ASTM D5845 Standard Test Method for Determination of MTBE, ETBE, TAME, DIPE, Methanol, Ethanol and tert-Butanol in Gasoline by Infrared Spectroscopy
8. Sampling and Sample Handling
8.1 General Requirements:
8.1.1 Gasoline samples must be handled with meticulous care to prevent evaporative loss and composition changes.
8.1.2 Gasoline samples to be analyzed by the test method shall be obtained using method(s) specified by governmental regulatory agencies or by the procedures outlined in Practice D4057 (or equivalent). Do not use the "Sampling by Water Displacement" method as some alcohols or ethers might be extracted into the water phase.
8.1.3 Protect samples from excessive temperatures prior to testing. This can be accomplished by storage in an appropriate ice bath or refrigerator at 0 °C to 5 °C.
8.1.4 Do not test samples stored in leaky containers. Discard and obtain a new sample if leaks are detected.
8.1.5 Perform the oxygenate determination on fresh samples from containers that are at least 80 % full. If sample containers are less than 80 % full or have been opened and sampled multiple times, a new sample shall be obtained.
8.2 Sample Handling During Analysis:
8.2.1 Prior to the analysis of samples by infrared spectroscopy, the samples should be allowed to equilibrate to the temperature at which they should be analyzed (15 °C to 38 °C).
8.2.2 After withdrawing the sample, reseal the container, and store the sample in an ice bath or a refrigerator at 0 °C to 5 °C.
9. Preparation, Calibration, and Qualification of the Infrared Test Apparatus
9.1 Preparation - Prepare the instrument for operation in accordance with the manufacturer's instructions.
9.2 Calibration - Each instrument must be calibrated by the manufacturer or user in accordance with Practice E1655. This practice serves as a guide for the multivariate calibration of infrared spectrometers used in determining the physical characteristics of petroleum and petrochemical products. The procedures describe treatment of the data, development of the calibration, and qualification of the instrument. Note that bias and slope adjustments are specifically not recommended to improve calibration or prediction statistics for IR multivariate models.
9.3 Qualification of Instrument - The instrument must be qualified according to the procedure in AnnexA1 to ensure that the instrument accurately and precisely measures each oxygenate in the presence of typical gasoline compounds or other oxygenates that, in typical concentrations, present spectral interferences. General classes of compounds that will cause interferences include aromatics, branched aliphatic hydrocarbons, and other oxygenates.
10. Quality Control Standards
10.1 Confirm the proper operation of the instrument each day it is used by analyzing at least one quality control standard of known oxygenate content for each oxygenate to be determined. These standards should be made up by mass according to Practice D4307 and should be at the expected concentration level for that oxygenate. The recommended quality control standard concentrations are found in Table 1.
10.2 The individual oxygenate values obtained must agree within +/- 5 % relative of the values in the prepared quality control standard (for example, MTBE 14.0 +/- 0.7 mass %) or to within +/- 0.3 mass % absolute, whichever is greater (for example, methanol 4.0 +/- 0.3 mass % ). If the individual values are outside the specified range, recalibrate the instrument according to the procedures in 9.2. The quality control standards should not be used for the calibration or recalibration of the instrument. Do not analyze samples without meeting the quality control specifications.
