This data sheet demonstrates that the Epsilon 4 – a benchtop energy dispersive X-ray fluorescence (EDXRF) spectrometer – is capable of analyzing sulfur and chlorine in waste oil, without the need of helium.
Waste oil with high chlorine concentrations (several countries:
> 0.1 wt %) is considered to be hazardous and must be treated differently than other waste oils. A common problem with the analysis of chlorine by energy dispersive XRF is the line overlap with sulfur due to the often high concentrations of sulfur in waste oils. The Epsilon 4 is equipped with a high resolution SDD detector, which improves the separation of S Kα, S Kβ and Cl Kα peaks. This improved separation leads to better quantification of S and Cl down to very low concentration levels, Figure 1. Moreover, use of a Ag-anode X-ray tube overcomes the common problem of tube lines overlapping the S Kα peak. In this way, improved accuracy and lowered limits of detection are achieved, compared to commonly used Rh- or Pd-anode X-ray tubes.
Measurements were performed using the Epsilon 4 EDXRF spectrometer, equipped with a 10 W, 50 kV Ag-anode X-ray tube, 6 filters, a helium purge facility, a high resolution silicon drift detector, a sample spinner and a 10-position removable sample tray.
A series of commercially available mineral oil standards manufactured by VHG Labs, Inc. (U.S.) were used to set up a calibration with varying amounts of S and Cl. The concentration range of the standards was 0 to 0.5 wt% for S and 0 to 0.05 wt% for Cl. Seven grams of each standard were analyzed in 45 mm diameter disposable sample cells using a 3.5 µm Mylar supporting film.
A single analytical condition was used for the analysis of S and Cl resulting in a total measurement time of 120 seconds per sample, Table 1. All analyses were performed in air
Table 1. Measurement conditions
Figure 1. Spectrum detail of standard #4 containing 0.01 wt% Cl and 0.5 wt% S, demonstrating separation of S and Cl peaks
Accurate calibration results and detection limits
The S line-overlap correction was automatically applied to the Cl calibration. Detailed calibration results for sulfur and chlorine as well as the average 3 σ lower limits of detection (LLD) are represented in Table 2.
Table 2. Calibration results and detection limits
The calibration curve for sulfur in the presence of chlorine using the Ag-anode X-ray tube is shown in Figure 2. It demonstrates an excellent correlation between the certified concentrations and the measured intensities.
Figure 2. Calibration curve of sulfur in mineral oil
Accuracy and Precision
Measurement precision is another important aspect of analysis and is an inherent characteristic of Epsilon 4. To test the precision of the instrument, one sample containing 0.01 wt% S and 0.02 wt% Cl was measured 10 times consecutively, Table 3. The standard deviation of the replicate measurements demonstrate excellent precision.
Table 3: Replicate analyses of a sample containing 0.01 wt% S and 0.02 wt% Cl.
The results clearly demonstrate that the Epsilon 4 EDXRF spectrometer is capable of performing accurate and precise analyses of varying concentrations of S and Cl in waste oils. The combination of the silver anode X-ray tube, excellent detector resolution, high sensitivity and powerful software contribute to the accuracy and precision of the results in just two minutes measuring time.