Name: Homogeneização e digestão ácida de amostras de alimentos para determinação multielementar
Uploaded: 2023-12-22T12:50:00
Description: Watch this Scientific Journal Video about Homogenization and Acid Digestion of Food Samples for Multi-Elemental Determination at JoVE.com

homogenization and acid digestion of food samples for multi-elemental determination

Homogeneização e digestão de amostras de alimentos para análise de vários elementos

Elemental analysis is an analytical process for determining the elemental composition of various samples. It can be used to control the intake of metals into human bodies (especially heavy metals1) since their high concentrations may cause unwanted health problems. Heavy metals are also one of the main environmental contaminants, therefore, control of their presence in the environment is necessary2. Moreover, elemental analysis can be employed to determine the geographical origin of food products3 and to control the quality of food and water resources4. In addition, it is used for the determination of micro- and macronutrients in soils5 and to gain insights into geological processes throughout history by examining the chemical composition of minerals and sediments6. Studies have also been made to determine the presence of rare metals in electrical and electronic waste for further metal regeneration7, to evaluate the success of drug treatments8, and to verify the elemental composition of metal implants9.
Inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma optical emission spectroscopy (ICP-OES) are commonly used techniques for the elemental analysis of various samples10. They allow simultaneous determination of multiple elements with limits of detection (LOD) and limits of quantification (LOQ) as low as ng/L. In general, ICP-MS has lower LOD values11 and a wider linear concentration range compared to ICP-OES12. Other techniques to determine elemental composition are microwave-induced plasma optical emission spectrometry13 and several variants of atomic absorption spectroscopy (AAS), including flame atomic absorption spectroscopy, electrothermal atomic absorption spectroscopy2, cold vapor atomic absorption spectroscopy, and hydride generation atomic absorption spectroscopy14. Furthermore, elemental determination with low LOD and LOQ is possible with different electroanalytical methods, especially with anodic stripping voltammetry15,16. Of course, there are other methods to determine the elemental composition of samples, but they are not as frequently employed as the above-mentioned methods.
Direct elemental determination of solid samples is feasible using laser-induced breakdown spectroscopy and X-ray fluorescence17. However, for elemental determination with ICP-MS, ICP-OES, and AAS it is necessary to convert solid samples into a liquid state. For this purpose, acid digestion is performed using acids and auxiliary reagents (in most cases H2O2). Acid digestion is carried out at elevated temperature and pressure, converting the organic part of the sample into gaseous products and converting the metal elements into water-soluble salts, thus dissolving them in the solution18.
There are two main types of acid digestion, open vessel digestion and closed vessel digestion. Open vessel digestion is cost-effective14 but has limitations, such as the maximum digestion temperature, which coincides with the boiling temperature of acids at atmospheric pressure. The sample can be heated on hot plates, heating blocks, water baths, sands baths2, and by microwaves19. By heating the sample in that manner, much of the generated heat is lost to the surroundings20, which extends the digestion time14. Other disadvantages of open vessel digestion include greater chemical consumption, the greater possibility of contamination from the surrounding environment, and possible loss of analytes due to the formation of volatile components and their evaporation from the reaction mixture21.
Closed vessel systems are more convenient for the digestion of organic and inorganic samples compared to open vessel systems. Closed vessel systems utilize a variety of energy sources to heat the samples, such as conduction heating and microwaves22. Digestion methods which use microwaves include microwave-induced combustion23, single reaction chamber systems24, and commonly used microwave-assisted wet acid digestion (MAWD)25,26. MAWD allows digestion at higher operating temperatures, ranging between 220 &#176;C and 260 &#176;C and maximum pressures up to 200 bar, depending on the instrument&#39;s working conditions27.
The efficiency and rate of MAWD depend on several factors, including the chemical composition of the samples, the maximum temperature, the temperature gradient, the pressure in the reaction vessel, the amount of acids added, and the concentration of acids used28. In MAWD, complete acid digestion can be achieved in a few minutes due to the elevated reaction conditions compared to longer-lasting digestions in open vessel systems. Lower volumes and concentrations of acids are required in MAWD, which is in line with current green chemistry guidelines29. In MAWD, a smaller amount of sample compared to open vessel digestion is needed to perform acid digestion, usually up to 500 mg of sample is sufficient30,31,32. Larger sample quantities may be digested, but they require a larger amount of chemicals.
Since the instrument for MAWD automatically controls the reaction conditions and the person does not come in direct contact with the chemicals during heating, MAWD is safer to operate than open vessel digestions. However, the person should always proceed with caution when adding chemicals to the reaction vessels to prevent them from coming into contact with the body and causing harm. Reaction vessels also need to be opened slowly as the pressure is built up inside them during acid digestion.
Although acid digestion is a useful technique for preparing samples for elemental determination, the person performing it should be aware of its possible limitations. Acid digestion may not be suitable for all samples, especially those with complex matrices and those that are highly reactive or could react explosively. Therefore, sample composition should always be evaluated to select the appropriate chemicals and reaction conditions for complete digestion that dissolves all desired elements in the solution. Other concerns that the user must consider, and address are impurities and loss of analytes at every step of sample preparation. Acid digestion must always be performed according to specific rules or using protocols.
The protocol described below provides instructions for the homogenization of food samples in a laboratory-sized mixer, a procedure for cleaning the mixer&#39;s components, properly weighing the sample, adding chemicals, performing acid digestion by MAWD, cleaning the reaction vessels after the digestion is complete, preparing the samples for elemental determination, and performing a quantitative multi-element determination with ICP-MS. By following the instructions given below, one should be able to prepare a sample suitable for elemental determination and perform the measurements of digested samples.

Autor em destaque: tecnologias e desafios na análise elementar de amostras de alimentos

Preparação de Amostras de Alimentos Utilizando Homogeneização e Digestão Ácida Úmida Assistida por Micro-ondas para Determinação de Multielementos com ICP-MS

Our research aims to determine the elemental composition of different food samples using different spectroscopic devices to, for example, control the quality of food samples. Besides ICP-MS, our laboratory can also perform elemental analysis of the digested food samples with ICP-OES, atomic absorption spectroscopy, and ion chromatography. However, we can also perform elemental analysis with X-ray photoelectron spectroscopy, and time-of-flight secondary ion mass spectrometry.Current experimental challenges that we face are mostly in the sample preparation process. Our goal is to improve the sample throughput and to optimize the cleaning procedure to minimize any carryover of the sample. The information in the article is about sample homogenization, acid digestion, and elemental analysis to better understand critical procedures for sample preparation and subsequent analysis as we highlight important steps, suggestions, and limitations of the entire process.We will focus on the optimization of the entire processes for samples such as vegetables, wine, ice creams, E-liquids, and in the future, even inorganic samples, which require different sample preparation techniques.

Watch this Scientific Journal Video about Homogenization and Acid Digestion of Food Samples for Multi-Elemental Determination at JoVE.com

Homogeneização e digestão ácida de amostras de alimentos para determinação multielementar

Para começar, use uma faca de cerâmica limpa para cortar manualmente amostras de alimentos em pedaços menores. Transfira as amostras para copos de vidro de 250 mililitros. Em seguida, coloque as amostras em um secador a 105 graus Celsius até que não haja alteração de peso.Em seguida, transfira a amostra seca para um copo misturador. Triture a amostra até que ela se transforme em um pó fino ou uma pasta homogênea. Com uma espátula de plástico limpa, transfira a amostra homogeneizada para um copo de vidro de 50 mililitros.Em seguida, pese 250 miligramas da amostra em um recipiente de reação aberto em uma balança analítica. Quando a pesagem estiver completa, cubra o recipiente de reação com sua tampa. Em seguida, transfira-o para um exaustor.Agora abra as tampas dos vasos de reação. Em seguida, pipetar cinco mililitros de ácido nítrico a 68% e um mililitro de peróxido de hidrogênio a 30% em cada recipiente de reação. Com uma pipeta de 200 microlitros, adicione 37,5 microlitros de solução padrão ICP multielemento em recipientes de reação para um teste de recuperação de picos.Certifique-se de que cada amostra sem cravos e com pontas seja preparada em triplicata. Coloque as tampas dos recipientes de reação e rosqueie a tampa de rosca nos vasos de reação para apertar as tampas de cobertura. Deixar que as amostras reajam com os ácidos durante dois a três minutos.Para realizar a digestão ácida úmida assistida por micro-ondas, distribua os vasos de reação fechados simetricamente no rack de micro-ondas. Insira o rack na câmara de micro-ondas e monte-o em um suporte. Em seguida, feche a porta do micro-ondas.Digerir as amostras usando o programa de digestão selecionado, enquanto monitora a mudança nas condições de reação na tela. Quando a digestão estiver completa, retire a cremalheira da câmara do forno. Feche a porta do instrumento e desligue-o.Agora abra lentamente as tampas dos vasos de reação para liberar quaisquer gases formados durante a digestão. Gire os vasos de reação em direção ao exaustor. Com um funil de vidro, transfira quantitativamente a amostra digerida para um balão volumétrico de vidro limpo de 25 mililitros.Diluir a amostra com água ultrapura até à marca no balão. Em seguida, feche a boca do balão com uma rolha e misture bem o conteúdo. Em seguida, conecte uma seringa de plástico de 20 mililitros a um filtro de seringa de poliamida.Encha a seringa com a amostra diluída. Em seguida, filtre seu conteúdo em um tubo de centrífuga de plástico de 50 mililitros. A homogeneização resultou em partículas finas da amostra, uniformes em tamanho e uniformemente distribuídas.A digestão ácida causou um aumento constante da temperatura com o tempo.

Research

JoVE Journal

Chemistry

Homogenization and Acid Digestion of Food Samples for Multi-Elemental Determination

Preparation of Food Samples Using Homogenization and Microwave-Assisted Wet Acid Digestion for Multi-Element Determination with ICP-MS

Sample preparation is crucial for elemental determination, and various techniques are available, one of which involves homogenization followed by acid ...