a Practical Approach Capillary GC Troubleshooting GC Troubleshooting: a Practical Approach Gas...

©1999 Sigma-AldrichCo.

SUPELCOCapillary GC Troubleshooting:

a Practical Approach

Gas Separations R&D

Katherine Stenerson

Supelco, Supelco Park, Bellefonte, PA 16823

©1999 Sigma-Aldrich Co. SUPELCO

Outline

✔ Basic Troubleshooting Strategy

✔ Preventing Problems

✔ Identifying Common Problems

✔ Recommended Reading

✔ Discussion


Troubleshooting Strategy

✔ Have appropriate equipment and supplieson hand.

✔ Establish a systematic approach.

✔ Know what to look for first.

✔ Record what you did to correct the problem.


Suggested Equipment to Have on Handfor Troubleshooting:

✔ Electronic Leak Detector

✔ Flow Meter

✔ “Test” Column

✔ Replacement Accessories (Syringes,Ferrules, Septa)

✔ Replacement Purifiers


Five Major Sources of ChromatographicProblems:

❶ Operator Error

❷ The Sample

❸ The Column

❹ The GC Electrical System

❺ The Gas Flow System (both internal andexternal to the GC)


Approaching the Problem

✔ Check first to see if a “fix” for the problemis already known.

✔ Check the Supelco Capillary GCTroubleshooting Guide (Bulletin 853.)

✔ Check back in the instrument maintenancerecord.

✔ Talk to others in your lab.


Check operating parametersRun Ref. Std.

OK Not OK

OKNot OK

Problem was sample related

Install Test

Column

OK Not OK

Problem was

Column related

Cap off Detector

OK

Not OK Problem is in the Detector

Problem is in the Inlet or with the carrier gas

Isolate the Source of the Problem

Correct the parameter


When reviewing operating methodparameters consider the following:

? Is my starting temp. low enough to allowsufficient sample focusing?

? For splitless injections, is my splitter opening atthe appropriate time?

? Is my column flow set to give me maximumefficiency at the most critical point?

? Are heated zones (injectors, detectors, interfaces)set appropriately?


The Best Way to Solve Problems is toPrevent Them!

✔ Install and maintain proper purification forall gases in the GC system.

✔ Maintain the injector by periodicallyinspecting and changing the liner, septa,and seal (H/P™.)

✔ Use the proper injection technique-thisincludes using the right liner for the job.

✔ When necessary, use a guard column toprotect the analytical column.


Gas Purification

✔ Carrier Gas– At minimum, remove hydrocarbons, water, and oxygen.

✔ Hydrogen (FID)– At minimum, remove hydrocarbons.

✔ Air (FID)– At minimum, remove water and hydrocarbons.

✔ Nitrogen make-up (FID, ECD)– At minimum, remove hydrocarbons.

✔ P-5 make-up (ECD)– At minimum remove hydrocarbons (especially halogen-

containing), oxygen.


Acceptable Purity Levels forChromatography Grade Gases

Impurity / Maximum Concentration

Gas O2 H2O CO2 COTotal

Hydrocarbons

Helium <1.0 ppm <1.0 ppm <1.0 ppm <1.0 ppm <1.0 ppmNitrogen <1.0 ppm <1.0 ppm <1.0 ppm <1.0 ppm <1.0 ppmAir 20-22% <1.0 ppm <1.0 ppm <1.0 ppm <1.0 ppmHydrogen <1.0 ppm <1.0 ppm <1.0 ppm <1.0 ppm <1.0 ppmArgon/ Methane <1.0 ppm <1.0 ppm <1.0 ppm <1.0 ppm <1.0 ppm


Suggested purifiers

Hydrocarbons Water Oxygen

Carrier Supelcarb HCSupelpure HC

Mole Sieve 5A OMI -2

H2

Air Mole Sieve 5A

N2 makeup

P-5 OMI -2 OMI -2

P-5


What are some signs that my purifiersneed to be changed?

Hydrocarbon TrapsNoise in the baseline (FID)

Increase in background peakson tune (MSD)

Higher than normal baselinereading on FID

Extra peaks visible in run

Molecular Sieve 5AIncrease in column bleed

Water visible in MSbackground

Poor peak shapes for gaseousVOCs (purge and trap)

Extra peaks visible in run

OMI™-2 color change


Injector Maintenance

✔ Change (as needed):

1. Liner and O-ring*

2. Seal and washer **H/P™ GCs

✔ Inspect the inlet periodically

-Look for contamination in the liner

-Look for residue on the seal


Using the right liner and injectiontechnique can also prevent problems:✔ Split Injection

– used for concentrated samples– high flow of carrier gas through liner during

injection– should use liner designed for split injection

✔ Splitless Injection– used for trace analysis– low flow of carrier gas through liner during

injection– inertness and internal volume of liner used are

critical


Some liners used for split injection

Cup (unpacked)

Cup (wool packed)

Split/splitless- wool packed


Some liners used for splitless injection

2 mm ID, straight

Dual-tapered

Single-tapered


If you must clean a liner….

✔ Handle liners with gloves or forceps.

✔ Use clean compressed gas and/or a finebrush to remove particles.

✔ Rinse liner in an appropriate solvent anddry with clean compressed gas.

✔ Use mineral acid and/or detergent only ifabsolutely necessary.


Using a Guard Column

✔ Choose a guard column which has beendeactivated.

✔ Usually, the ID of the guard matches theanalytical column.

✔ A 5-10 meter length is normally used.

✔ Connect with either a GlasSeal™ or buttconnector.


Common Problems

1 Poor Peak Shapes (either tailing, fronting,or just generally ugly.)

2 Nonlinearity

3 Baseline Noise and /or Drift

4 Ghost Peaks

5 Missing Peaks / Poor Response

6 Insufficient Resolution


1. Poor Peak Shapes

✔ Fronting can indicatecolumn overload.

✔ Tailing can indicateactivity in the system orimproper columninstallation.

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1. Poor Peak Shapes (cont.)

✔ Generally ugly peaks,such as a,a-dimethylphenethylamine,can be caused by avariety of problems.


➨ Column overload

➨ Detector overload

➨ Standards preparation

➨ Poor peak shape resulting in improperintegration

2. Nonlinearity

The most common causes are:


An Example of Overload:

Peaks have broad bases,fronting on last few visible inrun.


Preventing column overload for splitlessinjections:

✔ Inject a smaller amount / use a 1 ul syringe.

✔ Use a thicker film column.

✔ Use a column with a wider ID.

✔ Decrease upper limit of calibration range.

✔ Use a column of slightly different polarity.


An example of poor peak shape affectinglinearity:

✔ Benzoic acid istypically of poorshape when doingsplitless injections.


3. Common causes of baseline noise /drift.

✔ Column bleed

✔ Dirty detector

✔ Contaminants in carrier gas / carrier gaspurity


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Effect of carrier gas purity on baselinenoise:

H2 carrier from tank

H2 carrier from a generator


Column bleed results from the normaldegradation of the stationary phase.

✔ All columns bleed to some extent.

✔ Bleed increases with temperature.

✔ The amount of bleed will increase in thepresence of oxygen.


A Typical Bleed Profile:

4

Bleed measured as thedifference between 1 and 2.

1

2


Column Bleed on an MSD

✔ Visible as baseline rise in the TIC.✔ Check spectra for key bleed ions:

– PTE™-5: 207, 281– SPB™-1: 73, 207, 281– SPB™-624: 207, 269

✔ Make sure interface temp. is < columnmax. temp.


Ion 207 corresponds to a fragment known as D3:

O Si

SiO

Si

O

CH 3 CH 3

CH 3

CH 3

CH 3

+

©1999 Sigma-Aldrich Co. SUPELCO40 60 80 100120140160180200220240260280300320340360380400

0

500

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m/z-->

Abundance

Scan 2895 (27.487 min): 1118015.D207

2817313396

191

253

50

327223162 355115 415

MS spectra of bleed from a PTE™-5 Column

207

281


40 60 80 1001201401601802002202402602803003203403603804004200

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m/z-->

Abundance

Scan 1941 (28.793 min): 0122002.D73

44

207

147

281341

96 119 179 253 429401313

MS spectra of bleed from an SPB™-1 Column

73

207

281


MS spectra of bleed from an SPB™-624 Column

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m/z-->

Abundance

Scan 8581 (33.704 min): 1022006.D207

269

44253

19113373 96177147

283119 322 343239163 22359298

207

269


40 60 80 1001201401601802002202402602803003203403603804004200

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m/z-->

Abundance

Scan 604 (7.460 min): 1201001.D73

147

281

32745

207415399

131 191 343 383251 29795 223163115

MS Spectra of Septa Bleed

73

147

281


Prevent column bleed!

✔ Sufficiently purge column with carrier beforeramping it up in temperature.

✔ Make sure carrier gas is filtered for water andoxygen.

✔ Check integrity of all fittings leading to thecolumn.

✔ Do not heat the column above its maximum temp.

✔ Precondition the column prior to use.


4. Ghost Peaks

✔ Residue in the inlet liner and at the head ofthe column

✔ Contaminated syringe / and or washsolutions on an autosampler.

✔ Sample carryover

✔ Contaminated carrier gas


0

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Response test mix, before

If pieces of septa get into an inlet liner...


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Time-->

…even a simple analysis can be ruined.

Response test mix, after


5. Missing Peaks / Poor Response

✔ Sample decomposition– Activity in the inlet or column– Injection port temperature too high– Sample not stable enough for GC– Standards not stable

✔ Coelution✔ Insufficient run time / final temperature✔ Sample not volatile enough for GC✔ Improper column installation


0

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2,4-

din

itro

phen

ol

4-n

itro

phen

ol

2-m

ethy

l-3,

5-di

nitr

ophe

nol

pent

ach

loro

phe

nol

Nasty samples can damage a columnby creating active sites:

Before Sample Injection


0

100000

200000

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700000

800000

900000

Time-->

Abundance

2,4-

DN

P &

4-N

P s

hou

ld b

e he

re

2-m

ethy

l-3,

5-di

nitr

ophe

nol

Pen

tach

loro

phen

ol s

houl

d b

e he

re

After sample injection

Here, the responses of some acidswere affected:


Response can also be affected by theposition of the column in the inlet:

0

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8 mm above top of ferrule


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Here, the column was not inserted farenough:



Here, the column was inserted too far:

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6. Insufficient Resolution

✔ Wrong column– Longer columns increase resolution.

– Smaller ID columns increase resolution.

– A different phase altogether may be needed.

✔ Wrong Conditions– Carrier gas flow too fast or slow .

– Oven ramp rate too fast.


Recommended ReadingSupelco Bulletins

1. 741: The Supelco Guide to Leak-Free Connections2. 783: Cleaning Flame Ionization Detectors3. 853: Capillary Troubleshooting Guide4. 875: Supelco Capillary GC Selection Guide5. 895: Installation and Maintenance Instructions for .25

mm and .32 mm ID Fused Silica Capillary Columns6. 897: Installation and Maintenance Instructions for .53

mm ID Fused Silica Capillary Columns7. 898: Gas Management Systems for GC8. 899: Capillary GC Inlet Sleeve Selection Guide9. 916: Purge and Trap System Guide10. 918: Selecting Purifiers for Gas Chromatography


Help is just a phone call or mouseclick away!

✔✔ Supelco Technical ServiceSupelco Technical Servicephone: 1-800-359-3041email: [email protected]✔✔ Supelco Customer ServiceSupelco Customer Servicephone: 1-800-247-6628email: [email protected]✔✔ Sigma-Sigma-Aldrich WebsiteAldrich Websitewww.sigma-aldrich.com

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