Conversion of Agilent EI GC/MSD Systems To

Hydrogen Carrier Gas

Agilent TechnologiesBeNeLuxJan van Laar

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Introduction: Converting From He To H2

• Many GC/MS users are considering changing from helium to hydrogen carrier gas due to price/availability problems with helium.

• 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 H2

– Remove/bypass carrier gas filter (may be re-installed later if needed)– GC/MSD hardware changes– choosing new chromatographic conditions– a 2-5 fold reduction in signal-to-noise ratio– changes in spectra and abundance ratios for some compounds– activity and reactivity with some analytes

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Introduction: Converting From He To H2

• Methods that will generally require less optimization include analytes that:– are “durable” compounds– are at higher concentrations– are analyzed with split injections– are derivatized

• Methods that will generally require more optimization include analytes that:– are “fragile” compounds – are at trace concentrations

• Allow time for necessary updates to SOPs and validation.

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H2 Safety

Letter From Agilent Safety Engineer. Describes H2Safety Features of Agilent GCs

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Designed for Reliability – H2 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 H2

• Explosion Test– GC designed to contain parts in case of explosion

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Safety First: Read This Before You StartG3170-90010

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Da Vinci multi sensor: hydrogen

Carrier gas switch

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Source of H2 Carrierand

Plumbing

Source of Hydrogen: Use A Hydrogen Generator

• Higher initial expense than cylinders, much lower cost over time• Very clean H2, >99.9999% available• More consistant purity• Safety considerations

– H2 is only generated at needed pressure (like 40 psig)– Flow is limited (like 250 mL/min)– Auto-shutdown if setpoint pressure cannot be maintained– Minimal stored gas (like 50 mL at 40 psig) of H2 at any one time

• Make sure to buy a good one with a low spec for water and oxygen

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This is an example of the type of H2generator to use. Look for generators with the > 99.9999% specification and low individual specs on water and oxygen.

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Plumbing The Instrument

• Chromatographic 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.• 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 H2 generator, start out with no traps. Only add traps if

needed. Make sure the water and oxygen levels are low enough.

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Split Vent and Septum Purge Vent Should Be Connected to Exhaust

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MS Components Needed Before

Conversion:Magnet and

Drawout Lens

Check The Magnet In The 5975

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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. You should contact your Agilent service engineer to change it to a Helium and Hydrogen compatible magnet before converting the system to H2carrier. Note: all 5973 magnets are compatible with both He and H2

Replace The Standard 3 mm Drawout Lens With The Optional 6 mm When Using H2 Carrier

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G2589-200456 mm Drawout Plate, Inert

Standard 3 mmDrawout Plate, Inert

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Choosing A Column And Conditions

MSD Pumping Capacity For H2 Is Less Than For HeThis limits column choice • Complete info on H2 pumping specs are not yet available• These are approximate values for the 5975. Max flow of H2 to maintain

reasonable source pressure:– Performance turbo: 2 mL/min– Standard turbo: 1 mL/min– Diffusion pump: 0.75 mL/min– Pressure pulsing: turbos <= 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 10-5 torr. You can get useful data above this pressure, but performance starts to degrade rapidly

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Guidelines For Choosing Column Dimensions And Flows For Method Converted From He To H2

– Determine 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 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 method translator for this.

– These are only approximate guidelines. Sometimes you have to deviate from them

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Van Deemter Curves

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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 H2

Column Choice

– When 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/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 cals or samples– You may need to use pulsed injection to load sample into small bore

column with 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

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Using The Flow Calculator. Set Linear Velocity to 35 For H2 Carrier. If InletPressure Too Low, Raise Flow

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Inlet pressure is too low Set inlet pressure to 5 psig

Example: 30m x 0.25 mm id x 0.25 um Checkout Column With Perf Turbo

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Meets flow requirements for pump and column efficiency with 2 x speed gain

Example: 20m x 0.18 mm id x 0.18 um Column With Perf Turbo and Std Turbo

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Meets flow requirements for std turbo pump. Flow here is chosen to give a 2.5 x speed gain.

Status Of Calculators For Column Selection

• HP FlowCalc 2.0 and HP Method Translator used in earlier slides DO NOT WORK on Win 7

• Newer versions of these can also be found in:– GC/GCMS Instrument Utilities Kit. This CD ships with every Agilent GC,

GC/MS, and autosampler. It also has manuals for GC and a firmware updating tool.

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Initial Startup With Hydrogen

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Initial Problems With Switching GC/MS Methods to H2

High background that looks like hydrocarbons

Reduced signal to noise (worse MDL)

Significant tailing for many compounds

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Switch to H2. Early problem- High BackgroundYou will see this throughout work with H2. It will get much smaller with time and use. It used to takes days or weeks for this to fall to acceptable levels. Agilent has a new conditioning protocol to clean up the background much faster (see later slide).

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Tox Checkout Sample

2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00 11.00 12.00 13.000

200000400000600000800000

100000012000001400000

160000018000002000000

Time-->

Abundance

4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.000200000400000600000800000

10000001200000140000016000001800000200000022000002400000260000028000003000000

Time-->

Abundance

Hydrogen

Helium

Immediately after conversion to H2, peakshapes on TIC are poor and tailing badly.

20m x 0.18mm id x 0.18 um DB-5MSUI

GC/MS Toxicology Checkout Mixture 5190-0471

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2 4 6 8 10 12 14 16 18

1 Amphetamine2 Phentermine3 Methamphetamine4 Nicotine5 Methylenedioxyamphetamine(MDA)6 Methylenedioxymethamphetamine(MDMA)7 Methylenedioxyethylamphetamine8 Meperidine9 Phencyclidine10 Methadone11 Cocaine12 SKF-525a (RTL Compound)13 Oxazepam14

Tetrahydrocannabinol

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Codeine

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Lorazepam16 Diazepam17 Hydrocodone

19 Oxycodone20 Temazepam22 Diacetylmorphine23 Nitrazepam24 Clonazepam25 Alprazolam26 Verapamil27 Strychnine28 Trazodone

21 Flunitrazepam

1

2 3

4

5

6

7

8

9

1011

12

14

15

17

18

19

21

13

16

20

22

23 24

2526 27

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5 ng/uL each compound

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Tailing Peaks: There is More Going On Here Than Simple Tailing

7.20 7.40 7.60 7.80 8.00 8.20 8.40 8.60 8.80 9.00

40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 3400

2000

4000

6000

8000

10000

12000

14000

16000

18000

20000

22000

24000

m/z-->

Abundance

Average of 8.018 to 8.036 min.: ToxCKO_H2_4.D\data.ms82182

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105

5568

303198122 167152 272135 215 244230 259 341288 327

40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 3400

2000

4000

6000

8000

10000

12000

14000

m/z-->

Abundance

Average of 8.048 to 8.085 min.: ToxCKO_H2_4.D\data.ms91

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4164

115 167128141 207191 221154 281242 300265 341327314

Tail SpectrumPeak Spectrum

Cocaine

Cocaine Not Cocaine

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Main Ions Of Cocaine Do Not Tail. Tail Made Up of Other Ions

Tail is not cocaine ionsCocaine

Tail is different than peak. May be formed from catalytically shredded main component. This problem is reduced with time

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Minimizing The Time For Chromatography and Background To Stabilize• Have a good source of clean hydrogen like a >99.9999% purity hydrogen

generator. • Keep H2 flow limited to value suitable for your pumping system• Use 6 mm drawout lens• After setup, purging and pumpdown:

– Set the source to max temp for your source (check to see what your’s is)– Reduce the EMV to <= 800V– Leave the FILAMENT ON overnight. This cleans up background rapidly.

• Peakshape will be much better and background will be much lower in the morning.

• Lower the source temp to method value, retune, and run some samples• 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.

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H2 Method With 6 mm Drawout And Overnite Cleaned Source. Peakshape Much Better and Background is Lower.

2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00 11.00 12.00 13.00 14.00

200000400000600000800000

100000012000001400000160000018000002000000220000024000002600000

Time-->

Abundance

Performance Expectations

• Signal-to-noise ratio is usually 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

nitro and oxygen containing compounds (alcohols, aldehydes, ketones) like those found in flavor samples

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Other Considerations:H2 is not an inert gas, and therefore inertness problems will still exist or be worse. Some things to consider:• Use the lowest inlet temp that works (to reduce reactions with H2)• 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)

PN:G3452-60570 (bottom) PN:G3452-60586 (top)

• Avoid using methylene chloride as a solvent (especially wet). At higher inlet temps (like 300C), HCl is formed and causes problems. It can remove the gold from the seal and corrode the weldment. If DCM must be used, use lowest inlet temp and maybe a deactivated S/SL weldment (or MMI)

• Also avoid carbon dissulfide as a solvent• Use liners with a taper at bottom to minimize sample contact with gold seal• Use Agilent Ultra Inert Liners.

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Hydrogen Carrier Summary

1. Get a GOOD hydrogen generator and plumb it properly

2. Pick a column that meets the flow needs of method andMSD pump

3. Do magnet update (if necessary) and install 6 mm drawout lens

4. After purging and pumpdown, set source to max temp and quad to 200C. Leave filaments on all night.

5. Reset source temp, retune, and run samples. Run practice samples for a few days to let system stabilize