Analytical Chemistry

We are improving and applying highly accurate and precise isotope ratio measurement capabilities for compositional analysis and for identifying and tracking elements with unique isotopic signatures. Available instruments-inductively coupled plasma and thermal ionization mass spectrometers-have diverse capabilities. Research programs are possible in elemental, isotopic, and species measurement. Both stable and radioisotopes can be applied to study environmental and health problems, materials, and processes.

We also are studying ways to eliminate or minimize isobaric interference and to increase the speed and reliability of sample introduction. In addition, we are investigating various schemes for quantitative analysis, including refinements to the highly accurate, primary method of isotope dilution mass spectrometry. Research can be directed toward innovative development of instrumentation and methods, the characterization and interpretation of specific samples, or the determination of natural, absolute isotopic abundances.

Contact: John D. Fassett or Gregory C. Turk

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Quantitative Analysis Of Solids

Direct analysis of solids has characteristically been highly dependent on matrix-matched standards. We are studying ways to improve the accuracy of measurement while at the same time reducing this dependence on standards. Our ongoing research efforts include studying the techniques of glow discharge optical emission spectroscopy (GD-OES) and X-ray fluorescence spectrometry (XRF). Opportunities exist for innovative development of instrumentation and sample preparation techniques as well as and fundamental and diagnostic studies of the basic principles of instrument operation.

GD-OES can detect nearly every element in the periodic table in either conductive or non-conductive materials. This method is also potentially useful for rapid, quantitative depth profiling of thick and thin-film structures. Currently, we are emphasizing non-metallic analytes.

State-of-the-art XRF instrumentation includes a 4-kilowatt wavelength dispersive spectrometer, an energy dispersive spectrometer, a custom-built microfluorescence instrument, and glass fusion equipment. Research and development interests include:

	fundamental parameters computation methods;
	synthetic macro-reference samples for primary calibration and validation;
	microscale mapping and heterogeneity characterization;
	characterization of thin-film materials; and
	chemical speciation and correlation with other spectrochemical methods.

Contact: John R. Sieber or Michael R. Winchester

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High-Performance Spectrochemical Analysis

We recently have improved the precision and accuracy of spectrochemical analysis by orders of magnitude by developing a set of unique experimental designs, data analysis procedures, and sample-handling techniques for computer-controlled spectrochemical instrumentation. This approach, called high-performance spectrochemical analysis, has drawn attention from several industrial research sectors, including advanced materials, nuclear energy production, and precious metals. The high-precision measurements being made with this methodology are uncovering a more detailed view of the basic elements that assure the accuracy of spectrochemical analysis. Matrix interferences, detector linearity, and contamination issues can all be observed at a level of detail that has never before been available, and as a result a complete re-evaluation of basic spectrochemical procedures needs to be undertaken.

Contact: Marc L. Salit or Gregory C. Turk

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Analytical Mass Spectrometry for Organics and Biomolecules

We are developing advanced techniques in mass spectrometry and applying them to the detection, identification, and accurate quantitation of trace levels of organic compounds. Available instrumentation includes a triple quadruple mass spectrometer with electrospray, cesium ion bombardment, positive- and negative-ion chemical ionization, and electron ionization; a magnetic mass spectrometer with capabilities for high resolution, fast atom bombardment, and linked scanning; and a liquid chromatograph/mass spectrometer with electrospray and atmospheric pressure chemical ionization.

We encourage research related to electrospray and other techniques suitable for coupling liquid chromatography or capillary electrophoresis to mass spectrometry, particularly if the work may lead to techniques for the quantitation of polar and non-volatile analytes in complex matrices. Of particular interest are biomolecules that are health status markers.

We encourage research in understanding and applying ion trap technology to quantitative gas chromatography/mass spectrometry as well as understanding and applying collision-induced and surface-induced dissociation to analytical problems.

Contact: Michael J. Welch or Edward White V

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Chromatography and Electromigration Techniques

Solute retention in chromatography and electromigration systems is the result of a complex assortment of molecular interactions between the solute, the stationary phase, and the mobile phase. The diversity of these interactions can be utilized to improve efficiency of separations by varying separation parameters such as stationary phase and/or mobile phase composition and column temperature. An understanding of these fundamental retention and selectivity mechanisms facilitates the optimization of separations in gas chromatography (GC), liquid chromatography (LC), supercritical fluid chromatography and extraction (SFC and SFE), and capillary electrophoresis (CE).

Recently, we have focused on the synthesis and characterization of bonded stationary phases in LC and GC (e.g., monomeric/polymeric C18 phases and charge transfer phases in LC and liquid crystalline phases in GC), which offer unique capabilities for the separation of isomeric compounds or compound classes. We are investigating solute-stationary phase interactions using chromatographic and spectroscopic techniques and chiral interactions in LC, GC, SFC, and CE. In addition, we are studying molecular modeling of solutes and stationary phases to investigate retention mechanisms and to correlate molecular descriptors with retention. We also are investigating solute-matrix interactions in SFE.

Contact: Lane C. Sander or Stephen A. Wise

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Novel Analytical Separation Science Methodology

We are developing new, innovative approaches to separate and detect trace-level organic species in complex natural matrices. One priority is the design, synthesis, and characterization of bonded stationary phases for liquid chromatography (LC), gas chromatography (GC), and supercritical fluid chromatography (SFC). We also are developing novel separation media/modes for electromigration separation techniques, e.g., capillary electrophoresis (CE), capillary gel electrophoresis, micellar electrokinetic capillary chromatography, and capillary electrochromatography. In another effort, we are developing on-line multidimensional separation techniques based on orthogonal methodologies (such as LC-GC, LC-CE, LC-LC, and GC-GC) and fast separation technology in GC, LC, SFC, and CE. We also seek application of existing separation modes in novel combinations (e.g., chiral separations in SFC and CE), design of new separation systems based on micellar and liposomal phases, antibody/antigen associations, and size-selective networks.

We are studying sensitive and/or selective detection systems for microcolumn separations, e.g., mass spectrometry, laser-excited fluorescence, thermal-lens absorbance, chemical reaction, and chemiluminescence approaches. We also are developing supercritical fluid extraction systems for probing the interactions of analytes and matrices and for on-line coupled extraction and chromatography. We are investigating chromatographic and electrophoretic approaches for the measurement of physico-chemical properties such as octanol/water partition coefficients, aqueous solubilities, and vapor pressures. Another effort involves designing microfluidic systems for capillary flow injection analysis, electrophoresis, and electrochromatography. Our research will emphasize applications to environmental, clinical, nutritional, and forensic disciplines.

Contact: Stephen A. Wise or Lane C. Sander

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Separation Science Techniques for Trace Organic Analysis

We are developing and applying separation techniques such as gas chromatography (GC), liquid chromatography (LC), supercritical fluid chromatography (SFC), and capillary electrophoresis (CE) for trace-level determination of organic and organometallic compounds. We are developing extraction systems for selective removal of analytes from natural matrices, e.g., supercritical fluid extraction (SFE), pressurized fluid extraction (PFE), and microwave-assisted extraction. We also are developing chromatographic and electrophoretic approaches for sample preparation, clean-up, and analyte pre-concentration prior to analysis by LC, GC, SFC, or CE.

In another project we seek to develop off-line and on-line multidimensional separation procedures (e.g., LC-GC, LC-LC, SFE-GC, and LC-CE) to measure individual species in complex mixtures. We are developing and using simultaneous multiple and/or selective chromatographic and electrophoretic detection systems (e.g., mass spectrometric, electron capture, atomic emission, flame photometric, infrared, UV-visible diode array, fluorescence, electrochemical, and chemical reaction detectors) to enhance measurement selectivity, sensitivity, or both. Recent activities have emphasized applications in environmental, clinical, and forensic areas, including the determination of environmental contaminants such as polychlorinated biphenyls, polycyclic aromatic hydrocarbons, pesticides, and organometallic species in natural matrices such as sediment, tissue, and air particulate material; nutrients such as vitamins and carotenoids in food and serum; drugs of abuse in urine and hair; and biomolecules such as proteins, peptides, and DNA fragments. Research opportunities exist within our division for the application of these separation techniques to trace inorganic analysis problems.

Contact: Stephen A. Wise or Michele M. Schantz

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High-Accuracy Coulometry

Our coulometry program entails a broad spectrum of research interests and activities, including improving the precision and accuracy of coulometric methods, determining chemical stoichiometry, redetermining physical constants (such as atomic weights, and the Faraday constant), and developing new methods and instrumentation including microcoulometry. Also of prime concern to us is the application of absolute coulometric methods to the standardization of primary chemical standards and to the calibration of other analytical techniques. Instrumentation is available for constant-current and controlled potential coulometric measurements.

Contact: Kenneth W. Pratt

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Inorganic Electroanalytical Chemistry

Our research interests encompass all areas of inorganic electroanalytical chemistry, with specific emphasis on fundamental studies of pH, such as modeling the liquid junction potential; measurements of acid dissociation constants; theory and metrology of aqueous and non-aqueous electrolytic conductivity; high-precision coulometric research; and the development of electrochemical detection systems.

We give special attention to the development of novel electrochemical instrumentation and the application of electroanalytical techniques to matters of national importance. Instrumentation is available for precise pH, electromotive force, conductimetric, coulometric, potentiometric, and voltammetric measurements.

Contact: Kenneth W. Pratt

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Trace-Gas Analysis

We are using Fourier transform infrared spectroscopy (FTIR), tunable diode laser adsorption spectroscopy, gas chromatography, electrochemical analysis, and other specialized analysis techniques to develop primary standard gas mixtures and to measure trace gases in air, the environment, stack emissions, and process streams. One of our goals is to analyze complex mixtures of gases emitted from process streams in real time using spectroscopic techniques. We also are seeking to measure extremely low-level contaminant gases in ultrapure materials, to develop standards, and to analyze trace gases that are important in ambient atmospheric measurements. Additionally, we are pursuing analysis of environmentally important trace gases in air and from point sources and the development of very low concentration volatile organic standards.

Contact: Franklin R. Guenther

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Optical Techniques for Trace Gas Analysis

We are developing, characterizing, and validating spectroscopic techniques, such as Fourier-transform infrared (FT-IR), Fourier-transform microwave (FT-MW), and laser-based methods for trace gas analysis of complex matrices. Recent advances in instrumentation have promoted the use of these methods for environmental, industrial, and clinical applications. However, various properties of each method can impact the quantitative measurements. For example, in FT-IR instrumentation the individual instrument response function and detector non-linearities can significantly affect instrument-to-instrument calibration. FT-MW spectroscopy is a highly sensitive technique for species with a permanent dipole moment with near real-time response. We currently are examining in detail the linearity, frequency variation, sample matrix effects, short and long-term reproducibility, and calibration of an FT-MW instrument to validate the potential of this technique for quantitative analysis.

Contact: Pamela M. Chu

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Molecular Spectrometry Standards for Chemical Analysis

Spectrophotometers are important tools for quality assurance, process control, and regulatory compliance measurements. To ensure that these devices are performing properly, we manufacture and certify Standard Reference Material® optical filters. Currently, we provide materials and filters to measure wavelength accuracy, assess photometric accuracy, and determine the amount of stray light in ultraviolet and visible spectrophotometers. The NIST-Traceable Reference Materials program for optical filters leverages the NIST standards by extending visible absorbance filter manufacture and certification into the private sector. Since near-infrared spectroscopy has become a viable, routine technique, especially for process monitoring, we have begun to extend our offerings to the near infrared region with new wavelength standards and ongoing research on absorbance standards. Recent advances in laser and detection technologies have made Raman spectroscopy an important tool for process analysis and quality assurance determination. We are developing a series of Raman intensity correction standards that will pave the way for the development of Raman spectral libraries similar to their infrared counterparts. Luminescence spectrometry provides the analytical basis for much of the revolution in biotechnology. We are developing standards for fluorescence wavelength, intensity, and spectral correction to facilitate quantitative fluorescence measurements.

Contact: John C. Travis or Steven J. Choquette

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Automation and Data Interchange Standards for Analytical Chemistry

We are developing, evaluating, and demonstrating new concepts that eventually can lead to the successful, routine application of laboratory automation. The full potential of automated chemical analysis systems has not been achieved because the process of interconnecting analytical and clinical chemistry laboratory devices remains resource-intensive and difficult. To facilitate the automation of the analytical laboratory, standard methods for instrument-to-controller communication, device control, data and material transfer, and error and exception handling are needed to provide instruments with realistic plug-and-play interfaces. New information models are needed to support data exchange standards in analytical chemistry for instrument-to-instrument, instrument-to-application, and application-to-application interchanges.

Contact: Gary W. Kramer

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Lab-On-A-Chip Microfluid Systems

In the foreseeable future, an increasing number of analytical measurements will be made using miniaturized chip-based analytical devices. Our chemists and engineers are currently developing ever-smaller, faster versions of liquid handling and processing systems for chemical measurements now known as "lab-on-a-chip" systems. The goal is to devise microfluid analysis systems that operate with one millionth of a drop of liquid yet incorporate fluid metering, selective chemical interactions or separations, on-device detection, and information output. The purpose of our research program is to promote successful measurements in microscale analytical devices by addressing some of the key scientific issues that hinder the advancement of this technology. Fundamental research in the following three areas will assure that this emerging technology can provide reliable cost-effective quantitative measurements: understanding and harnessing microflow; incorporating highly sensitive detection strategies; and developing selective chemistries. This highly interdisciplinary program is a collaborative effort among several divisions at NIST.

Contact: Laurie E. Locascio

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Analytical Infometrics

To ensure that chemical information necessary for decision making can be provided in an efficient and timely manner, we are investigating all aspects of the measurement process, including experimental design; data validation, storage, and retrieval; chemometrics, multivariate statistics, and applied mathematics; data rectification and meta-analysis; quality control, assurance, and improvement; and instrument control and communications. We are using multivariate infrared and Raman spectroscopy for characterization of organic mixtures, and graphical methods for analysis and presentation of interlaboratory comparison studies. We also are developing control charts and quality assurance models for optical filters and improved methods for evaluating and utilizing analytical measurement uncertainties.

Contact: David L. Duewer

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Chemical Analysis with Neutron Beams

The use of prompt radiation from nuclear reactions is well established as a tool for elemental analysis and compositional mapping. We use two techniques relying on prompt nuclear radiation: neutron-capture prompt-gamma-ray activation analysis (PGAA) and neutron depth profiling (NDP). Each employs either thermal- and/or cold-neutron beams from the NIST Center for Neutron Research. We use PGAA to detect elements that are inaccessible by conventional neutron activation analysis, such as hydrogen, boron, carbon, and nitrogen, as well as those with large capture cross sections, such as cadmium, gadolinium, and samarium. We use NDP to measure the depth distribution of nuclides that emit charged particles on slow-neutron capture. We are developing methods with improved specificity, accuracy, sensitivity, and spatial resolution through detailed studies of the interaction of neutrons and their products with samples and detectors.

Contact: Richard M. Lindstrom and Robert R. Greenberg

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Neutron Activation Analysis

Neutron activation analysis (NAA) provides the sensitivity, selectivity, and capability for multielemental determinations that are often required in studies involving the role of trace elements in biological, environmental, and materials analysis studies. Due to their unique capabilities, we frequently use the various NAA techniques to analyze elemental concentrations for NIST Standard Reference Materials®. The accuracy and precision of the various forms of NAA ultimately are limited by the precision of counting statistics that in favorable cases may be a few tenths of a percent. However, to achieve this level of accuracy, all other sources of error must be reduced to comparable levels. We conduct experimental and computational studies to address such matters as new and improved chemical separation procedures, neutron and gamma-ray interactions with analytical samples and detectors, high-accuracy neutron flux monitoring, high and varying count-rate gamma-ray spectrometry, peak integration routines, and gamma-ray and fast-neutron interferences. A variety of nuclear spectrometry equipment, laboratory facilities, computing facilities, and the irradiation facilities of the NIST Center for Neutron Research are available for this work.

Contact: Robert R. Greenberg

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Focusing of Cold Neutrons for Analytical Measurements

The availability of long wavelength (cold) neutrons and recent advances in neutron optics provide an opportunity to design analytical probes for use in materials research. The purpose is to measure the concentration of the elements in a fine (sub-millimeter), two-dimensional array across the surface of a material. The detection limit of neutron absorption experiments will be improved by using optical elements to focus long wavelength neutrons onto small sample areas. Different methods can be used to focus cold neutrons; the emphasis is on those based on the principle of total external reflection of neutrons at small grazing angles. These include polycapillary glass fibers, metal capillaries, nickel-coated conic sections of revolution, nickel-coated curved micro-guides, and curved channel plates. However, in all cases, focusing is achieved at the expense of increased angular divergence. Consequently, the technique is useful for measurements that are dependent on the neutron capture reaction. Such a system improves the detection limits and spatial resolution for absorption measurements such as prompt gamma activation analysis and neutron depth profiling.

Contacts: David F.R. Mildner and H. Heather Chen-Mayer

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Date created: September 28, 2001
Last modified: Aug. 07, 2007
Contact: inquiries@nist.gov