for atrazine and 2,4-D, respectively). The developed immunoassay format could be used as convenient quantitative tool for the sensitive screening of pesticides in samples.     

Preparation of Complexes of Copper (II) Aryl Carboxylates with Morpholine

Complexes of copper (II) aryl carboxylates with morpholine were prepared by the interaction of the copper carboxylate with the morpholine equimolar as well as in large excess quantities in acetone medium. The complexes isolated correspond to 1:1 and 1:2 stoichiometry. In continuation of our work on the preparation of complexes of copper (II) aryl carboxylates with nitrogen donors like aliphatic amines,¹⁾ heterocyclic amines²⁾ and pyridine–N–Oxide³⁾, the present communication deals with the preparation of complexes of copper (II) aryl carboxylates with morpholine.     

Separation, identification, and quantification of selected withanolides in plant extracts of Withania somnifera by HPLC-UV(DAD)--positive ion electrospray ionisation-mass spectrometry

This paper describes a method for separation, identification, and quantification of selected withanolides in Withania somnifera plant extracts by HPLC-UV(DAD)-Mass Spectrometry (HPLC-MS). Withaferin-A (WS-3), 12-deoxywithastramonolide (WS-12DS), Withanolide A (WS-1), and Withanone (WS-2) were used as external standards. The compounds were isolated from Withania somnifera by repeated column chromatography of the root extract and their identity was established by 1H- and 13C-NMR and mass spectral data. The compounds were chromatographed on a Merck (250 x 4.6 mm ID, 5 microm) column and analyzed by Electrospray Ionization on a mass spectrometer in Selected Ion Mode (SIM). For quantification, [M + Na]+ ions were monitored. Linear calibration curves were obtained in the concentration range of 1.50 microg/mL to 6.5 microg/mL. The method was applied successfully to the detection and quantification of the said withanolides in a number of samples.     

Kinetic Connectivity for Unit Disks

We describe a kinetic data structure (KDS) that maintains the connected components of the union of a set of unit-radius disks moving in the plane. We assume that the motion of each disk can be specified by a low-degree algebraic trajectory; this trajectory, however, can be modified in an on-line fashion. While the disks move continuously, their connectivity changes at discrete times. Our main result is an O(n) space data structure that takes O(log n\slash \kern -1pt log log n) time per connectivity query of the form ``are disks A and B in the same connected component?' A straightforward approach based on dynamically maintaining the overlap graph requires Ω (n ² ) space. Our data structure requires only linear space and must deal with O(n ^{2 + ε} ) updates in the worst case, each requiring O(log ² n) amortized time, for any ε>0 . This number of updates is close to optimal, since a set of n moving unit disks can undergo Ω (n ² ) connectivity changes. Received September 20, 2000, and in revised form January 19, 2001. Online publication April 6, 2001.     

A Constant Bound for Geometric Permutations of Disjoint Unit Balls

Abstract. We prove that a set of n disjoint unit balls in R ^d admits at most four distinct geometric permutations, or line transversals, thus settling a long-standing conjecture in combinatorial geometry. The constant bound significantly improves upon the Θ (n ^d-1 ) bound for disjoint balls of unrestricted radii.     

Electrosynthesis of samarium hexaboride using tetra borate melt

Fine crystals of samarium hexaboride were synthesized by molten salt electrolysis using samarium oxide, sodium tetraborate and lithium fluoride. The electrolysis was performed at 900 °C in argon atmosphere at various current densities ranging from 1.0 to 2.3 A/cm². The molar ratio of the reactants [Sm:B] was varied from 1:6 to 1:12. The deposited crystals were examined for the phase purity using X-ray diffraction analysis. The effect of current density and the influence of molar concentration of the reactants were evaluated. The morphological features of the crystals were examined using scanning electron microscopy (SEM). Pure crystals of SmB₆ are obtained at a current density of 1.8 A/cm². The SEM images reveal that the crystals are packed in a cubic manner, exhibiting irregular morphology. The average crystallite size of the powders is found to be between 72 and 83 nm. The mechanism of formation of SmB₆ is explained by the joint deposition of B and Sm at the Mo cathode.     

Spectroscopy of laser-produced plasmas: Setting up of high-performance laser-induced breakdown spectroscopy system

It is a well-known fact that laser-induced breakdown spectroscopy (LIBS) has emerged as one of the best analytical techniques for multi-elemental compositional analysis of samples. We report assembling and optimization of LIBS set up using high resolution and broad-range echelle spectrograph coupled to an intensified charge coupled device (ICCD) to detect and quantify trace elements in environmental and clinical samples. Effects of variations of experimental parameters on spectroscopy signals of copper and brass are reported. Preliminary results of some plasma diagnostic calculations using recorded time-resolved optical emission signals are also reported for brass samples.