On‐line Liquid‐liquid Extraction Coupled to a Reversed Micellar‐mediated Chemiluminescence Detection System: Application to the Determination of Amino/Nitroaromatic Compounds

A simple and fast flow method for the trace level determination of p‐toluidine, 2‐methyl‐5‐nitroaniline, and 2,4‐dinitroaniline in aqueous samples is reported. These amino/nitroaromatics are related to trinitrotoluene (TNT) and appear during the degradation process of the explosive. The chemical principles of ion‐pair formation and liquid‐liquid extraction are applied: In aqueous acidic medium, the protonated analyte [HA]⁺ makes an ion‐pair with the tetrachloroaurate(III) ion, followed by on‐line ion‐pair extraction into the dichloromethane carrier used. After membrane separation, the CH₂Cl₂ containing the ion‐pair, [HA]⁺[AuCl₄]⁻, is mixed with the reversed micellar luminescent reagent of luminol (in 0.3 M Na₂CO₃) prepared from cetyl‐trimethylammonium chloride in CH₂Cl₂‐cyclohexane and the [AuCl₄⁻‐luminol chemiluminescence (CL) output is recorded. The detection limits (S/N> 3) are: p‐toluidine, 1.0 × 10⁻⁴M; 2‐methyl‐5‐nitroaniline, 1.0 × 10⁻⁷ M; 2,4‐dinitroaniline, 1.0 × 10⁻⁷ M, while the calibration curves are linear between 1.0 × 10⁻⁴ — 1.0 × 10⁻² M for all the compounds. Although spectral studies indicated the formation and extraction of a very small amount of the ion‐pair species, the reversed micellar‐mediated CL detection system provides an alternative procedure for the determination of degradation products of the explosive TNT in environmental aqueous samples.     

Stability of naturally occurring pyrazines and construction route of pyrazine rings

Naturally occurring pyrazines fit well the theory that conformity to the TCS rule gives a stable molecular system. Thus, many pyrazines so far synthesized and those in nature which are energetically very stable molecules can be synthetically quite accessible. The TCS rule applies very well to the construction route of pyrazine rings.     

Flow characteristics around a rotating grooved circular cylinder with grooved of different depths

The present paper describes the flow characteristics around a rotating grooved circular cylinder with grooves of different depths. The surface structure of a circular cylinder was varied by changing the depths of 32 arc grooves on the surface. The surface pressure on the cylinder is measured for theRe range of from 0.4×10⁵ to 1.8×10⁵ and for rotations of from 0 to 4500 rpm. The drag coefficient of a grooved cylinder increases as the spin rate ratio α (= rotational speed of the cylinder surface/uniform velocity) increases forRe>1.0×10⁵. As the groove depth increases, the drag coefficient of a grooved cylinder is independent from the spin rate ratio α. The direction of the lift force of a smooth cylinder is opposite to the Magnus force forRe>1.0×10⁵. However, the direction of the lift force of a grooved cylinder is the same as that of the Magnus force for allRe>1.0×10⁵. As the groove depth increases, the increase in the slope of the lift coefficient becomes small. These phenomena are related to the positions of the flow separation points, which are clarified from the pressure distribution and flow visualization by the spark tracing method. In addition, in the present study, the flow around a rotating grooved cylinder is clarified by flow visualization.     

Generation and evolution of cavitation in magma under dynamic unloading

The full system of equations for the problem of rarefaction-wave passage over the magma-melt column in the gravity field is derived with the use of the kinetic theory of phase transformations, and the problem is numerically solved. With allowance for diffusion zones and nucleation frequency as a function of supersaturation, the dependence of the number of cavitation nuclei formed in the course of phase transformations behind the rarefaction-wave front is found. The dynamics of the size distribution of cavitation bubbles along the magma-melt column (1 km) whose viscosity varies dynamically as a function of the concentration of dissolved water is studied.Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 46, No. 2, pp. 71–80, March–April, 2005.     

Computational study of shock wave focusing in a log-spiral duct

The mechanism of shock wave focusing in a two-dimensional log-spiral duct has been investigated here numerically using a finite volume method. This approach is based on a MUSCL TVD scheme with flux-vector splitting applied to the Euler equations. The isopycnics determined from the calculations are compared with the experimental results obtained by use of holographic interferometric photography and are found to be in excellent qualitative agreement with the experiments. The computational results clarify the details of the wave interactions very near to the focus. In particular, phenomena such as the formation of secondary shock waves prior to the implosion, their interaction with the reflected shock and the formation of vortices after the implosion have been examined.     

Attenuation of shock waves propagating over arrayed baffle plates

The paper reports results of shock tube experiments of the attenuation of shock waves propagating over arrayed baffle plates, which is motivated to simulate shock wave attenuation created accidentally at the acoustic delay line in synchrotron radiation factory upon the rupture of a metal membrane separating the acceleration ring at high vacuum and atmospheric test chambers. Experiments were carried out, by using double exposure holographic interferometry with double path arrangement, in a 100 mm×180 mm shock tube equipped with a test section of 180 mm×1100 mm view field. Two baffle plate arrangements were tested: Oblique and staggered baffle plates; and vertical symmetric ones. Pressures were measured along the shock tube sidewall at individual compartments for shock Mach numbers ranging from 1.2 to 3.0 in air. The results were compared with a numerical simulation. The rate of shock attenuation over these baffle plates was compared for vertical and oblique baffle plates. Shock wave attenuation is more pronounced in the oblique baffle plate arrangements than in the vertical ones. PACS 47.40.Nm; 42.40.Kw Communicated by C. Needham     

Unsteady interaction of shock wave diffracting around a circular cylinder in air

The reflection and diffraction of a planar shock wave around a circular cylinder are a typical problem of the complex nonlinear shock wave phenomena in literature. It has long been studied experimentally, analytically as well as numerically. Takayama in 1987 obtained clear experimental pictures of isopycnics in shock tube under the condition that the impinging shock wave propagates as far as 3 diameters away from the cylinder. To know more completely the whole unsteady process, it is desirable to get experimental results in a region which is more than 10 diameters away from the cylinder. This is what has been done in this paper by using the pulsed laser holographic interferometry for several shock Mach numbers of the impinging shock. Results for several moments are shown, giving more knowledge about the whole unsteady flow field. This is useful for a reliable and complete understanding of the changing force acting on the cylinder, and provides interesting data to check the performance of many recently developed high resolution numerical methods for unsteady shock wave calculation. The project suported partially by National Natural Science Foundation of China     

A novel approach for LC-MS/MS-based chiral metabolomics fingerprinting and chiral metabolomics extraction using a pair of enantiomers of chiral derivatization reagents

Chiral metabolites are found in a wide variety of living organisms and some of them are understood to be physiologically active compounds and biomarkers. However, the overall analysis of chiral metabolomics is quite difficult due to the high number of metabolites, the significant diversity in their physicochemical properties, and concentration range from metabolite-to-metabolite. To solve this difficulty, we developed a novel approach for chiral metabolomics fingerprinting and chiral metabolomics extraction, which is based on the labeling of a pair of enantiomers of chiral derivatization reagents (i.e., DMT-(S,R)-Pro-OSu and DMT-3(S,R)-Apy) and precursor ion scan chromatography of the derivatives. The multivariate statistics is also required for this strategy. The proposed procedures were evaluated by the detection of a diagnostic marker (i.e., d-lactic acid) using the saliva of diabetic patients. This method was used for the determination of biomarker candidates of chiral amines and carboxyls in Alzheimer's disease (AD) brain homogenates. As the results, l-phenylalanine (L-Phe) and l-lactic acid (L-LA) were identified as the decreased and increased biomarker candidates in the AD brain, respectively. Therefore, the proposed approach seems to be helpful for the determination of non-target chiral metabolomics possessing amines and carboxyls.