ASTM D7059 Standard Test Method for Determination of Methanol in Crude Oils by Multidimensional Gas Chromatography
13. Calculations and Reporting
13.1 Calculation of Methanol Concentration in Sample - After identifying the methanol and 1-propanol, measure the areas of the methanol and of the 1-propanol internal standard peaks. From the least squares fit calibrations, Eq 6, calculate the absolute mass of the methanol (Wi) in micrograms in the crude oil sample using the response ratio (rspi) of the area for the methanol peak to that ofthe 1-propanol internal standard as follows:
Wi = [{(Ai/Ais) - bi}/mi] x Wis
where:
Ai = area of the methanol peak in the sample,
Ais = area of the 1-propanol internal standard peak,
Wis = micrograms of 1-propanol internal standard added to the sample, and
Wi = calculated micrograms of methanol in the sample.
13.2 To obtain (Wo) ppm (m/m) methanol in the sample results:
Wo = (Wi/Wg)
where:
Wg = mass of crude oil sample, g, and
Wi = micrograms of methanol in the prepared sample from Eq 7.
13.3 Report results to the nearest ppm (m/m).
13.4 For samples containing less than 5 ppm (m/m) methanol, report results as less than 5 ppm (m/m).
14. Precision and Bias
14.1 Precision - The precision of this test method as determined by a statistical examination ofinterlaboratory test results is as follows:
14.1.1 Repeatability - The difference between successive test results, obtained by the same operator with the same apparatus under constant operating conditions on identical test material would, in the long run, in the normal and the correct operation of the test method, exceed the values in Tables 7 and 8 only in one case in twenty.
14.1.2 Reproducibility - The difference between two single and independent results, obtained by different operators working in different laboratories on identical test material would, in the long run, in the normal and the correct operation of the test method, exceed the values in Tables 7 and 8 only in one case in twenty.
NOTE 7 - The precision stated in Table 7 is applicable to a concentration range of 15 ppm (m/m) to 900 ppm (m/m) methanol. The concentration range of the samples in the cooperative study indicated that the range of at least 5 ppm (m/m) to 900 ppm (m/m) methanol was detectable with the instrument configurations described in 6.1.
14.2 Bias - Bias cannot be determined for the procedure in this test method because no material having an accepted reference value is currently available.
15. Limit of Quantification
15.1 The PLOQ is 15 ppm (m/m).
16. Keywords
16.1 alcohols; crude oils; gas chromatography; methanol; multidimensional gas chromatography
