Optimization of microwave digestion and inductively coupled plasma-based methods to characterize cassava, corn and wheat flours using chemometrics Felipo Obed Correia a,b , Denisson S. Silva b , Silvânio Silvério Lopes Costa a,b , Izabel Kalini V. Silva c , Djalma Ribeiro da Silva c , José do Patrocínio H. Alves b , Carlos A.B. Garcia b,d , Tatiane de A. Maranhão c,e , Elisangela Andrade Passos b , Rennan G.O. Araujo a,b,d, ⁎ a Universidade Federal da Bahia, Departamento de Química Analítica, Instituto de Química, Salvador (BA), Brazil b Universidade Federal de Sergipe, Departamento de Química, São Cristóvão (SE), Brazil c Universidade Federal do Rio Grande do Norte, Instituto de Química, Natal( RN), Brazil d Instituto Nacional de Ciência e Tecnologia do CNPq – INCT de Energia e Ambiente, Universidade Federal da Bahia, Salvador, BA, Brazil e Universidade Federal de Santa Catarina, Departamento de Química, Florianópolis (SC), Brazil abstract article info Article history: Received 15 February 2017 Received in revised form 3 September 2017 Accepted 11 September 2017 Available online 12 September 2017 In this work, microwave-assisted digestion sample treatment and two ICP-based method operational conditions were optimized to determine 17 elements in cassava, corn and wheat flours using experimental design. The pro- posed analytical methods showed acceptable sensitivity, with limits of quantification for Ba, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Mo, Ni, P, S, Sb, Sr and Zn ranging from 0.02 μgg -1 (Cd, Co and Sb) up to 0.002% (S) employing induc- tively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma optical emission spectrom- etry (ICP OES). The accuracy of the analytical methods was confirmed by analysis of certified reference materials of rice flour (NIST 1568a), wheat flour (NIST 1567a) and Tea (NCS DC 73351), with agreement between 82 ± 3% (Cr) and 108 ± 10% (Fe). Precision was expressed as relative standard deviation (RSD) and the found values were lower than 9% (Fe, n = 3) for all elements, except for Cd by ICP-MS, whose RSD value was 14%. The proposed methods were then used to determine the mineral composition of 37 samples of cassava, corn and wheat flours bought in commercial establishments in Aracaju city, Sergipe State, Brazil. The Ca, K, P, Mg and S concentrations ranged from 2.72 ± 1.09 μgg -1 for Ca up to 4253 ± 103 μgg -1 for K. The concentrations of the microelements and trace elements, such as Ba, Cd, Co, Cu, Fe, Mn, Sr and Zn, varied between b 0.02 μgg -1 for Sr up to 65.5 ± 9.7 μgg -1 for Fe. Cassava, corn and wheat flours were subsequently characterized through multivariate data analysis (principal component analysis and hierarchical cluster analysis). Three distinct groups of flour were observed ac- cording to the elemental compositions. © 2017 Elsevier B.V. All rights reserved. Keywords: Chemometrics Flour ICP-MS ICP OES Inorganic constituents Sample preparation 1. Introduction Several types of flour have an important role in human diet. They are consumed daily either directly or as ingredients in various types of food products, such as cakes, breads, cookies and toasted manioc flours (known as farofa in Brazil). Wheat flour is the most popular ingredient incorporated into the eating habits of most of the world's population [1]. In Brazil, cassava flour and corn flour are widely consumed, mainly in the north and northeast regions, where their consumption is strongly associated with the local culture [2,3]. Flours are characterized as a source of energy in the form of carbohydrates and proteins, but it also contain minerals, which are of great importance in studies on the nutri- tional contribution and toxicological potential of these elements [1,4–6]. Among the spectrometric techniques used for elementary determi- nation, inductively coupled plasma-optical emission spectrometry (ICP OES) and inductively coupled plasma mass spectrometry (ICP-MS) are outstanding, allowing multielement analysis with good sensitivity for a wide range of quantification [7–10]. Conventionally multi-elementary determination by ICP techniques requires the samples to be converted in a solution. This can be achieved with the use of oxidants and energy sources capable to break certain bonds and crystalline structures, promoting the partial or complete di- gestion of the solid [11,12]. Therefore, the use of dilute acids in micro- wave-assisted digestion has been a good alternative for sample preparation, particularly in promoting the well-known efficiency of Microchemical Journal 135 (2017) 190–198 ⁎ Corresponding author at: Grupo de Pesquisa para Estudos em Química Analítica e Ambiental (GPEQA 2 ), Departamento de Química Analítica, Instituto de Química, Universidade Federal da Bahia (UFBA), 40170-115 Salvador (BA), Brazil. E-mail addresses: rgoa01@terra.com.br, rennan@ufba.br (R.G.O. Araujo). http://dx.doi.org/10.1016/j.microc.2017.09.007 0026-265X/© 2017 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Microchemical Journal journal homepage: www.elsevier.com/locate/microc