A sustainable and simple energy dispersive X-ray fluorescence method for sulfur determination at trace levels in biodiesel samples via formation of biodiesel spots on a suitable solid support

Abstract

The aim of the present work is the development of a simple, sensitive and sustainable EDXRF method for the determination of trace amounts of sulfur in biodiesel samples. In this method, the deposition of several microliters of sample onto an organic thin layer and the analysis of the resulting adsorbed biodiesel spot by benchtop EDXRF is proposed. A careful study was performed to select the volume and the best solid support to deposit biodiesel samples, including filters made of different materials (glass fiber, Nylon, cellulose, paper) and a commercial disposable absorbent pad (UltraCarry, Rigaku). A critical issue that limits the use of most of these solid supports was the relative high blank signals that hamper the determination of sulfur at trace levels. Finally, it was found that best strategy was the deposition of 50 µL of biodiesel on the UltraCarry sample retainer. Operating conditions for EDXRF measurements were also evaluated to obtain the best instrumental sensitivity for sulfur determination (Excitation: 20 kV, no primary filter, measurement time: 300s). Using the best analytical conditions the quantification limit of the method was 7 mg kg-1 of sulfur. This value is even better than the one reported in the ASTM D4294 method (LOQ: 16.0 mg kg-1) but using a sample amount 100 times smaller. The linearity was confirmed in the range of 10-100 mg kg-1 by analyzing a set of commercial biodiesel standards. Accuracy and precision of the results, evaluated by the analysis of samples prepared with the same matrix as the standards, with levels of 20, 40 and 75 mg kg-1 of sulfur, and processed as unknowns, proved acceptable (Recoveries: 94.3-110.6%, RSD: 10.8-13.6%, n=3) for the intended purpose. Overall, the performance of the method developed is promising and it could be used to determine trace amounts of sulfur in biodiesel samples in a simple, sustainable and cost-effective way. Furthermore, since the original sample is adsorbed onto a solid support, repeat confirmatory analyses on the same specimen, if needed, can be carried out.

The Corrosive Effects of Aftermarket Oil Additives on High-Leaded Tin Bronze Alloy

“…According to [ 21 ], matrix effects significantly impact the quantitative determination of sulfur in petroleum-derived products when using EDXRF. Such effects arise from the fluid’s composition, like the oxygen content or the carbon/hydrogen ratio [ 21 ]. In this study, no corrective procedures to account for matrix effects or calibration curves were implemented.…”

Atomic spectrometry update: review of advances in the analysis of metals, chemicals and materials

“…The paper by Margui et al , described a method for the determination of S in biodiesel samples using ED-XRF after deposition on a solid support . 66 The presence of S is a big issue in diesel and other fuel samples with regulators looking to reduce limits and hence to reduce engine emissions. In this work various types of solid support were evaluated, however many had significant blank issues.…”

Determination of Organic and Reduced Inorganic Sulfur by Multi-element Scanning Thermal Analysis

“…Unlike liquid or gaseous samples, which are in a homogeneous phase, solid samples are heterogenous and lack an appropriate separation technology. In recent years, sophisticated direct methods like solid-state NMR spectroscopy combined with X-ray Photoelectron Spectroscopy (XPS) and sulfur X-ray Absorption Near Edge Structure (S-XANES), Energy Dispersive X-ray Fluorescence spectrometry (EDXRF) or Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS) have been applied to the analysis of organic sulfur in solid samples [5][6][7][8][9][10]. Those sophisticated methods, however, are expensive, and not available for routine analysis.…”