ASTM D3525 Gasoline Diluent in Used Gasoline Engine Oils
ASTM D3525 Standard Test Method for Gasoline Diluent in Used Gasoline Engine Oils by Gas Chromatography
7. Preparation of Apparatus
7.1 Column Preparation - Any satisfactory method used in the practice of gas chromatography that will produce a column meeting the requirements of 4.3 may be used. The column must be conditioned at the maximum operating temperature until baseline drift due to column bleeding has been reduced to less than 1 % per hour.
NOTE 8 - Difficulty in achieving the baseline drift requirement may indicate injection port or column overloading from contamination. Remove and clean the injection port. Reassemble and increase the temperature of the injection port, column oven, and detector to the maximum limits of the gas chromatographic column employed.
7.1.1 To test column resolution prepare a mixture of 1 volume % each of C14 and C16 normal paraffins in a suitable solvent such as octane (Warning - C14 and C16 n-paraffins, see Note 4) (Warning - n-octane, see Note 5). Inject the same volume of this mixture as to be used in analysis of samples and obtain the chromatogram by the procedure described below. Calculate the resolution, R, from the distance between C14 and C16 normal paraffin peaks at the peak maxima, d, and the width of the peaks at the baseline, Y1 and Y2, as follows:
R = [2(d1 - d2)]/(Y1 + Y2)
Resolution, R, using the above equation, must be at least 3 and not more than 8.
7.2 Chromatograph and Related Equipment - Place in service in accordance with manufacturer's instructions. Typical operating conditions are shown in Table 1.
7.2.1 The deposits formed in the flame ionization detector from combustion must be removed regularly, since they change the response characteristics of the detector.
7.2.2 If the sample inlet system is heated above 300°C, a blank run must be made after new septums are installed, to check for extraneous peaks produced by septum bleed. At the sensitivity levels employed in this method, conditioning of the septum at the operating temperature of the sample inlet system for several hours will minimize this problem. Recommended practice is to change septums at the end of the day's operation rather than at the beginning.
8. Preparation of Sample
8.1 Using a 1-mL syringe, inject 0.5 mL of sample in a tared 1-dram vial, weigh, and record. Into this vial add 10 µL of n-tetradecane (C14), weigh, and record. If the sample is too viscous for injection into the gas chromatograph at room temperature, add 0.5 mL of a suitable solvent to the vial. Use of n-hexadecane has been found to be acceptable as a solvent. Stopper the vial with a septum cap and shake for at least 2 min.
