5
sample components. In the split injectionmode, the residence time of the sample in the
injection port is very short because of the high carrier gas flow rate through the injection
port liner and out the split vent.As a result, vaporizationmust be completed as rapidly as
possible. However, injection port temperaturesmust not be so high that they cause sample
degradation.
When set up properly, split injections are very reproducible. Samples introduced under con-
stant temperature, pressure, and flow conditionswill vaporize and split consistently.
Split injections can be used for both qualitative and quantitativework. Internal or external
reference compounds are split under identical conditions compared to analytes in samples.
Any variations experienced by the sample also are experienced by the reference compounds
when the samplematrix and standardmatrixmatch exactly. In general, split inlet liners are
designed to have added surface area to helpwith sample vaporization. Improved vaporiza-
tion can be acheivedwith changes in liner geometry that increase the surface area.
Examples include incorporating fused silica or glasswool, CarboFrit
™
packing, or using a
laminar cup.
Equation 1.
Calculating the split ratio.
Split ratio =
column flow+ split vent flow
column flow
Equation 2.
Calculating the approximate column flow rate.
Flow=
(
π
) (column radius in cm)
2
(column length in cm)
dead volume time (min.)
where
π
= 3.14159
For example, a 30m x 0.53mm ID column operated at 20cm/sec. linear velocity (helium)
retainsmethane for 2.50min., and therefore has a flow rate of 2.65cm
3
/min.:
Flow=
(3.14159) (0.0265cm)
2
(3000cm)
= 2.65cm
3
/min.
2.50min.
Equation 3.
Calculating the approximate on-column concentration for split injections.
Concentration = concentration in sample (µg/µL)
×
sample vol. injected (µL)
split ratio
Caution!
When analyzing hazardous compounds in the split mode, make sure they do not enter
the lab atmosphere through the split vent.A small, charcoal-filled split vent trap con-
nected to the split vent protects you from breathing contaminated air (cat. # 20698).
MethaneCylinder
Setting the column flow rateby injecting
methane andoptimizing linear velocity
is apreferredmethod for establishing
reproducible retention times (ASTM
MethodE1510-93).Measuring the lin-
ear velocityof your carrier gas ismade
easybyusing theScotty
®
14 cylinder
containing1%methane inhelium. The
completekit includes theScotty
®
14
cylinder, aMINICYL regulator, a
syringe adaptor, and apackageof twenty
septa for the adaptor.
Description
qty.
cat.#
Complete Kit
kit
20197
Replacement Septa
20-pk.
20198
Replacement Cylinder
ea.
20199
✶
For customer service, call
800-356-1688, ext. 3
(814-353-1300, ext. 3)
or call your local
Restek representative.
High-Capacity Split
Vent Trap
• Reduces the release of hazardous
materials from the capillary split vent
into the lab.
• Lasts onemonth or 1,500 injections.
• Includes connecting lines andmount-
ing kit.
Description
qty.
cat.#
High-Capacity Split Vent
Trap
ea.
20698
High-Capacity Split Vent
Trap
5-pk.
20699
