Chemometric approach to the optimisation of LC-FL and GC-MS methods for the determination of nitrite and nitrate in some biological,food and environmental samples

Gas chromatography–mass spectrometry (GC-MS) method and a liquid chromatography–fluorescence (LC-FL) detection method using experimental design and optimisation approach were improved for the quantitative determination of nitrite and nitrate in biological, food and environmental samples. The obtained recoveries of nitrite and nitrate ions from samples based on both GC-MS and LC-FL results ranged from 98.5% to 98.9% for nitrite and 97.9% to 98.4% for nitrate. The precision of these methods, as indicated by the relative standard deviations (RSDs), was within the range from 2.4% to 3.6% for nitrite and 2.5% to 3.8% for nitrate, respectively. The limits of detection of nitrite and nitrate ions from samples based on GC-MS and LC-FL results ranged from 0.01 to 0.14 ng L^?1 for nitrite and 0.02 to 0.71 ng L^?1 for nitrate, respectively. The optimised isolation procedure by central composite design was successfully applied to real samples. The results revealed that the proposed procedure combined with GC-MS and LC-FL techniques is more sensitive, reliable and selective compared to the other methods available for the precise determination of trace levels of nitrite and nitrate in biological, food and environmental samples.     

800A高温超导电流引线的研制

介绍了800A双磁体高温超导(HTS)电流引线的结构、设计参数及制做过程,论述了其加工、组装、实验及调试结果,进而验证该设计方案较为合理地满足双磁体运行要求。     

Counting matrices over finite fields having a given number of rows of unit weight

We present a formula enumerating matrices over a finite field of a given rank and a given number of rows of unit weight, i.e., each having a single nonzero entry. We also determine the number of subspaces of a given dimension containing a given number of vectors of unit weight.     

Separation and preconcentration in a batch mode of Cd(II), Cr(III, VI), Cu(II), Mn(II, VII) and Pb(II) by solid-phase extraction by using of silica modified with N-propylsalicylaldimine

The complexes formed between IE11 and Cd(II), Cr(III), Cu(II), Mn(II) and Pb(II) were identified and confirmed by IR, UV and pH-metric titration. The uptake behavior of porous silica modified with N-propylsalicylaldimine (IE11) and these metal ions were studied. Log k(d) was found to be within the range 2.19-5.16 depending on pH and time of stirring. IE11 was used in the separation and preconcentration of Cd(II), Cr(III, VI), Cu(II), Mn(II, VII) and Pb(II) from some natural water samples. Data were compared with those obtained by the solvent extraction method APDC/MIBK. The proposed methodology allows to verify an improvement in the water quality of Nile River probably attributed to high to moderate floods in the last few years. The method was found to be accurate and not subject to random error, i.e. precise.     

Novel EPR characterization of the antioxidant activity of tea leaves

Electron paramagnetic resonance (EPR) spectroscopy is utilized to investigate several categories of green and black tea: Twining green tea (TGT), Chinese green tea (CGT), Red-labels black tea (RBT). Basically, two EPR signals from all the studied samples are observed: One of them is a very weak sharp EPR signal with deltaHpp approximately 10 G and g-factor = 2.00023 superimposed on the other broad signal with deltaHpp approximately 550 G and g-factor = 2.02489. The broad signal is a characteristic one of manganese(II) complex, while the sharp signal is related to a stable radical of aromatic origin exist in a powder condition. The feature of the manganese EPR signal is attributed to manganese(II) complex and reflected the molecular behavior of Mn(II) in the protein system of the natural leaves. The sharp signal, which is most probably due to a semiquinones radicals, is observed at room temperature and its intensity is remarkably affected by photo degradation of the studied samples. The intensity of manganese(II) EPR signal is found to be related to ageing and disintegration of the tea leaves. Moreover, direct relation between the relative intensity of the semiquinones radical signal and antioxidant activity of the studied samples was also correlated.     

Application of the weak-coupling model for calculating the binding energies of neutron-rich ${\rm A} \sim 32$ nuclei

The presence of an anomaly in binding energies for the island of inversion centered at Z = 11, N = 21 is obtained by comparison of macroscopic binding energies and experiment. The macroscopic calculations were done with a mass formula deduced from the reformulation of the liquid-drop model of Myers et al. ; this formula is described in detail such as its predictions for binding energies of neutron-rich A = 29-44 nuclei. These calculations have indicated the presence of anomalies in the island of inversion. A weak-coupling approximation is applied to study this deformed region. The binding-energy values obtained using this model show the absence of these anomalies.Received: 7 January 2004, Revised: 2 April 2004, Published online: 12 October 2004PACS: 21.10.Dr Binding energies and masses - 27.30. + t      

Extending the Balas-Yu bounds on the number of maximal independent sets in graphs to hypergraphs and lattices

A result of Balas and Yu (1989) states that the number of maximal independent sets of a graph G is at most ^p+1, where is the number of pairs of vertices in G at distance 2, and p is the cardinality of a maximum induced matching in G. In this paper, we give an analogue of this result for hypergraphs and, more generally, for subsets of vectors in the product of n lattices =₁××_n, where the notion of an induced matching in G is replaced by a certain binary tree each internal node of which is mapped into . We show that our bounds may be nearly sharp for arbitrarily large hypergraphs and lattices. As an application, we prove that the number of maximal infeasible vectors x=₁××_n for a system of polymatroid inequalities does not exceed max{Q,^logt/c(2Q,)}, where is the number of minimal feasible vectors for the system, , , and c(,) is the unique positive root of the equation 2^c(^c/log–1)=1. This bound is nearly sharp for the Boolean case ={0,1}ⁿ, and it allows for the efficient generation of all minimal feasible sets to a given system of polymatroid inequalities with quasi-polynomially bounded right-hand sides . This research was supported by the National Science Foundation (Grant IIS-0118635), and by the Office of Naval Research (Grant N00014-92-J-1375). The second and third authors are also grateful for the partial support by DIMACS, the National Science Foundation's Center for Discrete Mathematics and Theoretical Computer Science.Mathematics Subject Classification (2000):20E28, 20G40, 20C20     

Role of cationic gemini surfactants toward enhanced ninhydrin–tryptophan reaction

In this paper we report the effect of dicationic ‘gemini’ surfactants (CH₃)₂C₁₆H₃₃N⁺? (CH₂)_m? N⁺C₁₆H₃₃(CH₃)₂, 2Br^? (where m = 4, 5, 6) on the reaction of ninhydrin with DL ‐tryptophan. The gemini surfactant micellar media are comparatively more effective than their conventional monomeric counterpart cetyltrimethylammonium bromide (CTAB) micelles. Also, whereas typical rate constant (k_ψ) increase and leveling‐off regions, just like CTAB, are observed with geminis, the latter produce a third region of increasing k_ψ at higher concentrations. These subsequent increases are ascribed to changes in micellar morphologies, consistent with changes in ¹H NMR line widths. Quantitative kinetic analysis of the rate constant–[surfactant] data has been performed on the basis of modified pseudophase model. Copyright © 2007 John Wiley & Sons, Ltd.