Authors:Dong-Hyeon Ko, Ki-Won Gyak and Dong-Pyo Kim
Separation of various mixtures is essential for the synthesis and analysis in a continuous-flow system. Basically, the usual separation principles are also applicable to microseparator such as diffusion, extraction, distillation, solubility, and wettability
Authors:Jiaxing Fan, Yiyang Liu, Shenmin Su, Yiqing Cao and Yunqiu Yu
shortcomings, our work aimed to develop a new simple high performance liquid chromatography (HPLC) conditions to improve separation and selectivity for determination of these nine metabolites in TCA cycle, including lactic acid (Lac), pyruvic acid (Pyr), citric
Authors:H. W. Zhao, Y. L. Geng, H. Zhu, P. Yang and J. Q. Yu
, 3 ]. However, terpenoids and other compounds from olibanum had been isolated mostly based on some conventional techniques, such as silica gel column chromatography separation due to their lower polarities [ 4 ], which are waste organic solvent
Specific separation of thiamine hydrochloride from riboflavin, nicotinic acid, calcium D-pantothenate, pyridoxine hydrochloride, cyanocobalamin, and ascorbic acid has been achieved on commercial precoated silica gel 60F254 TLC plates with dioxane-water 1:1 (υ/υ) as mobile phase. The spots were visualized under UV light. The effect of impurities (metal cations and inorganic anions) on the chromatography of thiamine hydrochloride was examined. The detection limit for thiamine hydrochloride was 0.09 μg per spot and the relative standard deviation of the RF value of thiamine hydrochloride in five analyses was 14.99%. The applicability of the method to the identification of thiamine in pharmaceutical formulations was also tested.
We say that a convex set K in ℝdstrictly separates the set A from the set B if A ⊂ int(K) and B ⋂ cl K = ø. The well-known Theorem of Kirchberger states the following. If A and B are finite sets in ℝd with the property that for every T ⊂ A⋃B of cardinality at most d + 2, there is a half space strictly separating T ⋂ A and T ⋂ B, then there is a half space strictly separating A and B. In short, we say that the strict separation number of the family of half spaces in ℝd is d + 2.
In this note we investigate the problem of strict separation of two finite sets by the family of positive homothetic (resp.,
similar) copies of a closed, convex set. We prove Kirchberger-type theorems for the family of positive homothets of planar
convex sets and for the family of homothets of certain polyhedral sets. Moreover, we provide examples that show that, for
certain convex sets, the family of positive homothets (resp., the family of similar copies) has a large strict separation
number, in some cases, infinity. Finally, we examine how our results translate to the setting of non-strict separation.
Authors:X. H. Lv, P. Q. Kuang, Q. P. Yuan, H. Liang and G. Q. Zheng
In this article, a rapid, novel, and effective method was presented to separate pure steviol glycosides from leaves of Stevia rebaudiana Bertoni, including stevioside, rebaudioside A, and rebaudioside C, using resin-based column chromatography followed by preparative high-performance liquid chromatography under hydrophilic interaction liquid chromatography (HILIC) mode. The separation procedure was first optimized on an analytical HILIC column and then scaled up on a preparative HILIC column using a mobile phase consisting of 83% acetonitrile in water with flow rate of 10 mL·min−1 at 25°C. 200 mg of the crude extract containing 68.1% steviol glycosides yielded 79.2 mg stevioside, 9.4 mg rebaudioside C, and 33.7 mg rebaudioside A, with the purities of 97.5%, 96.8%, and 97.2%, respectively. Those products were identified by MS, 1H NMR, and 13C NMR.
An efficient method used to separate five bioactive compounds from Gelidium amansii was optimized by the HCI software. The optimum composition of mobile phase for high-performance liquid chromatographic (HPLC) separation was obtained. The elution profiles were calculated by the polynomial theory based on the retention factor ln k = A + BF + CF2 (F was the volume percentage of acetonitrile with 1.0% acetic acid); then, the theory was applied to calculate the elution profile in both isocratic and gradient modes by modifying different mobile phase conditions with HCI program. The calculated results of mobile phase condition suggested that acetonitrile-water (containing 1.0% acetic acid) with a linear gradient elution of 0∼30 min from 15:85 to 50:50 (v/v) was the optimized component. In the experimental conditions, the agreement between the experimental elution profiles and the calculated values of eluted concentration was relatively good.
A rapid high-performance liquid chromatography (HPLC) method for chiral purity determination of tenofovir disoproxil fumarate in raw material and pharmaceutical formulations was developed. The (S)-enantiomer appears to be as an impurity and pharmacologically inactive. The effects of various stationary phases, mobile phase composition, and column temperature on enantiomeric separation of tenofovir disoproxil were investigated and optimized. Chromatography resolution of tenofovir disoproxil enantiomers was performed on NUCLEOCEL ALPHA-RP S column (250 × 4.6 mm i.d., 5 μm). The elution was achieved by using 95:5% (υ/υ) methanol—acetonitrile, containing 0.1% triethylamine at a flow rate of 0.8 mL min−1. The ultraviolet (UV) detector was set at 260 nm. Calibration curves were linear in the range of 1–100 μg mL−1 and 0.2–20 μg mL−1 for (R)-tenofovir disoproxil and (S)-enantiomer, respectively. Limits of detection and quantitation for (S)-enantiomer were 0.06 and 0.2 μg mL−1. The run time of analysis was less than 7.0 min. The proposed method was used successfully for separation and quantification of tenofovir disoproxil enantiomers in raw material and pharmaceutical formulations.
For certain classes of neighbourly 4-polytopes P, any facet of P is strictly separated from an arbitrary fixed interior point of P by one of at most nine hyperplanes. This result, proved for the class of cyclic 4-polytopes by K. Bezdek and T. Bisztriczky, represents a verification of the Gohberg-Markus-Hadwiger Conjecture for the corresponding classes of dual polytopes P*.