SOLID PHASE MICROEXRACTION – SPME TROUBLESHOOTING
Contents
1. immersion sampling and at a consistent position above the sample during headspace sampling Apply uniformly across all extractions any pH or salt adjustments made to the samples Determine minimum time for equilibrium using a standard mixture and controlled extraction conditions Note that full equilib rium is not required to be reached for all applications to achieve reproducible results Dilute samples to minimize solvent interfer ence or use headspace sampling to minimize solvent effect Use internal standards surrogates or the standard addition technique to compensate for variations in sample matrix Minimize headspace volume to 50 or less and agitate the sample Maintain the same headspace volume and agitation conditions across all extractions Grind solid into small particles add to water and apply heat and agitation Reduce the extraction time to minimize displacementfor interference Verify that the fiber position depth desportion time temperature and splitless conditions are consistent Use an automated SPME system to improve reproducibility Use a stir bar or soncication system to agitate the sample during sampling Maintain consistent agitation conditions for all standards and samples Maintain consistent volumes for all standards and samples Remedy 1 Minimize oxygen in carrier gas condition fibers in oxygen free gas flow Reduce the injection port temperature2. not reached during extraction 5 Varying organic content in the samples 5 Varying headspace in sample vials during headspace extraction 5 Solid samples not releasing analytes for extraction 5 Competing analyte displaces compound of interestior interferes 5 Not reproducing desorption conditions D Not using agitation during sampling or apply it inconsistently 5 Sample volumes are inconsistent 5 Possible Cause 1 Fiber is oxidized during fiber conditioning or sample injection into GC S D 2 Heating during injection D P 1 Fiber is oxidized during fiber conditioning or sample injection into GC S D 2 Coating on fiber deteriorated P 3 Fiber was exposed to solvents that cause swelling of coating 5 Mai 2007 Remedy Pea Pea had E in an oo i no 10 Retract fiber into protective needle during insertion into vialinjection port and removal Injection port septum nut is overtightened Loasen the nut slightly to allow for improved injection Use pre drilled injection port septa or a septumless injector system e g Merlin Microseal Time of extraction and temperature are the two most critical conditions to control Use timing device and calibrated thermometer to ensure reproducible results Remember that room temperature fluctuations will influence the ambient sample temperature Position fiber just below sample surface for
3. system e g Merlin Microseal Do net expose POMS coated fibers to non polar solvents such as pentane methylene chloride or diethyl ether Do not expose Carbowax fibers to polar solvents Loosen the top screw on the holder assembly slightly to allow for free movement of the plunger To prevent the needle from bending when doing manual SPME sampling follow this procedure Adjust the SPME needle to the 0 2 depth gauge setting on the plunger first tick mark This will expose about 3mm of the needle through the end of the black holder Hold the SPME assembly on top of the sampling vial with the bottom of the black holder flush with the top of the vial cap Hold the sampling vial and black SPME holder base securely with one hand Twist the stainless steel plunger clockwise with the other hand Keep turning the plunger until the desired depth setting is achieved you will usually hear a pop when the needle pierces the septum Expose the fiber and perform sampling as usual To prevent the needle trom bending when doing manual SPME injections follow this procedure Adjust the SPME needle to the 0 2 depth gauge setting on the plunger first tick mark This will expose about 3mm of the needle through the end of the black holder Position the SPME assembly on top of the GC injection port or in the SPME inlet guide with the bottom of the black holder flush with the top of the injector or guide Hold the black SP
4. to the recom mended maximum setting Carbowax DWE coatings are especially sensitive to tempera ture lt 260 C is recommended 2 Does not usually affect the performance of the fiber Always minimize the oxygen content in the GC carrier gas to avoid oxidizing the fiber coating The polyacrlate coated fiber will discolor above 280 C Carbowasx DVB may slightly darken during use however if the fiber turns brown lower the injection port temperature 265 C is the recommended maximum and check the system for leaks 1 Minimize oxygen in carrier gas condition fibers in oxygen free gas flow Reduce injection port temperature to the recom mended fiber maximum 2 Replace fiber Fibers are reusable and will last for 50 injections on average 3 Do not expose PDMS coated fibers to non polar solvents such as pentane methylene chloride or diethyl ether Do not expose Carbowax fibers to polar solvents
5. Armelle Vallat Mai 2007 SOLID PHASE MICROEXRACTION SPME TROUBLESHOOTING GUIDE l SPME product related SPME fiber breakage is a potential problem when you apply excessive stress to the fiber during sampling or analysis SPME accessories such as the inlet guide sampling stand heat stir plate magnetic stirring bars and thermometer will improve the reproducibility and ease of the sampling and desorption steps Do not expose PDMS coated fibers to non polar solvents and do not expose Carbowax coated fibers to polar solvents The fiber coating will swell and cause damage may include breakage grooving or stripping of the fiber coating To avoid this problem dilute the sample with water before extraction to reduce the organic solvent percentage to less 3 Polydimethylsiloxane PDMS considered non polar for non polar analytes 100um non bonded red plain GC HPLC 30um non bonded yellow plain GC HPLC Zum bonded green plain GC HPLC Polydimethylsiloxane Divinylbenzene PDMS DVB ideal for many polar analytes especially amines 65um partially crosslinked blue plain 60um partially crosslinked brown notched 65um StableFlex highly crosslinked pink plain Polyacrylate highly polar coating for general use ideal for phenols 85um partially crosslinked white plain GC HPLC Carboxen Polydimethylsiloxane CAR PDMS ideal for gaseous volatile analytes high retention for trace analysis 7 5um partially crosslinked black p
6. ME holder base securely with one hand Twist the stainless steel plunger clockwise with the other hand Keep turning the plunger until the desired depth setting is achieved you will usually hear a pop when the needle pierces the septum Expose the fiber and perform sample desorption as usual Loosen slightly the vial closure or injection port nut Use LB 2 septa for injection port or silicone septa with lt 10mil Teflon on sampling vials Shorten the amount of exposed needle on SPME holder to 0 5 inch or 1cm before puncturing the vial septa Adjust the holder needle setting to the desired depth for sampling Do not use butyl rubber style septa Lise larger splitless inlet liners 0 7 5mm ID or larger without glass wool or adsorbents Reference autoinjector manual on alignment Armelle Vallat Problem Symptom 5 Fiber breaks 1 6 Reproducibility is poor 3 A Normal 5 6 Problem 10 11 Problem Symptom 7 Fiber discolored 8 Number of injections from the fiber is less than previously obtained Possible Cause The fiber was not retracted into the protective needle after removal from sample vial or injection port S D The end of the needle is plugged with a piece of septum D Time and temperature variations during sampling 5 Not consistently positioning the fiber at the same depth during sampling 5 PH or salt conditions varying during sampling S oe is
7. e if you are experiencing problems selecting the appropriate fiber for your application Replace septum and tighten nut properly Replace vial septum and seal cap properly Move the depth i lever of the portable field sampler to the top mast locking slot so the end of the septum piercing needle is totally withdrawn into the sealing septum of the sampler If the fiber will be stored for more than one day we recommend that it be stored at subambient temperature This reduces the chance of breakdown and oss of sample that could occur at higher temperatures Prebake the vial septa for 2 hours at 68 C prior to use Use low bleed LB 2 septa to minimize injection port septum bleed Precondition fiber at the recommended conditioning temperature in the fiber instruction sheet Once fiber is precondi tioned only 1 2 minutes is required to clean the fiber prior to sampling Replace the inlet liner Use pre drilled septum or a septumless injector system e g Merlin Micraseal Complete GC analysis temperature program before injecting another SPME extract and keep column at 150 C when not in use Change GC column or temperature program rate Bake out fiber at the recommended conditions for several additional minutes Do not expose the fiber to the laboratory environment at any time during the sampling or injection steps Analyze control blanks using the same handling process as the sample to determ
8. ine if technique or laboratory cross contamination is present Move the depth si mar lever of the portable field sampler to the top mast locking slot so the end of the septum piercing needle is totally withdrawn into the sealing septum of the sampler If the fiber will be stored for more than one day we recommend that it be stored at subambient temperature This reduces the chance of sample cross contamination Armelle Vallat Problem Symptom 3 Fiber will not retract or sticks in holder needle 4 Needle bends during i injection into sample vial or GC injection port D Needle bends with automated injection systems 6 l 2 Possible Cause The end of the needle is plugged with a piece of septum D The fiber was exposed to solvents that caused swelling of coating 5 The top screw in the holder assembly is too tight P Improper manual sampling technique 5 Improper manual desorption injection technique D Vial or injection port septum is too tight Septa in sample vialinjection port is too thick or coated with thick Teflon coating SD GC inlet liner is too narrow or packed with adsorbent material D Needle is out of alignment with injection port or sample vial 5 D Mai 2007 Remedy 1 5 6 Injection port septum nut is overtightened Loasen the nut slightly to allow for improved injection Use pre drilled injection port septa or a septumless injector
9. ion P 8 There is a leaking injection port septum or connection DB 9 There is a leaking sample vial 5 10 Loss during transport fram the field 5 1 Septa used in sampling vial or injection port is outgassing organic contaminants 5 4 2 Fiber is not preconditioned prior to sampling F 3 Inlet liner is contaminated or contains septa particles D 4 GC column is collecting analytes on the front of the column because it is not heated high enough in sample analysis 4 5 Interfering peaks coelute with analytes of interest A 6 Carryover from previous analysis of the fiber P 7 Cross contamination from laboratory air 5 8 Cross contamination during transport from the field 5 Remedy l lad Peo Inject standard mixture to verify detector response see GC troubleshooting guide for help Run splitless injection for 2 min Start with known concentration 1ppm of analyte in de ionized water mixture Optimize extraction by adjusting extrac tion time temperature and chemical con dition of pH and salt Minimize solvents in the sample to lt 3 by dilution in water Reduce headspace to 50 or less agi tate sample vigorously or increase the sampling temperature Replace fiber Fibers are reusable and will last for 50 injections on average This is beyond the scope of this guide Please contact technical service 800 359 3041 814 359 3041 for assistanc
10. lain GC 85um StableFlex highly crosslinked light blue plain GC Carbowax Divinylbenzene CW DVB for polar analytes especially for alcohols low temperature limit 65um partially crosslinked orange plain GC 70um StableFlex highly crosslinked yellow green plain GC Carbowax Templated resin CW TPR developed for HPLC applications e g surfactants 50um partially crosslinked purple notched Divinylbenzene Carboxen PDMS DVB CAR PDMS ideal for broad range of analyte polarities good for C3 C20 range 50 30um StableFlex highly crosslinked gray plain GC 50 30um StableFlex highly crosslinked gray notched GC Armelle Vallat Mai 2007 In the previous table StableFlex StableFex Supelco fiber is more flexible than Original fibers It is designed to minimize fiber breakage ll Troubleshooting table See in the table A Analysis related D P Desorption related Product related S Sampling related Problem Symptom 1 No peaks seen in GC analysis Norrrial k Prablern 2 Extraneous peaks in analysis Normal Problem Possible Cause 1 Instrument problems A 2 The splitter vent was left open D 3 The analyte concentration is too low to be detected Si 4 Solvents present in sample competing with SPME extraction 5 5 Headspace volume too large to establish equilibrium with fiber 5 6 Coating on fiber deteriorated F 7 Incorrect SPME fiber used for extract
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