ASTM D5480 Standard Test Method for Engine Oil Volatility by Gas chromatography
7. Preparation of Apparatus
7.1 Column Preparation - The column must be conditioned at the maximum operating temperature to reduce baseline shifts due to bleeding of column substrate. The column can be conditioned using the following procedure:
7.1.1 Disconnect the column from the detector.
7.1.2 Purge the column at ambient temperature for at least 30 min.
7.1.3 With carrier gas flowing through the column, raise the column oven temperature to the maximum temperature that will be used and maintain the temperature at this level for 12 to 16 h.
7.1.4 Cool the column to ambient temperatures.
7.1.5 Reconnect the column to the detector.
7.1.6 Set the detector temperature at least 5°C higher than the maximum column temperature to be used.
7.1.7 Program the column temperature up to the maximum several times with normal carrier gas flow until stable baseline is obtained.
7.2 Performance Standard - To test column resolution and linearity of response, a performance standard is prepared as follows: Prepare a stock solution by accurately weighing 0.1 g (to the nearest 0.1 mg) of decane, dodecane, hexadecane, octadecane and tetracosane(all 99+ % purity into a 100-mL volumetric flask. Dilute to the mark with carbon disulfide and mix well until each hydrocarbon is completely dissolved and the solution is uniform. the performance standard is prepared by pipetting 0.1 mL of the stock solution into a 10-mL volumetric flask, diluting to the mark with carbon disulfide and mixing well.
7.3 Column Resolution - To test column resolution, inject the same volume of performance standard as is used in the analysis of samples and obtain a chromatogram using the procedure described in Section 8. Referring to Fig.1, calculate resolution using the following equation:
R = [2(d2 - d1)]/[1.699(Y1 + Y2)]
R = column resolution
d2 = retention time for octadecane at peak maximum, s,
d1 = retention time for hexadecane at peak maximum, s,
Y1 = peak width of hexadecane at half height, s, and
Y2 = peak width of octadecane at half height, s.
The column resolution must be between 19 and 26 to be acceptable.
7.4 Linearity of Response - The relative response factor for each component in the performance standard (relative to octadecane) should be within 5% of unity. After obtaining the chromatogram of the performance standard, calculate the relative response factor for each n-paraffin in the mixture, in accordance with Test Method D4626, by relating the mass of each component to its respective peak area. Calculate the relative response factor for each component as follows:
RRF = (Mn/An)/(M18/A18)
RRF = relative response factor,
Mn = mass of the component in the mixture,
An = area of the component in the mixture,
M18 = mass of octadecane in the mixture, and
A18 = area of octadecane in the mixture.
Also, examine the peak shape of the components in the performance standard. If peak distortion is evident, a smaller sample size may need to be used or the column may need to be replaced.