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)
7. Apparatus
7.1 Mid-IR Spectrometric Analyzer:
7.1.1 Fourier Transform Mid-IR Spectrometer - The type of apparatus suitable for use in this test method employs an IR source, a liquid attenuated total internal reflection cell, a scanning interferometer, a detector, an A-D converter, a microprocessor, and a method to introduce the sample. The following performance specifications shall be met:
7.1.2 The noise level shall be established by acquiring a single beam spectrum using air or nitrogen. The single beam spectrum obtained can be the average of multiple of FTIR scans but the total collection time shall not exceed 60 seconds. If interference from water vapor or carbon dioxide is a problem, the instrument shall be purged with dry air or nitrogen. The noise of the spectrum at 100 % transmission shall be less than 0.3 % in the region from 1765 to 1725 cm(-1).
7.2 Absorption Cell, multi-bounce (multi-reflections) attenuated total reflectance cell. It shall meet one of the following requirements:
7.2.1 Conical Attenuated Total Reflectance (ATR) Cell, having similar specifications defined in Table 1. This cell is suitable for the low, medium, and high concentration ranges.
7.2.2 Horizontal Attenuated Total Reflectance (ATR) Cell, with ZnSe element ATR mounted on a horizontal plate. The absorbance at 1745 cm(-1) shall not exceed 1.2 absorbance units for the highest concentration calibration standard used in the calibration range. Therefore, for higher concentration measurements, careful consideration of element length and face angle shall be made to maximize sensitivity without exceeding 1.2 absorbance units at 1745 cm(-1).
8. Reagents and Materials
8.1 Purity of Reagents - Spectroscopic grade (preferred) or reagent grade chemicals shall be used in tests. Unless otherwise indicated, it is intended that all reagents shall conform to the specifications of the committee on analytical reagents of the American Chemical Society, where such specifications are available. Other grades may be used, provided it is first ascertained that the reagent is of sufficiently high purity to permit its use without lessening the accuracy of the determination.
8.1.1 B100 (Neat Biodiesel) - Used for calibration, qualification, and quality control standards shall be compliant with Specification D6751. The B100 shall be fatty acid methyl esters. Soy methyl ester (SME) was used in calibration standards for developing the precision of this test method. Esters derived from other feedstocks, for example animal fats, canola oil, jatropha oil, palm oil, rapeseed oil, and yellow grease may be used. Standards made with yellow grease methyl esters should not represent more than 50 % of the number of the calibration standards. A BQ-9000 certified producer for the biodiesel is recommended to ensure quality of product. See Annex A2 for further discussion.
8.1.2 Middle Distillate Fuel - Used for calibration, qualification, and quality control standards shall be compliant with Specification D975, free of biodiesel or biodiesel oil precursor, or both. As far as possible, middle distillate fuel shall be representative of petroleum base stocks anticipated for blends to be analyzed (crude source, 1D, 2D, blends, winter/summer cuts, low aromatic content, high aromatic content, and the like). See Annex A2 for calibration set.
8.1.3 Diesel Cetane Check Fuel - Low (DCCF-Low). (See A2.2 for alternative material.)
8.1.4 Diesel Cetane Check Fuel - High (DCCF-High).
8.1.5 Diesel Cetane Check Fuel - Ultra High (DCCF-Ultra High).
8.1.6 Acetone [67-64-1] - Reagent grade.
8.1.7 Toluene [108-88-3] - Reagent grade.
8.1.8 Methanol [67-56-1] - Reagent grade.
8.1.9 Triple Solvent - A mixture of equal parts by volume of toluene, acetone, and methanol.