This article demonstrates Cartesian Geometry EDXRF for the measurement of lead (Pb) in gasoline per ASTM D5059 using the Bi internal standard method Part C (ultra-low Pb) and Part A (high Pb). Cartesian Geometry EDXRF also offers compliance for ULS in gasoline and diesel, Mn in gasoline, and organic chlorides in crude, making it one of the most versatile systems on the market.
Tetraethyl lead (TEL) is an anti-knock agent added to gasoline or petrol. Lead is a toxic metal that interferes with anti-pollution devices and contributes to lead poisoning.
In the 1970s, regions around the world began phasing out lead in MoGas (motor gasoline), beginning in the United States and Europe. Lead is still used in AvGas (aviation gasoline) for some piston engine propeller aircraft; however, efforts are being made to lower and remove lead in this fuel as well.
One of the main international standard test methods for the measurement of lead in gasoline is ASTM D5059 using X-Ray spectroscopy and XRF (X-Ray fluorescence).
As efforts continue to reduce and remove lead from gasoline fuels worldwide, Rigaku offers the EDXRF analyzer NEX CG II which uses indirect excitation Cartesian Geometry for the measurement of lead by ASTM D5059 as well as many other applications in the petroleum and fuel industries.
Image Credit: Rigaku Corporation
Instrumentation
Model: Rigaku NEX CG II
X-Ray tube: 50 W Pd-anode
Excitation: Indirect with polarization EDXRF
Detector: Large-area SDD
Analysis time: 300* seconds
Environment: Air
Film: Etnom® 3 μm
*Shorter measurement times can be used if the precision and ultra-low detection limits demonstrated are not required.
Sample Preparation
Bi Internal Standard (0.793 g/l Bi in Mineral Oil)
- Part C: For each sample, homogeneously mix 2.0 ml Bi IS with 20.0 ml sample
- Part A: For each sample, homogeneously mix 10 ml sample with an equal amount of Bi IS
Ensure each sample is homogeneous and stable. Shake the sample gently and allow any bubbles to settle. Fill an XRF sample cup with 4.0 g of sample. Chemplex® Etnom® film (3 μm) is used, which does not react with isooctane, gasoline, or oxygenated gasoline.
The sample cup lid is vented with a small hole to ensure vapor pressure does not build. It is recommended to make the measurement immediately after filling the cup.
Calibration
Empirical calibration was made using commercially available standards. The user spikes each standard and the blank with the Bi IS, as described for Part C or A. Calibration is then g/US gal Pb vs. I, where I is the X-Ray intensity expressed as (Pb net cps / Bi gross cps).
Part C:
Table 1. Source: Rigaku Corporation
Image Credit: Rigaku Corporation
Part A:
Table 2. Source: Rigaku Corporation
Image Credit: Rigaku Corporation
Precision
Instrument repeatability (precision) is determined by five repeat analyses of each sample in a static position using a 300-second analysis time per measurement. To minimize evaporation error, five repeat measurements of each sample were taken for demonstration.
Table 3. Source: Rigaku Corporation
Detection Limits
Detection limits depend on the calibration concentration range and measurement time. The empirical method is used to determine detection limits using a 300-second measurement time.
Ten repeat analyses of a blank isooctane sample with the IS addition are taken with the sample in a static position, and the standard deviation (σ) is determined. The lower limit of detection (LLD) is then defined as three times the standard deviation (3σ).
Table 4. Source: Rigaku Corporation
LLDs shown are typical and may differ depending on measurement time used and the overall elemental composition of the sample being tested.
ASTM D5059
Standard Test Methods for Lead in Gasoline by X-Ray Spectroscopy
The test methods cover the determination of the total lead content of gasoline within the following concentration ranges:
Table 5. Source: Rigaku Corporation
Conversion factors: 3.7854 g/US gal = 4.5461 g/UK gal = 1.0000 g/L
Conclusion
The results shown in this article prove that NEX CG II easily meets ASTM D5059 Parts A and C using the Bi internal standard method for the measurement of lead in gasoline.
Chemplex and Etnom are registered trademarks of Chemplex Industries, Inc.
This information has been sourced, reviewed and adapted from materials provided by Rigaku Corporation.
For more information on this source, please visit Rigaku Corporation.