Sample Treatment Approaches for Trace Level Determination of Cesium in Hepatitis B Vaccine by Suppressed Ion Chromatography

The hepatitis B surface antigen manufactured by recombinant DNA technology is extracted from the culture media by density gradient centrifugation using cesium salts. Cesium is considered to be toxic, because it affects active ion transport by blocking potassium channels. The residual trace levels of cesium in hepatitis B vaccine samples are determined by suppressed ion chromatography. Hepatitis B vaccines contain various buffer salts, aluminum-containing adjuvants, proteins and traces of iron. The polyvalent cations (Al³⁺, Fe³⁺) and proteins degrade the chromatographic performance in terms of decreased retention time and poor reproducibility. Different sample preparation approaches were evaluated with the aim of eliminating these foulants: (1) filtration, (2) digestion and (3) digestion-protein precipitation. Quantitative elimination of these foulants was achieved in the digestion-protein precipitation sample clean-up approach. Cesium was separated on the IonPac CS17 column with suppressed conductivity detection. The results of the ion chromatography (IC) method were compared with ICP-MS analysis. The precision of determination was better than 6.5% (relative standard deviation) with a method detection limit of 45 ng mL⁻¹. The expanded uncertainty in the measurement at 95% confidence level (coverage factor 2) is better than 16.3%.

     

Simple Zeros of the Riemann Zeta-Function

Assuming the Riemann Hypothesis, Montgomery showed by meansof his pair correlation method that at least two-thirds of thezeros of Riemann's zeta-function are simple. Later he and Taylorimproved this to 67.25 percent and, more recently, Cheer andGoldston increased the percentage to 67.2753. Here we proveby a new method that if the Riemann and Generalized LindelöofHypotheses hold, then at least 70.3704 percent of the zerosare simple and at least 84.5679 percent are distinct. Our methoduses mean value estimates for various functions defined by Dirichletseries sampled at the zeros of the Riemann zeta-function. 1991Mathematics Subject Classification: 11M26.     

Quantum Zeno and anti-Zeno paradoxes

Continuous observation of a time independent projection operator is known to prevent change of state (the quantum Zeno paradox). We discuss the recent result that generic continuous measurement of time dependent projection operators will in fact ensure change of state: an anti-Zeno paradox.     

粉粒体两相流的电容层析成象测量

粉粒体系统中的固相浓度分布的在线测量是十分困难的问题．电容层析成象技术是一种近年来发展起来的非侵入式快速浓度场测量技术．它不干扰流场，不受流动中颗粒浓度、加速度、不透明等因素的制约．本文讨论其测量原理、应用、近期进展、存在的主要问题及其解决的对策．     

ac Conductivity of mixed spinel NiAl0.7Cr0.7Fe0.6O4

ac Conductivity measurements are carried out across the metal to insulator transition in NiAl_0.7Cr_0.7Fe_0.6O₄. The low frequency data is analyzed using Summerfield scaling theory for hopping conductivity. The exponent of the scaling behavior has significantly different values in the conducting and insulating regimes. The hopping frequency and the zero frequency conductivity are found to increase with temperature, slowly in the metallic regime and rapidly in the insulating regime.     

Determination of trace phosphorus in zirconium-niobium alloy and Zircaloy by UV-vis spectrophotometry

A spectrophotometric method has been developed for the determination of traces of phosphorus in zirconium based alloys (Zr-2.5Nb and Zircaloy). It is achieved by selective fluoride complexation controlled by boric acid. The samples were dissolved in HF and fluoro-complexes of the matrices were formed by maintaining the concentration of HF while the excess HF was controlled by boric acid. After the formation of phosphomolybdate, extracted into n-butyl acetate, ion-associated with crystal violet and the absorbance was measured at 582 nm. The results obtained by this procedure were in close agreement with the certified reference material (CRM) values and further these values were compared with the values determined by Glow Discharge-Quadrupole Mass Spectrometry (GD-QMS). The potential interferences like fluoride, silicon, arsenic(V), niobium, titanium, tantalum, etc., were tolerable to large level. LOD (3 s) was found to be 0.055 mg kg(-1) with a precision (R.S.D.) of 2-3% and molar absorptivity was 2.7x10(5) L mol(-1) cm(-1).     

Local canted spin behaviour in Co1.4−x Zn x Ge0.4Fe1.2O4 spinels: A macroscopic, mesoscopic and microscopic study

DC magnetization, neutron depolarization and neutron diffraction (with both polarized and unpolarized neutrons) measurements have been reported for the Co_1.1−x Zn _x Ge_0.1Fe_1.2O₁ spinels with x=0.5, 0.6 and 0.7. Neutron depolarization and neutron diffraction measurements confirm the presence of a long range ferrimagnetic ordering of the local canted spins in these ferrite samples. The observed features of low field magnetization have been explained under the framework of thermally activated domain wall movement of ferrimagnetic arrangement of local canted spins. An important role of magnetic anisotropy (due to the presence of Co²⁺ ions) in establishing the magnetic ordering and domain kinetics in these ferrites has been observed.