ASTM D6732 Determination of Copper in Jet Fuels by Graphite Furnace Atomic Absorption Spectrometry
11. Procedure
11.1 Set the spectrometer at a wavelength of 324.8 nm and a slit width of typically 0.7 nm. Align the hollow cathode lamp and furnace assembly to obtain maximum transmittance.
11.2 Condition new (or reinstalled) graphite tube and L'vov platform with the temperature program provided by the spectrometer manufacturer until the baseline shows no peaks.
11.3 Calibrate the graphite furnace temperature controller at 2300°C according to the spectrometer manufacturer's instructions.
11.4 When an autosampler is used with the graphite furnace, use odorless kerosine as the rinse solution. Use only autosampler cups made of polyethylene, polypropylene, or TFE-fluorocarbon. Do not use polystyrene cups as these degrade and leak when used with organic solvents.
11.5 Calibrate the instrument by pipetting a 10 µL aliquot of odorless kerosine as a blank and then 10 µL of each of the standards onto the platform in the graphite tube. Then pipette 10 µL of each sample into the furnace and carry each through the furnace program. Run each blank, standard, and sample through the furnace program listed in Table 1. Compare the integrated absorbance of each sample to the corrected calibration curve generated from the blank and standards to determine the copper concentration of each. Run each sample in duplicate.
NOTE 1 - Aliquots other than 10 µL may be pipetted into the furnace. Volumes from 5 to 40 µL may be used, as long as the volume used is consistent between blanks, standards, and samples. If this is done, dry temperatures, char temperature, ramp times, or hold times, or a combination thereof, may need to be adjusted.
12. Calculations
12.1 Standard Concentrations:
12.1.1 Calculate the copper concentration of the nominal 1 mg/kg intermediate stock standard as follows:
ci = cs ms/mt
where:
ci = copper concentration of the intermediate stock standard, mg/kg,
cs = copper concentration of the certified (nominal 100 mg/kg) organo-metallic standard, mg/kg,
ms = measured mass of certified organo-metallic standard, g, and
mt = measured mass of solution of organo-metallic standard and kerosine diluent, g.
12.1.2 Calculate the copper concentrations of the working standards (nominal 20, 40, 60, 80, and 100 µg/kg) as follows:
cw = 1000 ci mi/mf
where:
cw = copper concentration of a working standard, µg/kg,
ci = copper concentration of the (nominal 1 mg/kg) intermediate stock standard, mg/kg,
mi = measured mass of the intermediate stock standard, g, and
mf = measured mass of solution of intermediate stock standard and kerosine diluent, g.
12.2 Standard Calibration Curve Correction and Fuel Copper Determination:
12.2.1 Correct the standard calibration curve for any copper present in the kerosine blank and diluent by subtracting the kerosine blank integrated absorbance Ao from each of the integrated absorbances of the working standards, Aw:
corrected integrated absorbance = Aw - Ao
12.2.2 Plot the corrected integrated absorbance values for the working standards versus their concentrations to provide the corrected standard calibration curve. The fuel sample concentration is determined from its integrated absorbance value and the corrected standard calibration curve.
