A simple method for determining ammonia in water at the ppm level

Summary A simple colorimetric method is described for the determination of ammonia in water at the ppm level. Indophenol blue color is produced in an alkaline borate medium using phenol and hypo-chlorite as reagents. Comparison of color intensity is carried out by means of test tubes. When metal ions that interfere with ammonia determination are present in water, the interference can be prevented by applying a diffusion technique.

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Zusammenfassung Eine einfache kolorimetrische Methode zur Bestimmung von ppm-Mengen Ammoniak in Wasser wurde beschrieben. In Alkaliborat-Medium führen Phenol und Hypochlorit als Reagenzien zur Bildung von Indophenolblau. Der Farbvergleich wird in Reagensgläsern durchgeführt. Befinden sich im Wasser störende Metallionen, so kann man diese Störung mit Hilfe der Diffusionstechnik umgehen.

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Visiting professor at the University of Singapore, 1975–1976, on sabbatical leave from the City University of New York.     

A chronoamperometric method for determining total antioxidant activity

A novel version of a chronoamperometric method of antioxidant determination is described. It is based on the use of the oxidation current of ferrocyanide formed in the reaction of antioxidants to be determined with potassium ferricyanide as an analytical signal. So the total concentration of all antioxidants present in the analyzed solution, i.e., total antioxidant capacity, is measured. The results of blood plasma analysis by the newly presented and certified potentiometry method are in good agreement with each other, R ² = 0.9980. The detection limit makes 2 × 10⁻⁶ M for uric and ascorbic acids and 5 × 10⁻⁶ M for cysteine and glutathione.     

A rapid, simple method for determining formaldehyde in drinking water using colorimetric-solid phase extraction

Formaldehyde has been detected in drinking water supplies across the globe and on board NASA spacecraft. A rapid, simple, microgravity-compatible technique for measuring this contaminant in water supplies using colorimetric-solid phase extraction (C-SPE) is described. This method involves collecting a water sample into a syringe by passage through a cartridge that contains sodium hydroxide, to adjust pH, and Purpald, which is a well-established colorimetric reagent for aldehydes. After completing the reaction in the syringe by agitating for 2 min on a shaker at 400 rpm, the 1.0-mL alkaline sample is passed through an extraction disk that retains the purple product. The amount of concentrated product is then measured on-disk using diffuse reflectance spectroscopy, and compared to a calibration plot generated from Kubelka-Munk transformations of the reflectance data at 700 nm to determine the formaldehyde concentration. This method is capable of determining formaldehyde concentrations from 0.08 to 20 ppm with a total work-up time of less than 3 min using only 1-mL samples.     

A simple method for determining the absolute configuration of α-amino acids

Chiral α-amino acids react with 2-methoxy - 2,4 - diphenyl - 3 (2H) - furanone 1 to afford N-substituted 3,5 - diphenyl - 5 - hydroxy - 2 - pyrrolin - 4 - ones 2. The characteristic cotton effects given by these chromophoric derivatives provide a means for the determination of the absolute configuration of the parent amino acids. The longest wavelength(first) extremum in the chiroptical spectra (ORD and CD) of the l-amino acid derivatives is always positive, while it is negative for the d-amino acid derivatives.     

A simple microscale method for determining the relative stereochemistry of statine units

A simple method to determine the relative stereochemistry of statine amino acids (gamma-amino-beta-hydroxyacids) by using (1)H NMR spectroscopy is described. Configurational assignment of statine units within complex natural products is possible without degradation or derivatization as the syn and anti diastereomers can be distinguished by using a combination of chemical shift and coupling constant information derived from the alpha-methylene ABX system. Seventy-three examples are provided, demonstrating the scope and limitations of the methodology. These examples range in complexity from simple statine units to cyclic depsipeptides, such as tamandarin B.     

A simple method for determining potential parameters for anharmonic molecular vibrations

Analytical formulae allowing one to find in a simple way the parameters of a model potential for anharmonic molecular vibrations are presented.     

A simple automatic phototitrator for the determination of total carbonate and total alkalinity of sea water

An automatic photometric analyser based on the reversed use of a conventional motor syringe buret and modern optoelectronic components is described. The buret serves as a photometric titration vessel into which sample and reagents are selectively drawn through a set of solenoid valves. It has been applied to the photometric titration of total alkalinity and total carbonate concentration of sea water, giving precisions of 0.10% and 0.13%, respectively.     

一种确定煤基吸附剂内各扩散系数的简易方法

多孔介质内的扩散有分子扩散和表面扩散两种。在吸附温度较高时 ,表面扩散可忽略 ,而在温度较低的吸附过程中 ,两种扩散均须考虑。Ｓｃｈｎｅｉｄｅｒ和Ｓｍｉｔｈ[1 ] 曾用色谱法探讨了一种计算扩散系数的方法。他们认为等温吸附呈线性变化 ,引入了曲折系数 ,计算出分子扩散系数 (下称气相扩散系数 ) ,表面扩散系数 (下称吸附相扩散系数 )则由综合扩散系数减去分子扩散系数得到。文献 [2 ]则认为吸附过程非线性变化 ,服从Ｆｒｕｎｄｌｉｃｈ方程或Ｌａｎｇｍｕｉｒ方程。从质量平衡方程得出相对吸附量方程 ,再求出各扩散系数。前一种方法将…     

A simple method for determining water content in organic solvents based on cobalt(Ⅱ)complexes

A method to determine water content in organic solvents was developed based on the color change of cobalt(Ⅱ) nitrate in different solvents.The color-change mechanism and optimal conditions for determining the water content were investigated.The results showed that there was a good linear relationships between the absorbance of cobalt(Ⅱ) complexes in organic solvents and water contents withγin 0.9989～0.9994.This method has the advantages of low cost,good reproducibility,good sensitivity,simple in operation,fast in detection,friendly to the environment and no limitation on linear range for determining water content.It was used to determine water in samples with a satisfactory recovery in 97.81%～101.24%.     

Simple method for determining the amount of ion-exchange groups on chromatographic supports

The objective of this study was to develop a fast, simple, non-destructive, non-toxic and low-priced method for determining the amount of ionic groups on resins, since the conventional titration method fails to give proper results on methacrylate monoliths. After the column had been pre-saturated with a high concentration buffer solution, a low concentration buffer solution of the same pH value was pumped through the column. Measuring pH and absorbance, the profiles with a shape of typical break-through curve were obtained. It was shown that the time of the pH transient, which appeared under such conditions, could be used as a measure of the total ionic capacity of ion-exchange monolithic columns. The effect of the column length, linear velocity and varying concentrations of buffer solutions on the time of the pH transient was examined. The method was shown to be suitable for determining the amount of ionic groups on both anion and cation monolithic columns. In addition, it could also be applied to particle bed columns. The time of the pH transient and the protein dynamic binding capacity were also compared and it was concluded that for a given monolith the protein capacity can be derived from the data obtained by the new method.     

A test method for determining water in organic solvents

A test procedure is developed for determining water in acetone, dioxane, isobutanol, ethanol, petroleum ether, and ethyl acetate in the ranges 0.5–12; 0.5–10; 0.5–8; 0.5–6, and 0.5–4 vol %, respectively. Determination is based on the measurement of the acidity of a solution obtained upon adding citric acid or sodium hydrogen sulfate to organic solvents using an indicator test strip containing Congo red. The relative standard deviation of the results of analysis is 0.05–0.1; the duration of analysis is about 30 min.     

A semi-automated and manual method for determining the total phospholipid phosphorus in amniotic fluid

A rapid method for estimating the total phospholipid content of amniotic fluid has been described that requires 1 ml of sample. Perchloric acid containing a trace of molybdate is the acid digestant for inorganic phosphate release. After digestion at 225 °C for 30 min, dilution with water yields a solution with a hydrogen ion concentration of about 2.5 mol/liter that allows the use of stannous chloride-hydrazine sulfate as the reducing agent for phosphate color development. The color development and measurement may be carried out manually or with use of the AutoAnalyzer at an analysis rate of 40/hr. A coefficient of variation of about 7% and a standard deviation of 0.02 will be obtained with either the manual or semi-automated procedure.     

A simple rapid method for determining sucrose concentration in sucrose gradient centrifugation

Summary The red complex formed by hydroxyl groups with ceric ammonium nitrate served as a means for the rapid and direct determination of sucrose in sucrose gradient centrifugation both for analytical and preparative purposes. In the present work rabbit anti bovine serum albumin serum was separated into 7 S and 19 S components concentrating in the 17–20% sucrose and 26–28% sucrose range respectively.

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Zusammenfassung Die von Cerammoniumnitrat mit Hydroxylverbindungen unter Rotfärbung stattfindende Komplexbildung wurde zur raschen direkten Saccharosebestimmung bei der Rohrzucker- Gradientenzentrifugation für analytische und präparative Zwecke herangezogen. Im vorliegenden Fall wurde mit Antirinderserumalbumin sensibilisiertes Kaninchenserum in eine 7 S- und eine 19 S-Komponente getrennt, von denen erstere in 17- bis 20%igem Rohrzucker, letztere in 26- bis 28%igem Rohrzucker angereichert wurde.

     

A simple method for determining activation energies of organic reactions from DSC curves

An approximate formula for a rapid and simple estimation of activation energies from DSC curves is given and applied to various homogeneous reactions. The results obtained are compared with the approximate values of the Duswalt method and with the results by the mathematically more demanding method of Borchardt and Daniels (additional application of multiple linear regression). In this connection the efficiency of the new approximation method is demonstrated.     

A simple method for the determination of amitrole in drinking and ground water

Summary A high-performance liquid chromatographic method with amperometric detection is described for determining residue levels of amitrole in drinking and ground water. Samples with concentrations up to 1 ppb can be injected directly. By application of a simple evaporation enrichment step the limit of determination is 0.1 ppb.     

A simple method for determining the multilayer effects in adsorption of alcohols on silica gel

The excess adsorption isotherms ofn-pentanol, pentan-2-ol and 2-methylbutan-2-ol from binary and ternary solutions in benzene andn-heptane were measured. Experimental adsorption data are discussed in terms of a multilayer model of the surface phase. The main assumption of this model is that the surface layers being near the solid surface contain the molecules of the preferentially adsorbed component only. The phase-exchange reaction of molecules between bulk phase and last surface layer has been taken into account.On the basis of this theory it has been established for the investigated systems that the surface phase contains three molecular layers. Simultaneously appropriate surface phase capacities were determined.

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Eine einfache Untersuchungsmethode für Mehrschicht-Effekte bei der Adsorption von Alkoholen an Kieselgel

Zusammenfassung Die Adsorptionsisothermen binärer und ternärer flüssiger Mischungen vonn-Pentanol, 2-Pentanol oder 2-Methyl-2-butanol in Benzol und/odern-Heptan wurden bezüglich Kieselgel gemessen. Die experimentellen Daten der Adsorption wurden mittels des Mehrschichts-Modells der Oberflächenphase diskutiert. Die Hauptvoraussetzung dieses Modells ist die Annahme, daß die Oberflächenschichten, die sich in der Nähe des Kieselgels befinden, nur Moleküle der bevorzugt adsorbierten Komponente enthalten. Es wurde auch die Phasen-Austauschreaktion von Molekülen zwischen Phaseninnerem und der letzten Oberflächenschicht in Betracht gezogen.Auf der Basis dieser Theorie wurde für die untersuchten Systeme festgestellt, daß die Oberflächenphase aus drei Molekülschichten besteht. Außerdem wurden die ermittelten Volumina der Oberflächenphase berechnet.

     

A sensitive and simple extractive-spectrophotometric method for the determination of microgram amount of cobalt by using alpha-benzilmonoxime.

Alpha-benzilmonoxime has been used for the extraction and determination of cobalt at microgram amount. The reagent reacts with cobalt(II) in the pH range of 8.8 - 9.3 to form a yellow-color chelate, which is extracted in chloroform, toluene, and some other non-polar solvents. The chelate is stable in chloroform for about one day. Under the optimum conditions of the a-benzilmonoxime concentration and pH of 9.0, Beer's law was obeyed in the concentration range of 0.08 - 2.2 microg/ml cobalt. The molar absorptivity of the extracted species was 2.55 x 10(4) dm3/mol cm at 380 nm, with a detection limit of 0.01 microg/ml cobalt. Relative standard deviations of 0.4, 0.8 and 2.3% were found for the determination of cobalt concentrations of 2.2, 1.1 and 0.08 microg/ml, respectively. The effect of diverse ions on the determination of 1.00 microg/ml of cobalt has been studied. The method was applied to the determination of cobalt in vitamin B12 and B-complex ampoules, a Co2O3-Co3O4 laboratory chemical mixture and some synthetic alloy samples. The method is sensitive, simple, rapid and accurate.     

Karl Fischer titration A method for determining the true water content of cereals

A variation of the Karl Fischer titration was developed to measure the water content of cereals such as various grains and flours. The presented method is based on an elevated working temperature. It can even reach the boiling point of the working medium which contains methanol as solvent. The influence of different sample preparations is also discussed. A standardized procedure could be found to achieve highly reproducible and statistically safe results. The proposed titration method can be carried out with titrators of different manufacturers. The method may serve as a reference technique for these products and, by consequence, as calibration method for other more rapid methods, which may then be used in the daily laboratory practice or in industrial production lines. Received: 28 April 1997 / Revised: 17 July 1997 / Accepted: 24 July 1997