Tungsten coil electrothermal matrix decomposition and sample vaporization to determine P and Si in biodiesel by inductively coupled plasma mass spectrometry

Abstract

A tungsten coil extracted from commercially available microscope light bulbs is used to decompose the organic matrix and vaporize biodiesel samples for P and Si determination by electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS). The vaporization cell is connected to a modified sheath gas tube so that sample vapors are mixed with a continuous aerosol flow exiting the ICP-MS nebulization chamber. Helium and H 2 are used with a collision-reaction interface (CRI) to minimize spectral interferences and obtain low baseline spectra. These strategies contribute to improving repeatability and accuracy. A small solid state constant current power supply is used to resistively heat the vaporizer and 10 ml sample aliquots are introduced manually on the coil with a micropipette. Limits of detection of 0.4 and 0.1 mg kg À1 are obtained for P and Si, respectively.Reference biodiesel samples are used to check the accuracy of the procedure for P. A spike experiment is carried out to assess accuracy in Si determinations. No statistically significant differences are observed for reference and determined values by applying a t-test at a 95% confidence level. The direct analysis of biodiesel by tungsten coil ETV-ICP-MS is a fast and effective alternative to determine challenging elements like P and Si.

Direct determination of sodium, potassium, chromium and vanadium in biodiesel fuel by tungsten coil atomic emission spectrometry

“…Sample losses during the vaporization and atomization steps were observed in a previously published work using a more compact atomization cell to vaporize the analytes in an ETV-ICP-MS procedure [13]. To overcome this problem, the protecting gas flow was interrupted during these steps, which resulted in a more homogeneous temperature around the sample droplet, preventing the abrupt boiling process responsible for sample splashing.…”

“…Chaves et al [12], for example, reported RSD values as high as 20% in biodiesel analyses by ETV-ICP-MS using a graphite furnace as vaporizer. In a recently published work [13], RSDs of 14 and 20% were reported for P and Si determinations in biodiesel by ETV-ICP-MS using a tungsten coil vaporizer. Average repeatabilities for aqueous solution determinations by WCAES are typically in the 5-15% range [14][15][16][17][18][19][20][21][22].…”

“…In addition to the possibility of reaching higher atomization temperatures, this larger atomizer minimizes sample losses caused by splashing [13]. The heating cycle presented in Table 2 and a 400 W constant-current power supply (Vicor, VI-MU3-CQ-BM) were also employed in all Cr and V determinations.…”

“…Different sample preparation procedures (dilution with kerosene, ethanol or 1-propanol; ashing in muffle furnace; solid sampling; emulsion and micro-emulsion preparation; acid digestion; among others) and determination with flame or graphite furnace atomic absorption spectrometry (FAAS or GFAAS); inductively coupled plasma optical emission or mass spectrometry (ICP OES or ICP-MS), and microwave-induced plasma optical emission spectrometry (MIP OES) have been proposed to determine major and trace elements in biodiesel [3,[8][9][10][11]]. An interesting and fast alternative is to decompose the biodiesel organic matrix directly on an electrothermal vaporizer (ETV) and introduce the analyte vapors into an ICP-MS [12,13]. Despite the effectiveness of all these procedures, elements such as Na, K, Cr and V remain a challenge because of FAAS and ICP OES relatively low sensitivities and GFAAS and ICP-MS interferences.…”

Elementos traço em óleo cru: determinação total e estudo de especiação

“…Em unidades de refino ou de craqueamento catalítico, cobre, ferro, níquel e vanádio agem como envenenadores de catalisadores. Vanádio e níquel são os elementos traço mais avaliados em óleos combustíveis (CHIRINOS; OROPEZA e GONZÁLE, 2013; AYDIN I; AYDIN F e HAMAMCI, 2013; DONATI et al, 2013a;ELLIS et al, 2011;QUADROS et al, 2010). Em geral, vanádio produz efeitos negativos nos revestimentos refratários, superfícies de metal de diversos fornos, caldeiras, motores e turbinas pela formação de vanadatos.…”