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Split vs. Splitless Injection
Split vs. Splitless Injection

Split and splitless are the two most commonly used GC injection techniques.
Split and splitless are the two most commonly used GC injection techniques.

How are they different?
How are they different?

And which one should you use for your analysis?
And which one should you use for your analysis?

We’ll begin with split injection,
We’ll begin with split injection,

which is the most popular thanks to its versatility over a range of analyses.
which is the most popular thanks to its versatility over a range of analyses.

Inside a split/splitless inlet,
Inside a split/splitless inlet,

you will find the carrier gas supply,
you will find the carrier gas supply,

the septum,
the septum,

the septum purge,
the septum purge,

the split vent,
the split vent,

the liner,
the liner,

and the column.
and the column.

Now we’ll start the gas flow
Now we’ll start the gas flow

and simulate a split injection.
and simulate a split injection.

Let’s rewind and go through what happened.
Let’s rewind and go through what happened.

First, the gas entered the inlet with a total flow of 104 mL/min.
First, the gas entered the inlet with a total flow of 104 mL/min.

A small amount—3 mL/min—
A small amount—3 mL/min—

passed through the septum purge
passed through the septum purge

to reduce possible contamination from the septum,
to reduce possible contamination from the septum,

while the rest continued on to the liner.
while the rest continued on to the liner.

A fraction of the gas—1 mL/min—
A fraction of the gas—1 mL/min—

flowed into the column,
flowed into the column,

but most—100 mL/min—
but most—100 mL/min—

is swept away via the split vent.
is swept away via the split vent.

This ratio—
This ratio—

the split ratio—
the split ratio—

is determined by the user before starting the analysis.
is determined by the user before starting the analysis.

Split ratios typically vary between 5:1 to 500:1,
Split ratios typically vary between 5:1 to 500:1,

with the higher the ratio,
with the higher the ratio,

the lower the amount of sample that enters the column
the lower the amount of sample that enters the column

compared to what passes out the split vent.
compared to what passes out the split vent.

During injection,
During injection,

the sample is injected into the liner and vaporizes.
the sample is injected into the liner and vaporizes.

Since our example has a high split ratio of 100:1,
Since our example has a high split ratio of 100:1,

one part goes onto the column
one part goes onto the column

while one hundred parts of the sample exit out the split vent.
while one hundred parts of the sample exit out the split vent.

Now let’s look at an example of a splitless injection.
Now let’s look at an example of a splitless injection.

In a splitless injection,
In a splitless injection,

the split vent is closed and left closed before and during the injection.
the split vent is closed and left closed before and during the injection.

As there is no split flow,
As there is no split flow,

the total flow is set at a dramatically reduced flow rate.
the total flow is set at a dramatically reduced flow rate.

Here, it’s only 4 mL/min.
Here, it’s only 4 mL/min.

3 mL/min passed through the septum purge, while the remaining 1 mL/min entered the column.
3 mL/min passed through the septum purge, while the remaining 1 mL/min entered the column.

During injection,
During injection,

the sample remains within the liner for longer
the sample remains within the liner for longer

before entering the column due to the lower flow rate.
before entering the column due to the lower flow rate.

Once sufficient time has elapsed after injection,
Once sufficient time has elapsed after injection,

the split vent opens to purge the inlet.
the split vent opens to purge the inlet.

This duration—
This duration—

known as the splitless hold time—
known as the splitless hold time—

is calculated to be long enough
is calculated to be long enough

to allow the maximum vaporization and transfer of analytes to the column.
to allow the maximum vaporization and transfer of analytes to the column.

So which injection technique should you use?
So which injection technique should you use?

It depends on the concentration of your desired analytes within your sample,
It depends on the concentration of your desired analytes within your sample,

the sensitivity of your detector,
the sensitivity of your detector,

and any method requirements.
and any method requirements.

Split injection is ideal
Split injection is ideal

if your analyte concentration is high enough
if your analyte concentration is high enough

to afford an on-instrument dilution
to afford an on-instrument dilution

and still meet required detection limits.
and still meet required detection limits.

The higher flow rates through the inlet lead to sharp, narrow peaks,
The higher flow rates through the inlet lead to sharp, narrow peaks,

while simultaneously reducing the time for adverse interactions to occur.
while simultaneously reducing the time for adverse interactions to occur.

However, since most of your sample is vented,
However, since most of your sample is vented,

your detection limits are much higher.
your detection limits are much higher.

While this can be problematic for less-sensitive detectors,
While this can be problematic for less-sensitive detectors,

a detector with higher sensitivity
a detector with higher sensitivity

such as an ECD or an MS/MS help make split injection possible.
such as an ECD or an MS/MS help make split injection possible.

But if your analyte concentration is very low, you may need to perform a splitless injection.
But if your analyte concentration is very low, you may need to perform a splitless injection.

Splitless injections excel at trace analyses.
Splitless injections excel at trace analyses.

Since all the flow is directed to the column,
Since all the flow is directed to the column,

you can transfer the majority of your sample.
you can transfer the majority of your sample.

However, the slower flow rate
However, the slower flow rate

into the column can result in the degradation of active analytes through adsorption and breakdown.
into the column can result in the degradation of active analytes through adsorption and breakdown.

It also leads to increased diffusion, causing band broadening.
It also leads to increased diffusion, causing band broadening.

This is especially noticeable for more volatile analytes,
This is especially noticeable for more volatile analytes,

resulting in wider peaks
resulting in wider peaks

While choosing the right injection technique for your analysis is essential,
While choosing the right injection technique for your analysis is essential,

it’s also important to optimize your injection parameters.
it’s also important to optimize your injection parameters.

This allows you to maximize both analyte transfer
This allows you to maximize both analyte transfer

and injection to injection reproducibility.
and injection to injection reproducibility.

For more information about optimizing for split and splitless injections,
For more information about optimizing for split and splitless injections,

visit our resources below, or visit restek.com
visit our resources below, or visit restek.com