Scientific Papers

for Microwave Digestion with ETHOS systems

  • Agriculture

    There is a broad literature describing the use of microwave-assisted acid digestion for preparing agriculture samples. The use of closed vessels operated at high pressure allows exploring the oxidizing properties of nitric acid at high temperatures and avoids the use of perchloric acid. This is a major achievement coming from microwave technology and by itself justifies its large use for digestion of plant tissues. Additionally, it was demonstrated in several analytical procedures the feasibility of working with diluted acid nitric solutions and the effect of hydrogen peroxide in the recovery of nitric acid during the initial steps of digestion. Then, we may summarize that most digestions of plant tissues can be performed by using an oxidizing mixture composed by a nitric acid solution containing from 2 to 7 mol/L plus a small volume of concentrated hydrogen peroxide. Maximum temperatures around 220 C should lead to efficient oxidation processes resulting in digests containing residual carbon contents compatible with further measurements using spectro-analytical techniques. For plant tissues containing high amounts of silicon, such as grass and sugarcane leaves, the use of HF may be needed depending on the analytes that will be determined. In this case, residual HF must be removed or reacted with boric acid for avoiding chemical attack to glass and quartz parts of the equipment, such as ICP-OES and ICP-MS.

"An attempt to correlate fat and protein content of biological samples with residual carbon after microwave-assisted digestion"
Araujo et al, Spectrochimica Acta Part B 57 (2002) 2121–2132

"Effect of acid concentration on closed-vessel microwave-assisted digestion of plant materials"
Carrilho et al, Fresenius J Anal Chem (2001) 371 : 536–540

"A critical evaluation of digestion procedures for coffee samples using diluted nitric acid in closed vessels for inductively coupled plasma optical emission spectrometry"
Castro et al, Talanta 78 (2009) 1378–1382

"Direct determination of arsenic in acid digests of plant and peat samples using HG-AAS and ICP-SF-MS"
Frank et al, Analytica Chimica Acta 530 (2005) 307–316

"Inductively Coupled Plasma Application for the Classification of 19 Almond Cultivars Using Inorganic Element Composition"
Pratsmoya et al, J. Agric. Food Chem. 1997, 45, 2093 − 2097

"Fast method of elements determination in slim coffees by ICP OES"
Szymczycha-Madeja et al, Food Chemistry 146 (2014) 220–225
  • Beverage

    Selected applications deal with microwave-assisted digestions of fruit juices, coffee, milk, beer and wine samples aiming the determination of several elements using different analytical techniques. Standard digestions conditions are proposed and all procedures used mixtures containing nitric acid and hydrogen peroxide. Most procedures have used concentrated reagents, but it seems feasible to use nitric acid diluted solutions. Sample volumes should be chosen considering the volume of the closed digestion vessels to avoid over pressurization. The choice of the vessel is also related to the requested sample throughput. These applications represent typical examples where microwave radiation can efficiently be used for oxidation of organic compounds and reducing sample volumes in a clean closed environment compatible with trace analysis requirements using modern spectro- analytical techniques.

"Simultaneous determination of hydride (Se) and non-hydride-forming (Ca, Mg, K, P, S and Zn) elements in various beverages (beer, coffee, and milk), with minimum sample preparation, by ICP–AES and use of a dual-mode sample-introduction system"
Asfaw et al, Anal Bioanal Chem (2005) 382: 173–179

"Evaluation of the combined measurement uncertainty in isotope dilution by MC-ICP-MS"
Fortunato et al, Anal Bioanal Chem (2003) 377 : 111–116

"Determination of essential elements (Cu, Fe and Zn) in juices of commercially available in Pakistan"
Jalbani et al, Food and Chemical Toxicology 48 (2010) 2737–274

"Certification of the lead mass fraction in wine for comparison 16 of the International Measurement Evaluation Programme"
Quétel et al, J. Anal. At. Spectrom., 2001, 16, 1091–1100

"Determination of Inorganic and Total Arsenic in Wines by Hydride Generation Atomic Absorption Spectrometry"
Tasev et al, Microchim. Acta 149, 55–60 (2005)

"Determination of Inorganic and Total Arsenic in Wines by Hydride Generation Atomic Absorption Spectrometry"
Krste Tasev et al, Microchim. Acta 149, 55–60 (2005)

"Rapid assessment of metal contamination in commercial fruit juices by inductively coupled mass spectrometry after a simple dilution"
Luciano Tormen et al, Journal of Food Composition and Analysis 24 (2011) 95–102

"Evaluation of trace element contents of powdered beverages from Turkey"
Mustafa Tuzen et al, Journal of Food and Nutrition Research Vol. 47, 2008, No. 3, pp. 120–124

"Column system using diaion HP-2MG for determination of some metal ions by flame atomic absorption spectrometry"
Mustafa Tuzen et al, Analytica Chimica Acta 504 (2004) 325–334
  • Ceramics

    Generally ceramic materials have a refractory behavior with a high thermal and chemical resistance. These characteristics are useful for a plethora of technological applications, but make this class of materials hardly digested using conventional acid mixtures. Just as a parallel, we may say that nowadays most samples containing high amounts of organic samples can be digested using a mixture of nitric acid and hydrogen peroxide at high temperatures in a closed vessel able to support high pressure. On the other hand, the digestion of ceramic samples is critically dependent on the choice of the acid mixture. Despite its hazardous, frequently HF must be used for digesting materials with high amounts of silica or resistant metals, such as molybdenum, tungsten, and vanadium. All selected papers here listed used Milestone technology for digesting samples of alumina, aluminum nitride, boron nitride, silicon nitride, cements, niobium oxides, cobalt-substituted lithium nickelate, and pottery. Digestion mixtures were composed by nitric, hydrofluoric, boric, phosphoric acids and hydrogen peroxide. Time of heating programs varied up to 140 min and in general temperatures were not stated. It is important to point out that when using modern microwave technology for digesting pottery samples, nitric acid without any other acid lead to an efficient digestion. In this case, Rončević et al. emphasized that “the utilization of upgraded microwave digestion that allows pressure higher for an order of magnitude and higher pressure in reaction vessels has resulted in more effective decomposition of archaeological pottery shards” (Anal. Methods,4:2506-2514,2012). The reading of respective papers for specific and detailed information is strongly recommended.

"Direct Analysis of Tungsten in Crude Niobium Petoxide using microwave digestion and ICP-OES"
Gopala Anil et al, Acta Chim. Slov. 2003, 50, 335-342

"Determination of 14 trace element concentrations in two Dillinger Huttenwerke Portland cement reference materials by sector field and quadrupole ICP-MS"
Wim Devos and Christoph Moor, J. Anal. At. Spectrom., 2002, 17, 138–141

"Chemical characterization of ancient potteries from Himera and Pestavecchia necropolis (Sicily, Italy) by Inductively Coupled Plasma – Optical Emission Spectrometry (ICP–OES)"
Maria Rosaria Mannino, Santino Orecchio, Microchemical Journal 97 (2011) 165 – 172

"High-Pressure Microwave Dissolution of Ceramics Prior to Trace Metal Determinations by Microwave Induced Plasma Atomic Emission Spectrometry "
Henryk Matusiewicz , Mikrochim. Acta 111, 71-82 (1993)

"Microwave Digestion of Thermoluminescent Aluminium-Oxide Powders and Determination of Trace Impurities by Inductively Coupled Plasma Optical Emission Spectroscopy"
Gabor Molnar et al, Mikrochim. Acta 134, 193-197 (2000)

"Determination of major, minor and trace elements in cobalt-substituted lithium nickelate ceramic powders by inductively coupled plasma optical emission spectrometry"
Yodalgis Mosqueda et al, Anal Bioanal Chem (2006) 386:1855 – 1862

"Determination of chemical composition of pottery from antic Siscia by ICP-AES after enhanced pressure microwave digestion"
Sanda Roncevic et al, Anal.Methods, 2012, 4, 2506–2514
  • Biological

    Literature data about application of microwave-assisted digestion for clinical samples is abundant. Once again, the use of closed vessels operated at high pressure allows exploring the oxidizing properties of nitric acid at high temperatures and avoids the use of perchloric acid. Most selected procedures recommended the use of a digestion mixture composed by nitric acid and hydrogen peroxide. One work shown below has exploited the use of alkaline conditions, particularly tetra-methyl ammonium hydroxide, which is a convenient reagent for samples of animal tissues containing high amounts of fats. Two critical points to be considered for clinical samples are contamination and sample throughput. Contamination is a critical issue because the widespread use of inductively coupled plasma mass spectrometers with extremely high sensitivity. Most contamination and losses are solved by using closed vessels built using specially designed materials. Sample throughput may be addressed by proper choice of rotors with higher number of vessels and careful control of both pressure and temperature during digestion.

"Determination of chromium and nickel in human blood by means of inductively coupled plasma mass spectrometry "
Alimonti et al, Analytica Chimica Acta 306 (1995) 35-41

"Quantification of trace elements by sector field inductively coupled plasma mass spectrometry in urine, serum, blood and cerebrospinal fluid of patients with Parkinson’s disease"
Bocca et al, Spectrochimica Acta Part B 59 (2004) 559–56

"High-throughput microwave-digestion procedures to monitor neurotoxic elements in body fluids by means of inductively coupled plasma mass spectrometry"
Bocca et al, Anal Bioanal Chem (2003) 377 : 65–70

"Determination of silicon in biological samples by ICP-OES after non-oxidative decomposition under alkaline conditions"
S. Hauptkorn · J. Pavel · H. Seltner, Fresenius J Anal Chem (2001) 370 : 246–250

"Development of an ICP–HRIDMS method for accurate determination of traces of silicon in biological and clinical samples"
Patrick Klemens · Klaus G. Heumann, Fresenius J Anal Chem (2001) 371 : 758–763

"The Potential of Inductively Coupled Plasma Mass pectrometry (ICP-MS) for the Simultaneous Determination of Trace Elements in Whole Blood, Plasma and Serum "
Krachler and Irgolic, 1. Trace Elements Med. BioI. Vol. 13, pp. 157-169 (1999)

"Optimization of microwave digestion for determination of selenium in human urine by flow injection-hydride generation-atomic absorption spectrometry"
Fangshi Li et al, Anal. Commun., 1998, 35, 361–364
  • Cosmetics

    There are few applications of microwave-assisted digestion for preparing cosmetics samples. This sector is increasingly controlled because of public health concerns and this aspect certainly will lead to an expansion of these procedures. An overview of the literature shows that digestion is generally based on a reagent mixture composed by nitric acid plus hydrofluoric acid. The former acts as an oxidant since cosmetics samples typically contain high amounts of organic constituents; the latter is important for digesting silica and silicate compounds frequently present in cosmetics matrices. The use of hydrofluoric acid requires its removal by evaporation or its complexation with boric acid before measurements using inductively coupled plasmas for avoiding chemical attack to the sample introduction components and to the quartz torch.

"Levels of nickel and other potentially allergenic metals in Ni-tested commercial body creams"
B. Bocca et al, Journal of Pharmaceutical and Biomedical Analysis 44 (2007) 1197–1202

"Heavy metals in powder-based cosmetics quantified by ICP-MS: an approach for estimating measurement uncertainty "
B. Bocca et al, Anal.Methods, 2013, 5, 402
  • Environmental

    Determination of metals and organic compounds in environmental samples is required for many purposes and legislation clearly puts a demand on the development of modern analytical procedures able to prepare large amounts of samples in as short as possible time. Sample throughput and green chemistry procedures are critical needs and microwave- assisted procedures are helping to deal with this demand. Digestion and extraction procedures are frequently applied for preparing solutions before determinations using either spectro-analytical or chromatographic techniques. Taking into account the typical huge number of samples in environmental studies with temporal and spatial sampling the capability of treating large batches of samples simultaneously is required and using microwave technology this aspect is associated with fast heating and suitable control of losses and contamination. Additionally, the use of lower amounts of reagents and energy is compatible with modern trends in green chemistry.

"Fundamentals, methods and future trends of environmental microwave sample preparation"
A. Agazzi, C. Pirola, Microchemical Journal 67 2000 337-341

"Determination of lead and other metals in a residential area of greater Calcutta"
Amit Chatterjee U, R.N. Banerjee, The Science of the Total Environment 227 1999 175-185

"Chemical Oxygen Demand Using Closed Microwave Digestion System"
DHARMADHIKARI et al, Environ. Sci. Technol. 2005, 39, 6198 - 6201

"Multi-element analysis of soil and sediment by ICP-MS after a microwave assisted digestion method"
Falciani et al, J. Anal. At. Spectrom., 2000, 15, 561-565

"Microwave assisted sample preparation for determining water-soluble fraction of trace elements in urban airborne particulate matter: Evaluation of bioavailability"
Karthikeyan et al, Analytica Chimica Acta 576 (2006) 23–30

"The optimization of microwave digestion procedures and application to an evaluation of potentially toxic element contamination on a former industrial site"
Okorie et al, Talanta 82 (2010) 1421–1425

"Optimization and validation of a new method of analysis for polycyclic aromatic hydrocarbons in sewage sludge by liquid chromatography after microwave assisted extraction"
Villar et al, Analytica Chimica Acta 524 (2004) 295–304
  • Food

    Microwave-assisted digestion of food samples may be considered similarly to plant tissues, animal tissues or beverages depending on the main constituents of the matrices. Consequently, most procedures will rely on the combination of nitric acid and hydrogen peroxide. Selected procedures demonstrated the application of tetra-methyl ammonium hydroxide, extraction with an acetone-water mixture, use of hydrofluoric acid for a silicon-rich sample, and diluted solutions of nitric acid. As mentioned for other sample matrices containing high amounts of organic compounds, it is advisable to add the reagent to the sample and to left the vessel open in order to avoid the fast formation of gases that may cause sudden increase of pressure during the first step of microwave-assisted heating. Conditions established using closed vessels are fully compatible with trace analysis determination further carried out using spectro-analytical techniques. Contamination and losses are completely controlled by using closed vessels.

"Determination of trace element concentrations in tomato samples at different stages of maturation by ICP OES and ICP-MS following microwave-assisted digestion"
Fernanda C. Bressy et al, Microchemical Journal 109 (2013) 145 – 149

"Optimisation of the microwave-assisted extraction of pigments from paprika (Capsicum annuum L.) powders"
Gergely A. Csiktusnadi Kiss et al, Journal of Chromatography A, 889 (2000) 41–49

"Determination of cadmium, lead, iron, nickel and chromium in selected food matrices by plasma spectrometric techniques"
Francesco Cubadda, Andrea Raggi, Microchemical Journal 79 (2005) 91–96

"Determination of trace elements in pumpkin seed oils and pumpkin seeds by ICP-AES"
Iva Juranovic et al, J. Anal. At. Spectrom., 2003, 18, 54–58

"Analysis of 20 trace and minor elements in soy and dairy yogurts by ICP-MS"
E.J. Llorent-Martínez et al, Microchemical Journal 102 (2012) 23 – 27

"Determination of volatile elements in biological materials by isotopic dilution ETV-ICP-MS after dissolution with tetramethylammonium hydroxide or acid digestion"
Dirce Pozebon et al, Talanta 51 (2000) 903 – 911

"Certification measurement of the cadmium, copper and lead contents in rice using isotope dilution inductively coupled plasma mass spectrometry"
Emilia Vassileva, Christophe. R. Quétel, Analytica Chimica Acta 519 (2004) 79–86