James M. Harnly

New Phenolic Components and Chromatographic Profiles of Green and Fermented Teas

A standardized profiling method based on liquid chromatography with diode array and electrospray ionization mass spectrometric detection (LC-DAD-ESI/MS) was applied to establish the phenolic profiles of 41 green teas and 25 fermented teas. More than 96 phenolic compounds were identified that allowed the teas to be organized into five groups. Epigallocatechin gallate (EGCG) was the major phenolic component of green tea made from mature leaves (group 2), while green tea made from the younger buds and leaves (group 1) contained lower flavonoid concentrations. Partially fermented teas (group 3) contained one-half the EGCG content of the green tea. Fully fermented black teas (group 4) had a trace of EGCG, but contained theaflavins. Highly overfermented black tea (group 5) contained only trace amounts of flavonol glycosides and theaflavins. Over 30 phenolics are new for tea, and this is the first phenolic profile to simultaneously detect C- and O-glycosylated flavonoids, catechins, proanthocyanidins, phenolic acid derivatives, and purine alkaloids.

Solid-State Array Detectors for Analytical Spectrometry

Solid-state array detectors are revolutionizing the ® eld of atomic and molecular spectroscopy.1,2 They enable the analyst to acquire vast amounts of spectrally and/or spatially resolved data in short periods of time. These detectors offer high quantum ef® ciency, low read noise, wide dynamic range, low power requirements, and rugged, but compact, packaging. In addition, as solid-state technology improves at a rapid rate, the cost of these detectors is continuously decreasing, while exibility in design is increasing. As a result, a wide variety of arrays are currently commercially available, with even more on the horizon. The purpose of this article is, ® rst, to provide the reader with an introduction to the variety and the nature of solidstate array detectors and, second, to show how the design of complementary detectors and dispersion optics provides increased analytical capabilities. This article is not intended to be a comprehensive survey. The instruments chosen as examples were selected to illustrate the impact of solid-state array detectors on spectrometry.

Extended calibration ranges for continuum source atomic absorption spectrometry with array detection

Abstract Computer modeling has been used to construct calibration curves and relative concentration error plots for continuum source atomic absorption spectrometry with array detection and graphite furnace atomization. Model results are compared with experimental results obtained with a linear photodiode array detector. The model uses a Lorentzian absorption profile convoluted with a rectangular entrance slit (25, 50, 100, 200, or 500 μm wide) and detected with an array of pixels (each 25 μm wide) using a high resolution spectrometer. Transient furnace signals are modeled as triangular functions with a half-width of 2 s whose height and area are linearly dependent on concentration. With detector read noise limiting (characteristic of a photodiode array detector), the best signal-to-noise ratios have been obtained with a 500 μm entrance slit width and wavelength integrated absorbance (i.e. integration of absorbance over the whole absorption profile). The shapes of the modeled calibration curves agree well with those theoretically predicted and those obtained experimentally. Useful calibration ranges approaching six orders of magnitude of concentration have been achieved using a single calibration curve and integrating over a spectral region equivalent to 60 times the half width of the absorption profile (about 0.16 nm for Cd at 228.8 nm). When concentration is normalized by the intrinsic mass, all elements give the same curve shapes with the inflection point, from a slope of 1.0 to 0.5 (on a logarithmic scale), determined by the stray light. A hyperbolic function has been developed which accurately fits the modeled and experimental data. With photon shot noise limiting (characteristic of a charge coupled device), the signal-to-noise ratio is much less dependent on the entrance slit width. With a 25 μm entrance slit width, wavelength selected absorbances (i.e. absorbances computed for selected pixels or wavelengths) have been used to construct three calibration curves covering six orders of magnitude of concentration.

Sensitivities and detection limits for graphite furnace atomic absorption spectrometry using a continuum source and linear photodiode array detection

Abstract Analytical figures of merit have been examined for a series of elements (As, Cd, Co, Cu, Fe, Mn, Ni, Pb, Se, Sn, and Zn) using graphite furnace atomic absorption spectrometry (GFAAS) with a continuum source and a linear photodiode array detector. Intrinsic masses, m i were calculated for continuum source AAS based on wavelength and time integrated absorbance in units of pm-s. A simple triangular model, based on experimental values for the hollow cathode lamp linewidths and calculated widths for the absorption profiles, was used to compute m i values from tabulated characteristic mass values for conventional AAS. With the exception of As and Se, the m i values for continuum source and conventional AAS agreed within a factor of two. Continuum source detection limits obtained were similar to those reported for line source GFAAS. Two standard reference materials were analyzed and values for the elements studied were found to be in good agreement with the certified values.

Legacy of Wilbur O. Atwater: Human Nutrition Research Expansion at the USDA–Interagency Development of Food Composition Research

The systematic chemical analysis of foods for human consumption in the United States had its origin with Wilbur O. Atwater. This activity began in the 1860s while Atwater was a student at Yale University and continued through his tenures at Wesleyan University and the Storrs (Connecticut) Experiment Station. These activities moved with Atwater to the USDA in Washington, DC and ultimately to the Henry D. Wallace Beltsville Agricultural Research Center in Beltsville, MD early in the 1900s. During the first half of the 20th century, food composition activities were guided by the discovery of new essential nutrients and the need to measure and tabulate their levels in foods. Later in the century, the association between diet and chronic diseases was recognized. As a result, collaborations were established between other food- and health-related government agencies, the food industry, and many universities. At the same time, computer and communication technology greatly advanced, which became integral to laboratory instrumentation and allowed data in the National Nutrient Databank System to be available electronically. Simultaneously, accuracy of analytical data came under scrutiny and a new paradigm was established in collaboration with governmental metrology units worldwide. Advances in computer technology and the increased focus on accuracy of analytical data subsequently led to the development of quality indicators for all food composition data. Recently, increased consumption of dietary supplements resulted in the broadening of food composition efforts and development of new collaborations with government agencies, several industries, and universities.

Feasibility of Including Green Tea Products for an Analytically Verified Dietary Supplement Database

The Dietary Supplement Ingredient Database (DSID) is a federally funded, publicly accessible dietary supplement database that currently contains analytically derived information on micronutrients in selected adult and childrens multivitamin and mineral (MVM) supplements. Other constituents in dietary supplement products such as botanicals are also of interest and thus are being considered for inclusion in the DSID. Thirty-eight constituents, mainly botanicals were identified and prioritized by a federal interagency committee. Green tea was selected from this list as the botanical for expansion of the DSID. This article describes the process for prioritizing dietary ingredients in the DSID. It also discusses the criteria for inclusion of these ingredients, and the approach for selecting and testing products for the green tea pilot study.

Evaluation of Calibration Methods for Zeeman Graphite Furnace Atomic Absorption Spectrometry Using Computer Modeling

Computer modeling was used to compare calibration curves and relative concentration errors for normal, linearized, and three-field Zeeman GF-AAS. The model assumed that either photon shot noise or the combination of photon shot and analyte fluctuation noise were limiting and that the sole source of nonlinearity was stray light. For absorbance, the calibration range and the relative concentration error for all three methods are almost identical. The difference is a reduced-sensitivity curve for three-field Zeeman, which offers a relative concentration error advantage in the concentration region where the most sensitive curve rolls over. For integrated absorbance, the sum of absorbances over the analytical peak, linearized Zeeman provides a significant relative concentration error advantage over the other methods at the high concentration end of the calibration curve. The calibration range is effectively extended by at least 1.5 orders of magnitude. This advantage arises from integration of absorbances which have a linear relationship to concentration. At high concentrations, absorbances computed for normal and three-field Zeeman are nonlinear with respect to concentration. Three-field Zeeman offers no advantage over normal Zeeman for integrated absorbance.

Importance of Accurate Measurements in Nutrition Research: Dietary Flavonoids as a Case Study

Accurate measurements of the secondary metabolites in natural products and plant foods are critical for establishing relations between diet and health. There are as many as 50,000 secondary metabolites that may influence human health. Their structural and chemical diversity presents a challenge to analytical chemistry. With respect to flavonoids, putative identification is accessible, but positive identification and quantification are limited by the lack of standards. Quantification has been tested with use of both nonspecific and specific methods. Nonspecific methods, which include antioxidant capacity methods, fail to provide information on the measured components, suffer from numerous interferences, are not equatable, and are unsuitable for health research. Specific methods, such as LC with diode array and mass spectrometric detection, require the use of internal standards and relative molar response factors. These methods are relatively expensive and require a high level of expertise and experimental verification; however, they represent the only suitable means of relating health outcomes to specific dietary components.