26 Analytical Instrumentation
Get More Precision at Trace Level: Sulphur-Analysis in Automotive Fuels According to ISO 20884 and ASTMD 2622 By WDXRF
Dr. Kai Behrens, Dr. Arnd Bühler, Bruker AXS, Karlsruhe Germany Bruker AXS, Oestliche Rheinbrueckenstrasse 49, 76187 Karlsruhe, Germany Email:
Kai.Behrens@
bruker-axs.de • Tel: +49 721 50997 0 • Web:
www.bruker.com
In the last years fuel quality has been increasingly regulated by legislation to enforce more stringent automotive emission levels. Te most important characteristic is the sulphur concentration in different fuel types. Te allowable limit of sulphur in automotive fuels went down to the lowest mg/kg range. A limit of 50 mg/kg sulphur was announced in Europe for 2005, but tax incentives for fuels established even lower levels. Since 2009 Euro V Diesel is enforced with a maximum concentration of 10 ppm sulphur. In the US EPA regulations are enforcing a level of less than 15 ppm for Highway Diesel fuel. Te preferred technology to analyse low sulphur at this low level is wavelength dispersive X-ray fluorescence spectrometry (WDXRF). But these low levels are no longer covered by ISO 14596 or ASTM D 2622 for high ranges.
The norm which describes the low sulphur fuels analysis by WDXRF is now ISO 20884 and ASTM D 2622 for the very low range down to 5 ppm. As matrix effects hardly vary when analysing fuels, only ISO 20884 and ASTM D 2622 could be established without an external standardisation. The concentration range is subdivided in a low range (5 - 60 mg/kg) and a high range (> 60 - 500 mg/kg). This report describes how the modern WDXRF spectrometer S8 TIGER analyses effectively the low sulphur type fuels on a daily basis. The high spectral resolution and the enhanced light element determination the wavelength dispersive X-ray fluorescence (WDXRF) spectrometer S8 TIGER easily achieves detection limits down to 0.2 ppm.
The S8 TIGER comes for ISO 20884 and ASTM D 2622 with PETRO-QUANT and the ready-to-analyse solution containing the calibration inclusively the specific set of calibration standards, the optimised measurement method and drift correction samples. For instrument verification and the performance test in addition a quality check sample is supplied with the package. This helps to establish easily the analytical quality routine for audit conformity.
Sample preparation and measurement parameters
7 g of the gasoline sample are filled in a liquid cup with a 3.6 µm Mylar foil. This foil is transparent for the light element radiation, but provides chemical resistance against gasoline.
All data obtained using the following measurement parameters are listed in table 1. The helium mode with atmospheric pressure is applied, because of the high volatility of fuel samples.
Figure 2: SampleCare system to enable safe analysis of liquid samples
Figure 1: WDXRF spectrometer S8 TIGER Instrument
The S8 TIGER is perfectly suited for the low sulphur analysis in a refinery or a commercial testing lab. Even lowest traces are analysed efficiently and reliably based on the optimum instrument setup. With excitation power of up to 4 kW, a high resolution, high intensity optimised analyser crystal XS-GE-C the S8 TIGER provides optimal analytical performance. The system is optimised for the analysis of liquid samples to make the operation as simple and failsafe as possible:
Liquid samples are automatically detected during the loading and the helium mode is enforced to prevent spillage of the sample and damages on system components. The low temperature X-ray tube head and the unique atmospheric helium mode prevent volatile samples from boiling which finally protects the instrument and ensures the best analytical stability. Finally the SampleCare system ensures with the unique vacuum seal the protection of spectrometer components separating the sample and spectrometer chamber. Fumes and droplets will not enter the spectrometer chamber. This completely protects crystals and detectors versus against damage and avoids frequent system failures like with conventional spectrometers on the market.
Table 1: Measurement Parameters for ISO 20884 Anode
Voltage Current
Collimeter Crystal
Measuring Time S Line Position
Background Position Detector
Optical Path FIlm
Rhodium 30 kV
135 mA 0,46°
curved Germanium XS-GE-C Peak 30 s, Background 30s 110,738° 113,150°
Flow counter with discriminator settings at 50 - 160%
atm. Helium (with vacuum seal) 3.6 µm Mylar®
Annual Buyers’ Guide 2013 •
www.petro-online.com
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