UNCERTAINTY CONTRIBUTIONS TO SPECIES SPECIFIC ISOTOPE DILUTION ANALYSIS

Mercury speciation in solid sample matrices has been investigated using high performance liquid chromatography (HPLC) coupled with multicollector sector field (MCSF) and quadrupole (Q) inductively coupled plasma mass spectrometry (ICP-MS) for species specific isotope dilution mass spectrometry (IDMS). 199Hg enriched methylmercurychloride has been synthesised and recovered in the solid form for use as a spike material. The stability of methylmercury during the IDMS procedure was investigated using 199Hg and 13C labelled methylmercury isotopomers and ¹H Nuclear Magnetic Resonance spectroscopy. IntermoIecuJar exchange of the methylmercury halide counter ion was observed, the halide counter ion order of preference was l>Br>Cl. No evidence was found for the decomposition, or formation, of methylmercury during equilibration with soil (NIST2710 SRM) or dogfish muscle (DORM-2 CRM), or during chromatographic separation. The extent of equilibration between the spike and the particulate bound mercury compounds was studied by temporal monitoring of the 200Hg:199Hg isotope amount ratio and determining the amount of Hg species in the liquid phase. For N1ST2710, complete equilibration was only achieved when concentrated HNO3 in combination with a microwave digestion was employed. For DORM-2, complete equilibration was achieved when using 1:1 H2O.CH3OH v\v and 0.01 % 2-mercaptoethanol as the solvent, even though only 47% of the analyte was extracted into the liquid phase. The mass fraction of methylmercurychloride has been determined in E)ORM-2 and BCR464 lobster hepatopancreas CRM by two different procedures, single IDMS and approximate matching double IDMS. Mercury cold vapour generation of the HPLC column eluent allowed isotope amount ratios measurements by MC-SF-ICP-MS. For each CRM the mass fraction of methylmercury determined by the two IDMS methods was not statistically different, within the limits of uncertainty, from the certified values. An uncertainty budget for both IDMS procedures has been formulated to allow the performance of each method to be compared For single IDMS the major uncertainty contribution was derived from the within replicate uncertainty, Uwithin The combined standard uncertainty of each replicate analysis was dominated by two components, the uncertainty associated with the natural isotonic abundance 200Hg: 199Hg isotope amount ratio and the uncertainty associated with the 199Hg enriched methylmercurychloride spike mass fraction. The between blend standard uncertainty, Ubetween, was the major contributor to the expanded uncertainty for approximate matching double IDMS. The combined standard uncertainty for each individual replicate was dominated by the contribution from the standard uncertainty associated with the measured 200Hg:199Hg isotope amount ratios in the spiked sample and the mass bias calibration blend.LG

Club Pr project

University of Missouri College of Agriculture and the United States Department of Agriculture Cooperating--Page [16]."March, 1955."Title from caption

Lung Circulation Modeling: Status and Prospect

Mathematical modeling has been used to interpret anatomical and physiological data obtained from metabolic and hemodynamic studies aimed at investigating structure-function relationships in the vasculature of the lung, and how these relationships are affected by lung injury and disease. The indicator dilution method was used to study the activity of redox processes within the lung. A steady-state model of the data was constructed and used to show that pulmonary endothelial cells may play an important role in reducing redox active compounds and that those reduction rates can be altered with oxidative stress induced by exposure to high oxygen environments. In addition, a morphometric model of the pulmonary vasculature was described and used to detect, describe,and predict changes in vascular morphology that occur in response to chronic exposure to low-oxygen environments, a common model of pulmonary hypertension. Finally, the model was used to construct simulated circulatory networks designed to aid in evaluation of competing hypotheses regarding the relative contribution of various morphological and biomechanical changes observed with hypoxia. These examples illustrate the role of mathematical modeling in the integration of the emerging metabolic, hemodynamic, and morphometric databases

The cow and calf : a 4-H beef production project

March, 1953."University of Missouri College of Agriculture and the United States Department of Agriculture Cooperating"--Page 11.Title from caption.Includes "4-H Record" at end

Corn production : a 4-H project

November, 1949."University of Missouri College of Agriculture and the United States Department of Agriculture Cooperating"--Page [12].Title from caption

SPECT Imaging of Pulmonary Blood Flow in a Rat

Small animal imaging is experiencing rapid development due to its importance in providing high-throughput phenotypic data for functional genomics studies. We have developed a single photon emission computed tomography (SPECT) system to image the pulmonary perfusion distribution in the rat. A standard gamma camera, equipped with a pinhole collimator, was used to acquire SPECT projection images at 40 sec/view of the rat thorax following injection of Tc99m labeled albumin that accumulated in the rat\u27s lungs. A voxel-driven, ordered-subset expectation maximization reconstruction was implemented. Following SPECT imaging, the rat was imaged using micro-CT with Feldkamp conebeam reconstruction. The two reconstructed image volumes were fused to provide a structure/function image of the rat thorax. Reconstruction accuracy and performance were evaluated using numerical simulations and actual imaging of an experimental phantom consisting of Tc99m filled chambers with known diameters and count rates. Full-width half-maximum diameter measurement errors decreased with increasing chamber diameter, ranging from \u3c 6% down to 0.1%. Errors in the ratio of count rate estimates between tubes were also diameter dependent but still relatively small. This preliminary study suggests that SPECT will be useful for imaging and quantifying the pulmonary blood flow distribution and the distribution of Tc99m labeled ligands in the lungs of small laboratory animals

The 4-H baby beef project

At head of title: University of Missouri College of Agriculture, Agricultural Extension Service."January, 1949.""University of Missouri College of Agriculture and the United States Department of Agriculture Cooperating"--Page [24].Title from cover

Working dogs for the farm : 4-H club project

October, 1952."Acknowledgement and thanks are due to Dr. A. H. Groth, Dean of the School of Veterinary Medicine, for help in preparing the circular."--Page 3."University of Missouri College of Agriculture and the United States Department of Agriculture Cooperating"--Page [27].Title from caption

Corn production : a 4-H project

University of Missouri College of Agriculture and the United States Department of Agriculture cooperating."December, 1943."Title from cover