Determination of total N-nitroso compounds by chemical denitrosation using CuCl

A method for the determination of total N-nitroso compounds (NOC) by chemical denitrosation and subsequent chemiluminescence detection of evolved NO is described. Denitrosation was accomplished with CuCl in HCl at 70 degrees C. The detection limit for N-nitrosoproline (NPRO) was 1 pmol. NO formation from NPRO was linear (R(2) = 0.999) from 4 pmol to 2 nmol. Among the possible interfering compounds tested, only S-nitroso compounds contribute any significant interference. This method had several advantages over other similar methods: (1) A commercially available one-piece reaction vessel and a NO analyzer with software were used. (2) NO release occurred rapidly and was easily measured and quantified. (3) Compared to HBr or HI, CuCl was more convenient to work with and safe. (4) CuCl was suitable for samples in aqueous and most organic solvents. The application of this method to food, personal care products, and human body fluids demonstrates its utility.     

A quality assurance program and quality assessment of the acidic precipitation in Ontario study (APIOS) deposition monitoring networks

Kinetics of H+ consumption by mineral dissolution in a surface soil and a subsoil of an acid woodland soil were studied by means of batch type experiments and stationary pH titrations. Mineral dissolution in the subsoil could effectively be described by congruent dissolution of illite (K_0.6Mg_0.25A1_2.3S1₃0₁₀(OH)₂) followed by an incongruent dissolution stage. In the incongruent stage the concentration of Al decreased while concentrations of K and Mg continued to increase. Congruent dissolution rates of illite could be predicted with power type relationships from transition state theory. In the incongruent dissolution stage the activities of H and Al appeared to be controlled by precipitation of A1(OH)₃. Results of this kind of experiments could be helpful to understand the behavior of Al and base cations in acid soils and soils with high atmospheric loadings of acid. Comparison of the results of batch experiments for a surface soil and a subsoil showed that initially proton consumption in the surface soil is faster and more effective due to the presence of a relatively high cation exchange capacity and base saturation value. However with progressive proton consumption and increasing reaction times proton consumption in the subsoil becomes faster than in the surface soil, presumably due to higher rates of mineral dissolution in the subsoil. Lower dissolution rates in the surface soil may result from lower contents of easily weatherable minerals, due to excessive leaching in the past which is reflected in a 17% lower acid neutralizing capacity than in the subsoil.     

Simple automated wet digestion of animal tissues for determination of seven elements by atomic absorption spectroscopy

A simple, automated wet digestion procedure was developed for the quantitative determination by atomic absorption spectroscopy (AAS) of arsenic, cadmium, copper, mercury, lead, selenium, and zinc in animal tissue. A commercial digestion block system with automated temperature programming was used. Recoveries of all elements from spiked bovine liver and kidney samples exceed 95%. The analytical results obtained for samples of NBS Bovine Liver (No. 1577a) agree well with certified values. The procedure is safe and requires minimum analyst time.     

Concentration and deposition of trace metals in Ontario-1982

Results of trace metal concentrations in air and precipitation and the corresponding wet and dry deposition in Ontario in 1982 arc reported. In terms of the spatial patterns, in general, there was a decreasing gradient from south-to-north in both concentration and deposition. Patterns differed with each parameter although certain groups of metals (e.g., Fe and Al; Pb, Zn, and Mn) displayed similar patterns. In general, wet deposition was greater than dry deposition at all sites. Geographically, the variability in the wet to dry deposition ratio for coarse particles (MMD > 2.5 μm) was small. However, it increased from the south to the north for fine particles (MMD < 2.5 μm), being higher away from the source areas. Scavenging ratios (W) have been derived from the precipitation and air concentrations of trace metals. The scatter in W is quite large for all trace metals, up to 2 orders of magnitude. There was little seasonal variability in W for fine particles (Pb, Mn, Zn, and Cd). However, coarse particles (Fe, Al, and Cu) were more efficiently scavenged by snow than by rain.     

Determination of penicillin G residues in edible animal tissues by liquid chromatography

An improved method has been developed for the determination of benzyl penicillin in animal tissues. Tissues are fortified with a known amount of penicillin V (internal standard) and extracted with water. The extract is deproteinized with sulfuric acid and sodium tungstate, filtered, and concentrated on a conditioned C18 solid phase extraction column. Penicillin V and benzyl penicillin are then eluted from the column with 1 mL 60% acetonitrile-35% water-5% 0.2M phosphate buffer solution and derivatized with 1 mL 1,2,4-triazole-mercuric chloride solution at 65 degrees C for 30 min. An aliquot of this sample is analyzed by reverse phase liquid chromatography with UV detection at 325 nm. The limit of detection is 5 micrograms/kg (ppb) penicillin G (8.4 IU/kg) in liver, kidney, and muscle tissues).     

A unified approach for estimating population size in capture-recapture studies with arbitrary removals

A unified approach is suggested to estimate the population size for a closed population in discrete time. Individuals can be removed after capture at any time during the experiment. The usual recapture and removal experimentsare shown to be particular cases of the general formulation. The capture probability is assumed to have a logistic function that depends on individual covariates and can be time dependent. The unified approach involves a two-step procedure. A conditional likelihood function is used to estimate the covariates coefficients and a Horvitz-Thompson type estimator to estimate the population size. The asymptotic and small-sample properties of the resulting estimators are in vestigated. A real example is given.     

鸡败血支原体pMGA多基因家族及其免疫逸机制的研究进展

pMGA多基因家族主要编码一类黏附素／血凝素蛋白，存在于鸡败血支原体的细胞表面，其主要功能是促进支原体黏附到宿主细胞上。近年来的相关研究发现，编码pMGA的基因数量从32－70不等，主要转录水平上通过（GAA）n 基序的数量改变引发pMGA基因的选择性转录，造成pMGA的抗原发生变异，从而干扰宿主正常免疫功能的发挥，使支原体对宿主产生严重的免疫逃逸。其中，（GAA）n基序已被证实在pMGA基因表达调控中起重要作用，这一三联体重复基序数目的多少直接影响到pMGA基因的ON／OFF不，本文通过对鸡败血支原体pMGA多基因家分子生物学研究进展浅要综述，以提出pMGA基因可能的转录调控机制，这对研究鸡败血支原体的分子致病机理及其免疫机制大有裨益。