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Conversion of Agilent EI GC/MSD Systems From Helium To Hydrogen Carrier Gas Bruce D. Quimby, Ph.D. GPD Solutions Group and Harry F. Prest, Ph.D. GC/MS.

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Presentation on theme: "Conversion of Agilent EI GC/MSD Systems From Helium To Hydrogen Carrier Gas Bruce D. Quimby, Ph.D. GPD Solutions Group and Harry F. Prest, Ph.D. GC/MS."— Presentation transcript:

1 Conversion of Agilent EI GC/MSD Systems From Helium To Hydrogen Carrier Gas Bruce D. Quimby, Ph.D. GPD Solutions Group and Harry F. Prest, Ph.D. GC/MS Research and Development October 9, 2012 C&EN Webinar

2 Question: 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, 2012 C&EN Webinar 2

3 Introduction: Converting from He to H 2 Carrier Gas Many 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 H 2 –remove/bypass carrier gas filter (may be re-installed later if needed) –GC/MSD hardware changes –choosing new chromatographic conditions –potential reduction in signal-to-noise ratio (2-5x) –changes in spectra and abundance ratios for some compounds –activity and reactivity with some analytes October 9, 2012 C&EN Webinar 3

4 Introduction: Converting from He to H 2 Carrier Gas Methods that will generally require less optimization include analytes that are: –“durable” compounds –at higher concentrations –analyzed with split injections –derivatized Methods that will generally require more optimization include analytes that are: –“fragile” compounds –at trace concentrations Allow time for necessary updates to SOPs and validation October 9, 2012 C&EN Webinar 4

5 5 H 2 Safety October 9, 2012 C&EN Webinar

6 Letter from Agilent Safety Engineer: Describes H 2 Safety Features of Agilent GCs October 9, 2012 C&EN Webinar 6

7 Designed for Reliability – H 2 Safety Safety Shutdown When gas pressure set points are not met, the valve and heater are shut off to prevent explosion Flow Limiting Frit If valve fails in open position, inlet frit limits the flow Oven ON/OFF Sequence Fan purges the oven before turning on heater to remove any collected H 2 Explosion Test GC and MS designed to contain parts in case of explosion October 9, 2012 C&EN Webinar 7

8 Safety First: Read This Before You Start G October 9, 2012 C&EN Webinar 8

9 9 Source of H 2 Carrier and Plumbing October 9, 2012 C&EN Webinar 9

10 Source of Hydrogen: Use a Hydrogen Generator Higher initial expense than cylinders, much lower cost over time Very clean H 2, > % available More consistent purity Safety considerations –H 2 is only generated at needed pressure (like 40 psig) –Flow is limited (like 250 mL/min) –Auto-shutdown if set point pressure cannot be maintained –Minimal stored gas (like 50 mL at 40 psig) of H 2 at any one time Make sure to buy a good one with a low spec for water and oxygen October 9, 2012 C&EN Webinar 10

11 This is an example of the type of generator to use for H 2 carrier gas. Look for generators with a > % specification and low individual specs on water and oxygen. October 9, 2012 C&EN Webinar Hydrogen Generation 11

12 Plumbing the Instrument Chromatographic quality stainless steel tubing is often recommended for H 2 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 1/8 th copper that has been cleaned for GC use. Dirty tubing will cause huge contamination problems, as H 2 appears to carry dirt out of metal more than He does. Don’t 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 H 2 generator, start out with no traps. Only add traps if needed. Make sure the water and oxygen levels are low enough. October 9, 2012 C&EN Webinar 12

13 Split Vent and Septum Purge Vent Should be Connected to Exhaust October 9, 2012 C&EN Webinar 13

14 MS Components Required for Conversion: Magnet and Draw Out Lens October 9, 2012 C&EN Webinar 14

15 Check 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 H 2 carrier. Note: All 5973 magnets are compatible with both He and H2 October 9, 2012 C&EN Webinar 15

16 Replace the Standard 3 mm Draw Out Lens With the Optional Hydrogen Draw Out Lens G Hydrogen Draw Out Plate, Inert Standard 3 mm Draw Out Plate, Inert October 9, 2012 C&EN Webinar 16

17 Choosing a Column and Method Conditions October 9, 2012 C&EN Webinar 17

18 MSD Pumping Capacity for H 2 is Less than for He This Limits Column Choice These are approximate values for the Maximum flow of H 2 to maintain reasonable source pressure: –Performance turbo: 2 mL/min –Standard turbo: 1 mL/min –Diffusion pump: 0.75 mL/min –Pressure pulsing: turbo < 3 mL/min, diffusion < 2.5 mL/min It 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 torr. You can get useful data above this pressure, but performance may start to degrade October 9, 2012 C&EN Webinar 18

19 Guidelines for Choosing Column Dimensions and Flows for Method Converted from He to H 2 Determine max flow of H 2 into MS that will give source pressure of 5 x 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 pump −a flow > min column flow for efficiency −an inlet pressure of at least 5 psig Keeping 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, 2012 C&EN Webinar 19

20 Van Deemter Curves If the flow of He or H 2 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 H 2 October 9, 2012 C&EN Webinar 20

21 Column Choice When in doubt (or a hurry) use: −Use 20m x 180 um column and set constant flow at mL/min. −Try to get a linear velocity of at least 35 cm/sec Try 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 samples You may need to use pulsed injection to load sample into small bore columns when using a low flow rate. The flow range for your H 2 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, 2012 C&EN Webinar 21

22 Using the Agilent Flow Calculator: Set Linear Velocity to 35 for H 2 Carrier Inlet pressure is too lowSet inlet pressure to 5 psig If Inlet Pressure Too Low, Raise Flow October 9, 2012 C&EN Webinar 22

23 Using 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, 2012 C&EN Webinar 23

24 Using the Agilent Method Translator: With Perf Turbo and Std Turbo For 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, 2012 C&EN Webinar 24

25 Initial Startup with Hydrogen October 9, 2012 C&EN Webinar 25

26 Initial Problems with Switching GC/MS Methods to from He to H 2 Carrier Gas High background that looks like hydrocarbons  Reduced signal to noise (worse MDL)  Significant tailing for many compounds  October 9, 2012 C&EN Webinar 26

27 Switch to H 2 1st Problem: High Background You will see this throughout work with H 2. 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, 2012 C&EN Webinar 27

28 GC/MS Toxicology Analyzer Checkout Sample Amphetamine 2Phentermine 3Methamphetamine 4Nicotine 5Methylenedioxyamphetamine(MDA) 6Methylenedioxymethamphetamine(MDMA) 7Methylenedioxyethylamphetamine 8Meperidine 9Phencyclidine 10Methadone 11Cocaine 12SKF-525a (RTL Compound) 13Oxazepam 14 Tetrahydrocannabinol 15 Codeine 18 Lorazepam 16Diazepam 17Hydrocodone 19Oxycodone 20Temazepam 22Diacetylmorphine 23Nitrazepam 24Clonazepam 25Alprazolam 26Verapamil 27Strychnine 28Trazodone 21Flunitrazepam ng/uL each compound October 9, 2012 C&EN Webinar 28

29 Switch to H 2 2 nd Problem – Peak Tailing Hydrogen Time--> Abundance Helium Immediately after conversion to H 2, peak shapes on TIC are poor and tailing badly. 20m x 0.18mm id x 0.18 um DB-5MSUI October 9, 2012 C&EN Webinar 29

30 Switch to H 2 3 rd Problem: Spectrum Changes over Peak Profile Tail Spectrum Peak Spectrum Cocaine Not Cocaine There is More Happening Here than Simple Peak Tailing October 9, 2012 C&EN Webinar 30

31 Main Ions of Cocaine Do Not Tail. Tail Made Up of Other Ions Tail is not cocaine ions Cocaine Tail is different than peak. May be formed from catalytically shredded main component. This problem is reduced with time October 9, 2012 C&EN Webinar 31

32 H 2 Conversion Considerations for Success October 9, 2012 C&EN Webinar 32

33 Agilent’s Recipe for H 2 Success: Minimizing the Time for Chromatography and Background to Stabilize 1.Have a good source of clean hydrogen like a > % purity hydrogen generator. 2.Keep H 2 flow limited to value suitable for your pumping system 3.Use optional Hydrogen draw out lens 4.After setup, purging and pump down: –Set the source to max temp for your source (check to see what yours is) –Reduce the EMV to 800V –Leave the FILAMENT ON overnight. This cleans up background rapidly. 5.Peak shape will be much better and background will be much lower in the morning. 6.Lower the source temp to method value, retune, and run some samples 7.It is a good idea to have an extra set of filaments on hand in case one burns out. This hasn’t been a problem, but a good idea. October 9, 2012 C&EN Webinar 33

34 Agilent’s Recipe for H 2 : Success Peak Shape Much Better Background is Lower Better Signal-to-Noise October 9, 2012 C&EN Webinar 34

35 Agilent Toxicology Analyzer Features: Configured, tuned and tested for the application Retention time locked (RTL) with DRS database Constant flow to MS Backflush to reduce cycle time and remove matrix artifact Challenge: Convert from He to H 2 carrier without altering performance criteria October 9, 2012 C&EN Webinar 35

36 He Constant Flow Toxicology Analyzer 7890A GC Liquid Injector Column AUX EPC 15 m X 0.25 mm id X 0.25 um DB-5MSUI 5975C MSD S/S Inlet ~12psi Vent 1m x 0.15 mm id 1.7 mL/min PUU Parameters: Constant Flow to MS RTL DRS Method October 9, 2012 C&EN Webinar 36

37 H 2 Constant Flow Toxicology Analyzer 7890A GC Liquid Injector Column AUX EPC 15 m X 0.25 mm id X 0.25 um DB-5MSUI 5975C MSD S/S Inlet ~8psi Vent 0.81m x 0.12 mm id 1.7 mL/min PUU Parameters: Constant Flow to MS RTL DRS Method No Change in Performance October 9, 2012 C&EN Webinar 37

38 Converting Toxicology Analyzer from He to H Time--> Abundance Time--> Abundance Hydrogen Helium Toxicology Check Out Mix October 9, 2012 C&EN Webinar 38

39 Switching GC/MS Methods to from He to H 2 Carrier Gas Reduced high background that looks like hydrocarbons Improved signal-to-noise relative to pre-conditioned state Reduced tailing for many compounds October 9, 2012 C&EN Webinar 39

40 Performance Expectations October 9, 2012 C&EN Webinar 40

41 Performance Expectations Signal-to-noise ratio is often worse by about 2-5 x. This obviously varies from compound to compound While most spectra remain same, there are always exceptions. Users should check the reference spectra for important targets to make sure they have not changed Same comment for target/qualifier ratios Some compounds may disappear at low levels. Examples include: some nitrogen and oxygen containing compounds (alcohols, aldehydes, ketones) like those found in flavor samples October 9, 2012 C&EN Webinar 41

42 Library Match Factors – Helium and Hydrogen Carrier Gas Comparison In general, these 20 spectra in hydrogen carrier show lower match factors than in helium carrier gas. They can still be properly identified in library search. HeliumHydrogenHeliumHydrogen Dichlorvos Mevinphos Ethalfluralin Trifluralin Atrazine BHC-gamma (Lindane, gamma HCH) Chlorpyrifos-methyl Heptachlor Malathion Chlorpyrifos DDE, p,p' Dieldrin Hexazinone Propargite Leptophos Mirex Fenarimol Coumaphos Etofenprox (Ethofenprox) NIST (Forward)NIST (Reverse) October 9, 2012 C&EN Webinar 42

43 Lindane NIST Forward Match = 925 Helium Carrier Gas Hydrogen Carrier Gas Observations Ion ratios changed Extra peaks in H2 NIST Forward Match = 858 October 9, 2012 C&EN Webinar 43

44 Heptachlor Helium Carrier Gas Hydrogen Carrier Gas NIST Forward Match = 926 NIST Forward Match = 851 Observations Ion ratios changed October 9, 2012 C&EN Webinar 44

45 Other Considerations: H 2 is not an inert gas, and therefore inertness problems will still exist or be worse. Use the lowest inlet temp that works (to reduce reactions with H 2 ) Use pulsed injection, especially with small bore columns Consider using an MMI in cold splitless mode for fragile compounds Using a deactivated S/SL weldments might help (but don’t ever scrub it) Avoid using methylene chloride as a solvent (especially wet). –At higher inlet temps (like >280C), HCl is formed and causes problems. –If must be used, use lowest inlet temp and maybe a deactivated S/SL weldment, or Multimode inlet Avoid carbon disulfide as a solvent Use liners with a taper at bottom to minimize sample contact with gold seal –Use Agilent Ultra Inert Liners. October 9, 2012 C&EN Webinar 45

46 Hydrogen Carrier Summary 1.Get a GOOD hydrogen generator and plumb it properly 2.Pick a column that meets the flow needs of method and MSD pump 3.Do magnet update (if necessary) and install Hydrogen draw out lens 4.After purging and pump down, set source to max temp and EM to 800V. Leave filaments on all night. 5.Reset source temp, retune, and run samples. Run practice samples for a few days to make sure system has stabilized 6.Source cleaning will be needed much less frequently October 9, 2012 C&EN Webinar 46

47 For additional information please visit: Thank You for Your Attention October 9, 2012 C&EN Webinar 47


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