ASTM D7111 Standard Test Method for Determination of Trace Elements in Middle Distillate Fuels by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES)
4. Summary of Test Method
4.1 Calibration standards are prepared by mixing organometallic standard materials in kerosine. An internal standard material is added to the calibration standards and fuel samples. The calibration standards and the fuel samples are aspirated into the ICP-AES instrument. The concentrations of the elements in the fuel are calculated by comparing emission intensity ratios of the fuel and calibration standards to the internal standard.
4.2 Consult Practice D7260 regrading the optimum operation of any ICP-AES system.
5. Significance and Use
5.1 Trace elemental analysis is used to indicate the level of contamination of middle distillate fuels. Trace metals in turbine fuels can cause corrosion and deposition on turbine components at elevated temperatures. Some diesel fuels have specification limit requirements for trace metals to guard against engine deposits. Trace level copper in middle distillate aviation turbine fuel can significantly accelerate thermal instability of the fuel, leading to oxidation and production of detrimental insoluble deposits in the engine.
5.2 Gas turbine fuel oil Specification D2880 provides recommended upper limits for five trace metals (calcium, lead, sodium, potassium, and vanadium). Military specification MIL-DTL-16884 for naval distillate fuel sets requirements for maximum concentrations of the same five metals. Both specifications designate Test Method D3605, an atomic absorption/flame emission method, for the quantitative analysis of four of the metals. Test Method D3605 does not cover potassium. This test method provides an alternative to Test Method D3605, covers potassium and a number of additional elements.
5.3 There are several sources of multi-element contamination ofnaval distillate fuel. Sea water is pumped into the diesel fuel tanks (as ballast) to trim ships. Also, some of the oilers (fuel supply ships) have dirty tanks. Corrosion products come from unlined tanks, piping, pumps, and heat exchangers.
6. Interferences
6.1 Elemental wavelengths listed in Tables 1 and 2 have been found to be free of spectral interferences with all other elements listed in Tables 1 and 2 in the concentration range of this test method.
6.2 If a spectral interference does exist, then selecting an analytical wavelength other than those listed in Table 1 or Table 2 may be used as long as the new wavelength possesses appropriate sensitivity for the scope of the method.
6.3 Alternatively, the ICP spectrometer manufacturer's software may be used to provide corrections to interferences that cannot be avoided by wavelength selection and background correction.
6.4 An empirical method for correcting for spectral interferences is detailed in Test Method D5185, Section 6.1 (Spectral).
