troubleshooting of gc systems

8/20/2019 Troubleshooting of GC Systems

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Troubleshooting of GC Systems

Agilent RestrictedPage 1

Troubleshooting ofGC Systems

Techniques, Tips, and Tricks

Daron Decker

Chromatography Technical Specialist


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Troubleshooting Starts with Isolating the problem

Is it injection, flow, column, detection, electronic or some combination?

Know what can and can’t cause the symptom and what to do about it

Broad Solvent Peak – Injector Problems, Technique, Sample Problems

Split Peaks – Injector Problems, Mixed Solvent

No Peaks – Wasn’t Introduced, Wasn’t Detected

Bonus Peaks – In Sample or Back Flash

Response Changes – Activity, Inlet Discrimination, Detector Problem

Peak Tailing – Flow Path or Activity

Peak Fronting – Overload or Solubility Mismatch

Shifting Retention – Leaks, Column Aging, Contamination or Damage

Loss of Resolution – Peak Broadening, Separation DecreasingBaseline Disturbances – Column Bleed, Contamination, Temperature

Noisy or Spiking Baseline – Electrical or Contaminated Detector

Negative or Flat-topped Peaks – Detector Problems

Quantitation Problems – Activity, Inlet or Detector Problems

Logical Troubleshooting


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Broad Solvent Front (or Major Component)


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Broad Solvent FrontTechnique

Installation problem

Large injection volume

Very slow injection rate

Leak in the injector


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Broad Solvent FrontInjector Parameters

Split ratio too low

Purge off for split injection

No or long purge activation time (splitless)

Injector temperature too low/high


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Broad Solvent FrontSample Related

Dirty sample

Mixed sample solvent

Impure solvent

Column temperature < solvent BP


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Split Peaks

Injector problem (poor sample intro)

Mixed sample solvent (polarity difference)

Sample in syringe needle

Sample degradation in injector

Injection technique - erratic


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Injection technique - erratic

Which peaks? Early or late? Trends?


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No Peaks

Detector/recorder not operational

Plugged syringe/plunger not moving

Wrong injector or detector

Broken column

Huge leak

No carrier gas flow

No column


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A Real Troubleshooting Example

No Peaks

10 20 30 40 50

14

16

18

20

22

24

26

28

30


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Is the flame Lit?

put glass piece over FID outlet---- Answer in this case, Water condenses

look at output in instrument guage-- is the digital value greater than 0.0?

Answer in this case is approximately 16.2 pico amps

Is there flow through the column?

disconnect column from detector and measure flow with bubble solution or meter

Answer in this case was YES THERE IS FLOW

Assess the observations

Flame is lit and we have flow from end of column

Hypothesis: Sample not getting on column-syringe plugged?

Take syringe out and make injection manually on a dry paper towel

Answer – towel stayes dry (Syringe was clogged with septum)

Pull plunger out top, add solvent and replace plunger will usually dislodge septum particle

(should hear a little pop) If you can’t dislodge plug, Replace syringeReassemble the Injector & Re-inject

Logical Steps Taken to Find Peaks(most of our problems are leaks and plugs)


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Peaks !!

0 10 20 30 40 50

14

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Bonus Peaks or Ghost Peaks

Contamination in injector, column or carrier gas

Carry-over from a backflash or previous sample

Septum bleed


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Peak Response All Change in Size

DETECTOR response problem

Attenuation value

High background signal

Detector zeroed at a high signal level

Split ratio set incorrectly

Wrong purge activation time

Septum purge flow too high

Injector temperature too low

INJECTOR

Leaky syringe


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Peak ResponseSome Change in Size

Adsorption of active compounds (-OH, -NH, -SH) by liner,column or contaminants

Decomposition or evaporation from sample

Inlet Temperature Change – Discrimination


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Peak Tailing

Reversible adsorption of active compounds

(-OH, -NH, -SH) by liner, column or contaminants

Flow path problem - dead volume, obstruction, poorinstallation, or severe column contamination

Miscellaneous - overloading of PLOT columns, co-elution,polarity mismatch between phase, solute or solvent, and somecompounds always tail


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Peak FrontingShark Fin Shaped

Overload

– More pronounced with large solute andphase polarity differences


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Peak FrontingOther

Compound very soluble ininjection solvent

Column installation

Injection technique

Co-elution

Mixed sample solvent


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Retention Time Shift

2.00

3.25

4.75

2.75

4.00

5.50

Leak in the septum

Change in gas velocity

Change in injection solvent

Large change in sampleconcentration

Change in temperature

Loss of stationary phase

Contamination

Damaged stationary phase


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min8 9 10 11

1400 ng

7 ng

Effect of Sample Overload on

Retention Time and Peak Tailing


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Loss of Resolution

Resolution is a function of separation and peak width

Separation

Peak Width


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Loss of ResolutionSeparation Decrease

Different column temperature

Column contamination

Co-elution

Different column?


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Loss of ResolutionPeak Broadening

Change in carrier gas velocity

Column contamination

Column degradation

Injector (split flow, liner, installation)

Detector (flow, installation)


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Baseline Disturbances

Sudden Changes, Wandering, or Drifting

Column or detector not fully conditioned

Changes in carrier and detector gas flows

– Valves switching, leaks

Detector thermal or current instability

GC/MS scan range change

Contamination

WANDER

DRIFT


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Noisy Baseline

Contamination, gas, detector, etc.

Column in detector flame

Incorrect detector gas flows

Air leak - ECD, TCD

Detector electronics malfunction

MILD

SEVERE


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Spiking Baseline

Particles entering the detector

Random: poor connection

Regular: nearby "cycling" equipment


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Negative Peaks

Normal for TCD, ECD

All peaks - check recorderconnection and settings

Dirty or old cell if after largepeaks with ECD


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Flat-Topped Peaks

Maximum detector signal exceeded

Maximum recorder signal exceeded

Excessive sensitivity settings


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Quantitation ProblemsSystem

Detector problem (stability)

Outside detector's linear range

Recorder settings

Activity (adsorption)


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Quantitation ProblemsTechnique or Conditions

Injection technique or conditions

Syringe worn

Baseline disturbances

Co-elution

Matrix effects

Sample evaporation – leaky vials

Sample decomposition


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Page 31

Troubleshooting Tips

1. Isolate the problem.

(Blank Run, Inject Un-retained Compound, Jumper Tube Test)

2. Change only one variable at a time.

3. Compare before/after chromatograms.

(Peak shape, response, retention, baseline rise, background, etc.)

4. Utilize Technical Support.


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TECHNICAL SUPPORT

1-800-227-9770, #4, #1

1-972-699-6423 (Daron)

1-877-874-0307 (toll free)

281-997-9107 (FAX)

E-mail:[email protected]

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