ASTM D5600 Test Method for Trace Metals in Petroleum Coke by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES)
11. Procedure
11.1 Weigh 5 g (to 0.1 mg) of the dried petroleum coke prepared in Section 9 into a labeled 50 mL to 58 mL platinum dish.
11.2 Place the platinum dish in a cold muffle furnace and heat directly to 700 °C +/- 10 °C until all carbonaceous matter is removed. Transfer the platinum dish to a desiccator and cool to room temperature.
11.3 To convert the ash into a solution, weigh, on an analytical balance, onto a tared weighing paper, 0.5 g (+/- 0.0005 g) of lithium borate powder. Sprinkle the lithium borate evenly over the ash. Use platinum-tipped tongs to place the platinum dish into a muffle furnace at 1000 °C +/- 10 °C for one or two minutes. Use the platinum-tipped tongs to gently swirl the melt to dissolve the ash. Continue heating in the furnace for two to three minutes or until a clear, transparent melt is obtained.
11.3.1 The ideal fusion after cooling will look like clear glass inside the platinum dish. An opaque melt possibly indicates poor fusion and some of the ash can remain insoluble during the dissolution step. Full dissolution of the ash is required.
11.3.2 If a 1000 °C +/- 10 °C furnace is not available, the fusion can be performed using a Meker-type burner as follows. Place the platinum dish onto the crucible support resting on a ring stand over the burner and adjust the forced air gas flame so that the lithium borate melts in about 30 s. Using platinum-tipped tongs, gently swirl the melt to dissolve the ash. Continue heating over the burner for two or three minutes or until a clear, transparent melt is obtained.
11.4 Allow the melt to cool for 5 min to 10 min on a ceramic cooling plate, add stirring bar, add 25 mL of Solution No. 1, and place immediately on the stirring hot plate. Heat the solution to just below boiling temperature and maintain the liquid volume with water for not more than 30 min with constant stirring, until the melt has completely dissolved.
11.4.1 If stirring and liquid volume are not constantly maintained, some of the ash constituents can precipitate, primarily hydrous silica, due to heating the highly acidic solution. Repeat the analysis if this occurs.
11.5 Remove the dish from the hot plate, transfer the solution quantitatively to a 100 mL volumetric flask, rinse the dish into the flask with water, dilute to volume with water, and mix thoroughly.
11.6 Prepare any required dilution using Solution No. 2 diluted 1:1 with water.
11.7 Prepare a calibration standard using 50 mL of Solution No. 2 per 100 mL and containing the desired volume of standard stock solutions. Dilute with water.
NOTE 4 - Standard and sample solutions are of similar composition to minimize errors due to matrix effects.
11.8 Calibrate the ICP-AES instrument using the calibration standard prepared in 11.7 in accordance with manufacturer's directions.
11.9 Determine the concentration of each metal in the sample solution.
12. Calculation
12.1 Calculate concentration of each metal in the sample as follows:
M, mg/kg (ppm) = (A x V)/W x (C/D)
M, mass % = M, mg/kg/10 000
where:
M = metal being calculated,
A = mg/L (ppm) of metal M in solution analyzed,
V = volume of sample solution mL,
W = mass of sample, g, and
(C/D) = dilution factor if sample dilution is required (C = volume diluted to, D = amount of sample diluted) to bring the metal concentrations into the range of standard solutions).
