ASTM D3605 Test Method for Trace Metals in Gas Turbine Fuels
ASTM D3605 Standard Test Method for Trace Metals in Gas Turbine Fuels by Atomic Absorption and Flame Emission Spectroscopy
3. Summary of Test Method
3.1 The samples are prepared to conform with the requirements of the method of standard additions, which is selected to obviate problems encountered with the direct analysis of typical gas turbine fuels that exhibit significant variations in physical properties. Different, but known, amounts of analyte are added to two portions of sample. These, together with the unaltered sample, are burned in the flame of an atomic absorption instrument that measures light absorption by the atomized metals. The analysis of the sample portions with added analyte provides the calibration information necessary to calculate the analyte content of the unaltered sample.
3.2 Lead is determined by atomic absorption in a premixed air-acetylene flame, and sodium is determined by atomic absorption or atomic emission in a premixed air-acetylene flame. Calcium and vanadium are determined by atomic absorption or atomic emission in a premixed nitrous oxide-acetylene flame.
3.3 Most experience with this test method has been in the atomic absorption mode, although flame emission has been used successfully. Details in the subsequent sections are written for the atomic absorption mode. If the flame emission mode is used, minor details in the subsequent sections must be altered to conform to standard practice for flame emission spectroscopy. The precision statement applies only to the atomic absorption mode.
NOTE 1 - Some GT fuel users may wish to determine potassium in addition to other metals included in this method. Potassium can be determined in a manner similar to that for sodium using a potassium hollow cathode lamp, (unless flame emission mode is used) a wavelength of 766.4 mm, and an appropriate organo-potassium standard. Precision data for potassium have not been determined.
4. Significance and Use
4.1 Knowledge of the presence of trace metals in gas turbine fuels enables the user to predict performance and, when necessary, to take appropriate action to prevent corrosion.
