ASTM D5307 Determination of Boiling Range Distribution of Crude Petroleum by Gas Chromatography
10. System Performance
10.1 Resolution - Analyze an aliquot of the column resolution test mixture (see 7.7) utilizing identical conditions as used in the analysis of samples. The resolution of n-C16 and n-C18n-paraffin peaks must be between three and ten when calculated in accordance with the following equation (refer to Fig.1):
R = [2(t2 - t1)]/[1.699(Y2 + Y1)]
where:
R = resolution,
t1 = time for the n-C16 peak apex, in seconds,
t2 = time for the n-C18 peak apex, in seconds,
Y1 = peak width, at half height, of n-C16, in seconds, and
Y2 = peak width, at half height, of n-C18, in seconds.
10.2 Retention Time Repeatability - The system must be sufficiently repeatable, when testing with the calibration mixture, to obtain retention time repeatability (maximum difference between duplicate runs) of 6 s or less for each calibration peak.
10.3 System Performance Check - Analyze the detector response test mixture (see 7.8) utilizing identical conditions as used in the analysis of samples. Calculate response factors relative to n-decane as follows:
Fn = (Cn/An)/(C10/A10)
where:
An = area of that n-paraffin peak,
A10 = area of n-decane peak,
Cn = concentration of that n-paraffin in the mixture,
C10 = concentration of n-decane in the mixture, and
Fn = response factor relative to n-decane.
10.3.1 The response factor (Fn) of each n-paraffin must not deviate from unity by more than 10 %.
10.3.2 With some chromatographs, response factors for higher boiling n-paraffins (n-C20 to n-C44) have been observed to change after several crude oil samples have been analyzed. Check the stability of the system by repeating the performance test after analyzing ten samples. If the system still meets the performance specified (see 10.3.1), it is not necessary to repeat this check after subsequent analyses. However, it is good practice to repeat the performance test if detector components are changed.
