1、Designation: D 6520 06Standard 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 D 6520; the number immediately following the designation indicates the year
2、 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 (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice covers procedures for the extraction ofvo
3、latile 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 theyreside.1.3 Not
4、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 forquantitative
5、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 This standard
6、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 hazardstatements, s
7、ee Section 10.2. Referenced Documents2.1 ASTM Standards:2D 1129 Terminology Relating to WaterD 1193 Specification for Reagent WaterD 3370 Practices for Sampling Water from Closed ConduitsD 3694 Practices for Preparation of Sample Containers andfor Preservation of Organic ConstituentsD 3856 Guide for
8、 Good Laboratory Practices in Laborato-ries Engaged in Sampling and Analysis of WaterD 4210 Practice for Intralaboratory Quality Control Proce-dures and a Discussion on Reporting Low-Level Data3D 4448 Guide for Sampling Ground-Water MonitoringWells3. Terminology3.1 DefinitionsFor definitions of term
9、s used in this prac-tice, refer to Terminology D 1129.4. 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 coat
10、ed on a fusedsilica 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 c
11、lean-up procedures.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 consti
12、tuents for the 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
13、 to g/L. Thedetection limit, linear concentration range, and sensitivity ofthe test method for a specific organic compound will dependupon the aqueous matrix, the fiber phase, the sample tempera-ture, sample volume, sample mixing, and the determinativetechnique employed.1This practice is under the j
14、urisdiction of ASTM Committee D19 on Water andis the direct responsibility of Subcommittee D19.06 on Methods for Analysis forOrganic Substances in Water.Current edition approved July 1, 2006. Published July 2006. Originally approvedin 2000. Last previous edition approved in 2000 as D 6520 00.2For re
15、ferenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Withdrawn.1Copyright ASTM International, 100 Barr Harbor Drive, PO
16、Box C700, West Conshohocken, PA 19428-2959, United States.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 vary from a manual SPME fiberholder to automated commercial device specifically designedfor S
17、PME.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 end of this standard.Volatile Organic Compounds (1,2,3)Pesticides, General (4,5)Organochlorine
18、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 topurge and trap extraction to determine if dilution is necessary,thereby eliminating the possibi
19、lity 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 or equilibrium ofanalytes among the three phases present in the sampling vial:the aqueous samp
20、le 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 CFare the concentrations of the analyte inthese phases.6.1.1 Distribution of the analyte among the
21、 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 Reagents, glassware, septa, fiber coatings and othersample processing hardware may yield discre
22、te 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 in 103C oven. Additional cleaning steps may berequired when the analysis requires levels of g/
23、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-fluorocarbon should beavoided. They are a significant source of interference and canadsorb so
24、me 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 analyses for specific organic com-pounds, matrix interferences may be caused by materials andconst
25、ituents 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 be reduced by choosing an appropri-ate SPME adsorbing fiber.8. The Technique of SPME8.1 The t
26、echnique 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 of these. The coated,fused silica (SMPE fiber) is attached to a metal rod and theentire assem
27、bly 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 into a vial, andseal the vial with a septum cap.8.3 Push the sheath with fiber retracted through
28、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 approximately 0.8 mL of sample and direct samplingrequires 1.2 mL.8.4 Organic compounds are absorbe
29、d onto the fiber phasefor a predetermined time. This time can vary from less than 1min for volatile compounds with high diffusion rates such asvolatile 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
30、the sampling vial.NOTE 1This figure is Fig. 5, p. 218, Vol 37, Advances in Chroma-tography, 1997. Used with permission.FIG. 1 SPME Fiber Holder AssemblyD65200628.6 Immediately insert the sheath through the septum of thehot GC injector (see Fig. 3), push down the plunger, and insertthe fiber into the
31、 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 seal. These aremanufactured by several sources for specific GC injectors.8.6.2 A conventional GC sept
32、um 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.Pull off and discard any loose particles of septum material, andreinstall the septum.8.6.3 The user sho
33、uld 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 retention time or the presenceof air in a mass spectrometer.8.7 Ensure that the injector liner used wi
34、th 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 mm)may result in broadening of early eluting peaks. SPME insertsare available commercially and may be
35、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 normally10 to 20C below the temperature limit of the fiber or the GCcolumn (usually 200 to 280C), or bo
36、th. 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 extracted by the fiber, aqueous orheadspace,9.1.2 The volatility of the analyte such as gas phase hydro-car
37、bons 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 automated sam-pling.10.2 SPME Fiber Assembly.10.3 SPME Injector Liner, that is, inserts for gas chromato-
38、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 otherwise indicated, referenceto water shall be understood to mean reagent water that meetsthe purity spe
39、cifications of Type I or Type II water, presentedin Specification D 1193.11.2 Chemicals, standard materials and surrogates should bereagent or ACS grade or better. When they are not available asreagent grade, they should have an assay of 90 % or better.11.3 Sodium Chloride (NaCl), reagent grade, gra
40、nular.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 chemicals should be minimized. Each laboratory isresponsible for maintaining awareness of OSHA regul
41、ationsregarding 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.FIG. 2 Process for Adsorption of Analytes from Sample Vial withSPME FiberFIG. 3 Injection Followed by D
42、esorption of SPME Fiber inInjection Port of ChromatographD652006313. Sample Handling13.1 There are many procedures for acquiring representa-tive samples of water. The choice of procedure is site andanalysis specific. There are severalASTM guides and practicesfor sampling.4Two good sources are Practi
43、ces D 3370 andGuide D 4448.13.2 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 con-centration level of the analyte. VOA vials of 40-mL capacityare commonly used as sampling containers. Any
44、 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.13.3.2 Samples should be stored in a clean, dry place awayfrom samples containing high concentrations of or
45、ganics.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 of the sample to about 2by adding HCI. The constituent of concern must be stableunder acid conditions. For a
46、dditional information, See PracticeD 3694.13.4.2 If residual chlorine is present, add sodium thiosulfateas a preservative (30 mg per 4 oz bottle).14. Optimizing SPME Sampling Parameters14.1 Liquid sampling and headspace sampling give approxi-mately the same recovery for volatiles but not for semi-vo
47、latiles. 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 mixing is effective in increasing the responseof semi-volatile analytes. It reduces the equilibrium time fo
48、rthe 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 much less effective for volatiles and isgenerally not required.14.3 Matrix modification through the addit
49、ion 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 of Liquid to HeadspaceWith nonpolar ana-lytes, the sensitivity is enhanced when the proportion of liquidpha
