ASTM D6732 Determination of Copper in Jet Fuels by Graphite Furnace Atomic Absorption Spectrometry
10. Calibration and Standardization
10.1 Preparation of Standards:
10.1.1 Nominal 1 mg/kg Intermediate Stock Standard - Accurately weigh a nominal 0.50 g of the 100 mg/kg stock organo-metallic standard into a suitable container (capable of being sealed for mixing). (All masses are measured to the nearest 0.0001 g.) Suitable sample containers are described in Practice D4306. Add enough odorless kerosine to bring the total mass to a nominal 50.00 g. Seal the container and mix well. See 12.1.1 for calculation of actual concentration.
10.1.2 Working Standards of Nominally 20, 40, 60, 80, and 100 µg/kg - Accurately weigh a nominal 0.20, 0.40, 0.60, 0.80, and 1.00 g of the nominal 1 mg/kg intermediate stock standard into five suitable containers. (All masses are measured to the nearest 0.0001 g.) Add enough odorless kerosine to each container to bring the total mass to a nominal 10.00 g. Seal containers and mix well. This produces working standards of nominal 20, 40, 60, 80, and 100 µg/kg, respectively. See 12.1.2 for calculations of actual concentrations.
10.2 Calibration:
10.2.1 Prepare a standard calibration curve by using the odorless kerosine as a blank and each of the five working standards. The instrument measures the integrated absorbance Ai of 10 µL of each working standard and blank. The intermediate stock standard and working standards shall be prepared daily.
10.2.2 The calibration curve is constructed by plotting the corrected integrated absorbances (on y-axis) versus the concentrations of copper in the working standards in µg/kg (on x-axis). See 12.2.1 for calculating corrected integrated absorbance. Fig. 1 shows a typical calibration curve for atomic absorption spectroscopy. Many atomic absorption spectrometers have the capability of constructing the calibration curve internally or by way of computer software. Construct the best possible fit of the data with available means.
