Low-temperature ashing of organic materials for determination of chloride

The low-temperature plasma ashing technique was applied to organic materials containing sodium chloride and residual ash was analyzed for chloride using ion chromatography. Recovery of the chloride was approximately 50%, while 20–30% of the chloride had been converted to chlorate. The remaining fraction of the chloride could have been volatilized due to electron and ion bombardments onto the sample surface within the glow discharge region. Pretreatment of the sample by impregnating with potassium carbonate improved the recovery of the chloride to 90% with practically no production of chlorate.     

Thick-target PIGE analysis of plant materials preconcentrated by dry ashing

An analytical methodology has been developed for the UV-spectrophotometric determination of carbaryl in waters after its preconcentration onto a polyether type polyurethane foam followed by on-line elution. The aforementioned strategy offers an easy way for in-field sampling and to improve the analytical sensitivity. Several chemical and flow variables (mass of sorbent, sample flow rate, sample volume and carrier flow rate) were studied to ensure the best performance of the system. Recovery studies, carried out on natural water samples spiked with known amounts of carbaryl at concentration levels between 250 and 500 mug l(-1), provided recovery percentages between 94 and 105%. A detection limit of 12 mug l(-1) was achieved and a variation coefficient of 3.4% was obtained at 0.50 mug ml(-1).     

Automated wet ashing and multi-metal determination in biological materials by atomic-absorption spectrometry

Ohne Zusammenfassung

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Automated wet ashing and multi-metal determination in biological materials by atomic-absorption spectrometry

     

Detection of defects in components made of dispersion-filled polymeric materials by the method of infrared thermography

A method allowing one to determine the presence of hidden defects in dispersion-filled polymeric materials by means of a thermal imager is studied. The results of studies of the determination of hidden defects in samples of dispersion-filled polymeric materials are reported. The dependence of the determination of hidden defects in samples of dispersion-filled polymeric materials on the method of the transfer of excess temperatures to the tested object is established.     

Use of high pressure in the reduction of organic chlorides with tri-n-butyltin hydride

The use of the high pressure technique enables reduction of organic halides by tri-n-butyltin hydride to be carried out in the absence of a catalyst or free radical initiator. It leads to a better conservation of the structure of the starting material during the reduction. In the case of some unsaturated halides, a new chemoselectivity has been observed in favour of the addition of the hydride on the carboncarbon double bond.     

Decomposition of aminotetrazole based energetic materials under high heating rate conditions

A T-jump/time-of-flight mass spectrometer (T-Jump/TOFMS) is used to probe the decomposition of several aminotetrazole containing energetic materials under very high heating rates of 10(5)-10(6) K/s. The materials investigated are 5-amino-1-methyl-1H-tetrazolium dinitramide (MeHAT_DN), 1,5-diamino-4-methyl-1H-tetrazolium dinitramide (MeDAT_DN), 1,5-diamino-1H-tetrazolium nitrate (DAT_N), 1,5-diamino-4-methyl-1H-tetrazolium azide (MeDAT_N3), and 5-aminotetrazolium dinitramide (HAT_DN). Subtle differences between materials in functional group placement and anion composition allow for further understanding of the decomposition pathway of the tetrazole structure and various anions. Two decomposition pathways for the tetrazole ring are observed, which result in the primary formation of HN(3) or N(2). The N(2) formation pathway occurs when functional groups are placed symmetrically around the tetrazole ring, whereas asymmetric placement results in HN(3) production. The differing anion compositions also show effects on thermal stability of the salts, as is demonstrated by a lower decomposition temperature for the azide containing salt compared to the similar dinitramide containing material. For the decomposition of the dinitramide molecule, high temperature (N(2)O forming) and low temperature (NO(2) forming) decomposition pathways are observed, as has been previously suggested.     

Determination of deuterium in organic compounds by infrared spectrophotometry

The Trenner-Arison-Walker method for the micro-analysis of deuterium in organic compounds involves oxidation of the compound with copper oxide in a sealed tube, collection of the water by vacuum distillation, and analysis of the water by infrared spectrophotometry. Experience in applying this technique to a variety of organic compounds in our laboratory has suggested a number of procedural modifications. These principally affect the methods of sample handling and water collection. Difficulties associated with temperature changes on the spectrophotometry of the deuterium-enriched water are overcome by differential analysis against natural-abundance water using a double-beam spectrophotometer.     

Thermal analysis of the dissociation of carbonate materials at high heating rate

The dissociation of carbonate materials under a high heating rate has been studied by means of specially constructed original apparatus which allows avoidance of the influence of gas diffusion on the decarbonation process, and acceleration of the measurements.

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Zusammenfassung Die Dissoziation von Calciumcarbonat bei hoher Aufheizgeschwindigkeit wurde mit einer eigens entwickelten DTA-Apparatur untersucht, bei der der Einfluss der Gasdiffusion vermieden und die Messung beschleunigt werden kann.

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Synthesis of tetrazoles by the reaction of furan and thiophene nitriles with organic azides under high pressure

Conclusions The reactions of furan and thiophene nitriles with organic azides under high pressure yielded compounds containing tetrazolefuran and tetrazolylthiophene fragments.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 461–463, February, 1985.     

Non-invasive identification of organic materials in wall paintings by fiber optic reflectance infrared spectroscopy: a statistical multivariate approach

The aim of this study is to develop a method for the non-invasive and in situ identification of organic binders in wall paintings by fiber optic mid-FTIR reflectance spectroscopy. The non-invasive point analysis methodology was set-up working on a wide set of wall painting replicas of known composition and using statistical multivariate methods, in particular principal component analysis (PCA), for the interpretation, understanding, and management of data acquired with reflectance mid-FTIR spectroscopy. Results show that PCA can be helpful in managing and preliminary sorting of the large amount of spectra typically collected during non-invasive measurement campaigns and highlight further avenues for research. The developed PCA model was finally applied to the case of a Renaissance wall painting by Perugino assessing it predictability as compared to the interpretation of the single spectrum.     

Raman and infrared vibrational modes of tricosane paraffin under high pressure

This paper reports an experimental study about the pressure dependence of the vibrational modes of tricosane paraffin (C₂₃H₄₈) investigated by in situ Raman and infrared spectroscopy in a diamond anvil cell (DAC). The main vibrational bands were followed up to 11 GPa and the observed behavior indicated a conformational disorder induced by pressure, corresponding to a transition from ordered to disordered state of the linear chains from 2 to 5 GPa followed by a transition to an amorphous state under pressure above 5 GPa. However, this behavior was reversible after compression–decompression cycle showing that this linear compound was structurally and chemically stable up to 11 GPa at room temperature.     

Accurate quantification and transformation of arsenic compounds during wet ashing with nitric acid and microwave assisted heating

Arsenous acid, dimethylarsinic acid (DMA), methylarsonic acid (MA), arsenic acid, arsenobetaine bromide (AB), trimethylarsine oxide (TMAO), arsenocholine iodide (AC), and tetramethylarsonium iodide (TETRA) were heated in a microwave autoclave with nitric acid to 100-300 degrees C. The arsenic compounds in the digests were separated with anion- and cation-exchange chromatography and determined with an inductively coupled plasma mass spectrometer as arsenic-specific detector. Arsenous acid was completely oxidized to arsenic acid at 100 degrees C. For a complete oxidation of MA and DMA to arsenic acid temperatures > 220 degrees C and > 280 degrees C were necessary. AB decomposed to arsenic acid via TMAO. Complete conversion was only obtained after heating the sample for 90 min to 300 degrees C. For a complete conversion of TMAO similar harsh conditions were necessary. AC was already substantially degraded to TMAO, TETRA and two unknown compounds at 100 degrees C. The unknown arsenic compounds were found only in the digests up to 160 degrees C. Quantitative conversion of AC to arsenic acid went also via TMAO. At temperatures above 220 degrees C TETRA started to convert to TMAO, which then was further converted to arsenic acid. To investigate whether the results obtained for the arsenic standards are transferable to real samples, the certified reference material DORM-2 was also heated in nitric acid with variable digestion temperatures and times. For an almost complete conversion of the AB present in DORM-2 90 min at 300 degrees C were necessary. Total organic carbon (TOC) was less < 0.2% when DORM-2 was heated at temperatures > or = 260 degrees C for 60 min. UV photo-oxidation of DORM-2 was investigated as an alternative sample decomposition. Only 6% of AB was converted to arsenic acid when DORM-2 was irradiated for 2 h at 1000 W. In contrast to microwave heating substantial amounts of MA were observed as degradation product.     

The loss of lead in biological materials following different drying and ashing procedures

The loss of lead in various kinds of biological materials after drying and ashing is studied by using²⁰³Pb as tracer which is intraveneously injected into mice. The experimental results show that although the oven ashing can be used for determining the lead in samples of lung, kidney, and liver, etc., the oxygen plasma and high pressure digestion are the most suitable methods for the determination of lead in biological materials.     

Analysis of organic acids in wines by Fourier-transform infrared spectroscopy

Fourier-transform infrared (FTIR) spectroscopy has been a major point of development in many wine laboratories in recent years. It enables almost instant analysis of several properties of wine, usually with very good precision and accurate results. Nevertheless, validation procedures should not be forgotten and should be fully performed. Recovery experiments were performed by spiking wine samples with different amounts of organic acids (tartaric, malic, lactic, acetic and citric—the most prominent in wines). After FTIR analysis of the total acidity and of each organic acid concentration, recoveries were calculated. For total acidity recovery results were, in general, good and very close to 100% (64–111%). On the other hand, for individual organic acid concentrations, the recovery results were lower than 100% (11–73%) for all spiking additions. These results could be explained by spectroscopic interferences between the organic acids. Because they have similar infrared spectra, it is not easy to distinguish between them and, therefore, to achieve accurate calibration. When total acidity, with a different infrared spectrum from the other abundant compounds in the wine, was taken as a single property the recovery results were acceptable.     

Determination of total fluorine in vegetables and plants by open-flame ashing and microdiffusion : Comparison with furnace ashing and oxygen-flask combustion

The sample is ashed in a nickel crucible over an open flame with calcium hydroxide as the fixative; fluoride is separated by micro-diffusion and measured with a fluoride-selective electrode. The calcium hydroxide fixative permits a temperature of 800–850°C during the final ashing, so that insoluble silicates are decomposed and fluoride is converted to an acid-soluble form. Other advantages over furnace ashing at 600°C are less contamination and more rapid ashing (20 min compared to 6 h). The interference of aluminium and silica on microdiffusion was studied: perchloric acid was found to be preferable to sulphuric acid as medium. A new way for preparing calcium hydroxide suspension, low in fluoride, is described. The values found by the proposed method generally compare well with those obtained by oxygen flask combustion. Direct diffusion (i.e. without ashing) gave much lower values than the ashing methods, except for tea leaves.     

Thermally induced processes in mixtures of aluminum with organic acids after plastic deformations under high pressure

DSC is used to measure the thermal effects of processes in mixtures of solid organic dibasic acids with powdered aluminum, subjected to plastic deformation under pressures in the range of 0.5–4.0 GPa using an anvil-type high-pressure setup. Analysis of thermograms obtained for the samples after plastic deformation suggests a correlation between the exothermal peaks observed around the temperatures of degradation of the acids and the thermally induced chemical reactions between products of acid degradation and freshly formed surfaces of aluminum particles. The release of heat in the mixtures begins at 30–40°C. The thermal effects in the mixtures of different acids change according to the order of acid reactivity in solutions. The extreme baric dependences of enthalpies of thermal effects are associated with the rearrangement of the electron subsystem of aluminum upon plastic deformation at high pressures.     

An investigation on eutectic binary phase diagram of volatilizable energetic materials by high pressure DSC

The eutectic binary phase diagrams of volatilizable energetic material 1,3,3-trinitroazetidine (TNAZ) with 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX) and 1-methyl-2,4-dinitroimidazole (MDNI) have been investigated by high pressure differential scanning calorimeter (PDSC), respectively. The liquefying and melting processes of TNAZ/RDX and TNAZ/MDNI volatilizable systems have been studied. On the basis of the data of apparent fusion heat and liquefying temperature, the phase diagrams of apparent fusion heat (H) with composition (X) and liquefying temperature (T) with composition (X) were constructed, respectively. The results showed that the gasification or volatilization of easy volatile energetic materials could be efficiently restrained by high pressure atmosphere, and the perfect and ideal phase diagrams can be constructed. The eutectic temperatures for TNAZ/RDX and TNAZ/MDNI are measured to be 95.5 and 82.3 °C, respectively. The eutectic compositions of mole ratios for the two systems are obtained to be 93.55/6.45 (T–X method), 93.79/6.21 (H–X method) and 62.25/37.75 (T–X method), 63.29/33.71 (H–X method), respectively.     

Identification and quantification of the main organic components of vinegars by high resolution 1H NMR spectroscopy

A detailed analysis of the proton high-field NMR spectra of vinegars (in particular of Italian balsamic vinegars) is reported. A large number of organic substances belonging to different classes, such as carbohydrates, alcohols, organic acids, volatile compounds and amino acids, were assigned. The possibility of quantification of the substances identified in the whole vinegar sample, without extraction or pre-concentration steps, was also tested. The data validity was demonstrated in terms of precision, accuracy, repeatability and inter-day reproducibility. The effects of the most critical experimental parameters (sample concentration, water suppression and relaxation time) on the analysis response were also discussed. ¹H NMR results were compared with those obtained by traditional techniques (GC-MS, titrations), and good correlations were obtained. The results showed that ¹H NMR with water suppression allows a rapid, simultaneous determination of carbohydrates (glucose and fructose), organic acids (acetic, formic, lactic, malic, citric, succinic and tartaric acids), alcohols and polyols (ethanol, acetoin, 2,3-butanediol, hydroxymethylfurfural), and volatile substances (ethyl acetate) in vinegar samples. On the contrary, the amino acid determination without sample pre-concentration was critical. The ¹H NMR method proposed was applied to different samples of vinegars, allowing, in particular, the discrimination of vinegars and balsamic vinegars.     

Determination of beta-carotene in supplements and raw materials by reversed-phase high pressure liquid chromatography: collaborative study

Twelve laboratories representing 4 countries participated in an interlaboratory study conducted to determine all-trans-veta-carotene and total beta-carotene in dietary supplements and raw materials. Thirteen samples were sent as blind duplicates to the collaborators. Results obtained from 11 laboratories are reported. For products composed as softgels and tablets that were analyzed for total beta-carotene, the reproducibility relative standard deviation (RSDR) ranged from 3.35 to 23.09% and the HorRat values ranged from 1.06 to 3.72. For these products analyzed for trans beta-carotene, the reproducibility relative standard deviation (RSDR) ranged from 4.28 to 22.76% and the HorRat values ranged from 0.92 to 3.37. The RSDr and HorRat values in the analysis of a beadlet raw material were substantial and it is believed that the variability within the material itself introduced significant variation in subsampling. The method uses high pressure liquid chromatography (LC) in the reversed-phase mode with visible light absorbance for detection and quantitation. If high levels of alpha-carotenes are present, a second LC system is used for additional separation and quantitation of the carotene species. It is recommended that the method be adopted as an AOAC Official Method.