title: Direct determination of sodium, potassium, chromium and vanadium in biodiesel fuel by tungsten coil atomic emission spectrometry.
abstract: High levels of sodium and potassium can be present in biodiesel fuel and contribute to corrosion, reduced performance and shorter engine lifetime. On the other hand, trace amounts of chromium and vanadium can increase the emission of pollutants during biodiesel combustion. Sample viscosity, immiscibility with aqueous solutions and high carbon content can compromise biodiesel analyzes. In this work, tungsten filaments extracted from microscope light bulbs are used to successively decompose biodiesel's organic matrix, and atomize and excite the analytes to determine sodium, potassium, chromium and vanadium by tungsten coil atomic emission spectrometry (WCAES). No sample preparation other than simple dilution in methanol or ethanol is required. Direct analysis of 10-μL sample aliquots using heating cycles with less than 150 s results in limits of detection (LOD) as low as 20, 70, 70 and 90 μg kg(-1) for Na, K, Cr and V, respectively. The procedure's accuracy is checked by determining Na and K in a biodiesel reference sample and carrying out spike experiments for Cr and V. No statistically significant differences were observed between reference and determined values for all analytes at a 95% confidence level. The procedure was applied to three different biodiesel samples and concentrations between 6.08 and 95.6 mg kg(-1) for Na and K, and between 0.22 and 0.43 mg kg(-1) for V were obtained. The procedure is simple, fast and environmentally friendly. Small volumes of reagents, samples and gases are used and no residues are generated. Powers of detection are comparable to other traditional methods.
authors: Department of Chemistry, Wake Forest University, Winston-Salem, NC 27109, USA.
authors: Stacia E
authors: SE
authors: Dancsak
authors: Group of Applied Instrumental Analysis, Department of Chemistry, Federal University of São Carlos, São Carlos, SP, Brazil.
authors: Sidnei G
authors: SG
authors: Silva
authors: Group of Applied Instrumental Analysis, Department of Chemistry, Federal University of São Carlos, São Carlos, SP, Brazil.
authors: Joaquim A
authors: JA
authors: Nóbrega
authors: Department of Chemistry, Wake Forest University, Winston-Salem, NC 27109, USA.
authors: Bradley T
authors: BT
authors: Jones
authors: Department of Chemistry, Wake Forest University, Winston-Salem, NC 27109, USA. Electronic address: georgedonati@yahoo.com.br.
authors: George L
authors: GL
authors: Donati
mesh_terms: D056804:Biofuels / Q000032:analysis*; D002623:Chemistry Techniques, Analytical / Q000379:methods*; D002857:Chromium / Q000032:analysis; D007477:Ions / Q000737:chemistry; D008670:Metals / Q000032:analysis*; D011188:Potassium / Q000032:analysis; D012964:Sodium / Q000032:analysis; D013054:Spectrophotometry, Atomic; D014414:Tungsten / Q000737:chemistry*; D014639:Vanadium / Q000032:analysis
chemical_list: D056804:Biofuels; D007477:Ions; D008670:Metals; D014639:Vanadium; D002857:Chromium; D012964:Sodium; D011188:Potassium; D014414:Tungsten
keywords: Atomic emission; Biodiesel fuel; Dilute-and-shoot; Direct analysis; Trace metal analysis; Tungsten coil