ASTM D6277-16
Standard Test Method for Determination of Benzene in Spark-Ignition Engine Fuels Using Mid Infrared Spectroscopy
ASTM D6277 covers the determination of benzene in spark-ignition engine fuels by FT mid-infrared spectroscopy.
The method applies to gasoline samples containing benzene from 0.1 to 5 volume %.
Oxygenates in general can be added to spark-ignition engine fuels as a replacement of toxic organometallic octane boosters like tetra-ethyl-lead (LED)with an additional purpose of reducing SOx and NOx emissions. The new EPA regulations to lower sulfur and increase ethanol with strict control on benzene, olefines, aromatics and RVP are found in the Code of Federal Regulations for TIER III gasoline 40 CFR Part 80.
Standard Specification for gasoline D4814 regulates the composition, quality and properties of these valuable engine fuel formulations.
Reference Documents:
ASTM Standards:
D1298 Test Method for Density, Relative Density (Specific Gravity), or API Gravity of Crude Petroleum and Liquid Petroleum Products by Hydrometer Method
D4052 Test Method for Density, Relative Density, and API Gravity of Liquids by Digital Density Meter
D4057 Practice for Manual Sampling of Petroleum and Petroleum Products
D4177 Practice for Automatic Sampling of Petroleum and Petroleum Products
D4307 Practice for Preparation of Liquid Blends for Use as Analytical Standards
D5769 Test Method for Determination of Benzene, Toluene and Total Aromatics in Finished Gasoline by Gas Chromatography/Mass Spectrometry
D5842 Practice for Sampling and Handling of Fuels for Volatility Measurements
D5854 Practice for Mixing and Handling of Liquid Samples of Petroleum and Petroleum Products
E168 Practices for General Techniques of Infrared Quantitative Analysis
E1655 Practice for Infrared Multivariate Quantitative Analysis
E2056 Practice for Qualifying Spectrometers for Use in Multivariate Analysis, Calibrated Using Surrogate Mixtures
Summary of Test Method
This method utilizes a Fourier transform mid infrared spectrometer fitted with a transmission sample cell with a specified path length. A beam of infrared light is passed through the sample and the motion of the spectrometer mirrors enables determination of the sample absorption spectrum. Specific regions of the spectrum where benzene shows strong absorption are used for the analysis. Users should prepare the sample according to instrument manufacturer instructions after the correct validation and instrumental checks of the instrument. Wavelengths of the spectrum, that correlate highly with benzene or interferences, are selected for analysis using selective bandpass filters or by mathematically selecting areas of the whole spectrum.
Calculations take place when a multivariate mathematical analysis is carried out which converts the detector response for the selected regions in the spectrum of an unknown to a concentration of desired component.
Figure 1. Eraspec FT-IR Spectrometer
Significance and Use:
Benzene is a carcinogenic organic aromatic compound strongly limited by environmental protection agencies due to its toxic effect on human health.
The EPA control on hazardous air pollutants from mobile sources (MSAT2) requires that refiners and importers shall not exceed an annual average benzene content of 0.62 volume %.
This test method is faster, simpler, less expensive and more portable than current GC methods. This test method may be applicable for quality control in the production of gasoline. This test method is not suitable for testing for compliance with federal regulations.
Interferences
The primary spectral interferences are toluene and other monoaromatics. Oxygenates can interfere with measurements made with filter apparatus. Proper choice of the apparatus, proper design of a calibration matrix, and proper utilization of multivariate calibration techniques can minimize these interferences.
Apparatus
ERASPEC is rugged, robust and portable, can operate off line and at line. Primarily it determines the overall absorption spectrum of the sample in the Middle Infrared region, approximately from 450 up to 6500 cm -1. After a mathematical transformation of the firstly obtained raw interferogram spectrum illustrated in Fig.2, signal is transformed in plots of frequencies vs. absorption intensities. Since all hydrocarbon types absorb in the Mid-IR in a characteristic manner following Beer – Lambert’s Law, the absorption spectrum of bands and intensities can be integrated and related to chemical composition, physical properties and product quality parameters scanned over the frequency range from 600 to 6000 cm-1 .
The resolution of these systems is typically 4 cm–1 and the noise of the single beam spectrum at 100 % transmission shall be less than 0.3 % peak-to-peak in the region from 1725 cm–1 to 1765 cm–1.
Figure 2. Diagram of the FT_IR Spectrometer
Reagents and Materials
Samples for Calibration and Quality Control Check Solutions—Use of chemicals of at least 99 % purity is highly recommended for preparing calibration standards and quality control check samples. If reagents of high purity are not available, an accurate assay of the reagent must be performed using a properly calibrated GC or other techniques. Alkyl Benzenes, oxygenates and heavy aromatic/reformate streams are to be used for standard references and quality checks. See Section 8 of D6277 for more details.
Warning—These materials are flammable and may be harmful if ingested or inhaled.
Sampling and Sample Handling
Samples for Calibration and Quality Control Check Solutions—Use of chemicals of at least 99 % purity is highly recommended for preparing calibration standards and quality control check samples. If reagents of high purity are not available, an accurate assay of the reagent must be performed using a properly calibrated GC or other techniques. Alkyl Benzenes, oxygenates and heavy aromatic/reformate streams are to be used for standard references and quality checks. See Section 8 of D6277 for more details.
Warning—These materials are flammable and may be harmful if ingested or inhaled.
Preparation and Qualification of the Apparatus
The calibration of the instrument must proceed according to the manufacturer’s instructions. This calibration is performed by Eralytics prior to delivery of the instrument to the end user. The user can however, perform a calibration as described in Annex 1 of D6277 standard test method.
The instrument must be qualified according to the procedure in method D6777 to ensure that the instrument accurately and precisely measures each analyte concentrations in the presence of typical gasoline compounds.
Quality Control Checks
Prepare standards of known concentrations of benzene in mass % according to A1.1 of D6277 and converted to volume 5 as per Section 12. The concentration values of at least one sample must be made up at 1.2 ± 0.2 mass % which is nominally 1.0 volume %. Re calibrate the instrument if necessary according to the procedures in D5845 Annex1 and Eraspec Operation Manual. The quality control standards should not be used for the calibration or recalibration of the instrument. Samples without meeting the quality control specifications should not be analyzed.
Standard(s) should be prepared in sufficient volume to allow for a minimum of 30 quality control measurements to be made on one batch of material. Properly package and store the quality control samples to ensure that all analyses of quality control samples from a given lot are performed on essentially identical material.
Procedure
After sample temperature stabilization the determination of the benzene content in Gasoline should proceed according to the Instruction Manual of the manufacturer after sample temperature equilibration. Eraspec comes pre calibrated from the factory. Eraspec automatically performs a background spectrum used in the calculations. The validation of the instrument and the revision of the IQT parameters should be obtained prior to the introduction of the QC reference standard.
Rinsing of the absorption cell introduction of sample and the rest of the D6277 analysis steps is performed automatically by the Eraspec after the settings parameters and method had been selected.
Calculations
Conversion to Volume % of Benzene—To convert the calibration and qualification standards to volume % use the Eq:
Vb = Mb (Df /0.8844)
where: Vb = benzene volume %,
Mb = benzene mass %, and
Df = relative density at 15.56 °C of the calibration or qualification standard being tested as determined by Practice D1298 or Test Method D4052.
Eraspec has a built-in module ES10-D4052 for the simultaneous density determination according to D4052 with a precision of 0.0001 g/cm3.
Report
Report concentrations of oxygenates in either mass % or Volume % by test method D6277, to the nearest 0.1%.
Table 1 below shows a correlation study of Eraspec data on benzene at different concentrations compared to D5580 the GC method for the determination of alkyl monoaromatic compounds in gasoline. The linear regression coefficient of R2 = 0.9971 denotes an excellent correlation.
Precision and Bias
Bias – For benzene concentrations between 0.1 volume % and 1.8 volume %, the difference between successive test results obtained by the same operator with the same apparatus under constant operating conditions on identical test samples would, in the long run, and in the normal and correct operation of the test method, exceed the following values only in one case in twenty.
r = 0.047+0.043 X
where X is the benzene concentration determined.
For one sample at 4 volume % benzene, the difference between successive test results obtained by the same operator with the same apparatus under constant operating conditions on identical test samples would, in the long run, and in the normal and correct operation of the test method, exceed 0.18 only in one case in twenty.
Bias – For concentrations between 0.1 volume % to 1.8 volume %, the difference between two single and independent results obtained by different operators working in different laboratories on identical test samples would, in the long run,
and in the normal and correct operation of the test method, exceed the following values only in one case in twenty.
R = 0.099+0.031 X
where X is the determined benzene concentration. For the one sample at 4 volume % benzene, the difference between two single and independent results obtained by different operators working in different laboratories on identical test samples would, in the long run, and in the normal and correct operation of the test method, exceed 0.23 only in one case in twenty.
Bias – Since there were no suitable reference materials included in the interlaboratory test program, no statement of bias is being made.
References
1. D4814 Standard Specifications for Automotive Spark-Ignition Engine Fuel
2. D6277 Standard Test Method for the Determination of Benzene in Spark-Ignition Engine Fuels Using Mid Infrared Spectroscopy
3. ERALYTICS Eraspec – Operation Manual