ASTM D6417 Estimation of Engine Oil Volatility by Capillary Gas Chromatography
6. Apparatus
6.1 Chromatograph - The gas chromatographic system used must have the following performance characteristics:
6.1.1 Column Oven, capable of sustained and linear programmed temperature operation from near ambient (for example, 35 to 50°C) up to 400°C.
6.1.2 Column Temperature Programmer - The chromatograph must be capable of linear programmed temperature operation up to 400°C at selectable linear rates up to 20°C/min. The programming rate must be sufficiently reproducible to obtain the RT repeatability of 0.1 min (6 s) for each component in the calibration mixture described in 7.6.
6.1.3 Detector - This test method requires a FID. The detector must meet or exceed the following specifications as detailed in Practice E 594.
6.1.3.1 Operating Temperature, up to 400°C.
6.1.3.2 Sensitivity, >0.005 coulombs/g carbon.
6.1.3.3 Minimum Detectability, 1 x 10(-11) g carbon/s.
6.1.3.4 Linear Range, 10(6).
6.1.3.5 Connection of the column to the detector must be such that no temperature below the column temperature exists. Refer to Practice E 1510 for proper installation and conditioning of the capillary column.
6.1.4 Sample Inlet System - Any sample inlet system capable of meeting the performance specification in 7.6 may be used. Programmed temperature vaporization (PTV) and programmable cool on-column injection systems have been used successfully.
6.2 Microsyringe - A microsyringe with a 23 gage, or smaller, stainless steel needle is used for on-column sample introduction. Syringes of 0.1 µL to 10 µL capacity have been used.
6.2.1 Automatic syringe injection is recommended to achieve best precision.
6.3 Column - This test method is limited to the use of nonpolar wall coated open tubular (WCOT) columns of high thermal stability. Glass, fused silica, and stainless steel columns with a 0.53-mm diameter have been successfully used. Cross-linked or bonded methyl silicone liquid phases with film thickness from 0.10 to 1.0 µm have been used. The column length and liquid phase film thickness must allow the elution of at least C60 n-paraffin (boiling point = 615°C). The column and conditions must provide separation of typical petroleum hydrocarbons in order of increasing boiling point and meet the column resolution requirements of 8.2.1.
6.4 Carrier Gas Flow/Pressure Control - The optimum carrier gas flow for the column and chromatographic system should be used. It is recommended that the system be equipped with a constant pressure/constant flow device capable of maintaining the carrier gas at a constant flow rate throughout the temperature program.
6.5 Data Acquisition System:
6.5.1 Recorder - A 0 to 1 mV range recording potentiometer, or equivalent, with a full-scale response time of 2 s, or less, may be used to provide a graphical display.
6.5.2 Integrator - Means must be provided for determining the accumulated area under the chromatogram. This can be done by means of an electronic integrator or computer based chromatography data system. The integrator/computer system must have normal chromatographic software for measuring the retention time and areas of eluting peaks (peak detection mode). In addition, the system must be capable of converting the continuously integrated detector signal into area slices of fixed duration (area slice mode). These contiguous area slices, collected for the entire analysis, are stored for later processing. The electronic range of the integrator/computer (for example, 1 V, 10 V) must be within the linear range of the detector/electrometer system used.
NOTE 1 - Some gas chromatographs have an algorithm built into their operating software that allows a mathematical model of the baseline profile to be stored in memory. This profile is automatically subtracted from the detector signal on subsequent sample runs to compensate for the column bleed. Some integration systems also store and automatically subtract a blank analysis from subsequent analytical determinations.
7. Reagents and Materials
7.1 Carrier Gas - Helium, nitrogen, or hydrogen of high purity. (Warning - See Notes 2 and 3.) Additional purification is recommended by the use of molecular sieves or other suitable agents to remove water, oxygen, and hydrocarbons. Available pressure must be sufficient to ensure a constant carrier gas flow rate.
NOTE 2 - Warning: Helium and nitrogen are compressed gases under high pressure.
NOTE 3 - Warning: Hydrogen is an extremely flammable gas under high pressure.
7.2 Hydrogen - Hydrogen of high purity (for example, hydrocarbon free) is used as fuel for the FID. (Warning - See Note 3.)
7.3 Air - High purity (for example, hydrocarbon free) compressed air is used as the oxidant for the FID. (Warning - See Note 4.)
NOTE 4 - Warning: Compressed air is a gas under high pressure and supports combustion.
7.4 Carbon Disulfide (CS2) (99+ % pure), may be used as a viscosity reducing solvent. It is miscible with asphaltic hydrocarbons and provides relatively little response with the FID. The quality (hydrocarbon content) should be determined by this test method prior to use as a sample diluent. (Warning - See Note 5.)
NOTE 5 - Warning: Carbon disulfide is extremely flammable and toxic.
7.5 Cyclohexane - (99+ % pure), may be used as a viscosity reducing solvent. It is miscible with asphaltic hydrocarbons; however, it responds well to the FID. The quality (hydrocarbon content) should be determined by this test method prior to use as a sample diluent. (Warning - See Note 6.)
NOTE 6 - Warning: Cyclohexane is flammable.
7.6 Calibration Mixture - A qualitative mixture of n-paraffins (nominally C8 to C60) dissolved in a suitable solvent. The final concentration should be approximately 1 part of n-paraffin mixture to 100 parts of solvent. It is recommended that at least one compound in the mixture have a boiling point lower than the IBP of the sample being analyzed, as defined in the scope of this test method (see 1.1). It is recommended that the calibration mixture contain at least eleven known n-paraffins (for example, C8, C9, C10, C12, C16, C20, C30, C40, C50, C52 and C60). Boiling points of n-paraffins are listed in Table 1.
NOTE 7 - A suitable calibration mixture can be obtained by dissolving a synthetic wax in a volatile solvent (for example, carbon disulfide or cyclohexane). Solutions of 1 part synthetic wax to 200 parts solvent can be prepared. Lower boiling point paraffins will have to be added to ensure conformance with 7.5.
7.7 Response Linearity Mixture - Prepare a quantitatively weighed mixture of about ten individual paraffins (>99 % purity), covering the boiling range of the test method. The highest boiling point component should be at least n-C60. The mixture must contain n-C40. Use a suitable solvent to provide a solution of each component at approximately 0.5 % to 2.0 % by mass.
