Absorption spectra of carbohydrates and related compounds in H2SO4

Abstract

582.962+581.192 The possibility of modifying the Dreywood anthrone method for spectrophotometric determination of carbohydrates in order to increase the accuracy and reproducibility of the results was examined. The classical method and a developed modification were compared. The relative uncertainty in a determination by the modified method was less than 4%.Sulfuric acid is widely used to analyze organic compounds. It gives colored products with carbohydrates in the presence of several phenols, in particular, a solution of anthrone in H 2 SO 4 gives stable colored compounds [1]. In the classical method (CM), hydroxymethylfurfurol formed upon dehydration of monosaccharides reacts with anthrone in conc. H 2 SO 4 to give bluishgreen condensation products with absorption maxima at 520-625 nm [2]. The CM was used to develop several quantitative methods for determining monosaccharides [3,4]. A drawback of these is the magnitude of the relative uncertainty and technical difficulties in working with concentrated mineral acids. Table 1 gives results from a metrological analysis of the CM using certain monosaccharides as examples. The large uncertainty is probably due to the viscosity of conc. H 2 SO 4 , which causes the colored products to be unevenly distributed in the sample volume.We examined the possibility of thinning the samples with less viscous and more available solvents such as ethanol and water for phytochemical analysis in order to eliminate these drawbacks. Use of the latter is excluded because of the poor solubility of anthrone in aqueous H 2 SO 4 solutions at concentrations less than 70%. Therefore, we used ethanol. The sample was diluted with 95% ethanol after the colored complex was formed.The studied compounds were representatives of the pentose and hexose series, oligosaccharides, and polymeric compounds. The viscosities of the resulting solutions were satisfactory and facilitated even mixing of the reaction mixture. However, yellow solutions formed instead of the expected bluish-green ones. A check of the effect of temperature on the color of the formed complex showed that it affected only the intensity of the color of the final solution. Carrying out the reaction at 20-100°C gave identical results. After dilution with ethanol, yellow solutions were obtained.Absorption spectra of the reaction products exhibited a characteristic band at 405-411 nm. Unreacted anthrone in the mixtures caused absorptions in the range 320-400 nm. This could be avoided by using an anthrone solution as a control. This improved the shape of the spectra and shifted the maxima to 428-431 nm (Fig. 1). The characteristic absorption spectrum was the same for all studied compounds except for galacturonic acid, the principal peak of which was located at 424 nm. The optica l density was linear for 0.2-0.7 relative units for solutions with concentrations 5-35 µg/mL (Fig. 2). The exception was arabinose, for which the range was 25-120 µg/mL.The time required to form the colored complex at 100°C was 10 min. Adding a cooling step afte...

Quantitative analysis of polysaccharides from Plantago major leaves using the Dreywood method

“…The isolation and separation of the PSa complex has been described previously [4]. The hydrolysis kinetics of the components of the PSa complex were studied as follows.…”

“…Herein we propose a method for quantitative determination of the PSa content using the Dreywood method [4] for standardizing active substances from P. major leaves.…”

Chemical composition of Callisia fragrans juice. II. Carbohydrates

“…13 C NMR spectra were recorded on a VXR 500S NMR spectrometer (Varian) at operating frequency 125.7 MHz for DMSO-d 6 solutions (1%). Carbohydrate content was determined by the anthrone method [9]; uronic acids, by reaction with 3,5-dimethylphenol [10]; hexosamines, according to Elson-Morgan [11]; acetyl groups, by hydroxylamine [12] and IR spectroscopy methods [13]; quantitative monosaccharide composition, by HPTLC [14] and GC/MS (5973N GC/MS with Agilent Technoologies 6890N mass-selective detector with a diffusion pump, PH-Innowax capillary column, 30 m/250 Pm/0.50 Pm; 150-250°C temperature gradient, 2°C/min heating rate, He carrier gas, flow rate 1 L/min). Analytical gel chromatography was carried out over Sephadex G-100 (Pharmacia, 1.5 u 90 cm column); preparative, over Acrylex P-60 (Reanal, 4 u 80 cm column) with acetate buffer eluent (0.2 M NaOAc-2% AcOH, 1:1) and detection of yields by phenol-H 2 SO 4 [15] and Elson-Morgan [11] methods.…”

Lamiaceae carbohydrates. VII. Glucoarabinogalactan from Panzerina lanata

“…Arabinose C-3 gave two resonances due to the presence in PLW H -2 of acetylated and nonacetylated units, the ratio of integrated intensities of which were 1:3.95, i.e., four of five arabinose units were acetylated. Acetylation of arabinose C-3 was confirmed by a second resonance for C-2 at 68.14 ppm due to the β-effect of acetylation (strong-field shift of the resonance for the neighboring atom) [4]. The glucose C-2 resonance shifted to weak field relative to that of free α-glucopyranose due to the α-effect of acetylation of C-3, which shifts the position of the resonance of the neighboring C atom to weak field [10].…”