ASTM D7371 test method for biodiesel content in diesel fuel oil
ASTM D7371 Standard Test Method for Determination of Biodiesel (Fatty Acid Methyl Esters) Content in Diesel Fuel Oil Using Mid Infrared Spectroscopy (FTIR-ATR-PLS Method)
12. Procedure
12.1 Equilibrate the samples to between 15 and 27°C before analysis.
12.2 Clean the sample cell of any residual fuel according to the manufacturer's instructions. Remove the fuel by flushing the cell with sufficient solvent or the subsequent sample to ensure complete washing. For difficult to remove substances like B100, precede flushing with triple solvent. Evaporate the residual solvent with either dry air or nitrogen.
12.3 Obtain a baseline spectrum in the manner established by the manufacturer of the equipment.
12.4 Prior to the analysis of unknown test samples, establish that the equipment is running properly by collecting the spectrum of the quality control standard(s) and comparing the estimated biodiesel concentration(s) to the known value(s) for the QC standard(s). Introduce enough standard into the cell to ensure that the cell is washed by at least three times the cell volume.
12.5 Introduce the unknown fuel sample in the manner established by the manufacturer. Introduce enough of the fuel sample to the cell to ensure that the cell is washed by at least three times the cell volume.
NOTE 3 - Biodiesel and biodiesel blends containing high concentrations of biodiesel are difficult to remove from the cell surface of an ATR crystal. Flush several times with sample or use a solvent rinse between samples. When in doubt, repeat steps 12.5 through 12.7 and compare the results to ensure adequate rinsing occurred.
12.6 Obtain the spectral response of the fuel sample.
12.6.1 Acquire the digitized spectral data for the fuel sample over the frequency region from 4000 to 650 cm(-1).
12.7 Determine the biodiesel concentration (volume %) according to the appropriate calibration equation developed in Annex A1.
12.7.1 Determine the biodiesel concentration using the calibration models developed in A1.2.4 by following the steps outlined as follows:
12.7.1.1 Estimate the biodiesel concentration in the fuel sample by applying the low calibration (see A1.2.4.1) to the spectrum in the region of 1800 to 1692 cm(-1) and 1327 to 940 cm(-1) using no baseline correction.
12.7.1.2 If the estimated biodiesel concentration determined in 12.7.1.1 is equal to or less than 10.00 volume %, determine the biodiesel concentration by applying the low calibration (see A1.2.4.1).
12.7.1.3 If the estimated biodiesel concentration determined in 12.7.1.2 is greater than 10.00 volume %, estimate the biodiesel concentration by applying the medium calibration (see A1.2.4.2) to the spectrum in the region of 1800 to 1700 cm(-1) and 1399 to 931 cm(-1) using no baseline correction.
12.7.1.4 If the value estimated by application of the medium calibration determined in 12.7.1.3 is less than or equal to 10.50 volume %, report the value determined by the low calibration (even if the value is greater than 10.5 volume %). For estimated values greater than 10.50 volume % and less than or equal to 30.00 volume % determined in 12.7.1.3, report the value obtained.
12.7.1.5 If the estimated biodiesel concentration determined in 12.7.1.4 is greater than 31.00 volume %, estimate the biodiesel concentration by applying the high calibration (see A1.2.4.3) to the spectrum in the region of 1851 to 1670 cm(-1) and 1371 to 1060 cm(-1) using no baseline correction.
12.7.1.6 If the value estimated by application of the high calibration determined in 12.7.1.5 is less than or equal to 31.00 volume %, report the value determined by the medium calibration (even if the value is greater than 31.00 volume %). For estimated values greater than 31.00 volume % (determined in 12.7.1.5), report the value obtained.
NOTE 4 - Clean cell thoroughly after use. Occasionally, clean cell of any water soluble substances by first cleaning with acetone. Place a solution of 30 % alcohol (ethyl or methyl) in water in the cell and let it soak for at least one hour. Finally, clean cell with acetone and dry. No acids or bases should be used in cleaning ZnSe elements.
13. Calculation
13.1 Conversion to Volume % of Biodiesel - To convert the calibration and qualification standards to volume % use Eq 1.
Vb = Mb(Df/Db)
where:
Vb = biodiesel volume %,
Mb = biodiesel mass %,
Df = relative density at 15.56°C of the calibration or qualification standard being tested as determined by Practice D1298 or Test Method D4052, and
Db = B100 biodiesel blend stock relative density at 15.56°C of the calibration or qualification standard being tested as determined by Practice D1298 or Test Method D4052.
