Autosampler

What is an autosampler?

An autosampler automatically selects and introduces samples into an analytical system. It replaces manual injection and allows large sequences of samples, standards, blanks and quality controls to be analysed reproducibly.

Autosamplers are widely used with LC–MS and GC–MS.

How it works

Samples are placed in vials, wells or plates at defined positions. Software instructs the autosampler to select a particular sample and withdraw a programmed volume.

In an LC system, a typical sequence is:

Sample vial → sampling needle → sample loop → injection valve → mobile phase → LC column

The mobile phase then carries the injected sample through the chromatographic system.

GC autosamplers commonly use a syringe to withdraw a small volume of sample and inject it through the GC inlet septum.

Main components

Typical components include:

• sample tray or well plate

• sampling needle

• syringe or metering device

• sample loop

• injection valve

• needle wash station

• waste line

• temperature-controlled sample compartment

Important parameters

Injection volume determines how much sample enters the system. Excessive injection volumes can overload the chromatographic column.

Needle wash conditions affect carryover.

Sample temperature can influence analyte stability.

Draw and injection speed can matter for viscous samples or very small volumes.

Carryover

Carryover occurs when material from one injection appears in a later injection.

A useful diagnostic sequence is:

High-concentration sample → blank

If analyte signal appears in the blank, carryover should be investigated.

Possible sources include the needle, injection valve, sample loop, tubing and column.

Common problems

Key takeaway

The autosampler determines how reproducibly a defined amount of sample enters the analytical system.