2
Overview of Split/Splitless Injection Techniques
In capillary andmicropacked gas chromatography (GC) there are four primary techniques
for vaporizing a sample and transferring it onto the inlet of the analytical column: split, split-
less, direct, and on-column injections. Of these, split and splitless injections are themost
commonly used techniques. This technical guide focuses on split and splitless injections—
their optimization, troubleshooting, and systemmaintenance.
Split and splitless injections are techniques that introduce the sample into a heated injection
port as a liquid, and then rapidly and completely vaporize the sample solvent aswell as all of
the analytes in the sample. The vaporized sample is transferred to the head of the column.
In the split injectionmode, only a fraction of the vaporized sample is transferred onto the head
of the column. The remainder of the vaporized sample is removed from the injection port via
the split vent line. Split injections should be used onlywhen sample concentrations are high
enough to allow a portion of the sample to be discarded during the injection process, while still
maintaining a sufficient concentration of analytes at the detector to produce a signal.
When target analyte concentrations are so low that splitting the sample in the injection port
will not allow an adequate signal from the detector, the injector should be operated in the
splitless injectionmode. In the splitless injectionmode, most of the vaporized sample is
transferred to the head of the column.
The process of performing either a split or splitless injection is controlled by changing the
flow path and flow rate of carrier gas through the injection port. The position of a switching
valve in the injection port determines the flow path. In split injections, a high carrier gas
flow rate rapidlymoves the vaporized sample through the injection port liner, past the col-
umn (with only aminimal amount directed to the head of the column), and out the split vent.
In splitless injections, a relatively slow carrier gas flow rate directsmost of the vaporized
sample into the head of the column.
Split/splitless injection ports can be either backpressure-regulated or headpressure-regulated
systems.Most modernGCs are backpressure regulated. However, someGCmanufacturers
still find headpressure regulation advantageous and use this design in their split/splitless
injectors. It is important for analysts to be familiar with their injection port hardware and the
operating principles of their instruments, so that they factor in the variables affecting the
accuracy and reproducibility of their results.
Backpressure-Regulated Injection Systems
Figure1 illustrates the components of a typical backpressure-regulated split/splitless injection
system (e.g.,Agilent 5890, 6850, 6890GCs;Varian3300, 3400, 3500, 3600, 3800GCs;
Shimadzu17AGCs).A flow controller, positionedupstream from the injectionport, controls the
total amount of carrier gas that enters the injectionport.Abackpressure regulator, locateddown-
stream from the injectionport body, regulates thepressure inside the injectionport. Carrier gas
flow rate in the column is determinedby thepressure that ismaintained in the injectionport. The
outlet of thebackpressure regulator is theoutlet of the split vent line. The split vent lineoutlet is
at the ambient pressureof the laboratory. The flow controller and thebackpressure regulatorwork
together todetermine the column flow rate, septumpurge flow rate, and split vent flow rate.
Split and splitless injections in backpressure-regulated systems are controlled by the position
of the 3-way solenoid valve. In the split injectionmode, the flow path is always open from
the injection port body through the 3-way solenoid valve to the split vent line. In the splitless
injectionmode, the flow path is temporarily closed from the injection port body to the split
vent line. The carrier gas flow rate through the injection port liner is simply the column flow
rate.Any excess flow is directed through the septum purge line, into the 3-way solenoid
valve, and out the split vent line.
In backpressure-regulated systems, the split vent flow rate is changed by adjusting the flow
controller.An increase in the total flow being delivered to the injection port will result in a
higher split vent flow rate and a higher split ratio. Column flow rate is not affected by
changes in the total flow being delivered to the injection port, but by the backpressure regu-
lator. Tomaintain the same pressure at all times, use the backpressure regulator to compen-
sate for a change in the total flow delivered to the injection port.
Table of Contents
Overview of Split/Splitless Injection
Techniques ......................................2
Backpressure-Regulated InjectionSystems..2
Headpressure-Regulated Injection
Systems..........................................3
Operating in the Split InjectionMode ......4
Inlet Liners for Split Injectors ................6
Operating in the Splitless InjectionMode ..7
Solvent Focusing and Analyte Focusing
......9
Inlet Liners for Splitless Injections ........11
SeptumPurgeOptimization ..................12
Problems Associatedwith Split and Splitless
Injections ......................................13
Thermal Decomposition
. . . . . . . . . . . . . .13
Active Compounds
. . . . . . . . . . . . . . . . . .13
MolecularWeight Discrimination
. . . . . . .13
Needle Discrimination
. . . . . . . . . . . . . . .14
Backflash
. . . . . . . . . . . . . . . . . . . . . . . . .15
Sample Size and Injection Port
Temperature
. . . . . . . . . . . . . . . . . . . . .15
Optimizing the Rate of Injection
. . . . . . . .16
Pressure Programming
. . . . . . . . . . . . . .16
Direct Injection as an Alternative to Splitless
Injection........................................16
Hints for AnalyzingDirty Samples ..........18
Hints for PerformingRouting Injection Port
Maintenance ..................................19
Cleaning andDeactivating Injector Liners
. .19
Replacing Critical Seals
. . . . . . . . . . . . . .19
Changing Septa
. . . . . . . . . . . . . . . . . . . .19
Product Listing ........4, 5, 9, 18, 19, 20–35
Restek Flowmeter 6000
. . . . . . . . . . . . . . .4
Soap FilmBubble Flowmeters
. . . . . . . . . . .4
Split Vent Trap
. . . . . . . . . . . . . . . . . . . . . .5
Methane Cylinder
. . . . . . . . . . . . . . . . . . . .5
Split andSplitless Injection inCapillary
GC, 4th Ed. book
. . . . . . . . . . . . . . . . . . .9
MiniWool Puller/Inserter
. . . . . . . . . . . . .18
Nylon Tube Brushes andPipe Cleaner
. . . .19
LeakDetective
II
LeakDetector
. . . . . . . . .19
Siltek
™
Inlet Liners
. . . . . . . . . . . . . . . . . .20
Base-Deactivated Inlet Liners
. . . . . . . . . .20
Prepacked Liners
. . . . . . . . . . . . . . . . . . .20
Liners for Agilent/FinniganGCs
. . . . . .21–22
O-rings
. . . . . . . . . . . . . . . . . . . . . . . . . .23
Inlet & FIDMaintenance Kits
. . . . . . . . . .23
Vespel
®
Ring Inlet Seals for Agilent
5890/6890 and 6850GCs
. . . . . . . . . . .24
Rethreading Tool
. . . . . . . . . . . . . . . . . . .24
Replacement Inlet Seals
. . . . . . . . . . . . . .25
Replacement Inlet Cross-Disk Seal
for Agilent GCs
. . . . . . . . . . . . . . . . . . .25
Liners for VarianGCs
. . . . . . . . . . . . .26–27
Varian Inlet Liner Seals
. . . . . . . . . . . . . .27
Inlet Liner Removal Tool
. . . . . . . . . . . . .27
Liners for PerkinElmer GCs
. . . . . . . . . . .28
Liners for ShimadzuGCs
. . . . . . . . . . . . .29
Liners for Thermo FinniganGCs
. . . . .30–31
Inlet Liner Seal for TRACE
™
2000GCs
. . . .31
Graphite SealingRing andWasher for 8000
Series and TRACE
™
GC Inlet Liners
. . . . .31
Septa
. . . . . . . . . . . . . . . . . . . . . . . . . . . .32
Press-Tight
®
Connectors
. . . . . . . . . . . . .33
Polyimide Resin
. . . . . . . . . . . . . . . . . . . .33
MXT
®
-Union Connector Kits
. . . . . . . . . . .34
Valco
®
Connectors
. . . . . . . . . . . . . . . . . .34
Gerstel GRAPHPACK
®
3D/2 Connectors
. .34
Guard Columns and Transfer Lines
. . . . . .35
