Conversion of Agilent EI GC/MSD Systems From Helium To Hydrogen Carrier Gas
Embed Size (px)
Transcript of Conversion of Agilent EI GC/MSD Systems From Helium To Hydrogen Carrier Gas
Conversion of Agilent EI GC/MSD Systems from Helium to Hydrogen Carrier Gas
Conversion of Agilent EI GC/MSD Systems From Helium To Hydrogen Carrier GasBruce D. Quimby, Ph.D.GPD Solutions Group and Harry F. Prest, Ph.D.GC/MS Research and Development
October 9, 2012
1Question: Have You Ever Tried Converting Your GC/MS From Helium To Hydrogen Carrier Gas?Answer 1: No. Never thought of trying it. Too busy.
Answer 2: We did that several years ago. It took some effort, but it has been working fine.
Answer 3: We tried it once. The results were horrible and confusing! We had a very high background, high noise, and very bad peak shapes. After 4 days, we went back to helium. October 9, 2012C&EN Webinar 2Introduction: Converting from He to H2 Carrier GasMany GC/MS users are considering changing from helium to hydrogen carrier gas due to price/availability problems with helium. Read Chemical and Engineering News - July 16, 2012 (Page 32-34)
This talk describes the steps recommended for converting EI GC/MS methods.
It is important to recognize the differences with using hydrogen carrier. Time should be allotted for adapting the method, optimization, and resolving potential problems. Areas that will need attention include:choice of supply of H2remove/bypass carrier gas filter (may be re-installed later if needed)GC/MSD hardware changeschoosing new chromatographic conditionspotential reduction in signal-to-noise ratio (2-5x)changes in spectra and abundance ratios for some compoundsactivity and reactivity with some analytes
October 9, 2012C&EN Webinar 3Introduction: Converting from He to H2 Carrier GasMethods that will generally require less optimization include analytes that are:durable compoundsat higher concentrationsanalyzed with split injectionsderivatizedMethods that will generally require more optimization include analytes that are:fragile compounds at trace concentrationsAllow time for necessary updates to SOPs and validation
October 9, 2012C&EN Webinar 45H2 Safety October 9, 2012C&EN Webinar
Letter from Agilent Safety Engineer: Describes H2 Safety Features of Agilent GCsOctober 9, 2012C&EN Webinar 6Designed for Reliability H2 SafetySafety Shutdown When gas pressure set points are not met, the valve and heater are shut off to prevent explosion Flow Limiting FritIf valve fails in open position, inlet frit limits the flowOven ON/OFF SequenceFan purges the oven before turning on heater to remove any collected H2Explosion TestGC and MS designed to contain parts in case of explosion October 9, 2012C&EN Webinar 7Safety First: Read This Before You StartG3170-90010
October 9, 2012C&EN Webinar 89Source of H2 Carrierand PlumbingOctober 9, 2012C&EN Webinar 9Source of Hydrogen: Use a Hydrogen GeneratorHigher initial expense than cylinders, much lower cost over timeVery clean H2, >99.9999% availableMore consistent puritySafety considerationsH2 is only generated at needed pressure (like 40 psig)Flow is limited (like 250 mL/min)Auto-shutdown if set point pressure cannot be maintainedMinimal stored gas (like 50 mL at 40 psig) of H2 at any one timeMake sure to buy a good one with a low spec for water and oxygen
October 9, 2012C&EN Webinar 10
This is an example of the type of generator to use for H2 carrier gas.
Look for generators with a >99.9999% specification and low individual specs on water and oxygen. October 9, 2012C&EN Webinar Hydrogen Generation11Plumbing the InstrumentChromatographic quality stainless steel tubing is often recommended for H2 plumbing and is probably the best choice if available. Users may have to follow local codes or internal company guidelines.We have also used new 1/8th copper that has been cleaned for GC use. Dirty tubing will cause huge contamination problems, as H2 appears to carry dirt out of metal more than He does.Dont use really old copper tubing, as it becomes brittle and can break.Note that MSD leak checks will not always find big outgoing leaks. Leak check when complete with electronic leak detector. When plumbing a H2 generator, start out with no traps. Only add traps if needed. Make sure the water and oxygen levels are low enough.
October 9, 2012C&EN Webinar 12Split Vent and Septum Purge Vent Should be Connected to Exhaust
October 9, 2012C&EN Webinar 13MS Components Required for Conversion:Magnet and Draw Out LensOctober 9, 2012C&EN Webinar 14Check the Magnet in the 5975
If the magnet in the 5975 does NOT have a serial number along the left edge (as viewed through the source window), it is suitable for use with Helium, but not Hydrogen. If not, please contact your Agilent service engineer to change it to a Helium and Hydrogen compatible magnet before converting the system to H2 carrier. Note: All 5973 magnets are compatible with both He and H2October 9, 2012C&EN Webinar 15Replace the Standard 3 mm Draw Out Lens With the Optional Hydrogen Draw Out Lens
G2589-20045Hydrogen Draw Out Plate, InertStandard 3 mmDraw Out Plate, InertOctober 9, 2012C&EN Webinar 16Choosing a Column and Method ConditionsOctober 9, 2012C&EN Webinar 17MSD Pumping Capacity for H2 is Less than for HeThis Limits Column Choice These are approximate values for the 5975. Maximum flow of H2 to maintain reasonable source pressure:Performance turbo: 2 mL/minStandard turbo: 1 mL/minDiffusion pump: 0.75 mL/minPressure pulsing: turbo < 3 mL/min, diffusion < 2.5 mL/minIt is very helpful to have an ion gauge on the MS to monitor the vacuum vs. column flow. Try to avoid flows that produce pressures higher than 5 x 10-5 torr. You can get useful data above this pressure, but performance may start to degrade October 9, 2012C&EN Webinar 18Guidelines for Choosing Column Dimensions and Flows for Method Converted from He to H2Determine max flow of H2 into MS that will give source pressure of 5 x 10-5 torr or less source pressure. This is your max column flow. Choose column dimensions at initial oven temp of method to give:a flow < max column flow for vacuum pumpa flow > min column flow for efficiencyan inlet pressure of at least 5 psigKeeping a temperature ramp of the same number of C/void time will give similar elution order. Use the Agilent method translator for this.
These are only approximate guidelines. Sometimes you may have to deviate from them.
October 9, 2012C&EN Webinar 19Van Deemter Curves
If the flow of He or H2 is too low, you loose efficiency MUCH FASTER than if it is too high. This is why operating at or above minimum linear velocity is important. Use 35 cm/sec as minimum for H2October 9, 2012C&EN Webinar 20Column ChoiceWhen in doubt (or a hurry) use:Use 20m x 180 um column and set constant flow at 0.3-0.5 mL/min. Try to get a linear velocity of at least 35 cm/secTry to use the same phase and phase ratio to get similar elution order.Smaller bore columns have lower capacity. You may have overloading on high level calibration standards, or samplesYou may need to use pulsed injection to load sample into small bore columns when using a low flow rate.The flow range for your H2 setup is limited on the low side by the flow to get 35 cm/sec and on the high side by the vacuum pump capacity
October 9, 2012C&EN Webinar 21Using the Agilent Flow Calculator: Set Linear Velocity to 35 for H2 Carrier
Inlet pressure is too lowSet inlet pressure to 5 psigIf Inlet Pressure Too Low, Raise FlowOctober 9, 2012C&EN Webinar 22Using the Agilent Method Translator: 30m x 0.25 mm id x 0.25 um Checkout Column with Perf Turbo
Meets flow requirements for pump and column efficiency with 2x speed gain October 9, 2012C&EN Webinar 23Using the Agilent Method Translator: With Perf Turbo and Std TurboFor 20m x 0.18 mm id x 0.18 um Column:Meets flow requirements for standard turbo pump. Flow here is chosen to give a 2.5 x speed gain.
October 9, 2012C&EN Webinar 24Initial Startup with HydrogenOctober 9, 2012C&EN Webinar 25Initial Problems with Switching GC/MS Methods to from He to H2 Carrier Gas High background that looks like hydrocarbons Reduced signal to noise (worse MDL) Significant tailing for many compounds October 9, 2012C&EN Webinar 26Switch to H2 1st Problem: High Background
You will see this throughout work with H2. It will get much smaller with time and use. It used to takes days or weeks for background to fall to acceptable levels. Agilent developed a new conditioning protocol to clean-up the background much faster.(see later slide)October 9, 2012C&EN Webinar 27GC/MS Toxicology Analyzer Checkout Sample246810121416181Amphetamine2Phentermine3Methamphetamine4Nicotine5Methylenedioxyamphetamine(MDA)6Methylenedioxymethamphetamine(MDMA)7Methylenedioxyethylamphetamine8Meperidine9Phencyclidine10Methadone11Cocaine12SKF-525a (RTL Compound)13Oxazepam14Tetrahydrocannabinol15Codeine18Lorazepam16Diazepam17Hydrocodone19Oxycodone20Temazepam22Diacetylmorphine23Nitrazepam24Clonazepam25Alprazolam26Verapamil27Strychnine28Trazodone21Flunitrazepam123456789101112141517181921131620222324252627285 ng/uL each compoundOctober 9, 2012C&EN Webinar 28Switch to H2 2nd Problem Peak Tailing2.003.004.005.006.007.008.009.0010.0011.0012.0013.000200000400000600000800000100000012000001400000160000018000002000000Time-->AbundanceHydrogen4.006.008.0010.0012.0014.0016.0018.00020000040000060000080000010000001200000140000016000001800000200000022000002400000260000028000003000000Time-->AbundanceHeliumImmediately after conversion to H2, peak shapes on TIC are poor and tailing badly.20m x 0.18mm id x 0.18 um DB-5MSUIOctober 9, 2012C&EN Webinar 29Switch to H2 3rd Problem: Spectrum Changes over Peak Profile7.207.407.607.808.008.208.408.608.809.0040608010012014016018020022024026028030032034002000400060008000100001200014000