Purifiers

Gas is used to perform several functions associated with the GC technique. Each function has specific contaminants that must be controlled. Listed here are several of those functions, the contaminants that must be controlled, the appropriate gas choices, and recommendations for purifier selection.
Column Carrier Gas
  • Description: The ′mobile phase′ in GC, it transports analytes through the column, between the injector and detector, when the analytes are not partitioned into the stationary phase.
  • Remove: Hydrocarbons, moisture, and oxygen. An overall gas purity of 99.9995% is desirable to optimize chromatography and column life.
  • Gas Choices: Helium, hydrogen, nitrogen, argon, or 5% methane in argon.
  • Purifiers (Option 1): [In series] Supelcarb HC hydrocarbon trap, molecular sieve 5A moisture trap, Supelpure-O oxygen trap, OMI (oxygen moisture indicating) polishing purifier.
  • Purifiers (Option 2, not for use with hydrogen): [In series] Supelcarb HC hydrocarbon trap, high capacity gas purifier, OMI (oxygen moisture indicating) polishing purifier.
  • Purifiers (Option 3, for helium delivery to GC-MS): Supelco helium purifier.

Purge Gas for Purge and Trap Operation
  • Description: Water, and soil mixed with water, can be gas purged to drive analytes onto a trap containing adsorbent beds. This adsorbent bed trap is subsequently desorbed to transport analytes to the head of the GC column.
  • Remove: Hydrocarbons.
  • Gas Choices: Helium or nitrogen. Helium can be used for both the purge and desorption modes. Nitrogen can only be used for the purge mode (to reduce costs).
  • Purifier: Supelcarb HC hydrocarbon trap.
Make-up Gas for ECD Operation
  • Description: An ECD requires a non-inert gas for proper operation. When helium, hydrogen, or argon is used as the carrier gas, a stream of non-inert gas is plumbed into the carrier gas line between the column outlet and the detector inlet.
  • Remove: Hydrocarbons, moisture, and oxygen. An overall gas purity of 99.9995% is desirable to optimize sensitivity and prolong detector life.
  • Gas Choices: Nitrogen or 5% methane in argon.
  • Purifiers: [In series] Supelcarb HC hydrocarbon trap, molecular sieve 5A moisture trap, Supelpure-O oxygen trap, OMI (oxygen moisture indicating) polishing purifier.

Fuel Gas to Support FID Combustion
  • Description: A fuel source, along with oxygen and heat, is required to generate/maintain a flame.
  • Remove: Hydrocarbons.
  • Gas Choices: Hydrogen.
  • Purifier: Supelcarb HC hydrocarbon trap.

Oxygen Source to Support FID Combustion
  • Description: An oxygen source, along with fuel and heat, is required to generate/maintain a flame.
  • Remove: Hydrocarbons and moisture.
  • Gas Choices: Air.
  • Purifiers: [In series] Supelcarb HC hydrocarbon trap, molecular sieve 5A moisture trap.
Fourier Transform Infrared Spectroscopy (FTIR) and Total Organic Carbon (TOC) Operation
  • Description: These detection techniques operate in a nitrogen or air environment, and are sensitive to the presence of carbon dioxide.
  • Remove: Carbon dioxide and moisture.
  • Gas Choices: Nitrogen or air.
  • Purifiers: [In series] Carbon dioxide trap (evolves moisture as carbon dioxide is absorbed), molecular sieve 5A moisture trap.

Pneumatic Control
  • Description: Pressure is used to drive equipment, such as autosamplers and valves.
  • Remove: Moisture.
  • Gas Choices: Air.
  • Purifier: Economy moisture trap.