ASTM D7059 Standard Test Method for Determination of Methanol in Crude Oils by Multidimensional Gas Chromatography
12. Procedure
12.1 Preparation of Sample - Sample the crude oil as described in Section 8. Weigh out 5.0 g of sample. Add 5.0 mL of a toluene solution containing 1000 micrograms/gram of the 1-propanol internal standard in toluene. Avoid having a large headspace volume above the mixed sample liquid. A headspace volume ofless than or equal to the liquid volume of the diluted sample is recommended. Obtain the exact mass of the 1-propanol internal standard added (Wis):
Wis = [concentration of 1 - propanol solution (for example, 1000 µg/g)] x [mass (in g) of the 5.0 mL of 1 - propanol internal standard solution added to the sample]
12.1.1 Record all masses to nearest 0.1 mg. Thoroughly mix the resulting solution for at least 1 min on a vortex or equivalent mixer. Transfer an aliquot of the solution into a glass GC vial. Seal the GC vial with a TFE-fluorocarbon-lined septum. If the sample is not to be immediately analyzed, store below 5 °C (40 °F).
NOTE 6 - Use the specified 5.0 g of sample. Sample sizes of less than 5.0 g may result in inaccurate determination of methanol.
12.2 Prepare the check standards similarly to 12.1. If the samples are not to be analyzed immediately, store the check standards along with the samples.
12.3 Chromatographic Analysis - Introduce a representative aliquot of the sample and check standards, containing 1-propanol internal standard, into the gas chromatograph, using the same technique and sample size as used for the calibration analysis. Start recording and integrating devices in synchronization with sample introduction. Obtain a chromatogram or integrated peak report, or both, which displays the retention time and integrated area of each detected component.
12.4 Interpretation of the Chromatogram - Compare the retention times of methanol and the 1-propanol internal standard in the sample with those obtained during the analysis of the calibration standards to determine the identities of the methanol and the 1-propanol.
