WHAT IT IS
An autosampler in liquid chromatography (LC) is a device that automates the process of introducing liquid samples into the chromatographic system. Autosamplers are widely used in analytical, preparative, and specialty LC systems. Depending on the instrument design, an autosampler may be fully integrated, modular, or optional.
HOW IT WORKS
The autosampler is located between the mobile phase delivery system and the chromatographic column. Its main functions are:
Sample Storage - Samples are placed in vials, tubes, or well plates. Advanced units include thermostats or cooling compartments to preserve temperature-sensitive analytes.
Positioning - A robotic arm or needle moves to the selected vial or well.
Aspiration - A defined volume of liquid is withdrawn with a syringe or needle.
Injection - The sample is delivered into the mobile phase stream through a valve system, ensuring reproducible transfer to the column.
Cleaning - Needles, loops, and syringes are rinsed between injections to minimize carryover.
Autosamplers can also schedule multiple runs, repeat injections, or dilute samples automatically, depending on system configuration.
TYPES
Integrated Autosamplers: Built directly into the LC system and controlled via the main software. They offer seamless operation and are the most common in modern instruments.
Modular Autosamplers: Stand-alone devices that can be connected to different LC setups, providing flexibility for system upgrades or reconfiguration.
Optional Autosamplers: Available as add-on modules for entry-level instruments that otherwise rely on manual injection.
Specialized Autosamplers: Tailored to specific needs, such as cooled autosamplers for thermally unstable samples, high-capacity autosamplers for screening studies, or low-volume autosamplers for micro- and nano-LC.
INJECTION MODES
Autosamplers typically support several injection techniques, which determine how the sample enters the flow path:
Full-Loop Injection: A sample loop is completely filled with liquid and then introduced into the system. Provides high reproducibility but requires larger sample volumes.
Partial-Loop Injection: Only part of the loop is filled, allowing smaller sample volumes while retaining good accuracy.
µL-Pickup Injection: The needle aspirates exactly the required sample volume with minimal waste, important for scarce or expensive samples.
ADVANCED FEATURES
Many autosamplers provide additional functionality:
High-Capacity Trays: Can hold dozens to hundreds of vials, or multi-well plates (96 or 384), supporting high-throughput workflows.
Temperature Control: Cooling (down to ~4 °C) or heating maintains sample stability during long sequences.
Sample Preparation: Some units can perform dilution, reagent addition, mixing, or internal standard spiking automatically.
Carryover Reduction: Enhanced washing protocols reduce contamination between injections.
Adaptability: Compatible with analytical LC, semi-preparative systems, and micro/nano-LC where extremely low injection volumes (nL to µL) are required.
ADVANTAGES
Reproducibility: Consistent injection volumes improve precision compared with manual handling.
High Throughput: Enables long, unattended sequences of injections, essential for routine testing and screening.
Flexible Formats: Accepts vials, tubes, or well plates depending on laboratory workflow.
Sample Protection: Cooling and sealing prevent degradation of unstable or volatile analytes.
Workflow Integration: Can be combined with dilution and mixing steps to streamline analysis.
CHALLENGES AND LIMITATIONS
Instrument Cost: Autosamplers significantly increase the price of LC systems, especially for high-capacity or specialty models.
Maintenance: Syringes, valves, and robotic arms are prone to wear and must be cleaned or replaced regularly.
Carryover Risk: Incomplete washing may contaminate subsequent samples.
Clogging: Fine needles and tubing are sensitive to particulates, requiring well-filtered samples.
Complexity: More moving parts and electronics increase the likelihood of mechanical errors compared with manual injection.