How To Achieve Higher Injection Volumes - Agilent Technologies 1290 Infinity LC System System Manual And Quick Reference

How to Achieve Higher Injection Volumes

The standard configuration of the Agilent 1290 Infinity Autosampler includes
a variable volume sample loop for up to 20 µl injections. The metering device
can inject a maximum volume of 40 µl and the sample loop cartridge can be
exchanged to allow this (refer to the 1290 Infinity Autosampler manual for
details). 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 big 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. A rough
guide to maximum injection volume can be gained by looking at the volume of
the column (see
volumes of about 5 % of the column volume might be achieved whilst
maintaining good resolution and peak dispersion.
Agilent 1290 Infinity LC System Manual and Quick Reference
Optimization of the Agilent 1290 Infinity LC System
Table 7 on page 44) – in a gradient separation injection

How to Achieve Higher Injection Volumes

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