A critical evaluation of digestion procedures for coffee samples using diluted nitric acid in closed vessels for inductively coupled plasma optical emission spectrometry

Determination of the Elemental Composition of Coffee Using Instrumental Methods

“…Roasted coffees (beans or ground beans) are usually purchased in local markets (Rajwanshi et al 1997;Haswell and Walmsley 1998;Jaganyi et al 1999;Magalhaes et al 1999;Martin et al 1999;Jaganyi and Madlala 2000;Anderson and Smith 2002;Vega-Carrillo et al 2002;Krejcova and Cernohorsky 2003;Santos et al 2004;Anthemidis and Pliatsika 2005;Fernandes et al 2005;Zaidi et al 2006;Filho et al 2007;Grembecka et al 2007;Santos et al 2008;Castro et al 2009;Frankova et al 2009;Ashu and Chandravanshi 2011). Powdered or ground solid coffee samples are usually subjected to further stages of the elemental analysis without any special treatment (Frankova et al 2009).…”

“…Powdered or ground solid coffee samples are usually subjected to further stages of the elemental analysis without any special treatment (Frankova et al 2009). Otherwise, coffee beans or powdered coffees are manually or mechanically grinded using pestles with mortars or different kind of mills (ball, knife, and cryogenic) and sieved to select required particle size fractions, i.e., 10-90, 15-260, 20-100, 30-190, 30-370, 50-100, 50-250, >70, and 100-500 μm, 1.7-2.0 mm (Magalhaes et al 1999;Jaganyi et al 1999;Jaganyi and Madlala 2000;De Nadai Fernandes et al 2002;Anthemidis and Pliatsika 2005;Tagliaferro et al 2007;Santos et al 2008;Castro et al 2009). Coffee beans could also initially be washed with distilled and de-ionized waters to remove surface contaminants.…”

“…This sample preparation step mostly aims at reducing matrix effects originating from organic compounds and releasing elements in the form of their simple ions (Filho et al 2007;Castro et al 2009). Apparently from the literature, two main types of digestion procedures are used for that purpose, i.e., the dry ashing in the atmosphere of air and the wet oxidative digestion.…”

“…Samples of laboratory roasted and ground green coffee beans, natural powdered, or soluble coffees (0.1-5.0 g) are commonly wet digested in pressurized closed vessel microwave assisted systems (Krejcova and Cernohorsky 2003;Fernandes et al 2005;Filho et al 2007;Oleszczuk et al 2007;Santos et al 2008;Castro et al 2009;Frankova et al 2009;dos Santos et al 2010), pressurized sealed vessels, i.e., Parr bombs (Anthemidis and Pliatsika 2005;Castro et al 2009), a Berghof apparatus (Krivan et al 1993), and open vessel systems with hot plates or heating blocks (Magalhaes et al 1999;Martin et al 1998aMartin et al , 1999Anderson and Smith 2002;Ribeiro et al 2003;Filho et al 2007), or a Kjeldahl apparatus (Ashu and Chandravanshi 2011). When samples of soluble coffee are digested, higher sample amounts (1-5 g) can be taken (dos Santos and de Oliveira 2001).…”

“…When samples of soluble coffee are digested, higher sample amounts (1-5 g) can be taken (dos Santos and de Oliveira 2001). In general, microwave-assisted digestion systems with pressurized (∼35 bars) closed vessels provide fast and complete decompositions of coffee samples under controlled temperatures (90-210°C) and without losses of volatile elements or the contamination of samples (Filho et al 2007;Oleszczuk et al 2007;Santos et al 2008;Castro et al 2009;dos Santos et al 2010). In addition, decomposition times and volumes of reagents in such systems can considerably be decreased (Castro et al 2009).…”