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91.
Andrews KW Schweitzer A Zhao C Holden JM Roseland JM Brandt M Dwyer JT Picciano MF Saldanha LG Fisher KD Yetley E Betz JM Douglass L 《Analytical and bioanalytical chemistry》2007,389(1):231-239
As part of a study initiating the development of an analytically validated Dietary Supplement Ingredient Database (DSID) in
the United States (US), a selection of dietary supplement products were analyzed for their caffeine content. Products sold
as tablets, caplets, or capsules and listing at least one caffeine-containing ingredient (including botanicals such as guarana,
yerba mate, kola nut, and green tea extract) on the label were selected for analysis based on market share information. Two
or three lots of each product were purchased and analyzed using high-pressure liquid chromatography (HPLC). Each analytical
run included one or two National Institute of Standards and Technology (NIST) Standard Reference Materials (SRMs) and two
products in duplicate. Caffeine intake per serving and per day was calculated using the maximum recommendations on each product
label. Laboratory analysis for 53 products showed product means ranging from 1 to 829 mg caffeine/day. For products with a
label amount for comparison (n = 28), 89% (n = 25) of the products had analytically based caffeine levels/day of between −16% and +16% of the claimed levels. Lot-to-lot
variability (n = 2 or 3) for caffeine in most products (72%) was less than 10%. 相似文献
92.
Updated estimates of the selenomethionine content of four NIST wheat reference materials have been obtained by use of a revised
gas chromatography–stable-isotope dilution mass spectrometric method. The revised method makes use of digestion with methanesulfonic
acid, which enables more complete recovery of endogenous selenomethionine than was previously achieved by overnight denaturing
treatment in 0.1 mol L−1 HCl. The NIST wheat reference materials each contain approximately 55% of their total Se content as selenomethionine. Information
about forms of Se in reference materials adds value to these materials in Se speciation studies. Estimates of selenomethionine
content are also provided for other wheat samples, including several grown under conditions of exposure to high Se levels.
These samples also contain approximately 55% of their total Se content as selenomethionine. The consistent level of 55% of
total selenium occurring in the form of selenomethionine when the total selenium content varies by a factor of 500 is suggestive
of an active mechanism of incorporation of selenium into wheat grain.
Figure Selenomethionine content of wheat samples 相似文献
93.
Standard reference materials for foods and dietary supplements 总被引:1,自引:0,他引:1
Sharpless KE Thomas JB Christopher SJ Greenberg RR Sander LC Schantz MM Welch MJ Wise SA 《Analytical and bioanalytical chemistry》2007,389(1):171-178
Well-characterized certified reference materials are needed by laboratories in the food testing, dietary supplement, and nutrition
communities to facilitate compliance with labeling laws and improve the accuracy of information provided on product labels,
so that consumers can make good choices. As a result of the enactment of the Nutrition Labeling and Education Act of 1990
and the Infant Formula Act of 1980, the National Institute of Standards and Technology (NIST) worked to develop a series of
food-matrix standard reference materials (SRMs) characterized for nutrient concentrations. These include SRM 1544 Fatty Acids
and Cholesterol in a Frozen Diet Composite, SRM 1546 Meat Homogenate, SRM 1548a Typical Diet, SRM 1566b Oyster Tissue, SRM
1846 Infant Formula, SRM 1946 Lake Superior Fish Tissue, SRM 1947 Lake Michigan Fish Tissue, SRM 2383 Baby Food Composite,
SRM 2384 Baking Chocolate, SRM 2385 Slurried Spinach, and SRM 2387 Peanut Butter. With the enactment of the Dietary Supplement
Health and Education Act of 1994, NIST has been working to develop suites of dietary supplement SRMs characterized for active
and marker compounds and for toxic elements and pesticides, where appropriate. An updated SRM 1588b Organics in Cod Liver
Oil, a suite of ephedra-containing materials (SRMs 3240–3245), a carrot extract in oil (SRM 3276), and a suite of ginkgo-containing
materials (SRMs 3246–3248) are available. Several other materials are currently in preparation. Dietary supplements are sometimes
provided in forms that are food-like; for these, values may also be assigned for nutrients, for example SRM 3244 Ephedra-Containing
Protein Powder. Both the food-matrix and dietary supplement reference materials are intended primarily for validation of analytical
methods. They may also be used as “primary control materials” in assignment of values to in-house (secondary) control materials
to confirm accuracy and to establish measurement traceability to NIST. 相似文献
94.
Charlie Pelling 《Acta Analytica》2007,22(3):169-182
According to the conceptualist view in the philosophy of perception, we possess concepts for all the objects, properties,
and relations which feature in our experiences. Richard Heck has recently argued that the phenomenon of illusory experience
provides us with conclusive reasons to reject this view. In this paper, I examine Heck’s argument, I explain why I think that
Bill Brewer’s conceptualist response to it is ineffective, and I then outline an alternative conceptualist response which
I myself endorse. My argument turns on the fact that both Heck, in constructing his objection to conceptualism, and Brewer,
in responding to it, miss a crucial distinction between perceptual demonstrative concepts of objects, on the one hand, and
perceptual demonstrative concepts of properties, on the other.
相似文献
Charlie PellingEmail: |
95.
本文叙述了Al-Li合金光谱分析用标准样品的制备过程和定值结果。在制备过程中采用了先进的氩气保护、新型熔剂覆盖盖技术防止锂元素的烧损,首创作了“间歇式半连续铸造法 ”、“分步调整成分法”等先进的工艺,解决了Al-Li标样铸锭不锡成形、成易偏析等技术难关;最后采用多家协作分析定值法和科学的数理统计方法对数据处理给出定值结果和不确定度。 相似文献
96.
从接口定义语言( I D L)、对象请求代理( O R B)、对象服务等几个方面对公共对象请求代理( C O R B A)体系结构参考模型进行了概括的分析和描述,并对 C O R B A 与因特网、 W W W 应用相结合后的三层结构模型进行了说明。 相似文献
97.
Fernando P. Carvalho Jean-Pierre Villeneuve Chantal Cattini 《Trends in analytical chemistry : TRAC》1999,18(11):1005-664
A seaweed sample (Fucus sp.) was prepared, homogenised and distributed to laboratories worldwide as the IAEA-140 intercomparison material for the analysis of organochlorine compounds and petroleum hydrocarbons. A total of 80 laboratories from 51 countries reported results for this sample. The data sets reported by laboratories were evaluated statistically and the mean concentration values could be computed with 95% confidence limits for a large number of analytes. The accuracy of the analytical performance of each laboratory has been introduced by using Z-scores. The spread of results reported generally indicates that the accurate determination of many persistent organic pollutants, such as hexachlorobenzene, lindane, Aroclors or fluoranthene, is still difficult for many laboratories. The final results of this intercomparison exercise enable individual participants to assess their performance and, where necessary, to introduce appropriate modifications in their analytical procedures. Furthermore, as a series of statistical criteria was fulfilled for a number of compounds, the sample IAEA-140 can now be used as a reference material for quality control in the determination of chlorinated compounds and petroleum hydrocarbons in environmental samples. 相似文献
98.
Functional magnetic resonance imaging (fMRI) is widely used to pinpoint active brain areas. Changes in neuronal activity modulate the local blood oxygenation level, and the associated modulation of the magnetic field homogeneity can be detected with magnetic resonance imaging. Thus, the blood oxygenation level-dependent (BOLD) fMRI indirectly measures neuronal activity. Similar modulation of magnetic field homogeneity was here elicited by other means to generate a BOLD-like change in a new phantom constructed to provide reference activations during fMRI. Magnetic inhomogeneities were produced by applying current to coils located near the phantom containing 1.5 ml of Gd-doped water. The signal-to-noise ratio of the images, produced by gradient-recalled echo-planar imaging, varied between 104 and 107 at a selected voxel when the field was and was not inhomogenized, respectively. The contrast of signals between homogeneous and inhomogeneous conditions was generally stable, except in 3% of time points. During the periods of greatest deviations an observable change would have been detected in a simultaneously measured BOLD signal. Such changes could result from the imaging method or occur through glitches in hardware or alterations in the measurement environment. With identical measurement setups, the phantom could allow comparing intersession or intersubject brain activations. 相似文献
99.
As part of the study of interaction of the Ba2RCu3O6+z (R=lanthanides and Y) superconductor with SrTiO3 buffer, phase equilibria of the subsystem, R2O3-TiO2-CuO (R=Nd, Y, and Yb), have been investigated in air at 960 °C. While the phase relationships of the two phase diagrams with smaller R (Y and Yb) are similar, substantial differences were found in the Nd2O3-TiO2-CuO system, partly due to different phase formation in the binary R2O3-TiO2 and R2O3-CuO systems. R2CuTiO6 and R2Cu9Ti12O36 were the only ternary phases established in all the three diagrams. R2Cu9Ti12O36 belongs to the perovskite-related [AC3](B4)O12 family which is cubic Im3. Depending on the size of R3+, R2CuTiO6 crystallizes in two crystal systems: Pnma (R=La-Gd), and P63cm (R=Dy-Lu). The structure and crystal chemistry of the Pnma series of R2CuTiO6 (R=La, Nd, Sm, Eu, and Gd) are discussed in detail in this paper. Patterns for selected members of R2CuTiO6 have also been prepared and submitted for inclusion in the Powder Diffraction File (PDF). 相似文献
100.
U. Guth F. Gerlach M. Decker W. Oelßner W. Vonau 《Journal of Solid State Electrochemistry》2009,13(1):27-39
The availability and application of solid-state reference electrodes for potentiometric electrochemical sensors are briefly
reviewed. For a long time, considerable efforts have been made to combine solid-state indicator electrodes with equivalent
reference electrodes to take advantage of the absence of liquid system components to full capacity. In spite of various suggestions
to solve the problem, no type of solid-state reference electrode is so far available with properties completely identical
to conventional ones. 相似文献