Optimizing the 6890 Series GC for High Performance MS Analysis ...

with the Automatic LiquidSampler (ALS) injection towerand only works with untapered,blunt tip syringe needles. TheMicroseal has been improvedover the past year. Older sealshave a maximum pressure ratingof 30 psi. The new seals are ratedto 100 psi. It is recommendedthat the new seal and nut be used.The gold nuts (stamped “303C”)are not compatible with the newseals. A gray nut, stamped “221B,”should be installed.Electronic pneumatic control(EPC) is an integral part of the6890 Series GC. The EPC versionof the 6890 is required whenusing an 5973 MSD. Themanual version of the 6890or any version of the 5890 willnot work with the 5973 MSD.Electronic control gives the bestrepeatability in retention time andarea counts. Using the electronicpulsed splitless mode allows forcomplete transfer of larger volumeinjections (up to 5 µL) onto thecolumn. Even larger volume injections(> 5 µL) may result in moreinlet maintenance, especially withdirty samples.The 6890 does have a new inletthat accommodates injections upto 250 µL. It is called the programmabletemperature vaporizer(PTV). It works with the ALSto deliver large volume injections(LVI). The inlet works by ventingthe solvent before analysis. Theanalyte is trapped and concentrated.It is then delivered to thecolumn as a single plug.The list of splitless inlet consumablesis• Molded Septa (11 mm, red,25/pk): P/N 5181-3383OR• High Pressure MerlinMicroseal starter kit:P/N 5182-3442• Merlin Microseal septum:P/N 5182-3444• Merlin Microseal septum nut:P/N 5182-3445• Liner, single taper, deactivated,no glass wool:P/N 5181-3316• Viton O-ring (12/pk):P/N 5180-4182• Gold plated seal:P/N 18740-20885• Washer (to go with seal):P/N 5061-5869• 10 µL Blunt needle syringe:P/N 9301-0713Column consumablesThe optimal choice of column isonce again dependent on the application.For trace-level, high-sensitivityapplications, a column witha thin film and low bleed is best.A 30 m, 0.25 mm ID, 0.25 µm film,5% phenyl–95% methyl siliconecolumn is a versatile column thatcan be used for many applications.Special low-bleed MS columnscost more but will give betterresults.The proper column nut and ferrulecombination are critical for a leaktightseal. Newer column nuts maynot be compatible with all ferrules.The proper ferrule will be dependenton column outer diameterand is specified below. The ferruleshould only be slightly larger thanthe column outer diameter. Theuse of 100% graphite ferrules is notrecommended as they are easilyover-tightened causing graphite toextrude into the injection port.This will be apparent when disassemblingthe injection port. Ifthere are pieces of graphite inthe bottom of the injection port,the ferrule(s) was (were) overtightened.The presence ofgraphite in a hot injection port cancause thermally labile compoundsto degrade. It can also affect thechromatography and cause tailing.Thus, 10% graphite, 90% Vespelferrules are highly recommended.Vespel ferrules will shrink asthey are heated. Conditioningthem for 4 hours in a 250°C ovenwill pre-shrink them before use.Alternatively, the column nuts(Figure 2, #16) can be retightenedafter the column oven cycles afew times.The column, column nut andferrules supplies are• 30 m column, 0.25 mm ID,0.25 µm, low bleed (HP-5MS):P/N 19091S-433• Column nuts(wrench-tighten only) 2/pk:P/N 5181-8830• Ferrules for 0.2 mm IDcolumns, 10/pk:P/N 5062-3516• Ferrules for 0.25 mm IDcolumns, 10/pk:P/N 5181-3323• Ferrules for 0.32 mm IDcolumns, 10/pk:P/N 5062-3514• Ceramic scoring wafer(column cutter), 4/pk:P/N 5181-8836A sharp column cutting tool isneeded for making clean cuts.The ceramic scoring wafers orsapphire square edge pens aredesirable. The diamond pointpens are harder to use. Ceramicscoring wafers are extremelysharp. They should be used withcare. An X-ACTO or Swiss Armyknife is not a column cutting tool.3

A 10x magnifier should be usedto assure that the cut is clean andno column shards are lodgedinside the column.Interfacing thecolumn to the MSThe column is connected to themass spectrometer through aninterface that is sealed with acolumn nut and ferrule. The specificferrule used depends on thecolumn diameter. A 100% graphiteferrule should never be used. 2 Theferrules required are 15% graphite,85% Vespel. The column nut listedis brass; stainless steel nuts shouldnever be substituted. Stainlessnuts may damage the threads onthe interface. Damaged threadscause air leaks and the entireinterface has to be replaced.The MS interface supplies are• Brass column nut:P/N 05988-20066• Ferrules for 0.2 and 0.25 mmID columns, 10/pk:P/N 5062-3508• Ferrules for 0.32 mmID columns, 10/pk:P/N 5062-3506Installation ofConsumablesThis section assumes that you aregoing to do a preventative maintenance(PM) on your 6890Series GC. If this is a newGC/MSD system, many of thesesteps will be completed by anCustomer Engineer duringinstallation. Before beginningthe preventative maintenance,please read this section carefully.Have on hand the 6890 SeriesGC site prep manual, the 6890Series GC operating manual, the6890 Series GC maintenanceand troubleshooting manual andthe MS hardware manual; they willbe referenced frequently.The manuals necessary are• 6890 Series GC site preparationand installation manual:P/N G1530-90300• 6890 Series GC operatingmanual: P/N G1530-90310• 6890 Series GC maintenanceand troubleshooting manual:P/N G1530-90320• MS hardware manual(HP 5973 MSD):P/N G1099-90001OR• MS hardware manual(HP 6890 Series MSD):P/N 05972-90026When all of the consumable supplies,previously mentioned, are athand, a proper preventative maintenancecan be completed. Tobegin a PM it is necessary for theGC zones to be cooled (oven, inlet,MS interface). The 6890 SeriesMSD has to be vented. Please referto the MS hardware manuals forventing instructions (p. 52 for the5973; pp. 58–59, for 6890Series MSD).Installation of gas suppliesFollowing the directions on pages14–20 in the GC site preparation/installation manual, install the gasline supplies. Care should be takenin making the Swagelok connections.The trap can be broken iftoo much stress is placed on theconnection during tightening.Leak check all connections with ahelium leak detector. (No Snoopplease!) Make sure that all thelines are purged with heliumbefore connecting them to the GC.Installation of split/splitlessinlet suppliesBefore handling any of theinjection port supplies, washhands and/or wear lint-free gloves.Oils on the hands will be transferredto these parts and becomebackground in the system, requiringextra bakeout time. Washingthe hands is especially importantafter eating. Following the instructionsin the GC operating manual(pp. 85–86), remove the septumnut, septum, and liner. Discardthe septum, liner and liner O-ring.Open the oven door, loosen the1/16-inch column nut and removethe column and nut. Remove theinsulation cup and any necessaryinsulation (Figure 2, #14) to provideaccess to the reducing nut(Figure 2, #12). If the lower insulationcup was not in place, find it,because this piece improves theinlet temperature profile.With a 1/2-inch wrench removethe reducing nut (Figure 2, #12).Due to heat cycling of the GC, thereducing nut will be very tight.Remove the seal and the washer(Figure 2, #10, #11) and discard.Place a new washer in the reducingnut and a new seal (flat sidewith groove up). Hand-tighten thereducing nut back into placewithin the retaining nut and thenwrench-tighten until very tight.Replace the insulation cup. Inserta new liner and O-ring. The singletaper liners are installed with thetaper down, toward the columnend of the inlet. Hand-tighten theinsert assembly (Figure 2, #3). Addthe Merlin Microseal or proper4

pre-conditioned septum and septumnut. The molded septum isinstalled with the hole up. Followthe directions supplied with theMerlin Microseal to insur properinstallation. If the green septumnut is used, wrench-tighten theweldment and septum nut withthe septum nut wrench until theC-ring lifts off the top of the greenseptum nut.Column Hanger PositionAt this point the inlet shouldbe leak checked. Follow thedirections in the GC maintenanceand troubleshooting manual(pp. 39–42).Marking the Column Position4Capillary ColumnSplit/Splitless Capillary InletColumn installationEach column ships with aquick reference guide (HP P/N5961-5652). Please read it beforeinstalling a new column. Workingwith fused silica columns maybe dangerous. Wear proper eyeprotection. Inspect the columnfor damage or breakage. Unweave0.5–1 coil of the column from itsbasket to make it easier to install.Push a septum onto the inletend of the column about 10 cm.Put the column nut and appropriateferrule on the column.Cut 5–10 cm off the inlet end ofthe column. Check the cut witha 10x magnifier, the cut shouldbe straight, not jagged, with nocolumn shards within the column.If the cut is jagged or shards areinside, try again. After a cleancut is obtained, mark the propercolumn position with the septum(Figure 3). The septum will holdthe column nut and ferrule inplace. Place the column on thecolumn hanger. Insert the columnnut into the inlet reducing nut andfinger-tighten. Wrench-tighten thecolumn nut. The column should be2cm4–6mmSeptumstationary in the ferrule. Carefullyslide the septum down away fromthe nut without disturbing the columnpositioning. The septum canbe left in place if desired.Using the GC keypad or the MSChemStation software, input theColumn Dimensions, set OutletPressure to Vacuum and ColumnInletReducingNutFerruleColumnNutSeptumCapillaryColumnFigure. 3 Proper installation of capillary columns in split/splitless inletFlow between 1 and 1.5 mL/minhelium (Table 1). The Split VentFlow should be approximately50 mL/min. These parameters areaccessed through the inlet andcolumn screens. Place the detectorend of the column into abeaker of water and check forbubbles to show helium flow.Heat the injection port. When the5

injection port reaches the setpointtemperature, retighten the columnnut in case it loosened. Checkonce again for column flow.Remove the end of the columnfrom the beaker and close theoven door. Condition thecolumn by slowly (5°C/min)ramping it to its maximumoperating temperature. Leaveit at that temperature for least2 hours; overnight is preferable.The maximum operatingtemperature for an HP-5 column is325°C. Cool the oven to ambientand insert the interface nut andferrule onto the column. Properlycut off 5–10 cm of the column.Properly place the column into theinterface by following the directionsin the MS hardware manual(pp. 26–29 for the 5973; pp.24–25 for the 6890 SeriesMSD). Hand-tighten the interfacenut and then wrench-tighten thenut. The nut should be tightenedonly until you hear two squeaks.This is a firm seal. Pump down thedetector as directed by the MSDmanual (pp. 36–37 for the 5973;pp. 36, 40–41 for the 6890Series MSD). Keep the oven atambient temperature until thesource is hot. Check the interfaceconnection after the interfaceis heated. The interface nut mayneed additional tightening.Tips for Better MethodPerformanceNumerous splitless parametersneed to be optimized for the bestsplitless injection. Table 2 (below)summarizes them.The proper inlet temperature isneeded to evaporate high boilingpoint compounds without thermallydegrading other compounds.Normally, the inlet temperature isTable 1. Head Pressures and Calculated Flowrates for a Splitless Inlet at anOven Temperature of 25 °C with the Outlet Pressure set to VacuumColumn Inner Length Head Pressure Linear Velocity Column FlowDiameter (mm) (meters) (psi) (cm/sec) (mL/min)0.20 12 6.0 57 1.00.20 25 15.0 39 1.00.20 50 28.0 28 1.00.25 30 6.2 36 1.00.32 30 3.4 50 2.00.32 50 5.5 34 1.5Table 2. Splitless ParametersInjection port temperatureLiner designSample volumeSplitless valve timeColumn flowSolventSample volatilityInjection speeda compromise between these twofactors. A good starting point is250°C.Liner design is one of the mostdifficult choices simply because ofthe variety of liners available. Thefeatures that are most important ina liner are the volume, whether itis deactivated or not, and whetheror not it contains deactivated glasswool. As a general choice for highsensitivity work, a 4 mm singletapered, deactivated liner with noglass wool is recommended. Forlarge volume injections (≥ 2 µL)and for the highest repeatability(especially with small volumeinjections of ≤ 0.5 µL 3 ), deactivatedglass wool is necessary.For dirty samples deactivatedglass wool helps to keep thenon-volatiles from getting to thecolumn, but too much deactivatedglass wool can greatly decreasesensitivity. Often, the most appropriateliner must be determinedthrough experimentation. Pleasenote: Removing and/or breakingdeactivated glass wool createsactive sites.Splitless valve timing is critical.The ON time (splitless mode)should to be long enough to assurethat all of the injected samplereaches the column.A textbook splitless injection hasthe liner volume swept at leasttwo times (during the “ON” time).A 4 mm liner has an approximatevolume of 1 mL. With a GC/MSflow rate of 1 mL/min, a twominute splitless injection wouldbe necessary.6

However, this long splitless timehas not been common. There aretwo reasons for this. (1) Conventional(manually controlled)split/splitless inlets were pressureregulated (constant pressure,regardless of oven temperature)and not flow regulated (changingpressure with oven temperature),so a higher-than-optimal flow wasset initially so that the flow did notgo to zero at high oven temperatures.Thus, a typical splitless or“OFF” time has been between0.5 to 1.5 minutes. (2) Linervolumes smaller than the textbookexamples have typically beenused. Since a 2 mm liner (250 µLvolume) was more commonlyemployed, the splitless time wasproportionally shorter.Finally, with the programmablecontrol afforded by EPC, flowscan be reliably pulsed during theinjection process. With pulsed splitlessinjections, flows during thesplitless time can be 2–6 mL/min,resulting in splitless times lessthan 2 minutes for a 4 mm ID liner.The pulsed splitless injection modeon the 6890 is recommendedfor GC/MS work. After the injectionpulse, the system returns to analyticalflow rates of 1–4 mL/min He.The highest flow allowable dependson the MSD. Refer to the appropriateMS hardware manual foryour detector’s limit.Unless all analytes have highboiling points, the initial oventemperature should be set to takeadvantage of the solvent effect. Thesolvent effect focuses the analyteson the head of the column. Theoven temperature should typicallybe set to ≥ 10°C below the boilingpoint of the solvent used (Table 3).On the other hand, the MS interfaceTable 3. Boiling and Initial Oven Temperatures for Common SolventsSolvent Boiling point (°C) Initial oven temperature (°C)Diethyl ether 36 10 to 25n-Pentane 36 10 to 25Methylene chloride 40 10 to 35Carbon disulfide 46 10 to 35Acetone 56 25 to 45Chloroform 61 25 to 50Methanol 65 35 to 55n-Hexane 69 40 to 60Ethyl acetate 77 45 to 65Acetonitrile 82 50 to 70n-Heptane 98 70 to 90Isooctane 99 70 to 90Toluene 111 80 to 1007

temperature should be hot enoughto avoid loss of analytes on coldspots. The interface should be setto the maximum oven temperaturefor the analysis or 10–15°C higherif the upper temperature limit forthe column is not exceeded. Thedefault method temperature is280°C; the interface temperatureshould be optimized as part ofmethod development.Finally, the rate of auto-injectionof a sample has been studied forsplitless injections. It has beenfound that fast injections, suchas with the ALS, tend togive the most repeatable andnon-discriminating results.Using PulsedSplitless InjectionsPulsed splitless injections are thebest way to do splitless injections.Electronic pneumatic control ofthe splitless inlet allows for highflow rates initially, followed bymore typical GC/MS flow rates. Apulsed splitless injection transfersmore of the sample onto the columnand allows for increasedinjection volumes up to 5 µL.When the injected volume is flashvaporized, the required expansionvolume for the solvent is greatlyincreased. (Solvent choice alsoeffects expansion volume.) Theuse of higher initial inlet pressuresreduces the volume (P 1 V 1 = P 2 V 2 )so the entire injected volume canmove to the column. The higherpressure also decreases the likelihoodthat highly volatile compoundswill escape out the top ofthe injection port through the septumpurge vent (Figures 4 and 5).In the case of thermally labilecompounds, the faster they leavethe hot injection port the lessSeptumSeptum Purge VentFlow Carrier Gas InInlet Purge (Off)Low Inlet Pressure/Low Column Flow= more volatile compound= less volatile compoundLinerColumnFigure 4. A low initial inlet pressure causes loss of volatile compounds.SeptumSeptum Purge VentFlow Carrier Gas InInlet Purge (Off)High Inlet Pressure/High Column Flow= more volatile compound= less volatile compoundLinerColumnFigure 5. With the correct inlet pressure there is no loss of volatile compounds.8

likely they are to degrade. 4 Theflow rate is then reduced to thevalue desired for the chromatographicseparation. This flow isheld constant by increasing thepressure as the oven temperatureincreases. Figure 6 is a graphicalrepresentation of the pulsed splitlesstechnique with constant flow.Pulsed splitless injections shouldalways be used when sensitivityand/or repeatability are critical.Refer to pages 99–100 in the GCoperating manual for how to setup a pulsed splitless injection.Electronic pressure and flowcontrol of carrier gases not onlyhelp with larger volumes, they alsohelp to decrease run times andmaintain stable MS sensitivityby keeping the carrier gas flowconstant. These lead to a shorteranalyses, higher sensitivity andhigher reproducibility. The benefitsfor the analyst are more chromatographicanalyses per shift,better data and higher revenuesper instrument.SummaryFollowing the instructions in thisguide will improve analyticalresults with your GC/MSD system.Contamination interferring withthe determination of your analyteswill be minimized and sampletransfer optimized, both improvingsensitivity.A final note: the choice of vialsand septa will affect your results.Screw cap vials are not recommendedfor GC/MS analyses.Application note 228-244, “Effectsof Vial Septa Used in GC/ECDAnalysis of Trace Organics,”P/N 5091-8980, will help youmake the right choice.Inlet Pressure ( )30 psi16 psi5.4 psiInjection90°C98 psi/min1.5 minutes130°C180°C2.0 minutes320°C30 m × 0.25 mm ID column;vacuum compensation on;constant flow rate, 0.8 mL/min0 5 10 15 20 25 30Run Time400°C300°C200°C100°CFigure 6. The pulsed splitless injection technique employing constant flowwith electronic pneumatic control (EPC). This technique allows larger injectionvolumes and inhibits the loss of volatile compounds out of the septum purge vent.References1. Another commonly usedcleaning technique is to heatthe copper tubing with aBunsen burner, propane torchor heat gun while helium isflowing through the tubing.This is done after connectingthe tubing to the helium supplybut before connecting it to theGC. This process bakes off allthe volatile contaminants.Safety precautions should betaken if this procedure is done.2. Similar to the injection port,pieces of graphite may extrudeinto the interface and contaminatethe MS.Oven Temperature ( )3. Reviewed in an MS ApplicationsBrief MS 95-1: Analyzingaromatics in reformulatedgasoline by GC/MS, P/N (23)5964-0116E.4. A excellent example of thiscan be found in the 1995Pittsburgh Conference paper#347: Improving the Analysisof Pesticides by OptimizingSplitless Injections, Philip L.Wylie et al., Hewlett-Packard Co.The complete article can befound in the Journal of OfficialAnalytical Chemistry International(JAOAC Int.) as ImprovedGas Chromatographic Analysisof OrganophosphorousPesticides with PulsedSplitless Injection, Philip L.Wylie and Katsura Uchiyama,Hewlett-Packard Co., Volume 79,Issue 2, pp. 571–577, 1996.9

Appendix ACapillary Inlet System LinersAPPLICATIONSLINER SEALSCONFIGURATIONFASTINJECTION(7673 ALS)SLOW &MANUALINJECTIONFLUORO-CARBONGRAPHITELINERPART NO.PRICEIDVOLUMEGLASS TYPEDEACTIVATEDGLASS**WOOL**PACKING**SPLITSPLIT-LESSSPLITSPLIT-LESS(MAX350°C)(350°CAND ABOVE)Single-Taper Liner5062-3587344 mm(0.8-mm end)900 µLBorosilicateYESYES**CC5180-4182(12/pk)125180-4173(12/pk)48Single-Taper Liner5181-3316314 mm(0.8-mm end)900 µLBorosilicateYESNO—A—5180-4182(12/pk)125180-4173(12/pk)48Double-Taper Liner55181-3315344 mm(0.8-mm end)800 µLBorosilicateYESNO—A—5180-4182(12/pk)125180-4173(12/pk)48Split/Splitless Liner19251-60540264 mm990 µLBorosilicateNOYES**DD5180-4182(12/pk)125180-4168(12/pk)48Split Liner18740-60840464 mmwith cupBorosilicateNOYES+ columnpacking——E—5180-4182(12/pk)125180-4168(12/pk)48Split Liner18740-80190414 mmwith cupBorosilicateNONO———5180-4182(12/pk)125180-4168(12/pk)48Splitless Liner18740-80220272 mm250 µLQuartz(Purity 8)NONO—A,B—B5180-4182(12/pk)125180-4173(12/pk)48Splitless Liner5181-8818302 mm250 µLQuartz(Purity 8)YESNO—A,B—B5180-4182(12/pk)125180-4173(12/pk)48Direct Liner18740-80200171.5 mm140 µLBorosilicateNONO—A,B—B5180-4182(12/pk)125180-4173(12/pk)48A. Can be used without the glasswool in some applications, butliners with glass wool are generallyrecommended for bestreproducibility in fast injections.B. Recommended only for small(< 0.5 µL) volumes, dependingon solvent and conditions.C. The glass wool packing as suppliedmay not provide adequatemixing for good precision in splitinjections. Liners can be packedwith silanized glass wool positionedas in the straight 4 mmsplit/splitless liner, part no.19251-60540.D. Taper liners are recommendedfor best performance in thisapplication, particularly withlabile samples and wide-boilingrangemixtures.E. Not recommended for use withelectronic pressure control.GeneralrecommendationSee notes at leftregarding use* Quality discountsavailable; please inquire.** Silanized glass wool,10 gm, (pesticide grade)(HP part no. 5181-3317).

Agilent Technologies shall not be liablefor errors contained herein or forincidental or consequential damagesin connection with the furnishing,performance or use of this material.Information, descriptions and specificationsin this publication are subjectto change without notice.Copyright © 1999Agilent Technologies CompanyAll rights reserved. Reproduction andadaptation is prohibited.Printed in the U.S.A. December 1999(23) 5965-6385E