Nancy Miller-Ihli - Profile on Academia.edu (original) (raw)

Papers by Nancy Miller-Ihli

Characterization of a diet reference material for 17 elements

Analytical Chemistry, 1986

A freeze-dried diet reference material was prepared from commonly consumed everyday foods. Concen... more A freeze-dried diet reference material was prepared from commonly consumed everyday foods. Concentrations of major (Mg, Ca, Na, K and P), minor (Mn, Zn, Fe, Cu, and Al), and trace elements (Cr, Ni, Co, Mo, As, Se, and Cd) in this diet material were determined by the authors and 10 collaborating laboratories using a total of 10 different analytical techniques. Good agreement between concentration values determined by the different laboratories enabled the authors to computer recommended values and uncertainties for these 17 elements. Values for proximates as well as several other nutrients were also reported by collaborators. This diet material is available to the scientific community as Reference Material 8431 through the National Bureau of Standard's Office of Standard Reference Materials.

Characterization of a mixed diet reference material (NBS RM 8431) for inorganic elements and selected organic nutrients

Fresenius' Zeitschrift f�r Analytische Chemie, 1987

ABSTRACT

Spectrochimica Acta Part B: Atomic Spectroscopy, 2004

Micro-high-performance liquid chromatography interfaced to inductively coupled plasma mass spectr... more Micro-high-performance liquid chromatography interfaced to inductively coupled plasma mass spectrometry was optimized for the determination and separation of a mixture of cobalt containing species. Four cobalamin species (cyanocobalamin, hydroxocobalamin, methylcobalamin, and 5V-deoxyadenosylcobalamin) representing the various forms of vitamin B12 as well as the harmful corrinoid analogue cobinamide dicyanide were separated using reversed-phase microcapillary chromatography with columns containing C18 packing material with a 2-Am particle size. Selection of organic solvents for the separation took into consideration compatibility with the inductively coupled plasma mass spectrometer being used for element specific detection. Optimized method conditions included use of a methanol gradient and make-up solution for the nebulizer. Some issues associated with dead volume were overcome by the extension of the gradient program. The total analysis time was 52 min. The column-to-column variability was evaluated and was found to be very reasonable (9% RSD on average), confirming that this method is rugged and that the technology should be easily transferred to other laboratories.

Trace element determinations in food and biological samples using ICP-MS

ABSTRACT

A direct comparison of electrothermal atomic absorption and emission spectrometry for the analysis of chromium in urine

Staircase modulation wave form for continuum source atomic absorption spectrometry

Analytical Chemistry, 1984

ABSTRACT A new staircase modulation wave form is implemented for extended range continuum source ... more ABSTRACT A new staircase modulation wave form is implemented for extended range continuum source AAS (atomic absorption spectrometry) measurements, which improves performance and simplifies the computation of concentrations. This wave form facilitates the computation of two absorbances of different sensitivity for every atomization. The resulting two calibration curves allow 4-6 orders of magnitude of concentration to be covered effectively. Calibration curves and concentration error curves are compared for Mn, Zn, Fe, Cu, and Mg with the old bi-Gaussian and the new staircase modulation wave forms. Linearities, sensitivities, and SNR's (signal-to-noise ratios) of the curves obtained by using the two modulation wave forms are compared. In addition, accuracy using the staircase modulation wave form was evaluated by running National Bureau of Standards (NBS) standard reference materials (SRM's). 6 references, 13 figures, 1 table.

Simultaneous multi-element analysis by carbon furnace atomic-emission spectrometry

The Analyst, 1983

The Analyst, 1998

The distribution concentration of chemical species in a sample is dictated by the physical and ch... more The distribution concentration of chemical species in a sample is dictated by the physical and chemical properties of the matrix. As such, when a sample is pre-treated, in any way, there is a potential for redistribution of homologous species. The extent of this analyte redistribution is determined by both thermodynamic properties of species (e.g., changes in concentrations of species according to their equilibrium expressions) and kinetic properties (e.g., the rate of the reactions compared with the duration of sample preparation and analysis). The redistributions of analyte species as a function of several experimental parameters (e.g., time, solution pH, injection methods and calibration methods) are illustrated in this paper. Whereas rabbit metallothionein protein showed a stability of more than a few days under certain storage conditions, coenzyme-B 12 was rapidly degraded in less than 2 h. pH studies showed that the migration of free Cd 2+ ions in rabbit metallothionein was not significantly affected unless the pH of the solution exceeds the solubility limit of the metal hydroxide. However, pH-sensitive compounds such as vitamin B 12 showed significant changes in the migration time and analyte composition. The injection studies suggested that electrokinetic injection may produce biased results, in favor of species that have higher electrophoretic mobility. Hydrodynamic injection will produce a result that is more representative of the initial sample composition.

Two simple interface designs for capillary electrophoresis–inductively coupled plasma mass spectrometry†

The Analyst, 1998

The design and implementation of two different interfaces for capillary electrophoresis–inductive... more The design and implementation of two different interfaces for capillary electrophoresis–inductively coupled plasma mass spectrometry (CE–ICP-MS) are described. These interfaces will allow for on-line analysis of CE effluents with ICP-MS detection. One interface is based on a ...

Simultaneous multi-element analysis by continuum source atomic-absorption spectrometry with graphite probe electrothermal atomisation

The Analyst, 1985

Spectrochimica Acta Part B: Atomic Spectroscopy, 2004

A low flow, parallel path Mira Mist CE nebulizer designed for capillary electrophoresis (CE) was ... more A low flow, parallel path Mira Mist CE nebulizer designed for capillary electrophoresis (CE) was evaluated as a function of make-up solution flow rate, composition, and concentration, as well as the nebulizer gas flow rate. This research was conducted in support of a project related to the separation and quantification of cobalamin (vitamin B-12) species using microseparation techniques combined with inductively coupled plasma mass spectrometry (ICP-MS) detection. As such, Co signals were monitored during the nebulizer characterization process. Transient effects in the ICP were studied to evaluate the suitability of using gradients for microseparations and the benefit of using methanol for the make-up solution was demonstrated. Co signal response changed significantly as a function of changing methanol concentrations of the make-up solution and maximum signal enhancement was seen at 20% methanol with a 15 Al/min flow rate. Evaluation of the effect of changing the nebulizer gas flow rates showed that argon flows from 0.8 to 1.2 l/min were equally effective. The Mira Mist CE parallel path nebulizer was then evaluated for interfacing capillary microseparation techniques including capillary electrophoresis (CE) and micro high performance liquid chromatography (AHPLC) to inductively coupled plasma mass spectrometry (ICP-MS). A mixture of four cobalamin species standards (cyanocobalamin, hydroxocobalamin, methylcobalamin, and 5V deoxyadenosylcobalamin) and the corrinoid analogue cobinamide dicyanide were successfully separated using both CE-ICP-MS and AHPLC-ICP-MS using the parallel path nebulizer with a make-up solution containing 20% methanol with a flow rate of 15 Al/min.

Spectrochimica Acta Part B: Atomic Spectroscopy, 2005

Four different, low flow parallel path Mira Mist CE nebulizers were evaluated and compared in sup... more Four different, low flow parallel path Mira Mist CE nebulizers were evaluated and compared in support of an ongoing project related to the use of microseparation techniques interfaced to inductively coupled plasma mass spectrometry for the quantification of cobalamin species (Vitamin B12). For the characterization of the different Mira Mist CE nebulizers, the nebulizer orientation as well as the effect of methanol on analytical response was the focus of the study. The position of the gas outlet on the nebulizer which consistently provided the maximum signal was when it was rotated to the 11 o'clock position when the nebulizer is viewed end-on. With this orientation the increased signal may be explained by the fact that the cone angle of the aerosol is such that the largest percentage of the aerosol is directed to the center of the spray chamber and consequently into the plasma. To characterize the nebulizer's performance, the signal response of a multielement solution containing elements with a variety of ionization potentials was used. The selection of elements with varying ionization energies and degrees of ionization was essential for a better understanding of observed increases in signal enhancement when methanol was used. Two different phenomena contribute to signal enhancement when using methanol: the first is improved transport efficiency and the second is the ''carbon enhancement effect''. The net result was that as much as a 30-fold increase in signal was observed for As and Mg when using a make-up solution of 20% methanol at a 15 AL/min flow rate which is equivalent to a net volume of 3 AL/min of pure methanol.

Spectrochimica Acta Part B: Atomic Spectroscopy, 1984

Several curve fitting methods, including linear, quadratic, and rational least squares fits and l... more Several curve fitting methods, including linear, quadratic, and rational least squares fits and linear, cubic sphne, and Stineman interpolations, are evaluated for their ability to fit highly nonlinear atomic absorption analytical calibration curves. In addition, the number of standards required to effectively calibrate a dynamic range covering 3 orders of magnitude of concentration is determined. Finally, the concentration ranges providing minimum relative concentration precision (RCP) are identified and the slopes of the calibration curves in these ranges are noted. Concentration ranges of minimum RCP also provide minimum curve fitting errors and generally have log-log slopes of approximately 0.5 indicating that linearity alone is not a sufficient criterion for choosing suitable calibration and curve fitting concentration ranges. AN IMPORTANT aspect of quantitative spectroscopic methods of analysis is the shape of the analytical calibration curve as well as the concentration range over which calibration may be achieved. The lower concentration limit has already received much attention [l-4] and is usually defined in terms of the signal-to-noise ratio (SNR) or reproducibility of the blank signal. The upper concentration limit is less well defined. Analysts have ordinarily preferred to work with linear calibration [S-6] and, as a result, the upper limit has sometimes been defined as the concentration at which the observed analytical curve deviates from linearity by some specified amount, Linear calibration curves are indeed ideal from the point of view of ease of curve fitting and the number of standards required to define the curve; however, the wide availability of on-line computational facilities has made it much easier for the analyst to practically deal with calibration curve nonlinearity [6-121. In atomic spectroscopy it is common for calibration curves to be linear at low concentrations and nonlinear at high concentrations, generally exhibiting concave down curvature toward the concentration axis. Sometimes the analytical signal exhibits a saturation effect, with the calibration curve approaching a constant value at high

Spectrochimica Acta Part B: Atomic Spectroscopy, 2001

Spectrochimica Acta Part B: Atomic Spectroscopy, 1995

An international collaborative study was initiated to evaluate the current state-of-the-art for s... more An international collaborative study was initiated to evaluate the current state-of-the-art for solid sampling. Samples were sent to 28 laboratories and data were received from 18 collaborators, 16 of which reported slurry results. A preliminary check of performance using NIST SRM 1643c acidified water, showed that at least 13 laboratories were able to provide accurate results within _+ 10% of the mean certified Pb and Cr concentrations. The focus of this work was slurry analytical data reported by collaborators. Average performance by collaborators for the determination of Pb in NIST SRM 2704 Buffalo River Sediment was 103% recovery based on the mean certified reference value and was 84% recovery based on the mean certified reference value for NRCC PACS-1, a marine estuarine sediment, which was identified to collaborators as an unknown sediment. Average performance by collaborators for Cr in SRM 2704 was 96% based on the mean certified reference value and was 78% recovery based on the mean certified reference value for PACS-1. The use of secondary wavelengths and the importance of analysis of a representative subsample are highlighted. Possible problems leading to inaccurate results being reported by collaborators are discussed including the use of mini-flows, matrix modifiers, low atomization temperatures, short atomization times, and expulsion losses. * This paper was published in the Special Issue on Sample Introduction in Atomic Spectrometry.

Journal of Food Composition and Analysis, 1989

Increasing interest in the copper (Cu) intake of Americans hasgenerated a need for the compilatio... more Increasing interest in the copper (Cu) intake of Americans hasgenerated a need for the compilation, evaluation, and improvement of data for Cu in foods. In order to estimate dietary Cu intake, accurate and precise Cu values for foods are needed. A system of criteria developed to evaluate the quality of published selenium data has been adapted to evaluate analytical data for Cu in foods. Mean Cu values for each food were calculated from the evaluated data and combined with USDA frequency of consumption data, resulting in a list of 2 18 major contributors of dietary Cu. The richest sources of Cu are legumes, wheat bran cereals, organ meats, shellfish, and grains. Confidence codes, indicators of the relative degree of confidence the user of the data can have in that mean value, were included. More than half of the mean values for the foods listed are of limited quality or result from a limited quantity of data, indicating a need for improvement in food Cu data. This proposed dynamic system for the compilation and evaluation of Cu data can be used to generate Cu data bases for specific purposes, provide a ranked list of foods which are significant contributors of that nutrient, and establish priorities for further improvements in the data base. o 1989 Academic press, IX.

Trace Element Composition of Municipal Waters in the United States: A Comparison of ICP-AES and ICP-MS Methods

Journal of Food Composition and Analysis, 2001

... Anal. 13 (2000), pp. 379–389. Abstract | PDF (161 K) | View Record in Scopus | Cited By in Sc... more ... Anal. 13 (2000), pp. 379–389. Abstract | PDF (161 K) | View Record in Scopus | Cited By in Scopus (58). 9. MA Saleh, E. Ewane, J. Jones and BL Wilson, Chemical evaluation of commercial bottled drinking water from Egypt. J. Food Comp. Anal. 14 (2001), pp. 127–152. ...

Journal of Food Composition and Analysis, 2003

Recently, a study was conducted to look at the trace element content of municipal waters sampled ... more Recently, a study was conducted to look at the trace element content of municipal waters sampled around the United States. This was a collaborative project defined by representatives of the Nutrient Data Laboratory and the Food Composition Laboratory of the United States Department of Agriculture. As part of the study, the fluoride content of nationally representative water samples was measured since water is one of the principal sources of fluoride in the US diet. This study served as a pilot for planning a more extensive future nationwide sampling. Samples were analyzed using a separate reference electrode and ion selective electrode with TISAB II buffer. The calibration range was from 0.5 to 3.0 ppm. Accuracy of the method was validated by analyzing NIST SRM 2671a Fluoride in Freeze-Dried Urine. Results from the municipal water study clearly showed that the distribution of fluoride in US municipal waters is bi-modal. That is to say, because of the fact that ambient levels are typically extremely low, the concentration of fluoride is basically quantized. Either the water is fluoridated and contains approximately 1 ppm of fluoride or it is not fluoridated with undetectable fluoride concentration. The distribution of these data make it difficult to assign a meaningful average value useful to health professionals and consumers to assess fluoride intake. This study revealed that approximately 40% of the water samples from this nationwide sampling were fluoridated with a mean concentration of 1.0170.15 mg/ml.

Conference reports

Journal of Analytical Atomic Spectrometry, 1989

Comparison of sodium chloride and magnesium chloride interferences in continuum source atomic absorption spectrometry with wall, platform and probe electrothermal atomization

Journal of Analytical Atomic Spectrometry, 1992

ABSTRACT Various masses between 10 and 500 µg of NaCl or MgCl2 were added to 1 ng of Cr, Cu and M... more ABSTRACT Various masses between 10 and 500 µg of NaCl or MgCl2 were added to 1 ng of Cr, Cu and Mn, 2 ng of Cd and Pb and 4 ng of Co, Mo, Ni and V to study the interferences encountered when wall, platform and probe atomization are applied in continuum source electrothermal atomic absorption spectrometry. No char step was used and a compromise atomization temperature of 2700 °C was selected for simultaneous multi-element measurements. No great difference was observed in the analyte signal recovery values obtained with the three atomization modes when NaCl was the interferent. However, with MgCl2, greater interferences were observed with wall atomization. Overall, probe atomization proved as good as, if not better than platform atomization for the elements considered. With both procedures, freedom from NaCl or MgCl2 interferences was achieved at chloride salt: analyte mole ratios of 1 × 103–1 × 105. Although it was not possible to make a definitive assessment of the procedures responsible for the interferences observed, there was some evidence that vapour-phase chemical effects are more important for MgCl2 than for NaCl, occlusion of Cd, Mn and Pb occurs in NaCl and expulsion of Co, Cr, Cu, Mn and Ni occurs due to co-vaporization with NaCl.

Characterization of a diet reference material for 17 elements

Analytical Chemistry, 1986

A freeze-dried diet reference material was prepared from commonly consumed everyday foods. Concen... more A freeze-dried diet reference material was prepared from commonly consumed everyday foods. Concentrations of major (Mg, Ca, Na, K and P), minor (Mn, Zn, Fe, Cu, and Al), and trace elements (Cr, Ni, Co, Mo, As, Se, and Cd) in this diet material were determined by the authors and 10 collaborating laboratories using a total of 10 different analytical techniques. Good agreement between concentration values determined by the different laboratories enabled the authors to computer recommended values and uncertainties for these 17 elements. Values for proximates as well as several other nutrients were also reported by collaborators. This diet material is available to the scientific community as Reference Material 8431 through the National Bureau of Standard's Office of Standard Reference Materials.

Characterization of a mixed diet reference material (NBS RM 8431) for inorganic elements and selected organic nutrients

Fresenius' Zeitschrift f�r Analytische Chemie, 1987

ABSTRACT

Spectrochimica Acta Part B: Atomic Spectroscopy, 2004

Micro-high-performance liquid chromatography interfaced to inductively coupled plasma mass spectr... more Micro-high-performance liquid chromatography interfaced to inductively coupled plasma mass spectrometry was optimized for the determination and separation of a mixture of cobalt containing species. Four cobalamin species (cyanocobalamin, hydroxocobalamin, methylcobalamin, and 5V-deoxyadenosylcobalamin) representing the various forms of vitamin B12 as well as the harmful corrinoid analogue cobinamide dicyanide were separated using reversed-phase microcapillary chromatography with columns containing C18 packing material with a 2-Am particle size. Selection of organic solvents for the separation took into consideration compatibility with the inductively coupled plasma mass spectrometer being used for element specific detection. Optimized method conditions included use of a methanol gradient and make-up solution for the nebulizer. Some issues associated with dead volume were overcome by the extension of the gradient program. The total analysis time was 52 min. The column-to-column variability was evaluated and was found to be very reasonable (9% RSD on average), confirming that this method is rugged and that the technology should be easily transferred to other laboratories.

Trace element determinations in food and biological samples using ICP-MS

ABSTRACT

A direct comparison of electrothermal atomic absorption and emission spectrometry for the analysis of chromium in urine

Staircase modulation wave form for continuum source atomic absorption spectrometry

Analytical Chemistry, 1984

ABSTRACT A new staircase modulation wave form is implemented for extended range continuum source ... more ABSTRACT A new staircase modulation wave form is implemented for extended range continuum source AAS (atomic absorption spectrometry) measurements, which improves performance and simplifies the computation of concentrations. This wave form facilitates the computation of two absorbances of different sensitivity for every atomization. The resulting two calibration curves allow 4-6 orders of magnitude of concentration to be covered effectively. Calibration curves and concentration error curves are compared for Mn, Zn, Fe, Cu, and Mg with the old bi-Gaussian and the new staircase modulation wave forms. Linearities, sensitivities, and SNR's (signal-to-noise ratios) of the curves obtained by using the two modulation wave forms are compared. In addition, accuracy using the staircase modulation wave form was evaluated by running National Bureau of Standards (NBS) standard reference materials (SRM's). 6 references, 13 figures, 1 table.

Simultaneous multi-element analysis by carbon furnace atomic-emission spectrometry

The Analyst, 1983

The Analyst, 1998

The distribution concentration of chemical species in a sample is dictated by the physical and ch... more The distribution concentration of chemical species in a sample is dictated by the physical and chemical properties of the matrix. As such, when a sample is pre-treated, in any way, there is a potential for redistribution of homologous species. The extent of this analyte redistribution is determined by both thermodynamic properties of species (e.g., changes in concentrations of species according to their equilibrium expressions) and kinetic properties (e.g., the rate of the reactions compared with the duration of sample preparation and analysis). The redistributions of analyte species as a function of several experimental parameters (e.g., time, solution pH, injection methods and calibration methods) are illustrated in this paper. Whereas rabbit metallothionein protein showed a stability of more than a few days under certain storage conditions, coenzyme-B 12 was rapidly degraded in less than 2 h. pH studies showed that the migration of free Cd 2+ ions in rabbit metallothionein was not significantly affected unless the pH of the solution exceeds the solubility limit of the metal hydroxide. However, pH-sensitive compounds such as vitamin B 12 showed significant changes in the migration time and analyte composition. The injection studies suggested that electrokinetic injection may produce biased results, in favor of species that have higher electrophoretic mobility. Hydrodynamic injection will produce a result that is more representative of the initial sample composition.

Two simple interface designs for capillary electrophoresis–inductively coupled plasma mass spectrometry†

The Analyst, 1998

The design and implementation of two different interfaces for capillary electrophoresis–inductive... more The design and implementation of two different interfaces for capillary electrophoresis–inductively coupled plasma mass spectrometry (CE–ICP-MS) are described. These interfaces will allow for on-line analysis of CE effluents with ICP-MS detection. One interface is based on a ...

Simultaneous multi-element analysis by continuum source atomic-absorption spectrometry with graphite probe electrothermal atomisation

The Analyst, 1985

Spectrochimica Acta Part B: Atomic Spectroscopy, 2004

A low flow, parallel path Mira Mist CE nebulizer designed for capillary electrophoresis (CE) was ... more A low flow, parallel path Mira Mist CE nebulizer designed for capillary electrophoresis (CE) was evaluated as a function of make-up solution flow rate, composition, and concentration, as well as the nebulizer gas flow rate. This research was conducted in support of a project related to the separation and quantification of cobalamin (vitamin B-12) species using microseparation techniques combined with inductively coupled plasma mass spectrometry (ICP-MS) detection. As such, Co signals were monitored during the nebulizer characterization process. Transient effects in the ICP were studied to evaluate the suitability of using gradients for microseparations and the benefit of using methanol for the make-up solution was demonstrated. Co signal response changed significantly as a function of changing methanol concentrations of the make-up solution and maximum signal enhancement was seen at 20% methanol with a 15 Al/min flow rate. Evaluation of the effect of changing the nebulizer gas flow rates showed that argon flows from 0.8 to 1.2 l/min were equally effective. The Mira Mist CE parallel path nebulizer was then evaluated for interfacing capillary microseparation techniques including capillary electrophoresis (CE) and micro high performance liquid chromatography (AHPLC) to inductively coupled plasma mass spectrometry (ICP-MS). A mixture of four cobalamin species standards (cyanocobalamin, hydroxocobalamin, methylcobalamin, and 5V deoxyadenosylcobalamin) and the corrinoid analogue cobinamide dicyanide were successfully separated using both CE-ICP-MS and AHPLC-ICP-MS using the parallel path nebulizer with a make-up solution containing 20% methanol with a flow rate of 15 Al/min.

Spectrochimica Acta Part B: Atomic Spectroscopy, 2005

Four different, low flow parallel path Mira Mist CE nebulizers were evaluated and compared in sup... more Four different, low flow parallel path Mira Mist CE nebulizers were evaluated and compared in support of an ongoing project related to the use of microseparation techniques interfaced to inductively coupled plasma mass spectrometry for the quantification of cobalamin species (Vitamin B12). For the characterization of the different Mira Mist CE nebulizers, the nebulizer orientation as well as the effect of methanol on analytical response was the focus of the study. The position of the gas outlet on the nebulizer which consistently provided the maximum signal was when it was rotated to the 11 o'clock position when the nebulizer is viewed end-on. With this orientation the increased signal may be explained by the fact that the cone angle of the aerosol is such that the largest percentage of the aerosol is directed to the center of the spray chamber and consequently into the plasma. To characterize the nebulizer's performance, the signal response of a multielement solution containing elements with a variety of ionization potentials was used. The selection of elements with varying ionization energies and degrees of ionization was essential for a better understanding of observed increases in signal enhancement when methanol was used. Two different phenomena contribute to signal enhancement when using methanol: the first is improved transport efficiency and the second is the ''carbon enhancement effect''. The net result was that as much as a 30-fold increase in signal was observed for As and Mg when using a make-up solution of 20% methanol at a 15 AL/min flow rate which is equivalent to a net volume of 3 AL/min of pure methanol.

Spectrochimica Acta Part B: Atomic Spectroscopy, 1984

Several curve fitting methods, including linear, quadratic, and rational least squares fits and l... more Several curve fitting methods, including linear, quadratic, and rational least squares fits and linear, cubic sphne, and Stineman interpolations, are evaluated for their ability to fit highly nonlinear atomic absorption analytical calibration curves. In addition, the number of standards required to effectively calibrate a dynamic range covering 3 orders of magnitude of concentration is determined. Finally, the concentration ranges providing minimum relative concentration precision (RCP) are identified and the slopes of the calibration curves in these ranges are noted. Concentration ranges of minimum RCP also provide minimum curve fitting errors and generally have log-log slopes of approximately 0.5 indicating that linearity alone is not a sufficient criterion for choosing suitable calibration and curve fitting concentration ranges. AN IMPORTANT aspect of quantitative spectroscopic methods of analysis is the shape of the analytical calibration curve as well as the concentration range over which calibration may be achieved. The lower concentration limit has already received much attention [l-4] and is usually defined in terms of the signal-to-noise ratio (SNR) or reproducibility of the blank signal. The upper concentration limit is less well defined. Analysts have ordinarily preferred to work with linear calibration [S-6] and, as a result, the upper limit has sometimes been defined as the concentration at which the observed analytical curve deviates from linearity by some specified amount, Linear calibration curves are indeed ideal from the point of view of ease of curve fitting and the number of standards required to define the curve; however, the wide availability of on-line computational facilities has made it much easier for the analyst to practically deal with calibration curve nonlinearity [6-121. In atomic spectroscopy it is common for calibration curves to be linear at low concentrations and nonlinear at high concentrations, generally exhibiting concave down curvature toward the concentration axis. Sometimes the analytical signal exhibits a saturation effect, with the calibration curve approaching a constant value at high

Spectrochimica Acta Part B: Atomic Spectroscopy, 2001

Spectrochimica Acta Part B: Atomic Spectroscopy, 1995

An international collaborative study was initiated to evaluate the current state-of-the-art for s... more An international collaborative study was initiated to evaluate the current state-of-the-art for solid sampling. Samples were sent to 28 laboratories and data were received from 18 collaborators, 16 of which reported slurry results. A preliminary check of performance using NIST SRM 1643c acidified water, showed that at least 13 laboratories were able to provide accurate results within _+ 10% of the mean certified Pb and Cr concentrations. The focus of this work was slurry analytical data reported by collaborators. Average performance by collaborators for the determination of Pb in NIST SRM 2704 Buffalo River Sediment was 103% recovery based on the mean certified reference value and was 84% recovery based on the mean certified reference value for NRCC PACS-1, a marine estuarine sediment, which was identified to collaborators as an unknown sediment. Average performance by collaborators for Cr in SRM 2704 was 96% based on the mean certified reference value and was 78% recovery based on the mean certified reference value for PACS-1. The use of secondary wavelengths and the importance of analysis of a representative subsample are highlighted. Possible problems leading to inaccurate results being reported by collaborators are discussed including the use of mini-flows, matrix modifiers, low atomization temperatures, short atomization times, and expulsion losses. * This paper was published in the Special Issue on Sample Introduction in Atomic Spectrometry.

Journal of Food Composition and Analysis, 1989

Increasing interest in the copper (Cu) intake of Americans hasgenerated a need for the compilatio... more Increasing interest in the copper (Cu) intake of Americans hasgenerated a need for the compilation, evaluation, and improvement of data for Cu in foods. In order to estimate dietary Cu intake, accurate and precise Cu values for foods are needed. A system of criteria developed to evaluate the quality of published selenium data has been adapted to evaluate analytical data for Cu in foods. Mean Cu values for each food were calculated from the evaluated data and combined with USDA frequency of consumption data, resulting in a list of 2 18 major contributors of dietary Cu. The richest sources of Cu are legumes, wheat bran cereals, organ meats, shellfish, and grains. Confidence codes, indicators of the relative degree of confidence the user of the data can have in that mean value, were included. More than half of the mean values for the foods listed are of limited quality or result from a limited quantity of data, indicating a need for improvement in food Cu data. This proposed dynamic system for the compilation and evaluation of Cu data can be used to generate Cu data bases for specific purposes, provide a ranked list of foods which are significant contributors of that nutrient, and establish priorities for further improvements in the data base. o 1989 Academic press, IX.

Trace Element Composition of Municipal Waters in the United States: A Comparison of ICP-AES and ICP-MS Methods

Journal of Food Composition and Analysis, 2001

... Anal. 13 (2000), pp. 379–389. Abstract | PDF (161 K) | View Record in Scopus | Cited By in Sc... more ... Anal. 13 (2000), pp. 379–389. Abstract | PDF (161 K) | View Record in Scopus | Cited By in Scopus (58). 9. MA Saleh, E. Ewane, J. Jones and BL Wilson, Chemical evaluation of commercial bottled drinking water from Egypt. J. Food Comp. Anal. 14 (2001), pp. 127–152. ...

Journal of Food Composition and Analysis, 2003

Recently, a study was conducted to look at the trace element content of municipal waters sampled ... more Recently, a study was conducted to look at the trace element content of municipal waters sampled around the United States. This was a collaborative project defined by representatives of the Nutrient Data Laboratory and the Food Composition Laboratory of the United States Department of Agriculture. As part of the study, the fluoride content of nationally representative water samples was measured since water is one of the principal sources of fluoride in the US diet. This study served as a pilot for planning a more extensive future nationwide sampling. Samples were analyzed using a separate reference electrode and ion selective electrode with TISAB II buffer. The calibration range was from 0.5 to 3.0 ppm. Accuracy of the method was validated by analyzing NIST SRM 2671a Fluoride in Freeze-Dried Urine. Results from the municipal water study clearly showed that the distribution of fluoride in US municipal waters is bi-modal. That is to say, because of the fact that ambient levels are typically extremely low, the concentration of fluoride is basically quantized. Either the water is fluoridated and contains approximately 1 ppm of fluoride or it is not fluoridated with undetectable fluoride concentration. The distribution of these data make it difficult to assign a meaningful average value useful to health professionals and consumers to assess fluoride intake. This study revealed that approximately 40% of the water samples from this nationwide sampling were fluoridated with a mean concentration of 1.0170.15 mg/ml.

Conference reports

Journal of Analytical Atomic Spectrometry, 1989

Comparison of sodium chloride and magnesium chloride interferences in continuum source atomic absorption spectrometry with wall, platform and probe electrothermal atomization

Journal of Analytical Atomic Spectrometry, 1992

ABSTRACT Various masses between 10 and 500 µg of NaCl or MgCl2 were added to 1 ng of Cr, Cu and M... more ABSTRACT Various masses between 10 and 500 µg of NaCl or MgCl2 were added to 1 ng of Cr, Cu and Mn, 2 ng of Cd and Pb and 4 ng of Co, Mo, Ni and V to study the interferences encountered when wall, platform and probe atomization are applied in continuum source electrothermal atomic absorption spectrometry. No char step was used and a compromise atomization temperature of 2700 °C was selected for simultaneous multi-element measurements. No great difference was observed in the analyte signal recovery values obtained with the three atomization modes when NaCl was the interferent. However, with MgCl2, greater interferences were observed with wall atomization. Overall, probe atomization proved as good as, if not better than platform atomization for the elements considered. With both procedures, freedom from NaCl or MgCl2 interferences was achieved at chloride salt: analyte mole ratios of 1 × 103–1 × 105. Although it was not possible to make a definitive assessment of the procedures responsible for the interferences observed, there was some evidence that vapour-phase chemical effects are more important for MgCl2 than for NaCl, occlusion of Cd, Mn and Pb occurs in NaCl and expulsion of Co, Cr, Cu, Mn and Ni occurs due to co-vaporization with NaCl.