A simple computer circuit for automatic spectrophotometric analysis of binary mixtures by differential reaction rates

A simple analogue computer circuit, for application with a continuous reading spectrophotometer to give automatic analysis of binary mixtures of closely related substances using a differential reaction rate technique, is described. The circuit solves the simultaneous equations of the Method of Proportional Equations for the concentrations of the components in the mixture. The method is useful for first- or pseudo-first order competitive reactions. A timing circuit automatically supplies the absorbance (converted as described from the transmittance) of the reacting solution at two chosen times during the reaction, to the computer. The output voltages are adjusted within the circuit to read directly in units of concentration.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/32026/1/0000069.pd

The anodic strippin voltammetry of trace silver solutions employing graphite electrodes application to silver analysis of rain and snow samples from silver iodide seeded clouds

The characteristics of the anodic stripping curves obtained from 10-11-10-7 M Ag+ have been studied using pyrolytic graphite and wax impregnated spectrographic grade carbon electrodes. It was found that the stripping curves on pyrolytic graphite electrodes (PGE) had essentially only one sharp dissolution peak, while those for wax impregnated carbon (SGE) exhibited multiple dissolution peaks. The nature of the Ag deposits was studied by X-ray fluorescence employing an electron microprobe which showed that PGE had a few preferred sites for deposition but the SGE exhibited a uniform distribution of the deposit. The optimum solution conditions, electrode pretreatments, and procedure are described, as well as the results of the analyses of snow samples containing 10-8-4 x 10-11 M Ag+.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/32817/1/0000191.pd

A polarographic method for following the rates of cholinesterase-catalyzed hydrolyses of acetylthiocholine

A rapid and simple polarographic method for following the rates of the cholinesterase-catalyzed hydrolysis of acetylthiocholine and the rates of inhibition of this hydrolysis is described. This method has the advantage that it can follow quite rapid reactions, as meaningful data can be obtained after 10 sec of mixing of the solutions. The method follows the rate of increase of the anodic polarographic wave of thiocholine produced by the hydrolysis. The validity of the method was determined by comparing the rates of production of thiocholine spectrophotometrically and polarographically. Also the values of Km for the hydrolysis, and Km and K1 for the inhibition reaction of neostigmine were determined and compared to values reported in the literature.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/31994/1/0000036.pd

The anodic dissolution of thin films of copper metal from pyrolytic graphite : A study of the multiple dissolution current peaks

The anodic stripping curves of electrodeposited thin films of copper have been investigated. Three distinct current peaks were observed. The more negative peak corresponded to copper macrolayers (copper on copper); the smaller peaks, found at more positive potentials were interpreted as mono-layer peaks which indicates that the copper interaction with pyrolytic graphite is greater than that of the copper-copper interaction. A method for preparing the monolayer films is described. Electronmicroprobe studies of the copper monolayer films indicated that the copper is uniformly distributed on the surface. These studies also showed that the macro layers started to grow at specific surface sites.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/33374/1/0000772.pd

Preconcentration techniques for trace analysis via neutron activation

A review is given of the methods that have been proposed for enrichment of trace elements in samples that are to be analysed by neutron-activation methods. The emphasis is on classification of methods, with full illustrations by means of practical examples.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/34169/1/0000457.pd

Addendum

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/22321/1/0000766.pd

»Programmable« Selective Inexpensive Potentiometric Detector for Flow Injection Analysis. Potassium Determination with a Nafion Membrane Modified Electrode

The study of a nafion membrane (ISE membrane) for the inexpensive potentiometric detection of potassium ion in a flow injection system is reported. The nafion membrane doped with potassium ion showed that excellent selectivity could be achieved for various cations, except for Rb+, and some interference for Cs+. A linear potential response of 10-2 - 10~® M for the potassium ion was obtained with a detection limit of about 0.5 x 10-6 M. This approach can be employed for constructing a potentiometric detector for virtually any cation (soluble at basic pH values) by simply changing the electrode pretreatment (or doping solution)

2,3,5-Triphenyl-2H-tetrazolium chloride as a reagent for the determination of sugar mixtures by a differential reaction-rate technique

The rates of reaction of 2,3,5-triphenyl-2H-tetrazolium chloride with the more common hexoses (glucose, fructose, mannose, sorbose and galactose) and pentoses (xylose and ribose) have been studied. Under certain conditions, over a limited range of reaction, the extent of the reaction is directly proportional to the time of reaction (a "pseudo zero-order" reaction). Also, the rates of reaction of the sugars are quite different in most cases. Thus, the behaviour of this reagent is quite satisfactory for the determination of binary mixtures of most of the sugars tested, by a simple differential rate technique developed for "zero-order" competitive reactions. The rates of reaction of 2,3,5-triphenyl-2H-tetrazolium chloride with ascorbic acid, creatinine and glutathione, often found in blood serum, which interfere with most blood serum sugar analysis methods, have also been examined to determine if they would interfere with the determination. Glutathione and creatinine do not react with the reagent and do not interfere with the analysis of sugar mixtures. Ascorbic acid, however, reacts rapidly, and as little as 1-2% leads to error in the sugar-mixture determination.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/32056/1/0000100.pd

Hundreds of variants clustered in genomic loci and biological pathways affect human height

Most common human traits and diseases have a polygenic pattern of inheritance: DNA sequence variants at many genetic loci influence the phenotype. Genome-wide association (GWA) studies have identified more than 600 variants associated with human traits, but these typically explain small fractions of phenotypic variation, raising questions about the use of further studies. Here, using 183,727 individuals, we show that hundreds of genetic variants, in at least 180 loci, influence adult height, a highly heritable and classic polygenic trait. The large number of loci reveals patterns with important implications for genetic studies of common human diseases and traits. First, the 180 loci are not random, but instead are enriched for genes that are connected in biological pathways (P = 0.016) and that underlie skeletal growth defects (P < 0.001). Second, the likely causal gene is often located near the most strongly associated variant: in 13 of 21 loci containing a known skeletal growth gene, that gene was closest to the associated variant. Third, at least 19 loci have multiple independently associated variants, suggesting that allelic heterogeneity is a frequent feature of polygenic traits, that comprehensive explorations of already-discovered loci should discover additional variants and that an appreciable fraction of associated loci may have been identified. Fourth, associated variants are enriched for likely functional effects on genes, being over-represented among variants that alter amino-acid structure of proteins and expression levels of nearby genes. Our data explain approximately 10% of the phenotypic variation in height, and we estimate that unidentified common variants of similar effect sizes would increase this figure to approximately 16% of phenotypic variation (approximately 20% of heritable variation). Although additional approaches are needed to dissect the genetic architecture of polygenic human traits fully, our findings indicate that GWA studies can identify large numbers of loci that implicate biologically relevant genes and pathways.

Morphology and Composition of the Surface of Mars: Mars Odyssey THEMIS Results

The Thermal Emission Imaging System (THEMIS) on Mars Odyssey has produced infrared to visible wavelength images of the martian surface that show lithologically distinct layers with variable thickness, implying temporal changes in the processes or environments during or after their formation. Kilometer-scale exposures of bedrock are observed; elsewhere airfall dust completely mantles the surface over thousands of square kilometers. Mars has compositional variations at 100-meter scales, for example, an exposure of olivine-rich basalt in the walls of Ganges Chasma. Thermally distinct ejecta facies occur around some craters with variations associated with crater age. Polar observations have identified temporal patches of water frost in the north polar cap. No thermal signatures associated with endogenic heat sources have been identified