S6 JAGUAR - Analysis of Lead in Gasoline - ASTM D5059 Method A and C

Introduction

Adding Lead (Pb) to gasoline seemed to be a great enhancement, when first discovered in the 1920ies. Early concerns about environmental and health safety began shortly after. A long and in the end heated battle between the governmental institutions and the strong industrial lobby followed, until the Clean Air Act was passed as one of the first measures for environmental protection. Soon after, unleaded gasoline was available and catalytic converters were adjusted to the new standard. Finally, in 1996 Pb in gasoline was banned in the US and is now absent from common fuel in most of the world.
Some aviation and specialty fuels however still use Pb and need to report the concentrations. Additionally, it sometimes is required to test for Pb in gasoline to make sure it is below the regulated limits.
The ASTM Standard Test Method D5059 describes how to measure high (0 - 5 g Pb / US gal) and low (0 – 0.30 g Pb / US gal) levels of Pb in gasoline with XRF spectrometry using Bi as an internal standard.

Instrumentation

The WDXRF spectrometer S6 JAGUAR is equipped with Bruker’s 400 W HighSense™ X-ray tube (Fig. 1). This makes the S6 JAGUAR the most powerful benchtop WDXRF unit on the market! Modern software with built-in audit-tracking and state-of-the-art hardware enables best-in-class analytical performance. The S6 JAGUAR achieves outstanding sensitivity for a wide range of elements (F to U) and the various configuration options allow us to optimise the system for your needs.

When using the S6 JAGUAR for gasoline analyses, you get the full power of a WDXRF system that fits in a benchtop unit. Especially when measuring only a few elements, the S6 JAGUAR is an excellent fit. In contrast to other methods like AAS (Atomic Absorption Spectroscopy) and ICP-OES (Induced Coupled Plasma – Optical Elemental Spectroscopy), a simple one-time calibration makes the
S6 JAGUAR ready for your application. Only running a drift correction sample is occasionally required for routine applications. In the case of this application, not even a drift correction is needed, because any drift is ratioed out by using an internal standard.
The S6 JAGUAR is an ideal choice for liquid sample analysis:
• Dedicated liquid cups for simple and rapid loading of liquid samples
• SampleCare™ technology, protecting critical system components for low maintenance
• (optional) Cup-in-cup technology for additional protection
• Intuitive software SPECTRA.ELEMENTS with  “one button” solutions
• Sturdy design and robust, high quality components for long lifetime
• (optional) Ergonomic TouchControl™ display for operation without PC peripherals

Sample Preparation and Standards

Two sets of standards – six samples for ASTM D5059 A and seven samples for D5059 C – were prepared. The internal standard Bi was in a separate bottle and was mixed with the other samples according to the ratio defined in ASTM methods D5059 A and C, see. The standards and their concentrations are listed in Tab. 1.
After mixing Bi and the standards, 7 g per sample were filled into liquid cups sealed with a thin film window, see Fig. 2. For heavy analytes like Pb and Bi the foil thickness does not affect the measured intensities.

Measurement Parameters

The analytical conditions for the D5059 methods are listed in Tab. 2. The total measurement time for method A was under 2 minutes. For method C longer times were chosen due to the low concentrations and the lower power of the instrument (compared to S8 TIGER).

Calibration

The calibration curves for ASTM D5059 method A and C are shown in Fig. 3 and Fig. 4. Both curves show excellent linearity with a low standard deviation s and squared correlation coefficient R2 better than 0.999.

Norm Compliance

Precision testing as stated in D5059 has been tested by running appropriate check samples 20 times on each method. The results are listed in Tab. 3 and Tab. 4. For each measurement a fresh sample was prepared. For method A, the allowed difference between two consecutive measurements must be within 0.029+0.008C, where C is the concentration of the test sample. For a 2.5 g/gal test sample, this leads to a permitted difference of 0.049 g/gal. For method C, the limit is set by 0.007+0.14C, which gives 0.020 g/gal for a 0.09 g/gal sample.

Conclusion

The S6 JAGUAR has a wide range of capabilities and this report demonstrates that it is reliable for analysis of Pb in fuels. The system easily fulfils the requirements for the WDXRF norm ASTM D5059 method A and C. The WDXRF spectrometer brings several advantages to your lab, when compared to AAS and ICP-OES, including lower costs of operation and minimal calibration effort.
The S6 JAGUAR enables time-efficient and accurate monitoring of additives, contaminants, and wear metals in fuels, lubricating and engine oils. When installed at refineries and oil-production plants, it can easily test the quality of incoming materials and optimise the used additives from day one. It ensures that all elements in fuels are analysed at best performance with highest accuracy and precision combined with low cost of ownership.