Determination of Arbutin in Herbal Medicinal Products

Arbutin is the main active ingredient in many herbal medicinal products that have diuretic, antimicrobial, bactericidal, and antioxidant effects. Many of these products are mixtures of different herbal substances. Therefore, the approaches to quality control of HMPs can vary significantly. The aim of the study was to compare arbutin assay procedures used in quality control of arbutin-containing products. Materials and methods. Samples of the following HMPs were used in the study: monocomponent Bearberry Leaf and multicomponent Brusniver® (herbal mixture, powder). The test methods used were titrimetry, ultraviolet-visible spectrophotometry, and high-performance liquid chromatography (HPLC). Results. The authors compared five arbutin assay procedures described in the monographs and product files for arbutin-containing HMPs. Conclusions. It has been established that the analysed procedures cannot be used interchangeably as equivalent test methods; the limits for arbutin have to be established for each specific procedure. Iodometric titration is the most labour- and time-consuming method, and the determined titration endpoint is a subjective assessment. Spectrophotometric methods do not require the use of an arbutin reference standard, but they can give overestimated results as compared to the HPLC and titrimetry methods. HPLC methods are more selective, but they require the use of reference standards. The recommended test methods for HMP quality control are HPLC and visible spectrophotometry; the titrimetric method is recommended for replacement.

Simple Modification of Karl-Fischer Titration Method for Determination of Water Content in Colored Samples

The most commonly used technique for water content determination is Karl-Fischer titration with electrometric detection, requiring specialized equipment. When appropriate equipment is not available, the method can be performed through visual detection of a titration endpoint, which does not enable an analysis of colored samples. Here, we developed a method with spectrophotometric detection of a titration endpoint, appropriate for moisture determination of colored samples. The reaction takes place in a sealed 4 ml cuvette. Detection is performed at 520 nm. Titration endpoint is determined from the graph of absorbance plotted against titration volume. The method has appropriate reproducibility (), accuracy, and linearity ().

Acid Number Measurements Revisited

Summary We propose an improved procedure for measuring acid numbers. Major changes include spiking crude oil samples and blank solutions with a known amount of stearic acid to force a clear titration endpoint, replacing potassium hydroxide with tetrabutyl ammonium hydroxide in the alcoholic titratant, and correctly accounting for changes in electrode response that occur upon exposure of the electrode to crude oil. Introduction Chemical methods of improved oil recovery are not equally effective in all reservoirs. An important factor that can influence a project's success is crude oil composition. Because crude oils are complex mixtures, evaluation of oil composition in a way that is meaningful with respect to specific chemical recovery processes can present many problems. In particular, there is a need for improvements in acid number (AN) measurements, also known as total acid number (TAN). AN is important in evaluating crude oils for alkaline and surfactant processes, but in order to be useful, measurements must be comparable from one laboratory to another and must also capture chemically meaningful information about the crude oil. Standardization (e.g., the current ASTM recommended procedure) should assist with the first requirement: that different labs be able to reproduce the AN value within some reasonable tolerance. Standardization does not, however, ensure that the measurement captures information about a crude oil that can be used to predict its interactions in chemical recovery processes. AN measurements are used to characterize an oil with respect to total concentration of strong and weak acids by means of nonaqueous potentiometric titration. The standard procedure (ASTM 2001) is designed to measure ANs in the range of 0.05 to 250 mg KOH/g oil. Stock-tank samples of crude oil usually have ANs that are at the low end of this range; strong acids are not encountered. Thus the sensitivity of the ASTM method is barely adequate for many samples of interest. According to the ASTM procedure, 20 g of oil should be used if AN is less than 1 mg KOH/g oil. Unfortunately, high-quality samples of crude oil are expensive to obtain and the quantity is very limited. Using 20 g for AN measurement would often preclude making any other measurements. The usefulness of AN data is greatly increased if it forms part of a matrix of information that includes, at a minimum, base number (BN), SARA fraction data, and information about asphaltene stability. There are few, if any, interfacial phenomena that correlate exclusively to AN. Basic constituents of an oil can also be assessed by nonaqueous potentiometric titration, but endpoints are often more difficult to detect because the organic bases that occur in crude oils can have a wide range of dissociation constants. More than a decade ago, Dubey and Doe (1993) published recommendations for improved base number measurements by adding a known amount of quinoline to force a readily detectible titration endpoint. Base numbers measured using spiked oil samples were significantly higher than those measured by the ASTM method and the higher base numbers were shown to correlate, together with AN for the same oils, with observations of wetting reversal on silica surfaces. A similar procedure was shown to improve the precision of AN titrations using stearic acid as the spiking agent for routine AN measurements (Monsterleet and Buckley 1996). Precipitated material was observed for some crude oils in the standard solvent (50% toluene, 49.5% isopropanol or IPA, and 0.5% water). Stearic acid and o-nitrophenol were used as spiking agents by Zheng and Powers (2003).