The hyphenation of chiral capillary electrochromatography (CEC) with electrospray ionization mass spectrometry (ESI-MS) is very challenging but promising due to the fact that it combines sensitivity with high specificity and selectivity. In this work, CEC capillaries packed with (3R,4S)-Whelk-O1 chiral stationary phase were used for simultaneous enantioseparation of (+/-)-warfarin and its internal standard, (+/-)-coumachlor. Furthermore, both the chiral CEC separation and MS detection parameters were examined in detail. First, the influence of different column fabrication was investigated. Second, enantioseparation was optimized by varying CEC parameters, including acetonitrile concentration, buffer pH, and ionic strength. Under the optimum chiral CEC conditions, ESI-MS parameters such as sheath liquid pH and composition, sheath liquid flow rate, drying gas flow rate, drying gas temperature, nebulizer pressure, and fragmentor voltage were investigated to achieve maximum MS signals of the separated enantiomers. Finally, using solid-phase extraction as sample preparation method, (+/-)-warfarin spiked in 100-microL human plasma samples were analyzed. The calibration curves showed good linearity for both (R)-warfarin (R = 0.9979) and (S)-warfarin (R = 0.9978) enantiomers. The experimental limit of detection was approximately 25 ng/mL for both enantiomers. Even though the data are still preliminary, we can state with confidence that chiral CEC-ESI-MS has the potential to establish itself as a very powerful technique for the determination of enantiomeric ratios in human body fluid. 相似文献
This paper presents a fast computational technique based on the wavelet collocation method for the numerical solution of an optimal control problem governed by elliptic variational inequalities of obstacle type. In this problem, the solution divides the domain into contact and noncontact sets. The boundary between the contact and noncontact sets is a free boundary, which is not known a priori and the solution is not smooth on it. Accordingly, a very fine grid is needed in order to obtain a solution with a reasonable accuracy. In this paper, our aim is to propose an adaptive scheme in order to generate an appropriate and economic irregular dyadic mesh for finding the optimal control and state functions. The irregular mesh will be generated such that its density around the free boundary is higher than in other places and high-resolution computations are focused on these zones. To this aim, we use an adaptive wavelet collocation method and take advantage of the fast wavelet transform of compact-supported interpolating wavelets to develop a multi-level algorithm, which generates an adaptive computational grid. Using this adaptive grid takes less CPU time than using a full regular mesh. At each step of the algorithm, the active set method is used for solving the optimality system of the obstacle problem on the adapted mesh. Finally, the numerical examples are presented to show the validity and efficiency of the technique. 相似文献
In this work, three amino acid-derived (l-leucinol, l-isoleucinol, l-valinol) sulfated chiral surfactants are synthesized and polymerized. These chiral sulfated surfactants are thoroughly characterized to determine critical micelle concentration, aggregation number, polarity, optical rotation, and partial specific volume. For the first time the morphological behavior of polymeric sulfated surfactants is revealed using cryogenic high-resolution electron microscopy. The polysodium N-undecenoyl-l-leucine sulfate shows distinct tubular structure, while polysodium N-undecenoyl-l-valine sulfate also shows tubular morphology but without any distinct order of the tubes. On the other hand, polysodium N-undecenoyl-l-isoleucine sulfate (poly-l-SUCILS) displays random distribution of coiled/curved filaments with heavy association of tightly and loosely bound water. All three polymeric sulfated surfactants are compared for enantioseparation of a broad range of structurally diverse racemic compounds at very acidic, neutral, and basic pH conditions in micellar electrokinetic chromatography (MEKC). A small combinatorial library of 10 structurally related phenylethylamines (PEAs) is investigated for chiral separation under acidic and moderately acidic to neutral pH conditions using an experimental design. In contrast to neutral pH conditions, at acidic pH, significantly enhanced chiral resolution is obtained for class I and class II PEAs due to the compact structure of polymeric sulfated surfactants. It is observed that the presence of a hydroxy group on the benzene ring of PEAs resulted in deterioration of enantioseparation. A sensitive MEKC-mass spectrometry (MS) method is developed for one of the PEAs (e.g., (+/-)-pseudoephedrine) in human urine. Very low limit of detection (LOD) is obtained at pH 2.0 (LOD 325 ng/mL), which is approximately 16 times better compared to pH 8.0 (LOD 5.2 microg/mL). Another broad range of chiral analytes (beta-blockers, phenoxypropionic acid, benzoin derivatives, PTH-amino acids, benzodiazepinones) studied also provided improved chiral separation at low pH compared to high-pH conditions. Among the three polymeric sulfated surfactants, poly-l-SUCILS with two chiral centers on the polymer head group provided overall higher enantioresolution for the investigated acidic, basic, and neutral compounds. This work clearly demonstrates for the first time the superiority of chiral separation and sensitive MS detection at low pH over conventional high-pH chiral separation and detection employing anionic chiral polymeric surfactants in MEKC and MEKC-MS. 相似文献
Heat transfer and friction factor in a tube with turbulator internally grooved and rib are studied using numerical simulation. Two different turbulator geometries, including only groove and both groove and rib, on the tube wall are investigated. The study is developed for different parameters of turbulator including pitch ratio (PR), groove and rib height (DR), and Reynolds number in the range of 10 000 to 38 000. The results revealed that the best Nusselt number is achieved for GR turbulator and for the tube wall with PR = 2 and DR = 1. Furthermore, for a specific turbulator parameter, Nusselt number is improved by 46% compared with the experimental result. The results show that the friction factor decreases by increase of both step and height ratios. For example, based on Reynolds number, 21% to 69% reduction in the friction factor was observed for PR = 7 and DR = 3. In addition, the correlations for Nusselt number and friction factor with acceptable deviation are presented for the studied turbulators. Finally, thermal performance enhancement factor is defined to be a good criterion for selection of the optimum turbulator and their parameters. 相似文献
The crystal structure of palm oil-based whipping cream was studied. Various proportions of refined, bleached, and deodorized
palm oil (RBDPO) and palm kernel oil (RBDPKO) were prepared and their crystal structure and thermal profile were observed
by an X-ray diffractometer and a differential scanning calorimeter, respectively. The results showed that all blends possessed
a stable and shiny β′ polymorph at 25°C, which showed that RBDPO and RBDPKO were appropriate for producing a nondairy whipping
cream. Some eutectic effect was observed in some blends, which was attributed to the complex combination of TAG in RBDPO and
RBDPKO. 相似文献
Benzo[a]pyrene, one of the most carcinogenic PAHs, has 12 monomethylated positional isomers (MBAPs). A strong correlation between the carcinogenicity of these isomers and methyl substitution has been reported. In this study, on-line coupling of capillary electrochromatography (CEC) and atmospheric pressure photoionization mass spectrometry (APPI-MS) provides a unique solution to highly selective separation and sensitive detection of MBAP isomers. The studies indicated that APPI provides significantly better sensitivity compared to electrospray ionization and atmospheric pressure chemical ionization modes of MS. A systematic investigation of APPI-MS detection parameters and CEC separation is established. First, several sheath liquid parameters (including type and concentration of volatile buffers, type and content of organic modifiers, use of dopants and inorganic/organic additives, and sheath liquid flow rate) and APPI-MS spray chamber parameters (capillary voltage, vaporizer temperature, nebulizer pressure) were found to have effects on detection sensitivity as well as the profile of mass spectrum. For example, when ammonium acetate was replaced with acetic acid in the sheath liquid, the MS signal was enhanced as much as 90% and the formation of ammonia adduct was effectively suppressed. Next, the separation of MBAP isomers was conducted on internal tapered columns packed with polymeric C18 stationary phase. With the use of a mobile phase consisting of slightly higher acetonitrile content (90%,v/v) and a small amount of tropylium ion, the analysis times were significantly shortened by 20 min without compromising the resolutions between the isomers. Finally, quantitative aspects of the CEC-APPI-MS method were demonstrated using 7-MBAP as the internal standard. The calibration curves of three of the most carcinogenic isomers, namely, 1-MBAP, 3-MBAP, and 11-MBAP, showed good linearity in the range of 2.5-50 microg/mL with a limit of detection at 400 ng/mL. 相似文献
In this paper, we present a method to simulate membrane-type micro check-valve using finite element method with fluid structure interaction formulation. The designed micro check-valve which is analogue of semiconductor device, diode, allows the fluid to pass in forward-mode and blocks it in reverse mode. To have a better understanding on the valve design we also studied the effect of design dimensions on the valve performance. Our study shows the valve flow rate-pressure curve is similar to diode current–voltage characterization curve. A series of simulations were carried out by using two-way fully-coupled Fluid Structure Interaction (FSI) analysis. Using Arbitrary Lagrangian–Eulerian (ALE) method in combination with high viscosity region instead of solid valve-seat enables the designer to overcome simulations difficulties and reduces the amount of calculation time by not considering the contact phenomenon of the membrane and the valve seat. The results show the valve can withstand pressures of up to 11 kPa in reverse-mode regardless of membrane’s hole-size and length of chamber-inlet. Also, chamber-inlet size has high effect on valve opening threshold point in a way that increment of chamber-inlet area will reduce opening threshold point and vice versa.
Scientometrics - Publications without authorship information have been indexed as anonymous in the Web of Science database over the years. However, discussions on this subject have not been... 相似文献
Nondairy creams are more stable than dairy creams, especially in hot climates. This paper considers the reasons for this stability
and which FA is most suitable for producing this effect in palm oil and palm kernel oil-based whipping cream. The results
show that an increase in unsaturated FA, particularly oleic acid, can produce a more stable foam in whipping cream. This study
also shows that an increase in iodine value has a positive impact on the stability of foam in nondairy whipping cream as well.
This study points out the advantages of a palm oil-based whipping cream over commercial dairy whipping cream, particularly
when the stability of the foam is important and the product is supposed to be consumed in hot weather. 相似文献