A novel and ultrasensitive chiral detector for high-performance liquid chromatography has been developed. This detector is based on the measurement of circular dichroism of chiral effluents by the thermal lens effect. In this instrument, the chromatographic effluent was sequentially excited by left circularly polarized laser light (LCPL) and right circularly polarized laser light (RCPL); both of these excitation beams were derived from the same argon ion laser whose linearly polarized output was transformed into circularly polarized light by means of a Pockels cell. The heat generated as a consequence of the sample absorption of the LCPL and RCPL was measured by the probe laser beam collinearly overlapping with the two excitation beams. A lock-in amplifier was used to measure the thermal lens-circular dichroism (TL-CD) signal which corresponds to the difference in the thermal lens signals produced by the LCPL and RCPL excitation beams. In addition to its high sensitivity, the advantages of this TL-CD chiral detector include its ability to provide, directly and in real time, information on the chirality (i.e., circular dichroism) and optical purity of chiral samples. A detection limit of 7.2 ng was achieved for (-)-tris(ethylenediamine)cobalt(III) (k' = 0.45) as well as for the (+)-tris(ethylenediamine)cobalt(III) (k' = 1.40) when these two enantiomers were chromatographically separated from the corresponding racemic mixture through the use of bis(mu-d-tartrato)diantiomonate(III) ion pair reversed-phase chromatography. This limit of detection was found by using a 10-microL flow cell and having 5-mm path length and 6-mW excitation laser beam (lambda = 514.5 nm) modulated at 2 Hz.
A novel, ultrasensitive crossed-beam thermal lens-circular dichroism spectropolarimeter (CBTL-CD) has been developed. In this instrument, the two excitation beams, left circularly polarized light (LCPL) and right circularly polarized light (RCPL), were derived from the same argon-ion laser. The chiral sample was sequentially excited by these two beams, and the corresponding thermal lens signals were monitored by a He-Ne probe laser intersecting perpendicularly with the two pump beams inside the sample. The apparatus is about three orders of magnitude more sensitive than the conventional circular dichroism spectropolarimeter. In addition, it can be used to detect chiral samples having very small volumes. A detection limit of 180 ng of optically active Co(en)3 complexes whose volume was as small as 8 μℓ has been estimated for this apparatus using 11-mW excitation laser power modulated at 2.3 Hz. The optics and instrumentation of the apparatus are described in detail.
Beta-carotene (BC) degradation was studied by liquid chromatography coupled to a quadrupole time of flight mass spectrometer. Throughout/After 21 days of dark storage, 56 nonvolatile degradants were chromatographically separated from pure BC crystal and their molecular formulas were identified. Their structure information was gained by comparing the fragments to a different, but structure-related compound. For example, a newly formed double bond position in dehydrogenated BC was determined by comparing the fragments between BC and dehydrogenated BC. One of their chemical structures was confirmed by comparing its precursor ion mass, retention time, isotopic ratio, and fragmentation to a pure trans-beta-apo-8 -apocarotenal. BC cleavage was observed on double bonds as well as single bonds in BC conjugation chain.Practical Application: As evidenced in this study, beta-carotene (BC) degradation is a spontaneous process initiated when the compound is exposed to air. The stoichiometric ratio of BC to oxygen is 1:0.03 at the first oxidation, therefore, only 0.3 mg oxygen or 1.2 mL air will degrade 10 mg BC, an average daily recommended intake. Not like in enzymatic BC degradation, spontaneous BC oxidation did not produce provitamin A, either in retina C20H38O or retinol C20H40O forms. For BC application in vitamin A deficiency, spontaneous BC oxidation should be avoided.
A novel, ultrasensitive thermal lens-circular dichroism spectropolarimeter (TL-CD) has been developed. In this instrument, a chiral sample is sequentially excited by the left circularly polarized laser light (LCPL) and right circularly polarized laser light (RCPL); both of these excitation beams are derived from the same argon ion laser. The heat generated as a consequence of the sample absorption of the LCPL and RCPL is measured by the probe laser beam collinearly overlapping with the two excitation beams. The TL-CD signal corresponds to the difference in the thermal lens signals produced by the LCPL and the RCPL excitation beams. Compared to characteristics of the conventional spectropolarimeters, the advantages of this TL-CD apparatus include its higher sensitivity, small volume capability, and wider applicability. A detection limit of 5 ng of optically active [Co(en)]3+ complexes whose volume was as small as 8 μL has been estimated for this apparatus with the use of 37 mW excitation power modulated at 1.1 Hz.
By using a high-resolution mass spectrometer, four vitamin A palmitate (VAP) degradants were identified from microencapsulated VAP degradation samples. Based on the degradants, VAP first breaks down into anhydroretinol (ANHR) and palmitic acid (PA) through ester thermal elimination (ETE). Sequentially, the formed ANHR reacts with remaining VAP to ANHR−VAP and with a second ANHR to ANHR−ANHR. The migration of H + in the transition state predicts that the H + concentration in media will affect the ETE. Based on the degradation mechanism discovered from this study, a new product was developed and its media pH changed from 4.2 to 6.2. The new microencapsulated VAP degraded from 22.3% to 4.8% on an annualized basis. In the VAP degradation, no oxidized apo-carotenoids were found. The oxidized apo-carotenoids were detected in the degradation of β-carotene, a pro-vitamin A, through natural oxidation by oxygen in air. This indicated that, in ambient and dry conditions on its own, VAP decay was unlike that of β-carotene through natural oxidation.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.