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229 records · Page 13Linked to original sources
USGS1983

Atomic-absorption determination of mercury in geological materials by flame and carbon-rod atomisation after solvent extraction and using co-extracted silver as a matrix modifier

Based on modifications and expansion of the original Tindall's solvent extraction flame atomic-absorption procedure, an atomic-absorption spectrophotometric method has been developed for the determination of mercury in geological materials. The sample is digested with nitric and hydrochloric acids in a boiling water-bath. The solution is made ammoniacal and potassium iodide and silver nitrate are added. The mercury is extracted into isobutyl methyl ketone as the tetraiodomercurate(ll). Added silver is co-extracted with mercury and serves as a matrix modifier in the carbon-rod atomiser. The mercury in the isobutyl methyl ketone extract may be determined by either the flame- or the carbon-rod atomisation method, depending on the concentration level. The limits of determination are 0.05-10 p.p.m. of mercury for the carbon-rod atomisation and 1 -200 p.p.m. of mercury for the flame atomisation. Mercury values for reference samples obtained by replicate analyses are in good agreement with those reported by other workers, with relative standard deviations ranging from 2.3 to 0.9%. Recoveries of mercury spiked at two levels were 93-106%. Major and trace elements commonly found in geological materials do not interfere.

The Analyst↗
USGS1984

Determination of arsenic, antimony, bismuth, cadmium, copper, lead, molybdenum, silver and zinc in geological materials by atomic-absorption spectrometry

Arsenic, antimony, bismuth, cadmium, copper, lead, molybdenum, silver and zinc are very useful elements in geochemical exploration. In the proposed method, geological samples are fused with potassium pyrosulphate and the fusate is dissolved in a solution of hydrochloric acid, ascorbic acid and potassium iodide. When this solution is shaken with a 10% V/V Aliquat 336 - isobutyl methyl ketone organic phase, the nine elements of interest are selectively partitioned in the organic phase. All nine elements can then be determined in the organic phase using flame atomic-absorption spectrometry. The method is rapid and allows the determination of Ag and Cd at levels down to 0.1 p.p.m., Cu, Mo, and Zn down to 0.5 p.p.m., Pb, Bi and Sb down to 1 p.p.m. and As down to 5 p.p.m. in geological materials.

The Analyst↗
USGS1985

Comparison of digestion methods for total elemental analysis of peat and separation of its organic and inorganic components

In order to find the most efficient digestion method for the total elemental recovery in peat, ten samples were subjected to different techniques and analysed for Ca, Mg, Fe, AI, Na, K, Mn, P, Zn, Cu, Li, Cd, Co, Ni, Pb and Si using atomic-absorption spectrophotometry. The most satisfactory procedures were dry ashing followed by hydrofluoric acid treatment and wet digestion using a mixture of hot nitric, perchloric and hydrofluoric acids. The wet digestion offers the advantage of a single decomposition method for the determination of Ca, Mg, Fe, AI, K, Na, Mn, Cu, Li, Zn and P. An alkaline fusion technique was required for the determination of Si. Hydrogen peroxide was used to separate the peat into its organic and inorganic components, leading to the total recovery of the elements for both fractions.

The Analyst↗
USGS1987

Application of microwave digestion to the analysis of peat

A microwave digestion technique for the dissolution of peat is described and compared with a dry ashing method and a nitric - perchloric - hydrofluoric acid wet digestion. Peat samples with different organic matter contents were used and Ca, Mg, Fe, AI, Na, K, Mn, Zn, Cu and Li were determined by atomic absoprtion spectrometry. The results obtained using the three dissolution techniques were in good agreement. The microwave method has the advantage of digesting the samples in less than 2 h and uses less acid than the conventional wet digestion method. Keeping the volume of the acid mixture as small as possible minimises contamination and leads to lower blank values.

The Analyst↗
USGS2010

Characterization of mannitol in Curvularia protuberata hyphae by FTIR and Raman spectromicroscopy

FTIR and Raman spectromicroscopy were used to characterize the composition of Curvularia protuberata hyphae, and to compare a strain isolated from plants inhabiting geothermal soils with a non-geothermal isolate. Thermal IR source images of hyphae have been acquired with a 64 × 64 element focal plane array detector; single point IR spectra have been obtained with synchrotron source light. In some C . protuberata hyphae, we have discovered the spectral signature of crystalline mannitol, a fungal polyol with complex protective roles. With FTIR-FPA imaging, we have determined that the protein content in cells remains fairly constant throughout the length of a hypha, whereas the mannitol is found at discrete, irregular locations. This is the first direct observation of mannitol in intact fungal hyphae. Since the concentration of mannitol in cells varies with respect to position and is not present in all hyphae, this discovery may be related to habitat adaptation, fungal structure and growth stages.

Analyst↗
USGS2023

Supervised discretization for decluttering classification models

Presented here is the first demonstration of supervised discretization to ‘declutter’ multivariate classification data in chemical sensor applications. The performance of multivariate classification models is often limited by the non-informative chemical variance within each target class; decluttering methods seek to reduce within-class variance while retaining between-class variance. Supervised discretization is shown to declutter classes in a manner that is superior to the state-of-the-art External Parameter Orthogonalization (EPO) by constructing a more parsimonious model with fewer parameters to optimize and is, consequently, less susceptible to overfitting and information loss. The comparison of supervised discretization and EPO is performed on three classification applications: X-ray fluorescence spectra of pine ash where the pine was grown in three distinct soil types, laser induced breakdown spectroscopy of colored artisanal glasses, and laser induced breakdown spectroscopy of exotic hardwood species.

Analyst↗
USGS1987

GEOLOGICAL APPLICATIONS OF WELL LOGS. AN INTRODUCTORY BIBLIOGRAPHY AND SURVEY OF THE WELL LOGGING LITERATURE, ARRANGED BY SUBJECT, UPDATE, OCTOBER 1986 THROUGH OCTOBER 1987.

This update includes new publications for the period October 1986-October 1987 as well as earlier publications of interest that were omitted from the original due either to oversight or because they had not been received in sufficient time for inclusion. Part A covers basic well logging. Part B covers geological applications.

Log Analyst↗
USGS1994

Permeability-porosity relationships in sedimentary rocks

In many consolidated sandstone and carbonate formations, plots of core data show that the logarithm of permeability (k) is often linearly proportional to porosity (??). The slope, intercept, and degree of scatter of these log(k)-?? trends vary from formation to formation, and these variations are attributed to differences in initial grain size and sorting, diagenetic history, and compaction history. In unconsolidated sands, better sorting systematically increases both permeability and porosity. In sands and sandstones, an increase in gravel and coarse grain size content causes k to increase even while decreasing ??. Diagenetic minerals in the pore space of sandstones, such as cement and some clay types, tend to decrease log(k) proportionately as ?? decreases. Models to predict permeability from porosity and other measurable rock parameters fall into three classes based on either grain, surface area, or pore dimension considerations. (Models that directly incorporate well log measurements but have no particular theoretical underpinnings from a fourth class.) Grain-based models show permeability proportional to the square of grain size times porosity raised to (roughly) the fifth power, with grain sorting as an additional parameter. Surface-area models show permeability proportional to the inverse square of pore surface area times porosity raised to (roughly) the fourth power; measures of surface area include irreducible water saturation and nuclear magnetic resonance. Pore-dimension models show permeability proportional to the square of a pore dimension times porosity raised to a power of (roughly) two and produce curves of constant pore size that transgress the linear data trends on a log(k)-?? plot. The pore dimension is obtained from mercury injection measurements and is interpreted as the pore opening size of some interconnected fraction of the pore system. The linear log(k)-?? data trends cut the curves of constant pore size from the pore-dimension models, which shows that porosity reduction is always accompanied by a reduction in characteristic pore size. The high powers of porosity of the grain-based and surface-area models are required to compensate for the inclusion of the small end of the pore size spectrum.

Log Analyst↗
USGS1998

Petrophysics of low-permeability medina sandstone, northwestern Pennsylvania, Appalachian Basin

Petrophysical core testing combined with geophysical log analysis of low-permeability, Lower Silurian sandstones of the Appalachian basin provides guidelines and equations for predicting gas producibility. Permeability values are predictable from the borehole logs by applying empirically derived equations based on correlation between in-situ porosity and in-situ effective gas permeability. An Archie-form equation provides reasonable accuracy of log-derived water saturations because of saturated brine salinities and low clay content in the sands. Although measured porosity and permeability average less than 6% and 0.1 mD, infrequent values as high as 18% and 1,048 mD occur. Values of effective gas permeability at irreducible water saturation (Swi) range from 60% to 99% of routine values for the highest permeability rocks to several orders of magnitude less for the lowest permeability rocks. Sandstones having porosity greater than 6% and effective gas permeability greater than 0.01 mD exhibit Swi less than 20%. With decreasing porosity, Swi sharply increases to values near 40% at 3 porosity%. Analysis of cumulative storage and flow capacity indicates zones with porosity greater than 6% generally contain over 90% of flow capacity and hold a major portion of storage capacity. For rocks with Swi < 20%, gas relative permeabilities exceed 45%. Gas relative permeability and hydrocarbon volume decrease rapidly with increasing Swi as porosity drops below 6%. At Swi above 40%, gas relative permeabilities are less than approximately 10%.

Log Analyst↗
USGS1962

Photometric microdetermination of malathion

Carboxylic esters and lactones react with alkaline hydroxylamine to yield hydroxamates; these in acidic solution form colored iron(III) complexes. A photometric determination of such esters and lactones is thus permitted and has been extensively applied ( I-6). Hestrin ( 3) utilized this method for the microdetermination of acetylcholine and his procedure is much used for the in vitro study of cholinesterase activity and inhibition (4-6).

Chemist-Analyst↗
USGS1995

Hydrostatigraphic characterization of coastal aquifer by geophysical log analysis, Cape Cod National Seashore, Massachusetts

The Cape Cod National Seashore comprises part of Provincetown, Massachusetts, which lies at the northern tip of Cape Cod. The hydrologic regime in this area consists of unconsolidated sand-and-gravel deposits that constitute a highly permeable aquifer within which is a freshwater lens floating on denser sea water. A network of wells was installed into this aquifer to monitor a leachate plume emanating from the Provincetown landfill. Wells were located along orthogonal transects perpendicular to and parallel to the general groundwater flow path from the landfill to the seashore approximately 1,000 m to the southeast. Temperature, epithermal neutron, natural gamma. and electronmagnetic induction logs were obtained in five wells to depths ranging from 23 to 37 m. These logs identify the primary contamination and show that its movement is controlled by and confined within a dominant hydrostratigraphic unit about 2 to 5 m thick that exhibits low porosity, large representative grain size, and high relative permeability. A relation is also found between the temperaturegradient logs and water quality, with the gradient traces serving as effective delineators of the contaminant plume in wells nearest the landfill. Contamination is not detectable in the well nearest the seashore and farthest from the landfill, and the induction log from this well clearly identifies the freshwater/seawater transition zone at a depth of about 18 m. The geophysical logs provide fundamental information concerning the spatial distribution of aquifer properties near the landfill and lend valuable insight into how these properties influence the migration of the leachate plume to the sea.

Log Analyst↗
USGS1993

Application of borehole geophysics in defining the wellhead protection area for a fractured crystalline bedrock aquifer

Wellbore geophysical techniques were used to characterize fractures and flow in a bedrock aquifer at a site near Blackwater Brook in Dover, New Hampshire. The primary focus ofthis study was the development of a model to assist in evaluating the area surrounding a planned water supply well where contaminants introduced at the land surface might be induced to flow towards a pumping well. Well logs and geophysical surveys used in this study included lithologic logs based on examination of cuttings obtained during drilling; conventional caliper and natural gamma logs; video camera and acoustic televiewer surveys; highresolution vertical flow measurements under ambient conditions and during pumping; and borehole fluid conductivity logs obtained after the borehole fluid was replaced with deionized water. These surveys were used for several applications: 1) to define a conceptual model of aquifer structure to be used in groundwater exploration; 2) to estimate optimum locations for test and observation wells; and 3) to delineate a wellhead protection area (WHPA) for a planned water supply well. Integration of borehole data with surface geophysical and geological mapping data indicated that the study site lies along a northeast-trending intensely fractured contact zone between surface exposures of quartz monzonite and metasedimentary rocks. Four of five bedrock boreholes at the site were estimated to produce more than 150 gallons per minute (gpm) (568 L/min) of water during drilling. Aquifer testing and other investigations indicated that water flowed to the test well along fractures parallel to the northeast-trending contact zone and along other northeast and north-northwest-trending fractures. Statistical plots of fracture strikes showed frequency maxima in the same northeast and north-northwest directions, although additional maxima occurred in other directions. Flowmeter surveys and borehole fluid conductivity logging after fluid replacement were used to identify water-producing zones in the boreholes; fractures associated with inflow into boreholes showed a dominant northeast orientation. Borehole fluid conductivity logging after fluid replacement also gave profiles of such water-quality parameters as fluid electrical conductivity (FEC), pH, temperature, and oxidation-reduction potential, strengthening the interpretation of crossconnection of boreholes by certain fracture zones. The results of this study showed that the application of these borehole geophysical techniques at the Blackwater Brook site led to an improved understanding of such parameters as fracture location, attitude, flow direction and velocity, and water quality; all of which are important in the determination of a WHPA.

Log Analyst↗