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How to Achieve Higher Injection Volumes
The standard configuration of the Agilent 1260 Infinity Autosampler can
inject a maximum volume of 100 µL with the standard loop capillary. To
increase the injection volume, the Multidraw upgrade kit (G1313- 68711)
can be installed. With the kit, you can add a maximum of 400 µL or
1400 µL to the injection volume of your injector. The total volume is then
500 µL or 1500 µL for the 1260 Infinity Autosampler with 100 µL
analytical head. Note that the delay volume of your autosampler is
extended when using the extended seat capillaries from the multi- draw
kit. When calculating the delay volume of the autosampler you have to
double the volume of the extended capillaries. The system delay volume
due to the autosampler will increase accordingly.
Whenever a method is scaled down from a larger column to a smaller
column it is important that the method translation makes an allowance for
reducing the injection volume in proportion to the volume of the column
to maintain the performance of the method. This is to keep the volume of
the injection at the same percentage volume with respect to the column.
This is particular important if the injection solvent is stronger (more
eluotropic) than the starting mobile phase and any increase will affect the
separation particularly for early running peaks (low retention factor). In
some cases, it is the cause of peak distortion and the general rule is to
keep the injection solvent the same or weaker than the starting gradient
composition. This has a bearing on whether, or by how much, the injection
volume can be increased and the user should check for signs of increased
dispersion (wider or more skewed peaks and reduced peak resolution) in
trying to increase the injection size. If an injection is made in a weak
solvent, then the volume can probably be increased further because the
effect will be to concentrate the analyte on the head of the column at the
start of the gradient. Conversely if the injection is in a stronger solvent
than the starting mobile phase then increased injection volume will spread
the band of analyte down the column ahead of the gradient resulting in
peak dispersion and loss of resolution.
Perhaps the main consideration in determining injection volume is the
diameter of the column as this will have a large impact on peak
dispersion. Peak heights can be higher on a narrow column than with a
larger injection on a wider column because there is less peak dispersion.
With 2.1 mm i.d. columns, typical injection volumes might range up to 5
to10 µl but it is very dependent on the chemistry of the analyte and
mobile phase as discussed above. In a gradient separation, injection
volumes of about 5 % of the column volume might be achieved while
maintaining good resolution and peak dispersion.
1260 Infinity Binary LC - System User Guide
Optimization of the Agilent 1260 Infinity Binary LC
How to Achieve Higher Injection Volumes
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