User manual

70 Agilent 1260 Infinity High Performance Autosampler User Manual

5 Optimizing Performance

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 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 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