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Chemistry

Analytical chemistry

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Displaying 526 - 550 of 2084

Cytochrome P450 27A1 Deficiency and Regional Differences in Brain Sterol Metabolism Cause Preferential Cholestanol Accumulation in the Cerebellum

February 11, 2017
Author(s)
Natalia Mast, Kyle Anderson, Joseph Lin, Yong Li, Illarion Turko, Curtis Tatsuoka, Ingemar Bjorkhem, Irina A. Pikuleva
Cytochrome P450 27A1 (CYP27A1 or sterol 27-hydroxylase) is a ubiquitous, multifunctional enzyme catalyzing regio- and stereo-specific hydroxylation of different sterols. In humans, complete CYP27A1 deficiency leads to cerebrotendinous xanthomatosis or

Believable Statements of Uncertainty

February 8, 2017
Author(s)
Richard M. Lindstrom
Nearly fifty years ago, two landmark papers appeared that should have cured the problem of ambiguous uncertainty statements in published data. Eisenhart’s paper in Science called for statistically meaningful numbers, and Currie’s Analytical Chemistry paper

Fabrication of Scanning Electrochemical Microscopy-Atomic Force Microscopy (SECM-AFM) Probes to Image Surface Topography and Reactivity at the Nanoscale

January 27, 2017
Author(s)
Jeyavel Velmurugan, Amit K. Agrawal, Sang M. An, Eric A. Choudhary, Veronika A. Szalai
Electrocatalysts, used in energy applications, rely on the solid-liquid interface to carry out productive chemistry. This interface is generally less amenable to standard surface-science characterization methods, making the investigation of the surface

Spatial variation in perfluoroalkyl acids in a population of wild American alligators (Alligator mississippiensis) at Merritt Island National Wildlife Refuge (MINWR) surrounding the Kennedy Space Center (KSC)

January 26, 2017
Author(s)
John Bowden, Jacqueline T. Bangma, Martin Jones, Russell H. Lowers, Frances Nilsen, Jessica L. Reiner, Thomas R. Rainwater, Stephen E. Somerville, Louis J. Guillette Jr.
This study aimed to quantify fourteen perfluoroalkyl acids (PFAAs) in the plasma of a population of alligators located at Merritt Island national Wildlife Refuge (MINWR). Male (n = 117) and female (n = 112) alligators were sampled in every month during

Least Squares Moving-Window Spectral Analysis

January 20, 2017
Author(s)
Young J. Lee
Least squares regression is proposed as a moving-windows method for analysis of a series of spectra acquired as a function of external perturbation. The least squares moving-window (LSMW) method can be considered an extended form of the Savitzky–Golay

Determination of Liquid Density

January 12, 2017
Author(s)
Lane C. Sander, Lorna T. Sniegoski
The determination of solution density is required for conversion of liquid solution levels from a mass fraction basis to a volume fraction basis. This presentation will provide information about three approaches in common use for the determination of

Liquid Chromatography: Introduction and Instrumentation

January 12, 2017
Author(s)
Lane C. Sander
Chromatography is an example of a process by which a mixture is separated into at least two fractions with different compositions. This presentation will provide a brief overview of the practice of liquid chromatography (LC), with an emphasis on

Measurement of Uranium-236 in Particles by Secondary Ion Mass Spectrometry

January 12, 2017
Author(s)
David S. Simons, John D. Fassett
The determination of the relative isotopic abundance by secondary ion mass spectrometry of 236U in uranium-containing material is complicated by the presence of 235U1H+ ions at the same nominal mass as the uranium isotopic peak. The net intensity of the

Plumbing for Liquid Chromatography

January 12, 2017
Author(s)
Lane C. Sander
The setup and maintenance of liquid chromatographic equipment requires a basic knowledge of chromatographic hardware. Tubing connections are an essential component in liquid chromatography instrumentation. System function and performance depend on the

Preparation of Calibration Solutions

January 12, 2017
Author(s)
Lane C. Sander, Michele M. Schantz
Calibration solutions provide the basis for quantitation for most instrumental techniques. The instrumental responses for analytes in calibrants of known composition are compared with corresponding responses in samples to provide quantitation of the

Pressurized Fluid Extraction

January 12, 2017
Author(s)
Lane C. Sander
Pressurized fluid extraction (PFE) is one of several sample preparation methods that can be used to extract targeted analytes from a sample matrix into a solvent, to permit subsequent analysis. With PFE, samples are extracted with solvent in a pressurized

Principles of Quantitation: Chromatography

January 12, 2017
Author(s)
Lane C. Sander
The accurate characterization of the chemical composition of a sample depends on a variety of factors that must be considered by the analyst. Knowledge of how different approaches to quantitation affect the measurement accuracy is requisite to the

Sample Concentration and Processing

January 12, 2017
Author(s)
Lane C. Sander
Sample Concentration and Processing Sample concentration is a common step in sample preparation prior to analysis that is performed to increase method sensitivity or to exchange solvent environment. Sample concentration can be thought of as a separation

Soxhlet Extractions

January 12, 2017
Author(s)
Lane C. Sander
Soxhlet extraction is one of several sample preparation methods that can be used to transfer targeted analytes from a sample matrix into a solvent, to permit subsequent analysis. With Soxhlet extraction, samples are repeatedly extracted with solvent

Troubleshooting Liquid Chromatographic Instrumentation and Methods

January 12, 2017
Author(s)
Lane C. Sander
The ability to assess analytical performance is a fundamental component of measurement science. Ultimately, measurement quality depends on the proper function of instrumentation in combination with appropriate methods. Evidence of proper function is

Use of Analytical Balances

January 12, 2017
Author(s)
Lane C. Sander
The determination of mass is a fundamental component in quantitative analysis, and weighing accuracy is an important factor for most applications. This presentation will highlight the use of different types of analytical balances and will demonstrate

Volumetric Transfer of Liquids

January 12, 2017
Author(s)
Lane C. Sander
Although volumetric measurements are usually less accurate than gravimetric based measurements, volumetric measurements are still in common use due to the convenience, and often higher throughput, that may be afforded by automatic pipettes. Analysts should

What is Chromatography All About?

January 12, 2017
Author(s)
Lane C. Sander
Chromatography is an example of a process by which a mixture is separated into at least two fractions with different compositions. Other separation methods exist, such as distillation, recrystallization, and extraction. Chromatography is used to analyze

Retention behavior of alkyl-substituted polycyclic aromatic sulfur heterocycle isomers in gas chromatography on stationary phases of different selectivity

January 10, 2017
Author(s)
Walter B. Wilson, Lane C. Sander, Jorge O. Ona Ruales, Stephanie Mossner, Leonard M. Sidisky, Milton Lee, Stephen A. Wise
Retention indices for 10 sets of alkyl-substituted polycyclic aromatic sulfur heterocycles (PASHs) isomers (total of 80 PASHs) were determined using gas chromatography with three different stationary phases: a 50% phenyl phase, a 50% liquid crystalline

Retention behavior of isomeric polycyclic aromatic sulfur heterocycles in gas chromatography on stationary phases of different selectivity

January 10, 2017
Author(s)
Walter B. Wilson, Lane C. Sander, Jorge O. Ona Ruales, Leonard M. Sidisky, Milton Lee, Stephen A. Wise
Retention indices for 70 polycyclic aromatic sulfur heterocycles (PASHs) were determined using gas chromatography with three different stationary phases: a 50% phenyl phase, a 50% liquid crystalline dimethylpolysiloxane (LC-DMPS) phase, and an ionic liquid
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