What is Septum Bleed? - Superchrom

1 CLeptum bleed can be the source of problems when analyzing samples by capillary gas chromatog-raphy. It occurs when volatile compounds, such as monomers or additives, are emitted from theu Septum . Septum bleed is amplified with capillary gas chromatography because capillary col-umns have higher efficiency and operate at much lower flow rates than packed columns. There aremany variables that affect the amount of Septum bleed during sample analysis (such as inlet tempera-ture, initial hold time, compression, etc.).Most of these variables can be controlled by the analyst. Thesingle most important variable in minimizing Septum bleed is the quality of the septa you are using. Ahigh quality, low- bleed Septum greatly reduces the need to adjust these GC is Septum Bleed? Septum bleed occurs when volatile compounds are emittedfrom the Septum . It is exhibited during a temperatureprogrammed run by either a baseline rise and/or extraneouspeaks not associated with the sample or the bleed is most noticeable during a temperatureprogrammed run because the volatiles emitted from theseptum collect on the head of the column during the cooldown period and the initial hold time.

2 These volatiles thenelute during subsequent runs. However, under isothermalconditions, Septum bleed is a continuous, steady state thatappears as part of the normal 1 shows Septum bleed during a temperature pro-grammed run at high sensitivity and injection port tempera-ture. Typically, Septum bleed occurs at column tempera-tures between 150 C and 300 Septum emits volatile compounds that come frommonomers used during manufacturing or additives used tocontrol characteristics such as thermal stability,puncturability, or resilience. Each brand of septa off-gasesdifferent types of voIatile compounds and yields different: ;:: ::,: ::: ..:I.::..IIndexWhat is Septum Bleed? inside coverBleed Comparisonsof Six Commercially Available Septa:FID2 ECD3 MSD4 Why is Septum bleed Such aProblem with Capillary Columns?5 Septum Troubleshooting:9 Problems10 Leaks10 Maintenance11 Capillary Chromatography Accessories12bleed profiles.

3 Mass spectral evaluation of Septum bleedindicates the typical off-gassing compounds. Septum bleedcan originate from phthalate esters (used to soften theseptum or from plastic packaging), low molecular weightsiloxane monomers and solvents (used to make sibconerubber), hydrocarbons (used on tools that die-cut the septa),or carboxylic acids (from finger oils or perfumes whenhandling septa). Figure 2 shows mass spectral data fromthree different septa 1 - Typical Septum bleed observed in a temperatureprogrammed run with a very hot injector at high I I4812 16 20minutes30m, ID, Rtx"-1 (cat.# 10125)Oven temp.:40 C to 300 C @ 15 & det. temp.:330 CInjection mode:DirectLinear velocity:80 gas:HydrogenAttn.:1 x 10-11 AFSF igure 2 - MSD data reveals the presence of phthalates, siloxanes, andhydrocarbons off-gassing from several Septum >60 80100120 1401601802002202402602809000800070000060 00500040001000200010000~731172ibl15m.

4 ID, Rtx-1 (cat.# 10152)Oven temp.:40 C (hold 15 min.) to 280C @ 15C/min.(hold 30 min.)Detector:HP 5971A MSDC arrier gas:HeliumLinear velocity:20 Scan range: 45-300 AMUI onization:EI2072652?9 II,,,,.i,,,~,~,l.,,,.,,.,,,, 191/z->101001150 200 250 300 350 400portwasheatedto250 Cfor15min., Procedure:A uniform piece was cut from the center of eachseptum type and installed into a clean splitless sleeve. The injection167 ISiloxanes99140166~.,.,,!,,,,,,,~,,,,,,. ,,,,,,,;,.,,;, 252 28260100120140 160 180 200 220 240 260 280; ..,,,: :..:..BleedComparisons of Six Commercially AvailableSeptaby Capillary GC FID, ECD, and MSDMany of the variables that contribute to Septum bleed (inlettemperature, initial hold time, and compression) can becontrolled by the analyst. Optimizing these variablessignificantly reduces the amount of bleed seen duringsample analysis.

5 If a low quality, high bleed Septum isused, no matter how these variables are optimized, signifi-cant Septum bIeed is apparent. Use a high quality, low- bleed Septum and reduce the need to adjust these bleed characteristics of six commercially availablelow- bleed septa were monitored. All septa were evaluatedby FID, ECD, and Comparison of Six Low- bleed SeptaFlame Ionization Detection (FID) was first used to examinemolecuIar weight siloxanes, solvents, and phthalate difference in Septum bleed between six commerciallyFigure 3 shows the FID bIeed testing resultson the follow-available low- bleed septa. The FID responds to organicing septa: Restek Thermolite , Supelco Thermogreencompounds that ionize in a hydrogen/air flame. Off-gassingLB-Z: CRS Septa 77QD, Chrompack Chromsep Red", Alltechvolatiles that respond on an FID include hydrocarbons, lowHi-Temp Blue , and HP Low- bleed Gray.

6 Figure 3 - FID comparison of six low- bleed septa shows that Thermolite septaexhibit the least amount of off-gassing materialRestek Thermolite Supelco Thermogreen LB-2"(Lot# 008)(Lot# 780-03C)CRS Septa 77"(Lot# 0021448)lb2b& Chromsep Red"Alltech Hi-Temp Blue (Lot# 220389)(Lot# H43)7010203040mhles506070HP Low- bleed Gray (Lot# R59 B7)50 60 70 80 20 30 40 50 60 70 20 30 40minutesminutes):I50 60 70l5m, lD, Rtx"-1 (cat.# 10152)Oven temp.:40 C (hold 15 min.) to 280 C@Linear velocity:40cm/sec. (flow rate: 5cc/min.)15C/min. (hold 30 min.)FID sensitivity:256 x 10-11 AFSInj. & det. temp.:300 CSplit vent:I00 gas:HydrogenSplitless hold procedure: A uniform piece was cut From the center face of each Septum type and installed into a clean splitless injection port was heatedto 250 C for 15 min., then turned parameters for comparison studies:A splitless sleeve was placed into the GC inlet and a blank runwas made to confirm system cleanliness.

7 After verifying systemcleanliness, a sample of unconditioned septa was cored from thecenter face of each Septum and cut in forceps, anequal weight of each Septum was placed into the clean, condi-tioned splitless sleeve. The sleeve was placed into a cooled inlet(40/60 C). The system was thoroughly checked for leaks witha Gow-Mac leak injection port was then heated to 250 C, while the GC ovenwas held at 40 15 minutes at 40 C, the oven wasprogrammed to 280 C @I 15 C/min. to elute the bleed volatilesthat had accumulated on the head of the column. After the 15minute initial hoId, the inlet system was cooled to preventadditional accumulation of Septum bleed in the inlet sleeve, Atthe end of each run, the Septum was removed from the sleeve anda blank run was performed to verify system cleanliness andprevent cross-contamination.

8 Two different lots of each septawere tested in triplicate to confirm Comparison of Six Low- bleed Septaoff-gassing from the Septum . Figure 5 shows total ionUsing low- bleed septa with an MSD is also very of Septum bleed from the same six septaThe MSD is a universal detector that responds to virtuallyused in the previous studies. The total ion abundance hasany organic species that can be chromatographed. It canbeen normalized so that all bleed levels for each Septum arealso be used to yield specific information on the compoundson the same 5 - Thermolite septa exhibit the lowest bleed by MSD comparedto six commercially available low- bleed Thermolite(Lot# 010)Chrompack Chromsep Red(Lot# 040788)Supelco Thermogreen LB-2(Lot# 780-03C)Alltech Hi-Temp Blue(Lot# 243)CRS Septa 77(Lot# 0021-4413)HP Low- bleed Gray(Lot# R59 B8)15m, ID, m Rtx"-1 (cat.)

9 # 10152)Oven temp.:Detector:Carrier gas:40 C (hold 15 min.) to 280 C (hold 30 min.)HP 5971A MSDH eliumLinear velocity:20cm/secScan rate:1 range:45-300 AMUI onization:ElTest procedure:A uniform piece was cut from the center face of each Septum type and installed into a clean splitless sleeve. The injection port was heatedto 250 C for 15 min., then turned is Septum bleed Such aProblem with Capillary Columns?Chromatographers have long realized that Septum bleed cancreate many problems during sample analysis. In anattempt to minimize Septum bleed problems, capillaryinjectors have been designed with purge systems to reducethe amount of off-gassing volatiles that can collect at thehead of the column. However, Septum particles can fallinside the inlet sleeve and create bleed problems that cannotbe controlled with a Septum purge system. Injection mode,flow rate, and column efficiency are the three primaryreasons that capillary columns tend to amplify Injection ModeIn the split or splitless injection modes, most of the off-gassing volatiles are swept away through the split or purgevent, minimizing bleed problems.

10 However, many analystsuse the direct injection mode, particularly with ID capillary columns. The direct injection modetends to amplify the bleed problem since all of the off-gassing volatiles from the Septum are trapped on the head ofthe column. Figure 6 shows a comparison of Septum bleedin the direct and split injection modes. Septum bleed isalmost non-existent in the split mode, but is significant inthe direct injection Capillary Column Flow RateColumn flow rate plays a major role in Septum bleedproblems with capillary columns. Capillary columnsoperate at much lower flow rates (less than 5cc/min.) thanpacked columns (20 to 40cc/min.), making Septum bleedmuch more pronounced. The higher flow rates used withpacked columns dilute the amount of Septum breed seenduring a Capillary Column EfficiencyCapillary columns also have higher theoretical plates andefficiency than packed columns.