ASTM D5622 Standard Test Methods for Determination of Total Oxygen in Gasoline and Methanol Fuels by Reductive Pyrolysis
7. Sampling
7.1 Take samples in accordance with the instructions in Practices D4057 or D4177.
7.2 Visually inspect the samples, and when there is evidence of nonuniformity, take fresh samples.
7.3 Store the samples in a cold room or a laboratory refrigerator designed for storage of chemicals.
8. Preparation of Apparatus
8.1 Prepare the instrument in accordance with the manufacturer's recommendations. These test methods require that correct operating procedures are followed for the model used. Instrument design differences make it impractical to specify all of the required operating conditions.
8.2 The carrier gas can be scrubbed to remove traces of oxygen and oxygen-containing compounds.
9. Calibration and Standardization
9.1 Calibration for Test Methods A, B, and C, Oxygenates in Gasoline:
9.1.1 Use a syringe to introduce 1 µL to 10 µL, or 1 mg to 10 mg, of the blank. The amount of specimen must be precisely known. Measure the response. Repeat the introduction and measurement until stable readings are observed.
9.1.2 In similar fashion, introduce 1 µL to 10 µL, or 1 mg to 10 mg, of SRM 1837 and measure the response. Repeat two times with the same quantity of the SRM. If the blank corrected responses do not agree within 2 % relative, take corrective action and repeat the calibration.
9.1.3 Calculate the K-factor as follows:
K = (Cstd x Mstd)/Ravg
where:
Cstd = mass % oxygen in the SRM,
Mstd = mass of the SRM, mg, = volume of the SRM (µL) x density of the SRM (g/mL), and
Ravg = average of the blank corrected responses.
NOTE 1 - Density can be determined by Test Method D1298 or Test Method D4052.
9.2 Calibration for Test Methods A, B, and C, Methanol Fuels - Repeat procedure 9.1; however, substitute anhydrous methanol for the SRM. For methanol fuels, a unique K-factor can be necessary.
9.3 Calibration for Test Method D - This test method does not require calibration; however, a quality control standard must be analyzed to ensure proper operation of the instrument. A blank must also be analyzed periodically to ensure consistent responses.
9.4 Quality Control (QC):
9.4.1 Introduce the QC standard SRM 1838 in the same manner as the calibration standards. Calculate the percent oxygen (m/m) as described in Section 10.
9.4.2 When results obtained on the QC standard do not agree with the certified values within 2 % relative, take corrective action and repeat the calibration and quality control.
9.4.3 For Test Method D, when the recovery of oxygen from the QC SRM is less than 0.85 (that is, 85 %), take corrective action and repeat the quality control. Recoveries that are greater than 0.85 but less than unity can be used to correct the calculated result (refer to the r parameter in Section 10).
9.5 Procedure:
9.5.1 Introduce the samples, and record the instrument response. Calculate the results as described in Section 10. Use the appropriate K-factor for oxygenates in gasoline and methanol fuels.
9.5.2 Recalibrate the instrument with the appropriate calibration standard after each set of ten samples.
