We usually encounter troubleshooting exercises where a more in-depth knowledge and pragmatic approach to GC fix-up would have been advantageous. This prompted u.s. to produce a GC/GC-MS preparation checklist. Reference this prior to assay to understand the actions, checks, tools, and consumable items that are required.

Cheque gases are of the correct purity (99.999%+).
Plow on the cylinders.
If cylinder bottle pressure less than xxx psi replace it.
If the line pressure (2d regulator stage or estimate at the bench) is beneath 80psi increase line pressure with a cylinder and/or bench regulator.
Verify right gas traps are installed.  Verify that the gas filters are not wearied and check when they were last replaced.

Comments;

  • If traps are cocky-indicating – cheque the colour of the tell-tales
  • For more data on gas filter option and installation check out:
    Video Guide to Gas Filters
    Chromacademy - Crimes Confronting GC Gas Filters
Is the GC column fit for purpose?
Has information technology been properly stored (out of sunlight with cavalcade ends capped)?  How did it perform terminal time it was used – bank check records?
Remove the inlet septum cap. Replace the inlet septum.

Comments;

  • Ensure you have the correct septum in terms of drain profile and temperature resistance
  • Employ pinch nose plastic tweezers to avoid scratching the metal surfaces of the inlet
  • Avoid applying excess torque pressure on the septum past following manufacturers guidelines for the inlet closure/septum nut tightening.  Failure to do this volition lead to septum coring and splitting.
Open the inlet.
Inspect the inlet liner and check for cleanliness including solid debris, discolouration and night patches of burned on matrix contaminants.
If in doubtfulness supervene upon the liner– check that the liner geometry/packing is appropriate for your method.
Utilise a fresh liner o-band every bit necessary.
Replace the inlet bottom seal if necessary (follow manufacturer'due south instructions).
Ensure that inlet surfaces and seals are included in medium-term maintenance / replacement schedules.

Comments;

  • Ensure that polymeric nitrile or vinyl lint-free glovesare used for all inlet maintenance operations - GC Inlet Maintenance
  • Check liner for debris, discolouration and dark contaminant residues
  • Utilize only plastic tweezers to remove the liner
  • A torch and dental mirror can exist very useful for internal inspection of the inlet
  • Liner o-rings should exist perfectly round in contour (doughnut-like) and any 'flattening' of the o-ring or sticking to the liner body indicates information technology needs to exist replaced
  • Option Guide - Capillary GC Liner Option Guide
  • The internal body of the liner should be periodically cleaned with a suitable solvent (methanol is a popular choice) using a lint-free swab.
  • Any bottom seals should be replaced periodically to ensure that the seal does non contribute to secondary retention (peak tailing/analyte adsorption)
Replace nuts and ferrules on each end of the column.

Comments;

  • Quarter a used inlet septum and slide one quarter onto both detector and inlet ends of the cavalcade – carefully removing any septum shards retained in the caput of the column.  These volition be used to maintain the correct distance between the ferrule and the tip of the cavalcade on installation.
  • Various ferule materials and sizes are available and vary with cavalcade dimensions and application.
  • Graphite ferrules with the through-hole bore matched to the cavalcade o.d. are suitable for general GC applications
  • When MS or specialist detectors are used, you may demand to consider a graphite/vespel blended ferrule.
Trim the ends of the cavalcade and inspect with a magnifier or depression power microscope to make sure the cutting is direct and there are no crude edges.
The quality of the column cut is straight related to height shape and quantitative reproducibility, therefore good cavalcade cutting technique is essential.

Comments;

  • The post-obit is a comprehensive guide to column installation - Chromacademy - GC Column Installation
  • Ceramic wafers and diamond-tipped bike cutters are available for column cutting and you should accept time to develop a adept cutting technique
  • The amount of cavalcade trimmed each time will depend upon the amount of phase deposition at each end of the column.  5-10cm trims will usually be sufficient, even so, upwardly to 1m of column may need to be trimmed if sample matrix deposition is heavy or phase stripping has occurred.  Consider using a non-coated, deactivated guard column if excess column trimming is required
  • The requirement to inspect the quality of the column cutting prior to installation will save you a lot of troubleshooting time one time the column is installed
Note your manufacturers recommended column insertion distance (inlet and detector).
Wipe the outer column surface of the column ends with a solvent suitable for removing contagion from fingerprints (isopropyl alcohol is a popular choice).
Adjust the nut/ferrule position and hold in identify with the ¼ septum from six.

Comments;

  • Compliance with the manufacturers recommended insertion distance is critical to a successful analysis
  • Incorrect insertion into the inlet will lead to wide and tailing peaks and quantitative reproducibility issues
  • Incorrect insertion into the detector will pb to summit broadening and loss of efficiency (if too low in the inlet) or noisy/spiking baselines and poor sensitivity (it too loftier in the inlet)
Insert the column into the inlet. Tighten the ferrule and gently pull the column to bank check if the plumbing equipment is tight enough.  Grip the column and continue to tighten well-nigh 1/8 plow until the column tin can't be moved. Echo with the detector connection.
Input column dimensions, carrier gas type, required catamenia rate and whether abiding flow/constant pressure is to exist used into the instrument.
Verify cavalcade flow at the detector using an electronic flow meter

Comments;

  • Using an electronic flow meter to verify cavalcade menstruation will non just cheque the GC functioning but too that the correct cavalcade dimensions and carrier gas blazon have been programmed into the instrument.
  • This is a common mistake when prospering for GC analysis.
Switch on the inlet and detector heaters, and the detector gas flows.
Ignite the detector if it is flame based.

Comments;

  • A dental mirror is good for checking if the detector flame has been established – hold 1 inch above the detector chimney and discover condensation on the mirror surface if the flame is burning
  • It is good practise to verify the period charge per unit of each detector gas using an electronic flow meter, although this may not be necessary prior to every analysis
Purge dissolved oxygen by assuasive carrier to flow through the column at ambient temperature for x – thirty mins. depending upon column dimensions.
This step is important and should not be omitted.  Failure to purge the stage may lead to unnecessary column damage and increased thermal equilibration times.
Set the oven to the conditioning temperature  - ten°C above the maximum oven temperature of your method or at the gradient upper-temperature limit of the column, whichever is lower.
Permit to thermally status for the catamenia recommended in the guide below.

Comments;

  • Column Conditioning Guide - GC Cavalcade Conditioning
Cool the oven to starting temperature of your analysis.
Load the test method into the GC / data system.
Check the split catamenia at the separate outlet port using an electronic flow meter.
Cheque the septum purge flow using an electronic menstruation meter.
Perform at least 1 total temperature program according to your analytical method.

Comments;

  • It is of import that the split menstruum is verified using an electronic flow meter every bit this flow path is more susceptible to partial blockage
  • When septum purge menstruum is automatically calculated, ensure that the flow is in the range 1 – 10 mL/min.
  • Running through the analytical temperature/flow program helps to elute stage degradants or inlet leachables/outgassing agents which have non been removed from the column during the initial thermal equilibration.  It also helps to check that inlet and detector connections are leak-gratuitous throughout the temperate / pressure program.
Perform a test injection/system suitability test to check method performance.

Comments;

  • Typical attributes to monitor with System Suitability tests which may betoken issues with system preparation
    • Peak efficiency
    • Peak shape
      Check out: 3 Peak Shapes you really don't desire to see in your Gas Chromatogram
    • Baseline noise and stability