1、Designation: D6520 06 (Reapproved 2012)Standard Practice forthe Solid Phase Micro Extraction (SPME) of Water and itsHeadspace for the Analysis of Volatile and Semi-VolatileOrganic Compounds1This standard is issued under the fixed designation D6520; the number immediately following the designation in
2、dicates the year oforiginal adoption or, 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. Scope1.1 This practice covers procedures for the
3、extraction ofvolatile and semi-volatile organic compounds from water andits headspace using solid-phase microextraction (SPME).1.2 The compounds of interest must have a greater affinityfor the SPME-absorbent polymer or adsorbent or combinationsof these than the water or headspace phase in which they
4、reside.1.3 Not all of the analytes that can be determined by SPMEare addressed in this practice. The applicability of the absor-bent polymer, adsorbent, or combination thereof, to extract thecompound(s) of interest must be demonstrated before use.1.4 This practice provides sample extracts suitable f
5、orquantitative or qualitative analysis by gas chromatography(GC) or gas chromatography-mass spectrometry (GC-MS).1.5 Where used, it is the responsibility of the user to validatethe application of SPME to the analysis of interest.1.6 The values stated in SI units are to be regarded as thestandard.1.7
6、 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use. For specific haza
7、rdstatements, see Section 10.2. Referenced Documents2.1 ASTM Standards:2D1129 Terminology Relating to WaterD1193 Specification for Reagent WaterD3370 Practices for Sampling Water from Closed ConduitsD3694 Practices for Preparation of Sample Containers andfor Preservation of Organic ConstituentsD3856
8、 Guide for Management Systems in LaboratoriesEngaged in Analysis of WaterD4210 Practice for Intralaboratory Quality Control Proce-dures and a Discussion on Reporting Low-Level Data3D4448 Guide for Sampling Ground-Water MonitoringWells3. Terminology3.1 DefinitionsFor definitions of terms used in this
9、 prac-tice, refer to Terminology D1129.4. Summary of Practice4.1 This practice employs adsorbent/liquid or adsorbent/gasextraction to isolate compounds of interest.An aqueous sampleis added to a septum-sealed vial. The aqueous phase or itsheadspace is then exposed to an adsorbent coated on a fusedsi
10、lica fiber. The fiber is desorbed in the heated injection port ofa GC or GC-MS or the injector of an HPLC.4.2 The desorbed organic analytes may be analyzed usinginstrumental methods for specific volatile or semi-volatileorganic compounds. This practice does not include sampleextract clean-up procedu
11、res.5. Significance and Use5.1 This practice provides a general procedure for thesolid-phase microextraction of volatile and semi-volatile or-ganic compounds from an aqueous matrix or its headspace.Solid sorbent extraction is used as the initial step in theextraction of organic constituents for the
12、purpose of quantify-ing or screening for extractable organic compounds.5.2 Typical detection limits that can be achieved usingSPME techniques with gas chromatography with flame ioniza-tion detector (FID), electron capture detector (ECD), or with amass spectrometer (MS) range from mg/L to g/L. Thedet
13、ection limit, linear concentration range, and sensitivity ofthe test method for a specific organic compound will depend1This practice is under the jurisdiction of ASTM Committee D19 on Water andis the direct responsibility of Subcommittee D19.06 on Methods for Analysis forOrganic Substances in Water
14、.Current edition approved June 15, 2012. Published June 2012. Originallyapproved in 2000. Last previous edition approved in 2006 as D6520 06. DOI:10.1520/D6520-06R12.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual B
15、ook of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Withdrawn. The last approved version of this historical standard is referencedon www.astm.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,
16、 United States.upon the aqueous matrix, the fiber phase, the sample tempera-ture, sample volume, sample mixing, and the determinativetechnique employed.5.3 SPME has the advantages of speed, no desorptionsolvent, simple extraction device, and the use of small amountsof sample.5.3.1 Extraction devices
17、 vary from a manual SPME fiberholder to automated commercial device specifically designedfor SPME.5.3.2 Listed below are examples of organic compounds thatcan be determined by this practice. This list includes both highand low boiling compounds. The numbers in parentheses referto references at the e
18、nd of this standard.Volatile Organic Compounds (1,2,3)Pesticides, General (4,5)Organochlorine Pesticides (6)Organophosphorous Pesticides (7,8)Polyaromatic Hydrocarbons (9,10)Polychlorinated biphenyls (10)Phenols (11)Nitrophenols (12)Amines (13)5.3.3 SPME may be used to screen water samples prior top
19、urge and trap extraction to determine if dilution is necessary,thereby eliminating the possibility of trap overload.6. Principles of SPME6.1 SPME is an equilibrium technique where analytes arenot completely extracted from the matrix. With liquid samples,the recovery is dependent on the partitioning
20、or equilibrium ofanalytes among the three phases present in the sampling vial:the aqueous sample and headspace (Phase 1), the fiber coatingand aqueous sample (Phase 2), and the fiber coating and theheadspace (Phase 3):Phase 1! K15 CL/Cg(1)Phase 2! K25 CF/CL(2)Phase 3! K35 CF/CG(3)where CL,CGand CFar
21、e the concentrations of the analyte inthese phases.6.1.1 Distribution of the analyte among the three phases canbe calculated using the following:C0VL5 CGVG1 CLVL1 CFVF(4)6.1.2 Concentration of analyte in fiber can be calculatedusing the following:CF5 C0VLK1K2/VG1 K1VL1 K1K2VF(5)7. Interferences7.1 R
22、eagents, glassware, septa, fiber coatings and othersample processing hardware may yield discrete artifacts orelevated baselines that can cause poor precision and accuracy.7.1.1 Glassware should be washed with detergent, rinsedwith water, and finally rinsed with distilled-in-glass acetone.Air dry or
23、in 103C oven. Additional cleaning steps may berequired when the analysis requires levels of g/L or below.Once the glassware has been cleaned, it should be usedimmediately or stored wrapped in aluminum foil (shiny sideout) or under a stretched sheet of PTFE-fluorocarbon.7.1.2 Plastics other than PTFE
24、-fluorocarbon should beavoided. They are a significant source of interference and canadsorb some organics.7.1.3 A field blank prepared from water and carried throughsampling, subsequent storage, and handling can serve as acheck on sources of interferences from the containers.7.2 When performing anal
25、yses for specific organic com-pounds, matrix interferences may be caused by materials andconstituents that are coextracted from the sample. The extent ofsuch matrix interferences will vary considerably depending onthe sample and the specific instrumental analysis method used.Matrix interferences may
26、 be reduced by choosing an appropri-ate SPME adsorbing fiber.8. The Technique of SPME8.1 The technique of SPME uses a short, thin solid rod offused silica (typically 1-cm long and 0.11-m outer diameter),coated with a film (30 to 100 M) of a polymer, copolymer,carbonaceous adsorbent, or a combination
27、 of these. The coated,fused silica (SMPE fiber) is attached to a metal rod and theentire assembly is a modified syringe (see Fig. 1).8.2 In the standby position, withdraw the fiber into aprotective sheath. Place an aqueous sample containing organicanalytes or a solid containing organic volatiles int
28、o a vial, andseal the vial with a septum cap.8.3 Push the sheath with fiber retracted through the vialseptum and lower into the body of the vial. Inject the fiber intothe headspace or the aqueous portion of the sample (see Fig. 2).Generally, when 2-mL vials are used, headspace samplingrequires appro
29、ximately 0.8 mL of sample and direct samplingrequires 1.2 mL.8.4 Organic compounds are absorbed onto the fiber phasefor a predetermined time. This time can vary from less than 1min for volatile compounds with high diffusion rates such asNOTE 1This figure is Fig. 5, p. 218, Vol 37, Advances in Chroma
30、-tography, 1997. Used with permission.FIG. 1 SPME Fiber Holder AssemblyD6520 06 (2012)2volatile organic solvents, to 30 min for compounds of lowvolatility such as PAHs.8.5 Withdraw the fiber into the protective sheath and pullthe sheath out of the sampling vial.8.6 Immediately insert the sheath thro
31、ugh the septum of thehot GC injector (see Fig. 3), push down the plunger, and insertthe fiber into the injector liner where the analytes are thermallydesorbed and subsequently separated on the GC column.8.6.1 The blunt 23-gage septum-piercing needle of theSPME is best used with a septumless injector
32、 seal. These aremanufactured by several sources for specific GC injectors.8.6.2 A conventional GC septum may be used with SPME.A septum lasts for 100 runs or more. To minimize septumfailure, install a new septum, puncture with a SPME sheaththree or four times, and remove and inspect the new septum.P
33、ull off and discard any loose particles of septum material, andreinstall the septum.8.6.3 The user should monitor the head pressure on thechromatographic column as the fiber sheath enters and leavesthe injector to verify the integrity of the seal. A subtle leak willbe indicated by unusual shifts in
34、retention time or the presenceof air in a mass spectrometer.8.7 Ensure that the injector liner used with SPME is notpacked or contains any physical obstructions that can interferewith the fiber. The inner diameter of the insert should optimallyshould be about 0.75 to 0.80 mm. Larger inserts (2 to 4
35、mm)may result in broadening of early eluting peaks. SPME insertsare available commercially and may be used for split orsplitless injection. With splitless injection, the vent is timed toopen at the end of the desorption period (usually 2 to 10 min).8.8 Injector temperature should be isothermal and n
36、ormally10 to 20C below the temperature limit of the fiber or the GCcolumn (usually 200 to 280C), or both. This provides rapiddesorption with little or no analyte carryover.9. Selection of Fiber Phase9.1 The selection of the fiber phase depends on severalfactors, including:9.1.1 The media being extra
37、cted by the fiber, aqueous orheadspace,9.1.2 The volatility of the analyte such as gas phase hydro-carbons to semivolatile pesticides, and9.1.3 The polarity of the analyte.9.2 A selection of fiber phases and common applications isshown in Table 1.10. Apparatus10.1 SPME Holder, manual sampling or aut
38、omated sam-pling.10.2 SPME Fiber Assembly.10.3 SPME Injector Liner, that is, inserts for gas chromato-graphs.10.4 Septum Replacement Device, Merlin or Jade.10.5 Vials, with septa and caps, for manual or automation.For automation, use either 2- or 10mL vials.11. Reagents11.1 Purity of WaterUnless oth
39、erwise indicated, referenceto water shall be understood to mean reagent water that meetsthe purity specifications of Type I or Type II water, presentedin Specification D1193.11.2 Chemicals, standard materials and surrogates should bereagent or ACS grade or better. When they are not available asreage
40、nt grade, they should have an assay of 90 % or better.11.3 Sodium Chloride (NaCl), reagent grade, granular.12. Hazards12.1 The toxicity and carcinogenicity of chemicals used inthis practice have not been precisely defined. Each chemicalshould be treated as a potential health hazard. Exposure tothese
41、 chemicals should be minimized. Each laboratory isresponsible for maintaining awareness of OSHA regulationsregarding safe handling of chemicals used in this practice.12.2 If using either solvent, the hazard of peroxide forma-tion should be considered. Test for the presence of peroxideprior to use.FI
42、G. 2 Process for Adsorption of Analytes from Sample Vial withSPME FiberFIG. 3 Injection Followed by Desorption of SPME Fiber inInjection Port of ChromatographD6520 06 (2012)313. Sample Handling13.1 There are many procedures for acquiring representa-tive samples of water. The choice of procedure is s
43、ite andanalysis specific. There are severalASTM guides and practicesfor sampling.4Two good sources are Practices D3370 andGuide D4448.13.2 The recommended sample size is 40 to 100 mL. Moreor less sample can be used depending upon the sampleavailability, detection limits required, and the expected co
44、n-centration level of the analyte. VOA vials of 40-mL capacityare commonly used as sampling containers. Any headspaceshould be eliminated if volatiles analysis is required.13.3 Sample Storage:13.3.1 All samples must be iced or refrigerated to 4C fromthe time of collection until ready for extraction.
45、13.3.2 Samples should be stored in a clean, dry place awayfrom samples containing high concentrations of organics.13.4 Sample Preservation:13.4.1 Some compounds are susceptible to rapid biologicaldegradation under certain environmental conditions. If biologi-cal activity is expected, adjust the pH o
46、f the sample to about 2by adding HCI. The constituent of concern must be stableunder acid conditions. For additional information, See PracticeD3694.13.4.2 If residual chlorine is present, add sodium thiosulfateas a preservative (30 mg per 4 oz bottle).14. Optimizing SPME Sampling Parameters14.1 Liqu
47、id sampling and headspace sampling give approxi-mately the same recovery for volatiles but not for semi-volatiles. Semi-volatiles are best extracted with SPME liquidsampling. Headspace sampling is desirable if samples containnonvolatile compounds such as salts, humic acids, or proteins.14.2 Sample m
48、ixing is effective in increasing the responseof semi-volatile analytes. It reduces the equilibrium time forthe adsorption of the semi-volatile components. Mixing re-duces any analyte depleted area around the fiber phase andincreases the diffusion of larger molecules from the aqueousmatrix. Mixing is
49、 much less effective for volatiles and isgenerally not required.14.3 Matrix modification through the addition of salt to theaqueous phase may be used to drive polar compounds into theheadspace. It has very little effect on nonpolar compounds.Adding salts to the sample also minimizes matrix differenceswhen there are sample to sample variations in ionic strength14.4 Heating the sample is often used to increase thesensitivity in static headspace; it is much less effective withSPME. The equilibrium tends to be shifted to the headspacerather than to the fiber.14.5 Ratio
