Electrochemically assisted oxidation off-line combined with UPLC/ESI–MS and ion mobility mass spectrometry enabled us to gain insight into the oxidation mechanisms of xanthohumol. Several types of monomeric oxidation products were identified, i.e., monohydroxylated and dehydrogenated derivatives and related quinones. Besides, high contents of dimers were observed. The structures of four main oxidative condensation products of two xanthohumol molecules were proposed based on combination of retention time, exact mass measurement, fragmentation pattern, data from on-line ion mobility mass spectrometric experiments and with the support of independent electrochemical experiments. To the best of our knowledge, this is the first evidence on formation of xanthohumol dimers. The effect of the pH on the generation of oxidation products was further investigated. The monomeric and dimeric oxidation products are favored at pH of 5.5 and 4.5, respectively.
Quality of botanical products is a great uncertainty that consumers, clinicians, regulators, and researchers face. Definitions
of quality abound, and include specifications for sanitation, adventitious agents (pesticides, metals, weeds), and content
of natural chemicals. Because dietary supplements (DS) are often complex mixtures, they pose analytical challenges and method
validation may be difficult. In response to product quality concerns and the need for validated and publicly available methods
for DS analysis, the US Congress directed the Office of Dietary Supplements (ODS) at the National Institutes of Health (NIH)
to accelerate an ongoing methods validation process, and the Dietary Supplements Methods and Reference Materials Program was
created. The program was constructed from stakeholder input and incorporates several federal procurement and granting mechanisms
in a coordinated and interlocking framework. The framework facilitates validation of analytical methods, analytical standards,
and reference materials. 相似文献
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
This article illustrates the importance of having analytical data on the vitamin and mineral contents of dietary supplements
in nutrition studies, and describes efforts to develop an analytically validated dietary supplement ingredient database (DSID)
by a consortium of federal agencies in the USA. Preliminary studies of multivitamin mineral supplements marketed in the USA
that were analyzed as candidates for the DSID are summarized. Challenges are summarized, possible future directions are outlined,
and some related programs at the Office of Dietary Supplements, National Institutes of Health are described. The DSID should
be helpful to researchers in assessing relationships between intakes of vitamins and minerals and health outcomes. 相似文献
Journal of Solid State Electrochemistry - The anodic oxide on titanium can be thickened by anodization, with the consequent corrosion properties of this oxide depending on many variables, including... 相似文献