A rapid method for the determination of organic carbon in soil

TIURIN'S method for the determination of organic carbon in soil is modified to give results practically identical with those of the dry combustion method. The standard deviation of a single determination is only 12%. By using 50 mg of soil and 10 ml of 0.2 N dichromate solution, soils with a carbon, content up to 12% can bo analysed. The method is suitable for all soils except those containing much chloride or reducing substances other than organic carbon Carbonates do not interfere.     

The titrimetric determination of sulphate,thiosulphate and polythionates in mining effluents

A titrimetric procedure is described for the determination of various forms of sulphur (sulphate, sulphite, thiosulphate, dithionate, tri- and tetrathionates after conversion to sulphate) in mining effluents. Metal ions are removed, after an oxidizing step, by a cationexchange resin, and the sulphate is precipitated with a known excess of 0.01 M barium chloride at pH 3.5. The excess of barium is back-titrated with standard 0.01 M ethylenediaminetetraacetic acid (EDTA) solution to a o-cresolphthalein complexone end-point at pH 11.0. The results obtained are in good agreement with those obtained by lengthy gravimetric procedures. Indirectly, dithionate can be determined, and sulphate and oxidizable thio salts such as thiosulphate and di-, tri-, and tetrathionates can be distinguished.     

Simple chemical method for the determination of carbon dioxide in air

A method was proposed for the direct determination of carbon dioxide in air using a sorption tube specially constructed for this purpose. The method is based on measuring the volume of air consumed for the neutralization of a known amount of barium oxide hydrate in the tube by carbon dioxide contained in air. The equivalence point is detected by the minimum electrical conductance of the barium hydroxide solution. To verify the accuracy of the method, a technique based on the use of a calibration mixture of air with the CO₂ concentration varying by the inverse exponential law was developed. The method is suitable for the determination of CO₂ in air in a wide concentration range and for the verification and calibration of indirect methods for the determination of CO₂. With an insignificant decrease in accuracy, the equivalence point can be detected by the change in the color of phenolphthalein. This significantly simplifies the method and allows its wide use in practice, e.g., in laboratory works in environmental science or for demonstration purposes in educational organizations.     

Notes on analytical procedures : Determination of carbon dioxide

For the determination of carbon dioxide, methods suitable for general applications are described. a. Macro-titration method. The CO2 is absorbed in sodium hydroxide in a bubble column filled with glass beads. The excess of NaOH is titrated after the addition of BaCI2. b. Scmi-micro-titration method. The CO2 is absorbed in barium hydroxide, the excess of which is determined by titration with 0.1 n hydrochloric acid on cresolphthalein as the indicator. The absorption and titration are performed in a special vessel in which the liquid is kept in circulation by the injected stream of air. c. Gravimetrical method.Method b. is specially recommended.     

The determination of nitrogen in nitrocellulose

A method for the determination of nitrogen in nitrocellulose has been developed. The sample is dissolved in concentrated sulphuric acid and a salicylic acid solution is added. The nitrosalicylic acid formed is reduced at room temperature with an excess of titanous chloride solution and the excess is estimated by titration with ferric alum. Statistically designed experiments were used to establish the conditions necessary for accurate results. The procedure is more rapid than the usual nitrometer method and gives results of high precision; e.g. on a mean result of about 13.8% nitrogen, the standard deviation is 0.014.     

Conductometric determination of carbon in uranium carbide and its solution in nitric acid

A simple but accurate method has been developed for the determination of carbon in uranium carbide powders/pellets as well as in solutions of uranyl nitrates. The methodology involves quantitative conversion of carbon present in the sample to carbon dioxide that is subsequently absorbed in a dilute solution of barium hydroxide. The conductivity shift of the barium hydroxide solution is monitored on-line continuously using a laboratory-built PC-based conductivity measurement system that has been developed in-house based on the direct conversion of conductance to the digital pulse frequency. A new gas absorption cell has been designed to ensure quantitative absorption during the residence time of the gas in the cell. The method is sensitive, accurate and precise to 1-3% at 600-1000 mug of carbon in samples of uranium carbide.     

A wet chemical method for the estimation of carbon in uranium carbides

A wet chemical method for the estimation of carbon in uranium carbides has been developed, based on oxidation with a saturated solution of sodium dichromate in 9M sulphuric acid, absorption of the evolved carbon dioxide in a known excess of barium hydroxide solution, and titration of the excess of barium hydroxide with standard potassium hydrogen phthalate solution. The carbon content obtained is in good agreement with that obtained by combustion and titration.     

The determination of sulphate by flow-injection analysis with exploitation of pH gradients and EDTA

A modified method for the turbidimetric determination of sulphate as barium sulphate is proposed. The carrier stream is an alkaline barium—EDTA solution; the sample zone is sufficiently acidic to allow precipitation of barium sulphate. The excess of EDTA in the carrier stream ensures that residual precipitate is redissolved and the system kept clean.     

A rapid spectrophotometric method for the determination of carbon monoxide in ambient air

A sensitive spectrophotometric method for the determination of carbon monoxide is described, based on the reduction of palladium(II) by carbon monoxide. The resulting elemental palladium is reacted with iodate in acidic medium in the presence of chloride, to produce an ICl(-)(n) species that is readily extracted as an ion-pair with Pyronine-G into benzene. Measurement of the absorbance of the extract at 535 nm permits the determination of carbon monoxide down to 1 mul/l. in air. The effect of interfering gases is discussed. The method is suitable for determination of carbon monoxide in motor vehicle exhaust gases and ambient air.     

Molecular absorption spectrometry by electrothermal evaporation in the graphite furnace-X Determination of chloride traces by AlCl ma in graphite cuvettes after liquid-liquid extraction of chloride with triphenyltin hydroxide

The determination of traces of chloride by means of the molecular absorption of AlCl in graphite cuvettes is described. An extraction method for separation and preconcentration of the chloride has been developed, to avoid matrix effects. Extraction was done with 0.03M triphenyltin hydroxide in o-xylene, and stripping with 0.025M barium hydroxide. The method is sensitive and specific for chloride. The detection limit is about 1.5 ng of chloride, and the chloride content of 20 ml of 10(-7)M solution can be determined. The determination is possible in presence of excess of bromide and iodide.     

Electrothermal atomic-absorption determination of barium in brines and caustic soda solutions

A method is described for the determination of barium at trace levels (0.2-2.5 ng) in the presence of a large amount of sodium chloride or sodium hydroxide (up to 750,000-fold) by electrothermal atomic-absorption spectrophotometry. The method involves making the sample solutions 1M with respect to nitric acid and directly injecting 5-mul aliquots into a pyrolytic-graphite furnace. Sodium chloride can be completely removed during the ashing stage of the heating cycle, without chemical pretreatment. On the basis of experimental results obtained, an explanation for the negative deviation of the calibration graphs noticed in ETA-AA is given, with nickel and barium atomization data as examples. Factors affecting the atomization peak shape and sensitivity for barium are also discussed.     

Gravimetric determination of barium in zirconium metal and in certain zirconium salts

Barium may be determined gravimetrically in quantities ranging from 0.2 to 2.0 mg (± o.1 mg) in hydrated zirconyl chloride and in zirconium metal after complete separation of the zirconium. As much as 10 g of zirconium may be removed by a double precipitation in a (3 to 1) hydrochloric acid medium followed by a cupferron precipitation-chloroform extraction of the residual zirconium. The barium is then determined gravimetrically as barium sulfate in the iron-free, zirconium-free filtrate by precipitation with an excess of ammonium sulfate. As much as 0.015% barium has been found in impure zirconyl chloride, 0.004% in commercial “purified” zirconyl chloride, 0.000% barium in crystal bar zirconium metal and 0.003% barium in zirconium metal sheet. Reproducibility is 0.001%.     

Titrimetric determination of gold by precipitation with hydroquinone

A rapid method for the volumetric determination of gold is described. Gold(III) is reduced to metal with excess of hydroquinone at room temperature and the excess is titrated with ceric sulphate. The effect of chloride ion on the reducibility of gold(III) to the metal is discussed. This method can be successfully employed for the determination of gold in presence of certain base and noble metals. The method was successfully adopted for the determination of gold in a commercial sample.     

The determination of zirconium in fluoride-containing solutions

In the recommended procedure the zirconium is first precipitated from solution as the insoluble barium fluozirconate. After separation, the precipitate is dissolved in a mixture of nitric and boric acids and the zirconium is then precipitated as its hydroxide. This precipitate is separated, dissolved in hydrochloric acid and this solution is evaporated to fumes of perchloric acid to remove completely fluoride ions. The zirconium content is then determined volumetrically by adding a slight excess of a standard solution of ethylenediaminetetra-acetic acid and back titrating with a standard iron solution at pH 2.3 using potassium benzohydroxamate as indicator and the photometric technique for end-point detection. This method is applicable to the determination of milligram amounts of zirconium in fluoride-containing nitric or hydrochloric acid solutions provided that the concentration of these acids is below 3N. It is also suitable for the determination of zirconium in the presence of any of the following elements - uranium, titanium, niobium, tantalum, molybdenum, tungsten, lead, iron, copper and tin.     

Spectrophotometric determination of chloride in barium sulphate precipitates following isolation of the analyte

A spectrophotometric method was developed for the determination of chloride concentrations between 0.2 and 5 mgL^?1 in barium sulphate precipitates, obtained by precipitation of sulphate in concentrations of 50 to 250 mgL^?1 or even lower. The proposed method involves prior dissolution of the barium sulphate precipitate in hot conc. sulphuric acid and collection of the released hydrogen chloride by means of gaseous nitrogen. The analytical calibration function was obtained by the least-squares procedure from 10 determinations at each of three concentration levels of a standard solution of chloride. The lack of fit of experimental points to the least-squares straight line was found to be negligible at a significance level of 5%. Blank measurements were required in all instances as the blank absorbance varied with time.     

Turbidimetric determination of some sulphur compounds in ethanol from fermentation

A simple method is described which can be used for the determination of certain sulphur compounds found in industrial ethanol obtained from fermentation of molasses. The method is based on the turbidimetric determination of sulphate after the sample has been treated with dilute hydrogen peroxide solution, by precipitation of the sulphate with barium chloride under appropriate conditions. Several samples of fermentation ethanol have been analysed by this method and the sulphur contents found compared with the total acidity.     

Voltammetric determination of bisphenol A in food package by a glassy carbon electrode modified with carboxylated multi-walled carbon nanotubes

A highly sensitive and mercury-free method for determination of bisphenol A (BPA) was established using a glassy carbon electrode that was modified with carboxylated multi-walled carbon nanotubes. A sensitive oxidation peak is found at 550?mV in linear sweep voltammograms at pH?7. Based on this finding, trace levels of bisphenol A can be determined over a concentration range that is linear from 10?nM to 10⁴?nM, the correlation coefficient being 0.9983, and the detection limit (S/N?=?3) being 5.0?nM. The method was successfully applied to the determination of BPA in food package.

Radiometric determination of sulfate

A radiometric procedure for the determination of sulfate based upon the precipitation of barium sulfate is described with a sensitivity of about 0.01 μg/ml. Carrier-free³⁵SO₄ is added to the sample to measure the chemical recovery. The sulfate is precipitated with an excess of barium having a known specific activity of¹³³Ba. The amount of¹³³Ba determined by gamma counting is directly related by stoichiometry to the amount of sulfate in the precipitate.     

Bioaccumulation and determination of lead using treated-Pennisetum-modified carbon paste electrode

The present work describes the development and application of a carbon paste electrode modified by treated-Pennisetum setosum for the determination of lead(II) by anodic stripping differential pulse voltammetry. Most experiments were performed using the preconcentration/voltammetry/regeneration scheme. The resulting modified electrode offers a preferential uptake of lead(II) from solutions. Operational conditions, such as percentage treated-Pennisetum loading in the carbon paste, pH of electrolyte solution, ionic strength, preconcentration time, voltammetric waveform and interference are characterized and optimized to allow quantitative determination of lead. The electrode surface can be regenerated by immersing the modified electrode in 0.05 mol l⁻¹ hydrochloric acid for 2 min. For the measurement step, the optimum conditions were acetate buffer pH 5.0 and 0.60 ionic strength with the preconcentration time of 5 min. The modified electrode contained 10% (w/w) treated-Pennisetum. The detection limit (3σ) was 0.01 mg l⁻¹ Pb(II). For 16 preconcentration/measurement/renewal cycles, the responses could be reproduced with a 5.39% relative standard deviation. This method has been be successfully applied to the determination of lead(II) in natural water samples using standard addition method.     

Colorimetric determination of carbon in titanium

A method is proposed for the colorimetric determination of carbon in titanium. In the method the sample is dissolved in a mixture of sulfuric and fluoboric acids, and nitric acid is added to dissolve the titanium carbide. The solution is boiled and filtered, and the yellow coloration from the nitrated organic complex is read with a spectrophotometer. A spectrophotometric study of the color was made. A comparison was made between the colorimetric determination of carbon in titanium and the colorimetric determination of carbon in steels. The proposed method is rapid and is readily adaptable to the determination of carbon in a large number of samples at one time. The procedure is designed for titanium containing up to 0.7 per cent. carbon. None of the elements encountered in “commercially pure” titanium metal interferes.