1、Designation: D7756 13D7756 18Standard Test Method forResidues in Liquefied Petroleum (LP) Gases by GasChromatography with Liquid, On-Column Injection1This standard is issued under the fixed designation D7756; the number immediately following the designation indicates the year oforiginal adoption or,
2、 in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This test method covers the determination, by gas chromatography, of soluble hy
3、drocarbon materials, sometimes called“oily residue,” which can be present in Liquefied Petroleumliquefied petroleum (LP) Gasesgases and which are substantially lessvolatile than the LPG product.1.2 This test method quantifies, in the range of 1010 mgkg to 600600 mg mg/kg kg (ppm mass), the residue w
4、ith a boilingpoint between 174C174 C and 522C522 C (C10 to C40) in LPG. Higher boiling materials, or materials that adhere permanentlyto the chromatographic column, will not be detected.1.3 Appendix X3 and Appendix X4 describe additional applications which could be performed based on the hardware an
5、dprocedures described in this test method. Appendix X3 describes a test procedure for expanding the analysis range to benzene, andAppendix X4 describes a test procedure for the analysis of diisopropanolamine in LPG.1.4 UnitsThe values stated in SI units are to be regarded as standard. The values giv
6、en in parentheses are for informationonly.after SI units are provided for information only and are not considered standard.1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appr
7、opriate safety safety, health, and healthenvironmental practices and determine theapplicability of regulatory limitations prior to use.1.6 This international standard was developed in accordance with internationally recognized principles on standardizationestablished in the Decision on Principles fo
8、r the Development of International Standards, Guides and Recommendations issuedby the World Trade Organization Technical Barriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2D1265 Practice for Sampling Liquefied Petroleum (LP) Gases, Manual MethodD1835 Specification for Lique
9、fied Petroleum (LP) GasesD2158 Test Method for Residues in Liquefied Petroleum (LP) GasesD2163 Test Method for Determination of Hydrocarbons in Liquefied Petroleum (LP) Gases and Propane/Propene Mixtures byGas ChromatographyD2421 Practice for Interconversion ofAnalysis of C5 and Lighter Hydrocarbons
10、 to Gas-Volume, Liquid-Volume, or Mass BasisD2598 Practice for Calculation of Certain Physical Properties of Liquefied Petroleum (LP) Gases from Compositional AnalysisD3700 Practice for Obtaining LPG Samples Using a Floating Piston CylinderD6299 Practice for Applying Statistical Quality Assurance an
11、d Control Charting Techniques to Evaluate Analytical Measure-ment System PerformanceD6300 Practice for Determination of Precision and Bias Data for Use in Test Methods for Petroleum Products and LubricantsD6667 Test Method for Determination of Total Volatile Sulfur in Gaseous Hydrocarbons and Liquef
12、ied Petroleum Gases byUltraviolet FluorescenceE355 Practice for Gas Chromatography Terms and RelationshipsE594 Practice for Testing Flame Ionization Detectors Used in Gas or Supercritical Fluid Chromatography1 This test method is under the jurisdiction ofASTM Committee D02 on Petroleum Products, Liq
13、uid Fuels, and Lubricants and is the direct responsibility of SubcommitteeD02.H0 on Liquefied Petroleum Gas.Current edition approved June 15, 2013Oct. 1, 2018. Published July 2013November 2018. Originally approved in 2011. Last previous edition approved in 20122013 asD7756D7756 13.12. DOI:10.1520/D7
14、756-13. DOI:10.1520/D7756-18.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.This document is not an ASTM sta
15、ndard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cas
16、es only the current versionof the standard as published by ASTM is to be considered the official document.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13. Terminology3
17、.1 Definitions of Terms Concerning ChromatographyThis test method makes reference to many common gas chromato-graphic procedures, terms, and relationships. Detailed definitions of these can be found in Practices E355 and E594.3.2 Definitions of Terms Concerning Liquefied Petroleum GasesThis test met
18、hod makes reference to the definitions ofliquefied petroleum gases as described in Specification D1835.3.3 Definitions of Terms Specific to This Standard:3.3.1 high pressure liquefied gas injector, nSample introduction device which injects liquefied gas samples under pressure andat room temperature
19、directly onto the chromatographic column thereby maintaining the sample in liquid phase during the injectionprocess.3.3.2 pressure station, nDevice that supplies high pressure nitrogen to a suitable sample cylinder and therefore maintainssample in the liquid phase during the injection procedure.4. S
20、ummary of Test Method4.1 A sample cylinder of LPG is pressurized to 2500 kPa (363 psi) 2500 kPa (363 psi) using nitrogen or helium.4.2 The injection system is flushed with LPG in liquid phase at room temperature.4.3 After flushing, the injection device is routed to the GC injector port and LPG (25 m
21、illiseconds activation time equivalentto 30 L) 30 L) is introduced via a high pressure valve and needle which is inserted into a large volume cold on-column injector.4.4 The gas chromatograph is equipped with a solvent vent which routes most of the LPG light components out of the analyticalsystem an
22、d leaves behind the components of interest.4.5 The oily residue to be determined is retained on a pre-column.4.6 After venting the LPG, the flow from the pre-column is switched to the analytical column and a temperature program isstarted.4.7 Oily residue contaminants are separated and identified bas
23、ed on differences in boiling point temperature.4.8 Total residue is quantified using area summation of components corresponding to the expected range of C10 to C40(174(174 C to 522C).522 C).5. Significance and Use5.1 Control over the residue content as specified in Specification D1835 is of consider
24、able importance in end-use applicationsof LPG. Oily residue in LPG is contamination which can occur during production, transportation, or storage.5.2 This test method is quicker and much more sensitive than manual methods, such as Test Method D2158, which is based onevaporation of large sample volum
25、es followed by visual or gravimetric estimation of residue content.5.3 This test method provides enhanced sensitivity in measurements of heavier (oily) residues, with a quantification limit of1010 mg mg/kg kg total residue.5.4 This test method gives both quantitative results and information about co
26、ntaminant composition such as boiling point rangeand fingerprint, which can be very useful in tracing the source of a particular contaminant.6. Apparatus6.1 Gas Chromatograph (GC)Gas chromatographic instrument equipped with a Large Volume Cold on-Column Injectorlargevolume cold on-column injector (L
27、VOCI), a linear temperature programmable column oven, and a flame ionization detector (FID).The temperature control shall be capable of obtaining a retention time repeatability of 0.05 min (3 s) 0.05 min (3 s) throughoutthe scope of this analysis.6.2 Data AcquisitionAny commercial integrator or comp
28、uterized data acquisition system may be used for display of thechromatographic detector signal and peak area integration.6.3 Solvent VentA controlled vent for venting the major part of the matrix.6.4 Retention GapUncoated stainless steel capillary. Successfully used columns and conditions are given
29、in Table 1.6.5 Retaining Pre-ColumnAcolumn with a polydimethylsiloxane stationary phase. Successfully used columns and conditionsare given in Table 1.6.6 Analytical ColumnAcolumn with a polydimethylsiloxane stationary phase. Successfully used columns and conditions aregiven in Table 1.6.7 Column Cou
30、plerCoupling DeviceSuitable for leak-free coupling of the retention gap to the retaining pre-column. (SeeFig. 1 for a schematic overview of the couplings inside the GC oven and the couplings to the solvent vent valve.)D7756 1826.8 Column SplitterSplitter suitable for leak-free coupling of the retain
31、ing pre-column to one side of the analytical columnand the deactivated capillary on the other side. (See Fig. 1 for a schematic overview of the couplings inside the GC oven and thecouplings to the solvent vent valve.)6.9 High Pressure Liquefied Gas InjectorAhigh pressure valve directly connected to
32、a needle which is inserted in the injectionport of the GC, after which the valve is triggered in order to introduce a representative aliquot into the GC system without samplediscrimination. (See Fig. 2.)6.10 Pressure StationThis shall ensure a sample in liquid phase at a constant pressure. See Fig.
33、3 for a typical configuration.TABLE 1 Typical Operating ConditionsOven program 35C for 3 minOven program 35 C for 3 min35 to 340C at 25C/min35 C to 340 C at 25 C min340C for 10 min340 C for 10 minInlet program Type: cool on-columnTemperature: 65C for 3 minTemperature: 65 C for 3 min55 to 340C at 25C
34、/min55 C to 340 C at 25 C min340C for 9 min340 C for 9 minDetector settings Air flow: 400 mL/minHydrogen flow: 40 mL/minMake up gas flow: 45 mL/minTemperature: 350CTemperature: 350 CData rate: 20 HzColumn Retention gap: SulfinertA stainless steel capillary with inner diameter 0.53 mm andlength of 5
35、mRetaining pre-column: 3 m 100%Retaining pre-column: 3 m 100 %Dimethylpolysiloxane: 0.53 mm, 2.65 mAnalytical column: 100%Analytical column: 100 %Dimethylpolysiloxane 30 m, 0.32 mm, 0.25 mPressure station Sample flow: 2 mL/minNitrogen pressure: 2500 kPaNitrogen purge pressure: 500 kPaLiquefied GasIn
36、jectorInjection: 25 msA Sulfinert is a trademark of SilcoTek, 112 Benner Circle, Bellefonte, PA 16823, www.SilcoT.FIG. 1 Overview of the Couplings Inside the GC Oven and the Couplings to the Solvent Vent ValveD7756 1836.11 Typical Column OverviewSee Fig. 1.6.12 Typical Operating ConditionsSee Table
37、1.FIG. 2 High Pressure ValveA Sample cylinderB Sample line inC Injection deviceD Cool on column inletE Gas chromatographF Sample line outG RotometerH VaporizerI Waste systemP Pressure gaugeFIG. 3 Typical Configuration of a Pressure StationD7756 1847. Reagents and Materials7.1 Mineral Oil in LPG Cali
38、bration MixtureCertified calibration mixture with mineral oil in LPG. The concentration of themineral oil shall be close to the expected concentration of the contamination in the LPG sample.7.2 Mineral Oil in Pentane Calibration MixturePrepare a calibration standard of mineral oil in pentane. Record
39、 the weighedvalue to the nearest milligram of mineral oil and calculate the concentration in mg/kg. The concentration of the mineral oil shallbe close to the expected concentration of the contamination in the LPG sample.7.2.1 Standards that are prepared in pentane, normally liquid at room temperatur
40、e, should be stored in suitable containers underrefrigeration and transferred to sample cylinders prior to use. Alternatively, they may be stored in airtight cylinders.7.3 Mineral Oil or Local Hydrocarbon FractionBoiling point range approximately C10-C to C40. Alternatively, a wellcharacterized loca
41、l hydrocarbon fraction, within the range C10-C to C40, can be used to provide quantitative and qualitativecomparison to the contaminant in the sample. Care should be taken to ensure no significant fraction falls outside the C10-C to C40range.7.4 Validation Standard, Mineral Oil in PentanePrepare a v
42、alidation standard of mineral oil in pentane. Record the exactweighed value to the nearest milligram of mineral oil and calculate the concentration in mg/kg. The concentration of the mineraloil shall be close to the expected concentration of the contamination in the LPG sample.7.5 N-alkane Retention
43、 Time StandardMixture containing at least C10 and C40 in a concentration of (nominally) 55 mg mg/LL each, dissolved in pentane or heptane.7.6 SolventGC grade pentane.8. Hazards8.1 There is a significant fire hazard from LPG, and since the boiling point of LPG can be as low as -41C,41 C, there is ari
44、sk of freezing “burns.” Take appropriate safety precautions to prevent ignition or fire, and wear suitable protective equipment toprotect against skin contact with LPG.8.2 An appropriate laboratory ventilation system shall be used.8.3 An appropriate waste line shall be installed. The pressure statio
45、n and injector shall be connected to this line. The waste lineshould vent outside the building.8.4 Pressure station, cylinder, injector, and controller shall be grounded appropriately.9. Preparation of Apparatus9.1 Gas ChromatographInstall and verify performance in accordance with the manufacturersm
46、anufacturers instructions.Typical operating conditions are shown in Table 1.9.2 Pressure StationInstall in accordance with the manufacturersmanufacturers instructions. Purge sample and checkcarefully for leaks.9.3 High Pressure Liquefied Gas InjectorInstall in accordance with the manufacturersmanufa
47、cturers instructions.9.4 Column ConfigurationInstall the columns as shown in Fig. 1. Use low dead volume connections, and check for leaks.10. Calibration10.1 Perform a one point calibration at the startup of the instrument, when the result of the validation sample falls outside theacceptable SQC lim
48、its in accordance with Section 14 or after changes in the application hardware or gas supply, or both.10.2 To verify system linearity over the range of expected sample residues, a linearity check should be performed. Moreinformation can be found in Appendix X5.10.3 Run a blank run, without sample in
49、jection. Cycle the GC several times until the baseline is stable.Abaseline is stable whenthe start and end signal (in pA) of two consecutive blank runs are within 5%.5 %. An unstable baseline can be caused by a leak,detector gases, or by high boiling point components or materials that have not yet eluted from the column. The signal height (inpA) at the end of an analysis of a calibration, validation, or sample shall be equal or higher than the blank baseline.Asignal higherthan 5%5 % could indicate
