ASTM D5600 Test Method for Trace Metals in Petroleum Coke by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES)
4. Summary of Test Method
4.1 A test sample of the petroleum coke is ashed at 700 °C. The ash is fused with lithium borate. The melt is dissolved in dilute hydrochloric acid (HCl), and the resultant solution is analyzed by inductively coupled plasma atomic emission spectrometry (ICP-AES) using simultaneous, or sequential multielemental determination of elements. The solution is introduced to the ICP instrument by free aspiration or by an optional peristaltic pump. The concentrations of the trace metals are then calculated by comparing the emission intensities from the sample with the emission intensities of the standards used in calibration.
5. Significance and Use
5.1 The presence and concentration of various metallic elements in a petroleum coke are major factors in determining the suitability of the coke for various end uses. This test method provides a means of determining the concentrations of these metallic elements in a coke sample.
5.2 The test method provides a standard procedure for use by buyer and seller in the commercial transfer of petroleum coke to determine whether the petroleum coke meets the specifications of the purchasing party.
6. Interferences
6.1 Spectral - Follow the instrument manufacturer's operating guide to develop and apply correction factors to compensate for the interferences. To apply interference corrections, all concentrations shall be within the previously established linear response range of each element.
6.2 Spectral interferences are caused by: (1) overlap of a spectral line from another element; (2) unresolved overlap of molecular band spectra; (3) background contribution from continuous or recombination phenomena; and (4) stray light from the line emission of high-concentration elements. Spectral overlap can be compensated for by computer-correcting the raw data after monitoring and measuring the interfering element. Unresolved overlap requires selection of an alternate wavelength. Background contribution and stray light can usually be compensated for by a background correction adjacent to the analyte line.
6.3 Physical interferences are effects associated with the sample nebulization and transport processes. Changes in viscosity and surface tension can cause significant inaccuracies, especially in samples containing high dissolved solids or high acid concentrations. If physical interferences are present, they shall be reduced by diluting the sample, by using a peristaltic pump, or by using the standard additions method. Another problem that can occur with high dissolved solids is salts buildup at the tip of the nebulizer, which can affect aerosol flow rate and cause instrumental drift. This problem can be controlled by wetting the argon prior to nebulization, using a tip washer, or diluting the sample.
6.4 See Practice D7260 for explanation of ICP-AES interferences and other operational details.
