Determination of traces of molybdenum in foods by electrothermal atomic absorption spectrometry

Low levels of molybdenum in different food samples were determined by atomic absorption spectrometry with electrothermal atomization after destruction of organic matter using four different methods, involving dry ashing at 600°C, wet digestion with heating with nitric/sulphuric and nitric/sulphuric/perchloric acid mixtures or direct extraction with dilute hydrochloric acid. In all cases the working conditions, reproducibility, precision and accuracy were investigated. The dry ashing method was generally the optimum destruction method.     

Extraktions-spektrophotometrische Bestimmung von Zinn in Fein- und Hüttenblei

A method suitable for the determination of 0.001–0.2% of tin in lead is described. Quadrivalent tin is extracted from the sample solution (6–8 N in hydrochloric acid) by a solution of Amberlite LA-2 in xylene and back-extracted into the aqueous phase by dilute nitric acid. After evaporation of the acidic extract and destruction of the organic matter tin is determined in the residue by Lukes method with 9-phenylfluorone as reagent.     

Electrolytic destruction of organic matter in urine

A novel electrolytic method has been developed for destroying organic matter in urine. A combination of potassium permanganate, sulfuric acid and nitric acid has yielded about 99% destruction in initial organic content of urine within two hours when electrolysis is carried out with an applied voltage of about 2.5 V, while maintaining a current density of 8.23 mA/cm² at 373 K.     

Measurement of low vapour pressures according to the Knudsen effusion method

The exact measurement of low vapour pressures during recent years has become increasingly important, particularly for environmental problems caused by organic chemicals. Not only for this but for many other fields information about the phase transition solid - gas and liquid - gas is of great scientific interest. In this work a brief survey of the determination of vapour pressures with thermo-analytical methods is made. In particular the thermo-gravimetric vapour pressure measurements by means of a Knudsen cell and a newly developed vapour pressure balance for exact measurement of very low vapour pressures are described. Applications for organic materials (fungicides, benzoic acid, oils) are discussed.     

Determination of carboxylic acid vapour by a thickness-sheer-mode acoustic wave sensor coated with crown ethers

The frequency response sensitivities for 39 organic vapours by thickness-sheer-mode (TSM) acoustic wave sensors coated with monobenzo-15-crown-5 (B15C5), monobenzo-18-crown-6 (B18C6) and dibenzo-30-crown-10 (DB30C10) have been reported. It shows that crown ethers are the most efficient adsorptively active material for sensing carboxylic acid vapour, particularly B15C5 can be used for sensing formic acid vapour. The B15C5 based sensor possesses good reproducibility, high stability and short response time with wide linear detection range and a low detection limit down to 0.0201 mg l(-1) (about 5.70 ppm, V/V) of formic acid vapour while coating with 12 mug of B15C5. There is no significant interference from other organic vapours except for some nitrogen containing compounds such as diethylamine, pyridine and N,N-dimethylformamide, and carboxylic acid homologues such as acetic and propionic acids. The effect of humidity is easily controllable. Compared with acid-base titration method, the sensor can be used for the determination of HCOOH vapour with recovery rate of 98.4 approximately 103.8%, the analytical results are in good agreement with those obtained by the more time consuming acid-base titration method.     

Use of x-ray microtomography to visualise dynamic adsorption of organic vapour and water vapour on activated carbon

X-ray microtomography coupled with image analysis was used to quantify the adsorption of vapours on activated carbon beds. This technique was tested using three different challenges: CCl₄, water vapour and a mixture of water- and organic vapour. It is shown that the used technique allows determining the adsorption front progress in the case of organic vapour and mixture of water and organic vapour whereas the existence of this front was not so obvious in the case of water vapour. Experimental results obtained for organic vapours were interpreted on the basis of the Wheeler-Jonas equation: a good agreement was found between experimental and theoretical breakthrough times.     

Determination of Thallium In Solid Environmental Samples By Electrothermal Atomic Absorption Spectrometry

Abstract

A method for the determination of thallium in solid environmental samples is developed. After destruction of the sample, TI(III) is extracted from 0.5 M hydrobromic acid solution into diisopropyl-ether. the organic phase is evaporated and the residue taken up in a mixture of sulfuric and nitric acids. Measurements are carried out with an atomic absorption spectrometer with Zeeman background corrector. the accuracy of the method is tested by analysis of certified reference materials and the method is applied to fly ash and emitted particulate matter from a municipal refuse incinerator and to soil samples.     

Digestion method for the determination of mercury in vegetable matrices by cold vapour atomic absorption spectrometry

A simple and rapid wet-digestion procedure is described for the determination of total mercury in botanical samples by cold vapour atomic absorption spectrometry. The method is based on the oxidising properties of potassium dichromate in dilute sulphuric acid and was tested on two National Institute of Standards and Technology Standard Reference Materials. The mass of the samples taken for analysis was about 0.5 g in all instances, corresponding to an amount of mercury of the order of 0.075-0.040 micrograms depending on the material. The results were compared with those obtained using the Association of Official Analytical Chemists official digestion technique, which involves the use of nitric and sulphuric acids, and a second technique based on the action of nitric and perchloric acids. The proposed method provided better accuracy and showed good precision. Its ability to achieve the decomposition of two organomercurials for full mercury recovery was verified.     

Microanalytical determination of tin in organotin compounds

Existing procedures for the determination of tin in organotin compounds are reviewed, and a new procedure is described which can be used for the rapid microanalysis of most organotin compounds. Wet oxidation with sulphuric acid and 30% hydrogen peroxide is followed by spectrophotometric determination of the extracted ternary tin(IV)-chloride-oxine complex in chloroform. Time for a single determination is 20 min, and the relative standard deviation is 0.7% for 1-5 mg of tin. On account of their volatility, methyltin compounds must be subjected to a sealed-tube wet oxidation in sulphuric-nitric acid mixture. Addition of sulphamic acid after boiling to remove most of the nitric acid makes this compatible with the solvent extraction step. Tin present as organotin stabilizer in PVC samples can also be determined by this method, after destruction of the organic matter with sulphuric acid and 50% hydrogen peroxide.     

Determination of the total iron content of used lubricating oils by atomic-absorption with use of emulsions

A new method is proposed for the determination of the total iron content of used lubricating oils. It is based on treatment of the samples with a mixture of hydrofluoric and nitric acids (without destruction of the organic matter) and emulsification, followed by atomic-absorption measurement. This allows the use of aqueous standards and provides a simple, rapid, inexpensive and accurate method, that is not affected by the particle size of the solids in the oil.     

Determination of saturated organic vapour concentrations by a spectroscopic method

A spectroscopic method for determination of organic saturated vapour concentrations is presented. From absorption spectra, an empirical equation is established relating absorbance with the temperatures of the cell and its side arm. Application to determination of benzene vapour concentrations, as well as the heat of vaporization referred to 0 K is described: the value 47.90 ± 0.03 kJ mol⁻ was obtained.     

Critical comparison of two standard digestion procedures for the determination of total mercury in natural water samples by cold vapour atomic absorption spectrometry

Two pretreatment procedures for total mercury determinations in natural water samples were compared. The first, the Swedish Standard method (DP1), involves digestion of water in the presence of concentrated nitric acid at 120°C and under pressure for 30 min. In the West German Standard method (DP2), small volumes of nitric and sulphuric acids, permanganate and peroxodisulphate are added to the sample, and digestion proceeded at 50°C in an ultrasonic bath. Mercury was determined after both digestion procedures using a modified cold vapour atomic absorption spectrometric method, in which mercury generated on addition of a reducing agent is collected and subsequently atomized in a platinum-lined graphite furnace. The efficacy of the two digestion procedures was tested using various standard organic mercury compounds and it was found that only DP2 provided quantitative recoveries. Purification of the reagents required by DP2 was achieved using a mercury-selective ion-exchange resin, Chelite S, resulting in blank levels below 1.5 ng Hg l^?1. Both methods were applied to the determination of total mercury in an unpolluted marsh water sample, giving 2.0 ng Hg l^?1 (DP1) and 2.7 ng Hg l^?1 (DP2). The West German Standard digestion procedure (DP2) is recommended for the determination of total mercury in natural water samples.     

Determination of Cd, Cu, Pb and Zn in environmental samples: microwave-assisted total digestion versus aqua regia and nitric acid extraction

We validated the determination of the content of Cd, Cu, Pb and Zn using two digestion protocols: a microwave-assisted total digestion and an aqua regia extraction procedure based on the International Organization for Standardisation (ISO) 11466 method. Our goal in validating these two protocols, along with a nitric acid digestion, is to propose a rapid, cheap and easily automated digestion method for monitoring heavy metal content in environmental samples. We applied the digestion protocols to samples with a wide range of organic matter such as sediments, soils, sludges and plant material.For samples with a low carbonate or organic matter contents, such as sediments and agricultural soils, aqua regia digestion in an aluminium block was revealed to be an optimum estimator for the total metal content. For samples with a high organic matter content, such as organic horizons of forest floor layers, plant material and organic soils, nitric acid digestion could substitute microwave (MW)-hydrofluoric acid (HF) digestion. Except in a few samples with high organic matter or low heavy metal content, the RSD values obtained after the application of the proposed digestion procedures were lower than 5%. Based on the obtained results, a decision flow chart for choosing the fit-for-purpose digestion procedure is suggested.     

Indirect determination of low vapour pressures using solid-phase microextraction--application to tetrachlorobenzenes and tetrachlorobenzyltoluenes

There is still a gap of reliable vapour pressure data at ambient temperature for low volatile organic substances due to the difficult and time-consuming determination using the classical methods. Static headspace extraction with a solid-phase microextraction (SPME) fibre in combination with gas chromatographic analysis provides an inexpensive tool for the indirect determination of low vapour pressures down to 10(-5) Pa. The procedure consists of two steps: (a) exposure of SPME fibre in the headspace above the test chemical over minutes to hours and (b) desorption and quantification of extracted amount. The calibration was performed using low volatile reference substances with well-known vapour pressures. A good correlation was found between substance uptakes of SPME fibre and vapour pressures. The method was applied, e.g. to tetrachlorobenzenes and to selected tetrachlorobenzyltoluenes with questionable vapour pressures. We obtained values between 0.98 and 13.5 Pa for the former and results between 0.13 and 0.68 mPa for the latter group of congeners. The scope of the method can be extended to substances with even lower vapour pressures, provided that reliable reference data are available.     

Thermogravimetric analysis for boiling points and vapour pressure

A TGA instrument has been adapted for rapid measurement of boiling points and vapour pressure at temperatures from ambient up to 400°C and pressures from ambient down to 20 mm Hg. Samples were contained in sealed holders having a laser-drilled aperture. Several organic liquids in the 100 to 300 gMW range showed good agreement with reference vapour pressure data. Sample mass, heating rate, and use of inert diluents were important variables affecting accuracy of vapour pressure measurements.     

A novel sequential injection--Cold vapour atomic absorption spectrometric system for rapid and reliable determination of mercury

A simple and rapid method is described for reliable determination of ultra-trace concentrations of mercury based on a novel combination of a sequential injection (SI) system with cold vapour atomic absorption spectrometry (CVAAS). The SI-CVAAS method achieved a very high sampling frequency of 180h(-1), a detection limit of 0.2-0.3ngmL(-1), a dynamic range of 0-60ngmL(-1) and requires only 0.2-0.6mL of sample. The presence of common metal ions, such as Cu(2+), Pb(2+), Cd(2+), Zn(2+), Fe(3+), Co(2+), Ni(2+) and Mn(2+), did not interfere with the measurement of mercury by this method. Also the interference from organic matter, such as humic substances, was easily reduced or eliminated by appropriate sample dilution. The method was successfully applied to the determination of mercury in lake sediment samples and a river sediment reference material. An average percentage recovery of 101.2% was achieved by the SI-CVAAS method for mercury in the reference material with a R.S.D. of 1.8%.     

Electro-oxidative process for the mineralization of solvent and recovery of plutonium from organic wastes

Mediated electrochemical oxidation is a promising technique for the destruction of organic compounds. Destruction of tributyl phosphate (TBP) in normal paraffin hydrocarbon (NPH) in nitric acid medium containing electro-generated Ag(II) was studied. Initially, the effect of uranium, presence of DBP along with uranium in the organic phase and direct electrochemical oxidation without catalyst (Ag) on the destruction of 30% TBP/NPH system was evaluated. For a comparison, the rate of destruction of NPH alone was studied. Further, radioactive laboratory waste solution was tested for the destruction of organic waste under similar experimental conditions. The electrolyte used in the system was 0.5 M AgNO₃ in 8 M HNO₃ at 333 K. The uniqueness in all these experiments is the use of a double end open porcelain diaphragm for the isolation of electrodes. Though there would be a slight reduction in the efficiency, two major hurdles viz., reduction in the concentration of nitric acid and reduction in the volume of catholyte resulting in an increase in cell voltage were avoided. The problem of the migration of Ag⁺/Ag²⁺ and accumulating at the cathode site was overcome by using double end open diaphragm and thorough mixing. The results revealed that the rate of destruction of organics is favoured in the presence of uranium in organic phase and with increase in temperature.     

Mercury speciation in environmental samples by cold vapour atomic absorption spectrometry with in situ preconcentration on a gold trap

A method has been developed for the determination of total and organic mercury in biological materials and sediments. A microwave assisted mineralization of the organic mercury, after its extraction from the matrix, is described. This procedure warrants complete transformation of Hg(II) and, consequently, the quantitative reduction to Hg(0). The conditions for mercury reduction were optimized by a central composite design. The preconcentration of the analyte has been achieved by amalgamation on a trap system, consisting in a pyrolytic graphite platform wound by a gold wire. Mercury was determined by cold vapour atomic absorption spectrometry. The method was validated by the analysis of two certified reference materials and applied to the determination of total and organic mercury species in mussel tissues and sediments. The method is simple and practical, and offers the advantage of not requiring special equipment to measure inorganic and organic mercury simultaneously.     

Isothermal microcalorimetry perfusion experiments: A method to verify the relative vapour pressure of organic liquids inside the sample vessel

Perfusion microcalorimetry is frequently applied to expose pharmaceutical solids to specific relative vapour pressures (RVP) of organic liquids or water. The aim was to set up a general procedure to check the performance of a vapour pressure control device used to create a specific RVP. This was achieved by identifying and checking the significant factors in the creation of the RVP inside the reaction vessel. The flow switch valve was tested by volume flow measurements whereas the saturation of the wet line was verified in a calorimetric experiment employing methanol as model solvent. The results of the measurements were used to calculate the RVP inside the reaction vessel. The method developed is suitable to test the vapour pressure control device. It can be applied for any solvent.     

Mutual irradiation graft copolymerization of acrylic acid on to nylon-6 via liquid and vapour phases

Liquid phase and vapour phase grafting of acrylic acid on to nylon-6 were performed by the mutual irradiation technique. Liquid phase direct irradiation grafting was carried out in air either in the presence or in the absence of redox salt. The redox salt led to a sharp increase in the grafting yield and prevented excessive homopolymerization of acrylic acid. The effects of total dose, solvent type and composition, and monomer concentration on the direct grafting in the liquid and vapour phases were studied The data indicate that, if conditions were kept fixed, the vapour phase technique gives rise to lower grafting yields than the liquid phase method.