Microwave-Assisted Sample Combustion: A Technique for Sample Preparation in Trace Element Determination

Abstract

A novel digestion procedure based on sample combustion ignited by microwave radiation is proposed for organic samples. Certified samples of bovine liver, pig kidney, and skim milk were used as examples to demonstrate the performance of the proposed procedure. Cadmium and copper were determined in these samples by electrothermal atomic absorption spectrometry. Samples (between 50 and 250 mg) were wrapped with paper and placed on a homemade quartz holder that was positioned inside to quartz vessels used in a commercial microwave oven. Ammonium nitrate solution was added to the paper, and vessels were pressurized with oxygen to 15 bar. The rotor containing four vessels was placed inside the oven, and microwave radiation was applied for 20 s at 1400 W. Combustion was complete in few seconds, and an additional reflux step, which was optional, was applied. The agreement to the certified values was between 96 and 105% for both analytes. Only with the combustion step, the residual carbon (RC) was below 1.3%. The RC decreased to less than 0.4% when an additional reflux step with concentrated nitric acid was applied.

Microwave-Induced Combustion of Coal for Further Sulfur Determination by Inductively Coupled Plasma Optical Emission Spectrometry or Ion Chromatography

“…Even though MIC method can be considered simple and a general protocol can be proposed, 36 a careful optimization regarding sample mass and combustion behavior must be performed. Taking into account some differences in matrices and analytes, high pressure and incomplete combustion can be observed for some materials, providing a non-quantitative analytes recovery.…”

“…This is an important advantage of MIC in comparison with OFC and combustion bomb methods. 36 Thus, the use of a reflux step was evaluated (5 and 15 min of reflux or only combustion without reflux). For these experiments, the heating program was: (i) MIC without reflux: 60 s of microwave irradiation (1400 W) for burning the sample, followed by 20 min of cooling; or (ii) MIC with reflux: 5 or 15 min of microwave irradiation (1400 W) for burning the sample and reflux of the absorbing solution, followed by 20 min of cooling.…”

Determination of Trace Elements in Fluoropolymers after Microwave-Induced Combustion

“…The selection of absorber solution, particularly for combustion methods, impacts optimal recoveries and, while dependent on the nature of the analyte, should be compatible with the selected determination technique. 17 In general, concentrated acids are not required and dilute solutions can be used for most applications, thereby minimizing reagent consumption and its contribution to the procedural blank. Typically, nitric acid solutions are preferred due to their better compatibility with plasma conditions and because it is a convenient medium with which to keep analytes in solution.…”

“…16 A digestion method combining the advantages of classical combustion systems with those using closed systems heated by microwave radiation was recently proposed. 17 This microwave-induced combustion (MIC) method has been used for the digestion of organic samples in closed quartz vessels pressurized with oxygen and ignited by the application of microwave radiation. 18−28 In this system, the sample is placed on a small quartz holder positioned inside a high-purity quartz vessel.…”

Avaliação de métodos de extração para a determinação de cromo e níquel em formulações farmacêuticas e em matérias-primas usadas na fabricação de medicamentos à base de cefalexina e ciprofloxacino

“…16,17 Ainda, métodos alternativos podem ser utilizados, tais como, a piro-hidrólise 18 ou a combustão induzida por radiação micro-ondas. 19 Em muitos casos, a lixiviação dos analitos presentes nas amostras pode ser uma alternativa interessante aos métodos que empregam a destruição (ou dissolução) total da matriz, uma vez que os processos de extração são, em geral, mais rápidos e utilizam soluções diluídas de ácidos. 20,21 O objetivo desse trabalho foi avaliar a possibilidade de utilização de diferentes metodologias de extração para a determinação de Cr e Ni por GFAAS em amostras de formulações farmacêuticas e matérias-primas de uso farmacêutico contendo os antibióticos cefalexina e ciprofloxacino.…”