from a purge and trap unit. Alternatively, columns with an ID of 0.25mm or less are the best
choice for GC/MS applications— they provide optimal performancewith small flows of carrier
gas, and thus can be connected directly to the vacuum source of amass spectrometer,
eliminating the complications associatedwith a jet separator.
Use
Table1
to compare typical column characteristics according to column ID, then select the
ID that best matches your needs.
Table 1
Characteristics of thick film and thin film stationary phases.
SelectColumn ID:
ColumnParameters
Values
Typical Spitless PurgeTime
He split vent flow rate (50:1 split ratio)
H2 split vent flow rate (50:1 split ratio)
ColumnOD (Ferrule ID)
ColumnFlowRate (He@ 20cm/sec.)
ColumnFlowRate (H2@ 40cm/sec.)
ApproximateSampleCapacity
Typical EffectivePlates/m (80%CE)
Approximate column head pressure (He orH2 carrier gas)
Column (m):
6101215202530406075105150
HeadPressure (psig):
Always optimize the column flow rate by using linear velocity.
PhaseRatioCalculations
Changes in the column ID/stationary phase film thickness ratio, beta, are an important
considerationwhen youwant tomake a change in column internal diameter or in stationary
phase film thickness. Analyte retention increases as column internal diameter is decreased, and
analyte retention decreases as stationary phase film thickness is decreased. When other column
parameters and analysis conditions are held constant, a columnwith a smaller beta valuewill be
more retentive for a given analyte. To assure similar retention and resolutionwhen you increase
