G. Hieftje - Academia.edu (original) (raw)

Papers by G. Hieftje

Research paper thumbnail of Design and Construction of a Low-Flow, Low-Power Torch for Inductively Coupled Plasma Spectrometry

Applied Spectroscopy, 1982

A detailed study of the importance of various spatial dimensions in an ICP torch is described. Of... more A detailed study of the importance of various spatial dimensions in an ICP torch is described. Of the various dimensions which were examined, the annular spacing between the coolant (outer) and plasma (flared) tube is the most critical for plasma stabilization at low argon coolant flows and applied radio-frequency powers. Similarly, the inner diameter of the aerosol injection tube was found to be important, with the value of 1.0 mm chosen for a compromise between low-power, low-flow capability and routine analysis of high-solids sample solutions. A constriction at the inlet of the coolant argon was found not to affect plasma stability greatly, but altered significantly the applied powers and coolant flows which were necessary for plasma ignition. With these and other torch dimensions optimized, it was found to be possible to ignite a plasma at a coolant flow of 5 L/min and an applied radio frequency power of 450 W. Continued operation of the plasma during analysis of real samples or...

Research paper thumbnail of Effect of internal and external conditions on ionization processes in the FAPA ambient desorption/ionization source

Ambient desorption/ionization (ADI) sources coupled to mass spectrometry (MS) offer outstanding a... more Ambient desorption/ionization (ADI) sources coupled to mass spectrometry (MS) offer outstanding analytical features: direct analysis of real samples without sample pretreatment, combined with the selectivity and sensitivity of MS. Since ADI sources typically work in the open atmosphere, ambient conditions can affect the desorption and ionization processes. Here, the effects of internal source parameters and ambient humidity on the ionization processes of the flowing atmospheric pressure afterglow (FAPA) source are investigated. The interaction of reagent ions with a range of analytes is studied in terms of sensitivity and based upon the processes that occur in the ionization reactions. The results show that internal parameters which lead to higher gas temperatures afforded higher sensitivities, although fragmentation is also affected. In the case of humidity, only extremely dry conditions led to higher sensitivities, while fragmentation remained unaffected.

Research paper thumbnail of Noise characteristics of an inductively coupled plasma-mass spectrometer

Spectrochimica Acta Part B: Atomic Spectroscopy, 1989

Research paper thumbnail of Spatially resolved measurements as a vehicle for studying atomization mechanisms in an ICP

Spectrochimica Acta Part B: Atomic Spectroscopy, 1989

... ADRIANO F. PARISIJ: and GARY M. HIEFTJE Department of Chemistry, Indiana University, Blooming... more ... ADRIANO F. PARISIJ: and GARY M. HIEFTJE Department of Chemistry, Indiana University, Bloomington, IN 47405, USA (Received 2 January 1989; in revised form ... 4, the significant noise level on the signals, and the high degree to which the Abel transform is sensitive to such ...

Research paper thumbnail of Time-of-flight mass spectrometry as a tool for speciation analysis

Spectrochimica Acta Part B: Atomic Spectroscopy, 2000

Time-of-flight mass spectrometry TOFMS has recently been introduced as an alternative to scanning... more Time-of-flight mass spectrometry TOFMS has recently been introduced as an alternative to scanning-based mass analyzers for use in elemental analysis. Coupled with an inductively coupled plasma or alternative ion source, TOFMS can produce a complete atomic mass spectrum in less than 50 s. Because of this high spectral-generation rate, even very brief transient signals can be recorded with high fidelity. Furthermore, each mass spectrum is derived from the same sub-microsecond pulse of ions, so high precision can be achieved by using either isotope-ratioing or internal standardization techniques. All these features make TOFMS attractive for the measurement of transient signals, such as those commonly encountered in speciation analysis. In this paper, the capabilities of TOFMS in speciation will be demonstrated through the coupling of gas chromatography and capillary electrophoresis with an inductively coupled plasma-TOFMS. Additionally, the development of novel switched gas sampling glow discharge Ž. GSGD ionization sources will be described and their role in chemical speciation will be evaluated. The switched GSGD has the ability to collect both atomic and molecular mass spectra in rapid succession, to provide additional Ž information about chemical species. The coupling of various sample introduction systems flow-cell, exponential. dilutor, capillary gas chromatography and electrothermal vaporization to the GSGD is outlined.

Research paper thumbnail of First Distance-of-Flight Instrument: Opening a New Paradigm in Mass Spectrometry

Journal of The American Society for Mass Spectrometry, 2011

Research paper thumbnail of First inductively coupled plasma-distance-of-flight mass spectrometer: instrument performance with a microchannel plate/phosphor imaging detector

Journal of Analytical Atomic Spectrometry, 2013

ABSTRACT Here we describe the first combination of a Distance-of-Flight Mass Spectrometry (DOFMS)... more ABSTRACT Here we describe the first combination of a Distance-of-Flight Mass Spectrometry (DOFMS) instrument and an inductively coupled plasma (ICP) ion source. DOFMS is a velocity-based MS technique in which ions of a range of mass-to-charge (m/z) values are detected simultaneously along the length of a spatially selective detector. As a relative of time-of-flight (TOF) MS, DOFMS leverages benefits from both TOFMS and spatially dispersive MS. The simultaneous detection of groups of m/z values improves dynamic range by spreading ion signal across many detector elements and reduces correlated noise by signal ratioing. To ascertain the performance characteristics of the ICP-DOFMS instrument, we have employed a microchannel-plate/phosphor detection assembly with a scientific CCD to capture images of the phosphor plate. With this simple (and commercially available) detection scheme, elemental detection limits from 2-30 ng L-1 and a linear dynamic range of 5 orders of magnitude (10-106 ng L-1) have been demonstrated. Additionally, a competitive isotope-ratio precision of 0.1% RSD has been achieved with only a 6 s signal integration period. In addition to first figures of merit, this paper outlines technical considerations for the design of the ICP-DOFMS.

Research paper thumbnail of A new generation of instrumentation and capabilities for atomic mass spectrometry

Guangpuxue-yu-guangpu-fenxi, 1999

Research paper thumbnail of A new generation of instrumentation and capabilities for atomic mass spectrometry

Guang pu xue yu guang pu fen xi = Guang pu, 1999

Research paper thumbnail of How Constant Momentum Acceleration Decouples Energy and Space Focusing in Distance–of–Flight and Time–of–Flight Mass Spectrometries

Journal of The American Society for Mass Spectrometry, 2013

Resolution in time-of-flight mass spectrometry (TOFMS) is ordinarily limited by the initial energ... more Resolution in time-of-flight mass spectrometry (TOFMS) is ordinarily limited by the initial energy and space distributions within an instrument's acceleration region and by the length of the field-free flight zone. With gaseous ion sources, these distributions lead to systematic flight-time errors that cannot be simultaneously corrected with conventional static-field ion-focusing devices (i.e., an ion mirror). It is known that initial energy and space distributions produce non-linearly correlated errors in both ion velocity and exit time from the acceleration region. Here we reinvestigate an old acceleration technique, constant-momentum acceleration (CMA), to decouple the effects of initial energy and space distributions. In CMA, only initial ion energies (and not their positions) affect the velocity ions gain. Therefore, with CMA, the spatial distribution within the acceleration region can be manipulated without creating ion-velocity error. The velocity differences caused by a spread in initial ion energy can be corrected with an ion mirror. We discuss here the use of CMA and independent focusing of energy and space distributions for both distance-of-flight mass spectrometry (DOFMS) and TOFMS. Performance characteristics of our CMA-DOFMS and CMA-TOFMS instrument, fitted with a glow-discharge ionization source, are described. In CMA-DOFMS, resolving powers (FWHM) of greater than 1000 are achieved for atomic ions with a flight length of 285 mm. In CMA-TOFMS, only ions over a narrow range of m/z values can be energy-focused; however, the technique offers improved resolution for these focused ions, with resolving powers of greater than 2000 for a separation distance of 350 mm.

Research paper thumbnail of Optical waveguide sensors in analytical chemistry: today's instrumentation, applications and trends for future development

Fresenius' Journal of Analytical Chemistry

Current concepts for chemical and biochemical sensing based on detection with optical waveguides ... more Current concepts for chemical and biochemical sensing based on detection with optical waveguides are reviewed. The goals are to provide a framework for classifying such sensors and to assist a designer in selecting the most suitable detection techniques and waveguide arrangements. Sensor designs are categorized on the basis of the five parameters that completely describe a light wave: its amplitude, wavelength, phase, polarization state and timedependent waveform. In the fabrication of a successful sensor, the physical or chemical property of the determined species and the particular light wave parameter to detect it should be selected with care since they jointly dictate the sensitivity, stability, selectivity and accuracy of the eventual measurement. The principle of operation, the nature or the detected optical signal, instrumental requirements for practical applications, and associated problems are analyzed for each category of sensors. Two sorts of sensors are considered: those based on direct spectroscopic detection of the analyte, and those in which the analyte is determined indirectly through use of an analyte-sensitive reagent. Key areas of recent study, useful practical applications, and trends in future development of optical waveguide chemical and biochemical sensors are considered.

Research paper thumbnail of The 2017 Plasma Roadmap: Low temperature plasma science and technology

Journal of Physics D: Applied Physics

Research paper thumbnail of Theophilus Redwood Lecture. Models, measurements, methods and machines in analytical spectrometry

Analytical Proceedings, 1986

Research paper thumbnail of Plasma diagnostic on a low-flow plasma for inductively coupled plasma optical emission spectrometry

Spectrochimica Acta Part B: Atomic Spectroscopy, 2008

In order to elucidate the fundamental properties of a low-flow inductively coupled plasma (ICP) o... more In order to elucidate the fundamental properties of a low-flow inductively coupled plasma (ICP) operated under total Ar consumption of 0.6 L min − 1 , excitation temperatures, rotational temperatures, ionization temperatures, electron temperatures, and electron number densities were studied with optical emission based methods. The plasma was operated in the SHIP torch (Static High Sensitivity ICP), which was designed for optical emission spectrometric detection. For the first time, this plasma was studied in a laterally resolved manner and at selected observation heights. The Boltzmann plot method was used to obtain excitation and rotational temperatures in the range of 5000-8000 K and 3100-4000 K, respectively. Electron temperatures were determined from the line-to-continuum method to be as high as 9000 K in the analytical channel. The electron number densities were determined with the hydrogen-beta line method and found to be in the range of 5-8×10 15 cm − 3 at 1.1 kW radio frequency (rf) power. Ionization temperatures between 6250 and 7750 K were found at different observation heights in the plasma. The influence of applied rf powers between 0.9 and 1.2 kW on selected key parameters was investigated. The low-flow plasma exhibited temperature ranges similar to those prevailing in conventional ICP sources.

Research paper thumbnail of Surface elemental mapping via glow discharge optical emission spectroscopy

Spectrochimica Acta Part B: Atomic Spectroscopy, 2012

ABSTRACT Glow discharge optical emission spectroscopy (GDOES) has evolved in the last couple of d... more ABSTRACT Glow discharge optical emission spectroscopy (GDOES) has evolved in the last couple of decades from direct bulk solid analysis to a high resolution depth-profiling technique. However, the achievable lateral resolution has been historically restricted to the diameter of the sputtered area, i.e. some millimetres. Recently, there has been a push toward characterizing and improving the GDOES limits of lateral resolution. In consequence, a door has been opened for applications to take advantage of the new information dimensions that the technique affords.It is important to sum what has been accomplished so far to clarify the current possibilities and opportunities for development. It will become evident that the data acquisition requirements of GDOES elemental mapping can only be met via spectral imaging. Accordingly, the studies performed to date will be reviewed with emphasis on the spectral imaging geometry that has been utilized.

Research paper thumbnail of Spatially resolved ground-state number densities of calcium and strontium ion in an inductively coupled plasma in contact with an inductively coupled plasma mass spectrometry sampling interface

Spectrochimica Acta Part B: Atomic Spectroscopy, 2003

Radial profiles of Ca and Sr ion number densities in an ICP at 6, 7 and 8 mm above the load coil ... more Radial profiles of Ca and Sr ion number densities in an ICP at 6, 7 and 8 mm above the load coil (ALC) and at 1.25 kW of input rf power were measured by saturated fluorescence induced by an Nd:YAG laser-pumped dye laser at 396.85 nm and 421.55 nm, respectively. The measurements were performed in the presence and in the absence of an ICP-MS sampling interface. When in place, the orifice of the sampling cone was positioned 13 mm ALC on the axis of the plasma torch. The results show that the interface can either raise or lower the ion number densities, depending on the central-gas-flow rate, and can cause a vertical shift of their entire radial profiles with respect to the ICP axis. The introduction of Li, Cu and Zn as matrix elements reduced the ion number densities of the analytes, both in the presence and in the absence of the interface. This effect became more significant at higher central-gasflow rates. In addition, the peak value of the radial ion number density was found to depend strongly on the centralgas-flow rate maximum occurred at 1.1 lymin for both Ca ion and Sr ion under the ICP operating conditions used in this study. This behavior is very similar to the mass spectrometric signals previously observed downstream and reported in the literature. ᮊ

Research paper thumbnail of Fundamental studies on a planar-cathode direct current glow discharge. Part II: numerical modeling and comparison with laser scattering experiments

Spectrochimica Acta Part B: Atomic Spectroscopy, 2004

We have calculated the gas temperature, electron density, electron energy distribution function, ... more We have calculated the gas temperature, electron density, electron energy distribution function, and average electron energy, as a function of distance from the cathode, with a two-dimensional model for an argon direct-current glow discharge. The calculated results are compared with measured values from Rayleigh-and Thomson-scattering experiments, for different values of voltage, pressure and electrical current. The gas-temperature distribution and electron-density profile were found to be in reasonable agreement with experiment. For the electron energy, model and experiment give complementary information, since the experiment is able to detect only the thermal and low-energy electrons, whereas the model focuses mainly on the high-energy electrons. ᮊ

Research paper thumbnail of An apparatus for measuring Thomson scattering from an inductively coupled plasma

Spectrochimica Acta Part B: Atomic Spectroscopy, 1985

An experimental arrangement is presented which has been proven capable of measuring Thomson scatt... more An experimental arrangement is presented which has been proven capable of measuring Thomson scattering from an inductively coupled plasma (ICP). This system has been shown to reject stray light to a sufficient extent that useful scattering signals can be measured as near as 0.3 nm from the incident laser wavelength. In this paper, design considerations are discussed and a viable experimental system is described. Preliminary Thomson scattering results are presented.

Research paper thumbnail of Effect of mass spectrometric sampling interface on the fundamental parameters of an inductively coupled plasma as a function of its operating conditions

Spectrochimica Acta Part B: Atomic Spectroscopy, 2007

Research paper thumbnail of A steady-state approach to evaluation of proposed excitation mechanisms in the analytical ICP

Spectrochimica Acta Part B: Atomic Spectroscopy, 1986

A method is described for the eval~tion of propose-d analyte ionization and excitation mechanisms... more A method is described for the eval~tion of propose-d analyte ionization and excitation mechanisms in the analytical ICP. In the method, a steady-state kinetic expression is derived for each proposed mechaniim; the resulting expression predicts a linear re~tio~~p between analyte emission and the concentrations or concentration products of species important in the excitation and deactivation processes. The application of this approach to Ca ionization and excitation is described for the region 15 mm above the load coil and O-5 mm from the center of the plasma Importantly, the conumtration of ground-state Ca seems not to be important in the production of either excited Ca atoms or ions. Rather, Ca atom excitation appears to occur by means of three-body or radiative Ca *electron recombination. In contrast, Ca' seems to be excited directly by electron impact. Among the mechanisms evaluated here, depopulation of excited-state calcium species by collisional deactivation appears to be less significant than radiative decay to the ground state.

Research paper thumbnail of Design and Construction of a Low-Flow, Low-Power Torch for Inductively Coupled Plasma Spectrometry

Applied Spectroscopy, 1982

A detailed study of the importance of various spatial dimensions in an ICP torch is described. Of... more A detailed study of the importance of various spatial dimensions in an ICP torch is described. Of the various dimensions which were examined, the annular spacing between the coolant (outer) and plasma (flared) tube is the most critical for plasma stabilization at low argon coolant flows and applied radio-frequency powers. Similarly, the inner diameter of the aerosol injection tube was found to be important, with the value of 1.0 mm chosen for a compromise between low-power, low-flow capability and routine analysis of high-solids sample solutions. A constriction at the inlet of the coolant argon was found not to affect plasma stability greatly, but altered significantly the applied powers and coolant flows which were necessary for plasma ignition. With these and other torch dimensions optimized, it was found to be possible to ignite a plasma at a coolant flow of 5 L/min and an applied radio frequency power of 450 W. Continued operation of the plasma during analysis of real samples or...

Research paper thumbnail of Effect of internal and external conditions on ionization processes in the FAPA ambient desorption/ionization source

Ambient desorption/ionization (ADI) sources coupled to mass spectrometry (MS) offer outstanding a... more Ambient desorption/ionization (ADI) sources coupled to mass spectrometry (MS) offer outstanding analytical features: direct analysis of real samples without sample pretreatment, combined with the selectivity and sensitivity of MS. Since ADI sources typically work in the open atmosphere, ambient conditions can affect the desorption and ionization processes. Here, the effects of internal source parameters and ambient humidity on the ionization processes of the flowing atmospheric pressure afterglow (FAPA) source are investigated. The interaction of reagent ions with a range of analytes is studied in terms of sensitivity and based upon the processes that occur in the ionization reactions. The results show that internal parameters which lead to higher gas temperatures afforded higher sensitivities, although fragmentation is also affected. In the case of humidity, only extremely dry conditions led to higher sensitivities, while fragmentation remained unaffected.

Research paper thumbnail of Noise characteristics of an inductively coupled plasma-mass spectrometer

Spectrochimica Acta Part B: Atomic Spectroscopy, 1989

Research paper thumbnail of Spatially resolved measurements as a vehicle for studying atomization mechanisms in an ICP

Spectrochimica Acta Part B: Atomic Spectroscopy, 1989

... ADRIANO F. PARISIJ: and GARY M. HIEFTJE Department of Chemistry, Indiana University, Blooming... more ... ADRIANO F. PARISIJ: and GARY M. HIEFTJE Department of Chemistry, Indiana University, Bloomington, IN 47405, USA (Received 2 January 1989; in revised form ... 4, the significant noise level on the signals, and the high degree to which the Abel transform is sensitive to such ...

Research paper thumbnail of Time-of-flight mass spectrometry as a tool for speciation analysis

Spectrochimica Acta Part B: Atomic Spectroscopy, 2000

Time-of-flight mass spectrometry TOFMS has recently been introduced as an alternative to scanning... more Time-of-flight mass spectrometry TOFMS has recently been introduced as an alternative to scanning-based mass analyzers for use in elemental analysis. Coupled with an inductively coupled plasma or alternative ion source, TOFMS can produce a complete atomic mass spectrum in less than 50 s. Because of this high spectral-generation rate, even very brief transient signals can be recorded with high fidelity. Furthermore, each mass spectrum is derived from the same sub-microsecond pulse of ions, so high precision can be achieved by using either isotope-ratioing or internal standardization techniques. All these features make TOFMS attractive for the measurement of transient signals, such as those commonly encountered in speciation analysis. In this paper, the capabilities of TOFMS in speciation will be demonstrated through the coupling of gas chromatography and capillary electrophoresis with an inductively coupled plasma-TOFMS. Additionally, the development of novel switched gas sampling glow discharge Ž. GSGD ionization sources will be described and their role in chemical speciation will be evaluated. The switched GSGD has the ability to collect both atomic and molecular mass spectra in rapid succession, to provide additional Ž information about chemical species. The coupling of various sample introduction systems flow-cell, exponential. dilutor, capillary gas chromatography and electrothermal vaporization to the GSGD is outlined.

Research paper thumbnail of First Distance-of-Flight Instrument: Opening a New Paradigm in Mass Spectrometry

Journal of The American Society for Mass Spectrometry, 2011

Research paper thumbnail of First inductively coupled plasma-distance-of-flight mass spectrometer: instrument performance with a microchannel plate/phosphor imaging detector

Journal of Analytical Atomic Spectrometry, 2013

ABSTRACT Here we describe the first combination of a Distance-of-Flight Mass Spectrometry (DOFMS)... more ABSTRACT Here we describe the first combination of a Distance-of-Flight Mass Spectrometry (DOFMS) instrument and an inductively coupled plasma (ICP) ion source. DOFMS is a velocity-based MS technique in which ions of a range of mass-to-charge (m/z) values are detected simultaneously along the length of a spatially selective detector. As a relative of time-of-flight (TOF) MS, DOFMS leverages benefits from both TOFMS and spatially dispersive MS. The simultaneous detection of groups of m/z values improves dynamic range by spreading ion signal across many detector elements and reduces correlated noise by signal ratioing. To ascertain the performance characteristics of the ICP-DOFMS instrument, we have employed a microchannel-plate/phosphor detection assembly with a scientific CCD to capture images of the phosphor plate. With this simple (and commercially available) detection scheme, elemental detection limits from 2-30 ng L-1 and a linear dynamic range of 5 orders of magnitude (10-106 ng L-1) have been demonstrated. Additionally, a competitive isotope-ratio precision of 0.1% RSD has been achieved with only a 6 s signal integration period. In addition to first figures of merit, this paper outlines technical considerations for the design of the ICP-DOFMS.

Research paper thumbnail of A new generation of instrumentation and capabilities for atomic mass spectrometry

Guangpuxue-yu-guangpu-fenxi, 1999

Research paper thumbnail of A new generation of instrumentation and capabilities for atomic mass spectrometry

Guang pu xue yu guang pu fen xi = Guang pu, 1999

Research paper thumbnail of How Constant Momentum Acceleration Decouples Energy and Space Focusing in Distance–of–Flight and Time–of–Flight Mass Spectrometries

Journal of The American Society for Mass Spectrometry, 2013

Resolution in time-of-flight mass spectrometry (TOFMS) is ordinarily limited by the initial energ... more Resolution in time-of-flight mass spectrometry (TOFMS) is ordinarily limited by the initial energy and space distributions within an instrument's acceleration region and by the length of the field-free flight zone. With gaseous ion sources, these distributions lead to systematic flight-time errors that cannot be simultaneously corrected with conventional static-field ion-focusing devices (i.e., an ion mirror). It is known that initial energy and space distributions produce non-linearly correlated errors in both ion velocity and exit time from the acceleration region. Here we reinvestigate an old acceleration technique, constant-momentum acceleration (CMA), to decouple the effects of initial energy and space distributions. In CMA, only initial ion energies (and not their positions) affect the velocity ions gain. Therefore, with CMA, the spatial distribution within the acceleration region can be manipulated without creating ion-velocity error. The velocity differences caused by a spread in initial ion energy can be corrected with an ion mirror. We discuss here the use of CMA and independent focusing of energy and space distributions for both distance-of-flight mass spectrometry (DOFMS) and TOFMS. Performance characteristics of our CMA-DOFMS and CMA-TOFMS instrument, fitted with a glow-discharge ionization source, are described. In CMA-DOFMS, resolving powers (FWHM) of greater than 1000 are achieved for atomic ions with a flight length of 285 mm. In CMA-TOFMS, only ions over a narrow range of m/z values can be energy-focused; however, the technique offers improved resolution for these focused ions, with resolving powers of greater than 2000 for a separation distance of 350 mm.

Research paper thumbnail of Optical waveguide sensors in analytical chemistry: today's instrumentation, applications and trends for future development

Fresenius' Journal of Analytical Chemistry

Current concepts for chemical and biochemical sensing based on detection with optical waveguides ... more Current concepts for chemical and biochemical sensing based on detection with optical waveguides are reviewed. The goals are to provide a framework for classifying such sensors and to assist a designer in selecting the most suitable detection techniques and waveguide arrangements. Sensor designs are categorized on the basis of the five parameters that completely describe a light wave: its amplitude, wavelength, phase, polarization state and timedependent waveform. In the fabrication of a successful sensor, the physical or chemical property of the determined species and the particular light wave parameter to detect it should be selected with care since they jointly dictate the sensitivity, stability, selectivity and accuracy of the eventual measurement. The principle of operation, the nature or the detected optical signal, instrumental requirements for practical applications, and associated problems are analyzed for each category of sensors. Two sorts of sensors are considered: those based on direct spectroscopic detection of the analyte, and those in which the analyte is determined indirectly through use of an analyte-sensitive reagent. Key areas of recent study, useful practical applications, and trends in future development of optical waveguide chemical and biochemical sensors are considered.

Research paper thumbnail of The 2017 Plasma Roadmap: Low temperature plasma science and technology

Journal of Physics D: Applied Physics

Research paper thumbnail of Theophilus Redwood Lecture. Models, measurements, methods and machines in analytical spectrometry

Analytical Proceedings, 1986

Research paper thumbnail of Plasma diagnostic on a low-flow plasma for inductively coupled plasma optical emission spectrometry

Spectrochimica Acta Part B: Atomic Spectroscopy, 2008

In order to elucidate the fundamental properties of a low-flow inductively coupled plasma (ICP) o... more In order to elucidate the fundamental properties of a low-flow inductively coupled plasma (ICP) operated under total Ar consumption of 0.6 L min − 1 , excitation temperatures, rotational temperatures, ionization temperatures, electron temperatures, and electron number densities were studied with optical emission based methods. The plasma was operated in the SHIP torch (Static High Sensitivity ICP), which was designed for optical emission spectrometric detection. For the first time, this plasma was studied in a laterally resolved manner and at selected observation heights. The Boltzmann plot method was used to obtain excitation and rotational temperatures in the range of 5000-8000 K and 3100-4000 K, respectively. Electron temperatures were determined from the line-to-continuum method to be as high as 9000 K in the analytical channel. The electron number densities were determined with the hydrogen-beta line method and found to be in the range of 5-8×10 15 cm − 3 at 1.1 kW radio frequency (rf) power. Ionization temperatures between 6250 and 7750 K were found at different observation heights in the plasma. The influence of applied rf powers between 0.9 and 1.2 kW on selected key parameters was investigated. The low-flow plasma exhibited temperature ranges similar to those prevailing in conventional ICP sources.

Research paper thumbnail of Surface elemental mapping via glow discharge optical emission spectroscopy

Spectrochimica Acta Part B: Atomic Spectroscopy, 2012

ABSTRACT Glow discharge optical emission spectroscopy (GDOES) has evolved in the last couple of d... more ABSTRACT Glow discharge optical emission spectroscopy (GDOES) has evolved in the last couple of decades from direct bulk solid analysis to a high resolution depth-profiling technique. However, the achievable lateral resolution has been historically restricted to the diameter of the sputtered area, i.e. some millimetres. Recently, there has been a push toward characterizing and improving the GDOES limits of lateral resolution. In consequence, a door has been opened for applications to take advantage of the new information dimensions that the technique affords.It is important to sum what has been accomplished so far to clarify the current possibilities and opportunities for development. It will become evident that the data acquisition requirements of GDOES elemental mapping can only be met via spectral imaging. Accordingly, the studies performed to date will be reviewed with emphasis on the spectral imaging geometry that has been utilized.

Research paper thumbnail of Spatially resolved ground-state number densities of calcium and strontium ion in an inductively coupled plasma in contact with an inductively coupled plasma mass spectrometry sampling interface

Spectrochimica Acta Part B: Atomic Spectroscopy, 2003

Radial profiles of Ca and Sr ion number densities in an ICP at 6, 7 and 8 mm above the load coil ... more Radial profiles of Ca and Sr ion number densities in an ICP at 6, 7 and 8 mm above the load coil (ALC) and at 1.25 kW of input rf power were measured by saturated fluorescence induced by an Nd:YAG laser-pumped dye laser at 396.85 nm and 421.55 nm, respectively. The measurements were performed in the presence and in the absence of an ICP-MS sampling interface. When in place, the orifice of the sampling cone was positioned 13 mm ALC on the axis of the plasma torch. The results show that the interface can either raise or lower the ion number densities, depending on the central-gas-flow rate, and can cause a vertical shift of their entire radial profiles with respect to the ICP axis. The introduction of Li, Cu and Zn as matrix elements reduced the ion number densities of the analytes, both in the presence and in the absence of the interface. This effect became more significant at higher central-gasflow rates. In addition, the peak value of the radial ion number density was found to depend strongly on the centralgas-flow rate maximum occurred at 1.1 lymin for both Ca ion and Sr ion under the ICP operating conditions used in this study. This behavior is very similar to the mass spectrometric signals previously observed downstream and reported in the literature. ᮊ

Research paper thumbnail of Fundamental studies on a planar-cathode direct current glow discharge. Part II: numerical modeling and comparison with laser scattering experiments

Spectrochimica Acta Part B: Atomic Spectroscopy, 2004

We have calculated the gas temperature, electron density, electron energy distribution function, ... more We have calculated the gas temperature, electron density, electron energy distribution function, and average electron energy, as a function of distance from the cathode, with a two-dimensional model for an argon direct-current glow discharge. The calculated results are compared with measured values from Rayleigh-and Thomson-scattering experiments, for different values of voltage, pressure and electrical current. The gas-temperature distribution and electron-density profile were found to be in reasonable agreement with experiment. For the electron energy, model and experiment give complementary information, since the experiment is able to detect only the thermal and low-energy electrons, whereas the model focuses mainly on the high-energy electrons. ᮊ

Research paper thumbnail of An apparatus for measuring Thomson scattering from an inductively coupled plasma

Spectrochimica Acta Part B: Atomic Spectroscopy, 1985

An experimental arrangement is presented which has been proven capable of measuring Thomson scatt... more An experimental arrangement is presented which has been proven capable of measuring Thomson scattering from an inductively coupled plasma (ICP). This system has been shown to reject stray light to a sufficient extent that useful scattering signals can be measured as near as 0.3 nm from the incident laser wavelength. In this paper, design considerations are discussed and a viable experimental system is described. Preliminary Thomson scattering results are presented.

Research paper thumbnail of Effect of mass spectrometric sampling interface on the fundamental parameters of an inductively coupled plasma as a function of its operating conditions

Spectrochimica Acta Part B: Atomic Spectroscopy, 2007

Research paper thumbnail of A steady-state approach to evaluation of proposed excitation mechanisms in the analytical ICP

Spectrochimica Acta Part B: Atomic Spectroscopy, 1986

A method is described for the eval~tion of propose-d analyte ionization and excitation mechanisms... more A method is described for the eval~tion of propose-d analyte ionization and excitation mechanisms in the analytical ICP. In the method, a steady-state kinetic expression is derived for each proposed mechaniim; the resulting expression predicts a linear re~tio~~p between analyte emission and the concentrations or concentration products of species important in the excitation and deactivation processes. The application of this approach to Ca ionization and excitation is described for the region 15 mm above the load coil and O-5 mm from the center of the plasma Importantly, the conumtration of ground-state Ca seems not to be important in the production of either excited Ca atoms or ions. Rather, Ca atom excitation appears to occur by means of three-body or radiative Ca *electron recombination. In contrast, Ca' seems to be excited directly by electron impact. Among the mechanisms evaluated here, depopulation of excited-state calcium species by collisional deactivation appears to be less significant than radiative decay to the ground state.