title: Influence of microwave heating on fluoride, chloride, nitrate and sulfate concentrations in water.
abstract: This paper describes a study about the influence of microwave radiation using closed vessels on fluoride, chloride, nitrate and sulfate concentrations in aqueous media. The experiments were processed by heating water using PFA vessels and a microwave cavity oven, determining the anions by ion chromatography. The influence of the exposure time, the atmospheric composition, the kind of heating (water bath or microwave radiation) and the possible formation of hydrogen peroxide were investigated. The limits of quantification for fluoride, chloride, nitrate and sulfate were respectively of 0.17, 0.15, 0.55 and 0.57 μg L(-1), and precision, expressed as RSD, was <4% for all considered anions. The hydrogen peroxide was quantified by spectrophotometry, and the limit of quantification and precision were 24 μg L(-1) and <5% (n=10), respectively. The results demonstrate a significant increase in the anion concentration levels (between 63 and 89%) when microwave heating was used in comparison with heating by water bath. In addition, these changes observed can be mainly attributed to the species transfers, either between gaseous (atmospheric gases) and liquid (water) phases for nitrate, or between vessels walls and water for fluoride, chloride and sulfate. Additionally, hydrogen peroxide concentration higher than 45 μg L(-1) was determined when water was exposed to microwave radiation.
authors.affiliation: Faculty of Pharmaceutical Sciences, Gabriel Monteiro da Silva Street, 714, 37130-000, Federal University of Alfenas - UNIFAL-MG, Alfenas, MG, Brazil.
authors.forename: Eduardo Costa
authors.initials: EC
authors.lastname: Figueiredo
authors.forename: Jailson Cardoso
authors.initials: JC
authors.lastname: Dias
authors.forename: Lauro Tatsuo
authors.initials: LT
authors.lastname: Kubota
authors.forename: Mauro
authors.initials: M
authors.lastname: Korn
authors.forename: Pedro Vitoriano
authors.initials: PV
authors.lastname: Oliveira
authors.forename: Marco Aurélio Zezzi
authors.initials: MA
authors.lastname: Arruda
mesh_terms: D002712:Chlorides / Q000032:analysis*; D005459:Fluorides / Q000032:analysis*; D006861:Hydrogen Peroxide / Q000032:analysis; D006863:Hydrogen-Ion Concentration; D008872:Microwaves; D009566:Nitrates / Q000032:analysis*; D015203:Reproducibility of Results; D013431:Sulfates / Q000032:analysis*; D014867:Water / Q000737:chemistry*
chemical_list: D002712:Chlorides; D009566:Nitrates; D013431:Sulfates; D014867:Water; D006861:Hydrogen Peroxide; D005459:Fluorides