BS 15199-2:2006 pdf download – Petroleum products — Determination of boiling range distribution by gas chromatography method — Part 2: Heavy distillates and residual fuels
4 Principle A test portion is introduced into a gas chromatographic column, which separates hydrocarbons in the order of increasing boiling point. The column temperature is raised at a linear reproducible rate and the area under the chromatogram is recorded throughout the analysis. Boiling points are assigned to the time-axis from a calibration curve, which is obtained by running a mixture of known normal alkanes covering the test portion boiling range, under the same conditions. From these data, the boiling range distribution is obtained. The recovery at a specified temperature is determined by comparing the area under the chromatogram with that of a reference standard which has been completely eluted. The temperature at which the recovery was measured is recorded.
NOTE If the found recovery is less than 100 %, the final boiling point is reported as 720 °C or 750 °C at that recovery.
5 Reagents and materials
Unless otherwise stated, only chemicals of recognized analytical quality shall be used.
5.1 Liquid stationary phase, a methyl silicone stationary phase for the column.
5.2 Carrier gases, helium, nitrogen or hydrogen, of at least 99,999 % (V/V) purity. Any oxygen present is removed by a chemical resin filter.
Warning Follow the safety instructions from the filter supplier.
5.3 Hydrogen, grade suitable for flame ionisation detectors.
5.4 Compressed air, regulated for flame ionisation detectors.
5.5 Alkanes, normal alkanes of at least 98 % (m/m) purity from C 5 to C 10 , C 12 , C 14 , C 16 , C 18 , C 20 , C 24 and C 28 to be used with Polywax 655 or 1000 (5.6).
NOTE The calibration mixture from ISO 3924  is also suitable.
5.6 Polywax 655 or 1000
5.7 Carbon disulfide, with a minimum purity of 99,7 % (V/V).
WARNING — Extremely flammable and toxic.
NOTE To confirm the suitability of the carbon disulfide as a solvent, it is recommended to check elution profiles (see Figure 2).
5.8 Calibration mixture The mixture shall contain at least one normal alkane with a boiling point lower than the IBP of the sample, and at least one normal alkane with a boiling point close to the temperature at which the recovery is measured. Dissolve 0,1 g of Polywax (5.6) in 7 ml carbon disulfide (5.7), warming gently if necessary. Prepare an equal volume mixture of alkanes (5.5) and add 10 µl to the Polywax solution. NOTE 1 Commercially available alkane standards are suitable for column performance checks.
NOTE 2 The calibration mix is used to determine the column resolution, skewness of the C 20 peak, and retention time versus boiling point calibration curve.
5.9 Reference materials (RM)
5.9.1 A reference material has two functions:
External Standard: to determine the recovery of samples by comparing the total sample area (3.8) of the reference material with the total sample area of the unknown sample.
Boiling Point Distribution Standard: to check the proper functioning of the system by comparing the results with a known boiling point distribution on a routine basis. Typical example is given in (5.9.2).
5.9.2 Reference Material 5010, a reference sample that has been analyzed by laboratories participating in the test method cooperative study. Consensus values for the boiling range distribution of this sample are given in Table 1.
5.9.3 Cyclohexane. (C 6 H 12 )—(99+ % pure) may be used in place of CS 2 for the preparation of the calibration mixture.
5.9.4 Binary gravimetric blend, a binary distillate mixture with boiling points ranges that gives a baseline at the start, a baseline between the two peaks and an end time that is as close to the end of the chromatogram as possible (see Figure 3 and B.3). This mixture is used to check the relative response of the two distillates and to check the baselines at the start, middle and end of the chromatogram.
6.1 Gas chromatograph, with the following performance characteristics.