ASTM D6728 Standard Test Method for Determination of Contaminants in Gas Turbine and Diesel Engine Fuel by Rotating Disc Electrode Atomic Emission Spectrometry
7. Apparatus
7.1 Electrode Sharpener - An electrode sharpener to remove the contaminated portion of the rod electrode remaining from the previous determination. It also forms a new 160° angle on the end of the electrode.
7.2 Rotating Disc Electrode Atomic Emission Spectrometer - A simultaneous spectrometer consisting of excitation source, polychromator optics, and readout system. Suggested wavelengths are listed in Table 1. When multiple wavelengths are listed, they are in the order of preference or desired analytical range.
7.3 Heated Ultrasonic Bath (Recommended) - An ultrasonic bath to heat and homogenize fuel samples to bring particles into suspension. The ultrasonic bath shall be used on samples containing large amounts of debris, those that have been in transit or in storage for at least 48 h and for heavy residual fuels to reduce viscosity effects.
7.4 Power Mixer - A power mixer should be used before a sample is transferred from one container to another to ensure that a homogeneous mixture is created and maintained until the transfer is complete. Practice D5854 should be consulted for the mixing and handling of liquid samples.
8. Reagents and Materials
8.1 Base Oil - A 75 cSt (40 °C) base oil, free of analyte, to be used as a calibration blank or for blending calibration standards.
8.2 Check Sample and Quality Control (QC) Samples - One or more oil or fuel standards or samples of known concentration which are periodically analyzed as go/no-go samples to confirm the need for standardization based on an allowable accuracy limit as described in Appendix X1.
8.3 Cleaning Solution - An environmentally safe, non-chlorinated, rapid evaporating, and non-film producing solvent to remove spilled or splashed oil or fuel sample in the sample stand of the spectrometer.
8.4 Counter Electrode - The counter electrode is a rod electrode. The counter electrode shall be of high-purity graphite (spectroscopic grade). Dimensions of new counter electrodes shall conform to those shown in Fig. 1.
8.5 Disc Electrode - Graphite disc electrode of high-purity graphite (spectroscopic grade). Dimensions of the electrodes shall conform to those shown in Fig. 2.
8.6 Glass Cleaning Solution - Capable of cleaning and removing splashed oil or fuel sample from the quartz window that protects the entrance lens and fiber optic. Ammonia based window cleaner or 70 % isopropyl rubbing alcohol have been found to be suitable for this purpose.
8.7 Organometallic Standards - Single or multi-element blended standards for use as the high concentration standard for instrument standardization purposes or for use as a check sample to confirm calibration. Multi-element blends are used for fuel analysis applications that contain a 3:1 concentration ratio of magnesium to all other metals present. The typical concentration for the upper calibration point is 10 mg/kg for light fuels when ASTM No. 0-GT, No. 1-GT, No. 2-GT, Grade 1-D, Grade 2-D, and Grade 4-D fuel samples are analyzed. The typical concentration for the upper calibration point is 100 mg/kg for heavy fuels when No. 3-GT and No. 4-GT fuel samples are analyzed.
8.7.1 Standards have a shelf-life and shall not be used to standardize an instrument if they have exceeded the expiration date.
8.8 Specimen Holders - A variety of specimen holders can be used for the analysis of fuel samples. Disposable specimen holders must be discarded after each analysis and reusable specimen holders must be cleaned after each analysis. All specimen holders must be free of contamination and shall be stored accordingly. Specimen holder covers shall be used on those fuel samples that may catch on fire during the analysis.
