A pilot study (APMP.QM-P19) for the measurement of melamine in milk powder

A pilot study (APMP.QM-P19) of the Asia Pacific Metrology Program for the determination of melamine at two different levels in milk powder was organized in 2010. It was the first interlaboratory comparison programme in measuring melamine in food matrices for metrology institutes in the region. Melamine was chosen as the target analyte because of the recent crises that happened in 2007 and 2008 had caused substantial concern from consumers, food manufacturers, policy makers on food safety and the food testing communities. The objectives of APMP.QM-P19 were to evaluate the testing capability of participants on the quantification of trace level melamine in milk and milk products and to investigate the degree of equivalence with respect to the assigned values. In total, 19 laboratories (11 metrology institutes and eight food testing institutes) enrolled in the study. Analytical techniques reported by participants included liquid chromatography with ultra-violet and tandem mass spectrometry, gas chromatography with high-resolution mass spectrometry and enzyme-linked immunosorbent assay. Dispersion of analytical data in the two test materials was significant, and normal Gaussian distribution of data was not observed. The median was agreed to be used as the assigned values in the programme. Metrology institutes who employed isotope dilution mass spectrometry technique were found to give more consistent results and higher degree of equivalence than others. The performance of most of the food testing institutes was not satisfactory, and they were encouraged to have a thorough review of their validation procedure and estimation of uncertainty.     

Extensive spectral tuning of the proton transfer emission from green to red via a rational derivatization of salicylideneaniline

A series of salicylideneaniline derivatives la-1f were synthesized under mild condition in high yields,and characterized by ~1H NMR,HRMS,UV-vis and emission spectra.In solid and aprotic solvents 1a-lf exist mainly as E conformers that possess a sixmembered -ring hydrogen bond and undergo excited-state intramolecular proton transfer(ESIPT) reactions,resulting in a protontransfer tautomer emission.Depending on the electronic donor or acceptor strength of the substituent in either the HOMO or LUMO site,a broad tuning range of the emission from green(1c) to red(1a) has been achieved.     

Self-assembled amorphous drug-polyelectrolyte nanoparticle complex with enhanced dissolution rate and saturation solubility

The dissolution rate and solubility of poorly soluble drugs can be enhanced by formulating them into stable amorphous nanoparticle complex (nanoplex). For this purpose, a highly sustainable self-assembly drug-polyelectrolyte complexation process is developed, with ciprofloxacin and dextran sulfate as the drug and polyelectrolyte models, respectively. The nanoplex are prepared by mixing two aqueous salt solutions - one containing the drug and the other containing the oppositely charged polyelectrolyte. The nanoplex suspension is transformed into stable dry-powder form by freeze-drying. The effects of drug concentration, drug-to-polyelectrolyte charge ratio, and salt concentration on the complexation efficiency, yield, drug loading, and nanoplex morphology are examined. The dissolution rates and solubility of the nanoplex are characterized and compared to raw drug crystals. Nearly spherical amorphous nanoplex having fairly uniform sizes in the range of 200-400 nm and 80% drug loading are successfully produced at ≥80% complexation efficiency and yield. The complexation efficiency is governed by the drug concentration and its ratio to the salt concentration. The nanoplex powders exhibit approximately twice higher dissolution rate and solubility than raw drug crystals and remain stable after one-month storage. Overall, amorphous nanoplex represent a promising bioavailability-enhanced formulation of poorly soluble drugs owed to their superior characteristics and ease of preparation.     

Rapid determination of vitamin B12 concentration with a chemiluminescence lab on a chip

This paper reports a novel method for the rapid determination of vitamin B(12) concentration in a continuous-flow lab-on-a-chip system. This new method is based on luminol-peroxide chemiluminescence (CL) assays for the detection of cobalt(II) ions in vitamin B(12) molecules. The lab-on-a-chip device consisted of two passive micromixers acting as microreactors and a double spiral microchannel network serving as an optical detection region. This system could operate in two modes. In the first mode, samples are acidified and evaluated directly in the microchip. In the second mode, samples are treated externally by acidification prior to detection in the microchip. In the first mode, the linear range obtained was between 1.00 ng ml(-1) to 10 μg ml(-1), R(2) = 0.996, with a relative standard deviation (RSD) of 1.23 to 2.31% (n = 5) and a limit of detection (lod) of 0.368 pg ml(-1). The minimum sample volume required and the analytical time were 30 μl and 3.6 s, respectively. In the second mode, the linear range obtained was between 0.10 ng ml(-1) to 10 μg ml(-1), R(2) = 0.994, with the RSD of 0.90 to 2.32% (n = 6) and a lod of 0.576 pg ml(-1). The minimum sample and the analytical time required were 50 μl and 6 s, respectively. The lab on a chip working in mode II was successfully used for the determination of vitamin B(12) concentrations in nutritional supplemental tablets and hen egg yolks.     

Development of a candidate certified reference material of cypermethrin in green tea

This paper presents the preparation of a candidate certified reference material (CRM) of cypermethrin in green tea, GLHK-11-01a according to the requirements of ISO Guide 34 and 35. Certification of the material was performed using a newly developed isotope dilution mass spectrometry (IDMS) approach, with gas chromatography high resolution mass spectrometry (GC–HRMS) and gas chromatography–tandem mass spectrometry (GC–MS/MS). Statistical analysis (one-way ANOVA) showed excellent agreement of the analytical data sets generated from the two mass spectrometric detections. The characterization methods have also been satisfactorily applied in an Asia-Pacific Metrology Program (APMP) interlaboratory comparison study. Both the GC–HRIDMS and GC–IDMS/MS methods proved to be sufficiently reliable and accurate for certification purpose. The certified value of cypermethrin in dry mass fraction was 148 μg kg⁻¹ and the associated expanded uncertainty was 14 μg kg⁻¹. The uncertainty budget was evaluated from sample in homogeneity, long-term and short-term stability and variability in the characterization procedure. GLHK-11-01a is primarily developed to support the local and wider testing community on need basis in quality assurance work and in seeking accreditation.     

Justification of the drift-flux model for two-phase flow in a circular pipe

A flow of a gas-liquid dispersed mixture in a circular pipe with a variable inclination to the horizon, as applied to oil and gas flows in wells, is considered. Within the framework of a multi- fluid approach, the equations of an asymptotic drift-flux model, which contains an algebraic relation between the phase velocities and one momentum equation for the volume-averaged velocity of the mixture, are derived. It is shown that the drift-flux model in this formulation strictly follows from the balance laws under assumption of inertialess velocity slip of the phases in case of validity of one of the following conditions: (i) the dispersed-phase volume fraction is small; (ii) the phase velocity slip may be neglected; or (iii) the flow regime is inertialess and the acceleration of the mixture can be neglected. A numerical algorithm based on the SIMPLE method is implemented for solving the obtained equations of the drift-flux model. The possibility of modeling the gravitational segregation and the pressure buildup in a shut-in well and transient slug flows is demonstrated.     

On Homomorphisms Indexed by Semistandard Tableaux

We describe techniques which may be used to compute the homomorphism space between Specht modules for the Hecke algebras of type A. We prove a q-analogue of a result of Fayers and Martin and show how it may be applied to construct homomorphisms between Specht modules. In particular, we show that in certain cases the dimension of the homomorphism space is given by the corank of a matrix whose entries we write down explicitly.     

International comparison of the determination of cadmium and lead in herb: the Comité Consultatif pour la Quantité de Matière (CCQM) pilot study CCQM-P97

A Comité Consultatif pour la Quantité de Matière (CCQM) inter-laboratory comparison program, CCQM-P97, for the analysis of cadmium and lead in Herba Demodii Styracifolii was organized by the Hong Kong Government Laboratory. The objective of the program was to establish comparability of trace metals analysis in herbal matrices amongst the participating national metrology institutes. The arithmetic mean values of the 13 participants were 0.3186 mg kg⁻¹ (RSD = 11.3%) and 1.650 mg kg⁻¹ (RSD = 11.0%) for cadmium and lead, respectively. The participants using double-isotope dilution mass spectrometry technique for their quantification were found to provide similar mean values to those of non-isotope dilution mass spectrometry users. The observation indicated that trace metal analysis in herbal matrices was not method-dependent, but the use of the highest metrological IDMS approach gave a better precision than other routine calibration methods.     

离子色谱-脉冲安培检测器分析饮料中单糖和二糖

建立了等度离子色谱-脉冲安培检测分析饮料中葡萄糖、果糖、蔗糖和乳糖的方法。采用CarboPacPA10分离柱对分离条件进行了优化,确定柱温为30℃、淋洗液为52mmol.L-1的NaOH溶液,在0.10—20.0mg.L-1范围内葡萄糖、果糖、蔗糖、乳糖呈良好线性,回收率分别为93.3%—112.5%、102.2%—111.6%、96.8%—99.6%、88.0%—102.6%,检出限分别为0.8、4.0、5.0、10.0mg.kg-1,精密度分别为0.18%—1.21%、0.53%—3.76%、0.65%—2.54%、1.65%—5.11%。检测了饮料中的单糖和二糖,效果良好。