Microwave-assisted nitric acid digestion of organic matrices

Кубракова, И. В.; Formanovsky, A. A.; Kudinova, T. F.; Kuz’min, N. M.

doi:10.1070/mc1998v008n03abeh000935

Cited by 6 publications

(9 citation statements)

References 10 publications

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“…The most comprehensive information on the intensification of complexation under the action of MW has been obtained for platinum metal compounds (Table 2) some chemical forms of which are extremely inert towards ligand substitution. 43 It was found that radiation substantially intensifies the reduction of metals (at the same temperature), 25,50,57 markedly shortens the reaction time and often makes it possible to exclude the use of stabilising additives. The composition of complexes thus formed does not change.…”

Section: A Complex Formation In Solutionsmentioning

confidence: 99%

“…Microwave oxidation of individual organic compounds (amino acids, stearic acid, monosaccharides) forming the basis for the most important natural products (proteins, fats and carbohydrates) has been studied. 73,74 Figure 3 shows the temperature and pressure variation in the system vs. time during the oxidation of phenylalanine by nitric acid; Figure 4 presents the Arrhenius dependence of the total pressure in the system, which is proportional, in the chosen approximation, 4 to the rate constant for the oxidation, on the reciprocal temperature. The data for the calculation of the activation energies for the oxidation of some model compounds and natural products are listed in Table 3.…”

Section: Oxidation Of Organic Compounds By Inorganic Acidsmentioning

confidence: 99%

“…Later, the activation energies for the oxidation of a number of model organic compounds were determined; these data were shown to be suitable as the basis in choosing for conditions for decomposition of natural products. 74 The principles of selection of the conditions for microwave decomposition depending on the sample weight, the rate of temperature rise, the volume of the reaction mixture and the total volume of the vessel have been considered in detail by Knapp. 115…”

Section: Digestionmentioning

confidence: 99%

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Microwave radiation in analytical chemistry: the scope and prospects for application

Кубракова¹

2002

Russ. Chem. Rev.

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We examine the theoretical basis for the enhancement of classical, dielectric actuation by first imposing an elongation ('pre-strain') in one of the two directions in the plane of the working elastomeric filling between flexible electrodes. Such anisotropic actuation has been shown experimentally to be effective in delivering more mechanical work from a given applied voltage. A wrinkling instability in the in-plane direction perpendicular to the load limits the applicability of this strategy. It is shown to intervene before pull-in.

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Section: A Complex Formation In Solutionsmentioning

confidence: 99%

Section: Oxidation Of Organic Compounds By Inorganic Acidsmentioning

confidence: 99%

Section: Digestionmentioning

confidence: 99%

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Microwave radiation in analytical chemistry: the scope and prospects for application

Кубракова¹

2002

Russ. Chem. Rev.

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“…The higher temperatures reached in the closed system give microwave digestion a kinetic advantage over hot plate digestion, as described by the Arrhenius equation, which, when integrated, gives (1) In this expression, k 1 and k 2 are rate constants for the reaction of interest at temperatures T 1 and T 2 , respectively; E a is the activation energy; and R is the ideal gas constant. This equation shows that the reaction rate increases exponentially with increasing temperature, which translates into ~100-fold decrease in the time required to carry out a digestion at 175 °C when compared with a digestion at 95 °C (16,17). In addition, because the mineral acid converts the microwave energy into heat almost instantaneously, rapid sample heating is achieved, further decreasing the reaction times.…”

Section: Me Ec C F Fu Un Nd Da Am Me En Nt Ta Al Ls Smentioning

confidence: 99%

Peer Reviewed: Microwave-Enhanced Chemistry

Richter¹,

Link²,

Kingston³

2001

Anal. Chem.

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“…Nitric acid is frequently employed for digestion of organic samples due to its safe manipulation, facility of purification and oxidative characteristics. [15][16][17] Typically, 2-5 mL of nitric acid is sufficient for digestion of 200 mg of sample, 18,19 and H 2 O 2 is generally used as an auxiliary oxidant agent. 20 Excellent results also have been obtained by using diluted acids, 2,13,14 yielding greener procedures by drastic reduction of the wastes for large scale analysis.…”

Section: Introductionmentioning

confidence: 99%

A green analytical procedure for determination of copper and iron in plant materials after cloud point extraction

Silva

Oliveira

Rocha

2010

J. Braz. Chem. Soc.

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Um procedimento analítico limpo baseado em extração em ponto nuvem é descrito para a determinação de cobre e ferro em materiais vegetais. Após a digestão da amostra em frascos fechados em forno de microondas, empregando mistura oxidante diluída (HNO 3 + H 2 O 2 ), os íons metálicos foram simultaneamente extraídos como complexos hidrofóbicos formados com 1,2-tiazolilazo-2-naftol (TAN) usando Triton X-114 como agente extrator. Íons cobre e ferro foram determinados por espectrometria de absorção atômica com chama (FAAS) e ferro também por espectrofotometria de absorção molecular UV-Vis. Nas medidas por FAAS, os limites de detecção (99,7% de confiança) foram estimados em 1 e 10 µg L -1 para cobre e ferro, respectivamente. Respostas lineares para ambos os analitos foram observadas no intervalo de 25-200 µg L -1 . O fator de enriquecimento foi estimado em 30, com extração quantitativa dos complexos avaliada por medidas na solução sobrenadante remanescente após extração. Para a determinação de ferro por espectrofotometria UV-Vis, o limite de detecção (99,7% de confiança) foi estimado em 1 µg L -1 , com resposta linear entre 6 e 60 µg L -1 . A exatidão do procedimento foi avaliada pela determinação dos metais em materiais de referência certificados e os resultados foram concordantes com os valores certificados no nível de confiança de 95%. O consumo de reagentes foi de 1 mL HNO 3 , 1,1 mL H 2 O 2 , 50 mg Triton X-114 e 150 µg TAN por determinação.A green analytical procedure exploiting cloud point extraction for determination of copper and iron in plant materials is presented. After sample digestion with a diluted oxidant mixture (HNO 3 + H 2 O 2 ) in a closed vessel microwave oven, metal ions were simultaneously extracted as hydrophobic complexes formed with 1,2-tiazolylazo-2-naphthol (TAN) using Triton X-114 as extracting agent. Copper and iron were determined by flame atomic absorption spectrometry (FAAS) and iron also by UV-Vis spectrophotometry. For FAAS, the detection limits (99.7% confidence level) were estimated as 1 and 10 µg L -1 for copper and iron, respectively. Linear responses for both analytes were observed in the 25-200 mg L -1 range. The enrichment factors were estimated as 30 for both analytes and the extraction was quantitative, as evaluated by measurements in the supernatant solution remaining after extraction. For iron determination by UV-Vis spectrophotometry, the detection limit was estimated as 1 mg L -1 , with linear response within 6 and 60 mg L -1 . The accuracy of the procedure was evaluated by determination of the metals in certified reference materials and the results agreed with the certified values at the 95% confidence level. In the whole procedure, the reagent consumption was 1 mL HNO 3 , 1.1 mL H 2 O 2 , 50 mg Triton X-114 and 150 mg TAN per determination.Keywords: green analytical chemistry, cloud point extraction, FAAS, spectrophotometry, plant materials, copper, iron IntroductionCopper and iron are important for plant nutrition, being classified as essential micronutrients and usual...

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Microwave-assisted nitric acid digestion of organic matrices

Cited by 6 publications

References 10 publications

Microwave radiation in analytical chemistry: the scope and prospects for application

Microwave radiation in analytical chemistry: the scope and prospects for application

Peer Reviewed: Microwave-Enhanced Chemistry

A green analytical procedure for determination of copper and iron in plant materials after cloud point extraction

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