Search Results
You are looking at 11 - 18 of 18 items for
- Author or Editor: S. Alam x
- Refine by Access: All Content x
Novel, simple, and sensitive high-performance thin-layer chromatography (HPTLC) with fluorescence detection method has been successfully established and validated for the simultaneous determination of vulgarin and epivulgarin in different collections of Artemisia judaica. HPTLC method was carried out using glass plates coated with silica gel 60 F254 using petroleum ether‒acetone (7:3, v/v) as the mobile phase. After development, the plates were scanned and quantified densitometrically at 224 nm for both vulgarin and epivulgarin. The two compounds’ peaks from A. judaica were identified by comparing their single spot at R F = 0.30 ± 0.02 and R F = 0.36 ± 0.01, respectively, with those of vulgarin and epivulgarin. Linear regression analysis revealed a good linear relationship between peak area and amount of vulgarin and epivulgarin in the range of 100–700 ng band−1 for both compounds. The method was validated, in accordance with the International Conference on Harmonization (ICH) guidelines, for precision, accuracy, and robustness. The proposed method will be useful to measure the therapeutic dose of vulgarin and epivulgarin in A. judaica extracts.
Abstract
In this paper we present a brief review of the current state of positron annihilation research into the phase behaviour of fluids confined within restricted boundaries. We summarise, in the form of selected examples, the work done so far on: (1) fluids confined in the nanometer-size pores of VYCOR glass, with particular emphasis on the confined phase diagram and the mechanisms behind phase transitions compared to bulk. (2) The adsorption/physisorption of gases on internal surfaces of grafoil and the potential of positron technique for revealing physical properties, such as the intricate molecular arrangements during phase transitions of the layered fluid.
Abstract
The phase behaviour of carbon dioxide confined in VYCOR glass at pressures below that of the bulk triple point (0.51 MPa) has been investigated. The temperature at which freezing occurs appears to be pressure dependent below 0.3 MPa. As experiments are performed at successively lower pressures, the confined phase transitions gradually disappear, due to either partial pore filling, or the proximity of the confined triple point.
Abstract
Positron lifetime spectroscopy has been applied to estimate the free-volume hole size distribution in glassy polycarbonate (PC) and polystyrene (PS) as well as in plastically deformed and undeformed, semi-crystalline polyethylene (HDPE). The hole radius density distribution is determined from the ortho-positronium lifetime distribution which is obtained via a Laplace-inversion of the positron lifetime spectrum. The hole volume density distribution and the number density distribution of holes is estimated from the hole radius density distribution. In PC and in PS all of the distributions may be well approximated by a single Gaussian. The hole radius and the hole number density distributions have centres <r> and <v n > at 0.29 nm and 0.1 nm3 in PC, and at 0.28 nm and 0.09 nm3 in PS. The FWHM of the corresponding distributions are 0.042 nm and 0.040 nm3 (PC), and 0.039 nm and 0.34 nm3 (PS), respectively. Both, the shape and the width of the distributions correlate well with the free volume theory of BUECHE. In PE the lifetime spectra consist of four components. The o-Ps lifetime distribution is bimodal and may be attributed to o-Ps annihilation in the crystalline and in the amorphous phase of the polymer. The corresponding hole size distributions show definite changes of their position and width following plastic deformation which we attribute to homogeneous crystal lattice dilatation and/or a local disorder in the crystals and to an increase in the eccentricity of holes in the amorphous phase.
A new rapid, simple, economical, and environment-friendly reversed- phase high-performance thin-layer chromatography (RPHPTLC) method has been established for the simultaneous determination of glycyrrhizin and glabridin in Glycyrrhiza glabra roots, rhizomes and selected herbal formulations. The method was carried out using RP-18 silica gel 60 F254S HPTLC glass plates and methanol–water (7:3 v/v) as the mobile phase. The developed plates were scanned and quantified densitometrically at 256 and 233 nm for glycyrrhizin and glabridin, respectively. Glycyrrhizin and glabridin peaks from G. glabra roots and rhizomes and herbal formulations were identified by comparing their single spots at R F = 0.63 ± 0.02 and R F = 0.28 ± 0.01, respectively. Linear regression analysis revealed a good linear relationship between the peak areas and the amounts of glycyrrhizin and glabridin in the ranges of 1000–7000 and 100–700 ng band−1, respectively. The method was validated, in accordance with the International Conference on Harmonization (ICH) guidelines for precision, accuracy, and robustness. The proposed method will be useful to determine the therapeutic doses of glycyrrhizin and glabridin in herbal formulations as well as in bulk drug.
A simple and sensitive high-performance thin-layer chromatographic (HPTLC) method was developed for the evaluation of biomarker β-amyrin in the leaves of fve different species of genus Ficus (Ficus carica, Ficus nitida, Ficus ingens, Ficus palmata, and Ficus vasta) grown in the Kingdom of Saudi Arabia. Chromatography was performed on glass-backed silica gel 60 F254 HPTLC plates with solvents toluene–methanol (9:1, v/v) as the mobile phase. After development, the HPTLC plate was derivatized with p-anisalde-hydereagent to give well-resolved and compact spot of β-amyrin. Scanning and quantifcation were done at 550 nm. The system was found to give compact spot for β-amyrin at R F = 0.58. The linear regression analysis data for the calibration plots showed good linear relationship with r 2 = 0.998 with respect to area in the concentration range of 100–900 ng. The regression equation for β-amyrin standard was found to be Y = 5.835X + 87. The precisions (n = 6) for β-amyrin were found to be 1.64–1.77% and 1.68–1.84%, respectively, for intra-day and inter-day batches, and the recovery values were found to be 97.6–98.3%. β-Amyrin was found to be present in three species, i.e., F. carica (0.29%, w/w), F. nitida (0. 5 4% w/w), and F. p almata (0.31%, w/w), while it was absent in F. vasta and F. ingens. The statistical analysis proves that the developed method for the quantifcation of β-amyrin is reproducible; hence, it can beemployed for the determination of β-amyrin in plasma and other biological fuids as well as in fnished products avai lable in the market.
Fenugreek is one of the oldest medicinal plants known by mankind. The aim of this study is to evaluate the effect of environmental conditions on the saponin contents of the plant. The amount of diosgenin in different samples of fenugreek was estimated by high-performance thin-layer chromatography (HPTLC). The developed method was validated, in accordance with the International Conference on Harmonization (ICH) guidelines for precision, accuracy, and robustness. HPTLC was carried out using hexane‒acetone (8:2%, v/v) on 20 cm × 10 cm glass coated silica gel 60 F254 plates. The developed plates were scanned and quantified densitometrically at λ = 430 nm. Linear regression analysis revealed a good linear relationship between the area under the peak and the amount of diosgenin in the range of 50–400 ng per band. The amount of diosgenin which reflects the total saponin contents varied according to the country of origin. The sample obtained from Yemen showed the highest amount of diosgenin followed by the Saudi sample. Both locations represent areas with the highest altitude (Yemen) and the highest temperature (Saudi).
Summary
We have recently reported on the effect of the environmental conditions on the quantity of diosgenin. Attempts for the simultaneous quantification of trigonelline and diosgenin using normal-phase silica gel plates were not successful. A high-performance thin-layer chromatography (HPTLC) method was developed using glass-backed plates coated with RP-18 silica gel 60 F254S and acetonitrile-water (7.5:2.5, V/V) as the mobile phase. Trigonelline and diosgenin peaks were well separated with R F values 0.29 ± 0.02 and 0.17 ± 0.01, respectively. The TLC plates were directly scanned at 267 nm for trigonelline and at 430 nm after derivatization with vanillin-sulfuric acid for diosgenin. Linear regression analysis revealed a good linear relationship between the peak area and the amounts of trigonelline and diosgenin in the range of 200–1400 and 50–300 ng per band, respectively. The method was validated in accordance with the International Conference on Harmonization (ICH) guidelines for precision, accuracy, and robustness.