WHAT IT IS
Injection volume range and cycle time are performance specifications of LC autosamplers and injectors. Injection volume range defines the minimum and maximum sample amounts the system can deliver reproducibly. Cycle time is the time required for an autosampler to complete one injection cycle, including vial access, needle wash, injection, and valve reset. Together, these parameters determine flexibility, throughput, and suitability of the system for different LC applications.
HOW IT WORKS
Injection Volume Range - Controlled by the injector valve and loop, or by autosampler programming. Small-volume systems (nano- and micro-LC) require sub-µL precision, while preparative LC uses mL-scale injections. The autosampler must handle this range with minimal error.
Cycle Time - Autosamplers move to the sample vial, aspirate the programmed volume, wash the needle, switch the valve, and deliver the sample into the flow path. The duration of these steps defines the injection cycle. Faster cycle times enable higher throughput but require optimized mechanics and washing efficiency.
TYPICAL RANGES
Nano-LC: <1 nL to 500 nL.
Micro-LC: 0.1–5 µL.
Analytical HPLC: 1–100 µL (most common).
Semi-Preparative LC: 0.1–2 mL.
Preparative LC: 1–20 mL or more, depending on column size.
Cycle Time: Modern autosamplers achieve 10–30 seconds per injection, including wash steps. High-throughput systems can reduce this to <10 seconds, while more complex workflows (needle rinsing, multi-step injections) may take longer.
KEY FEATURES
Programmable Volumes: Autosamplers allow precise setting across their full volume range.
Loop Flexibility: Different loop sizes can extend the working range.
Wash Stations: Needle wash reduces carryover but adds to cycle time.
Throughput Design: Robotic loaders and plate-based systems minimize delays between injections.
Precision: Relative standard deviation (RSD) must remain <1% across the working range.
IMPACT ON PERFORMANCE
Quantitative Accuracy: Accurate injection volumes are essential for reproducibility.
Sample Economy: Narrow volume control reduces waste, important for limited samples.
Throughput: Short cycle times maximize productivity in routine or high-throughput screening.
Carryover Control: Adequate washing reduces contamination but lengthens cycle time.
System Flexibility: Wide injection volume ranges allow one autosampler to serve nano-, analytical-, and preparative applications.
CHALLENGES AND LIMITATIONS
Hardware Constraints: Each autosampler has fixed minimum and maximum volumes; outside this range precision drops.
Trade-Offs: Faster cycle times may compromise wash efficiency and increase carryover.
Scaling Issues: Injection volume must match column ID; overloading distorts peaks.
Maintenance Needs: Valves, syringes, and needles wear, reducing precision over time.
Application Limits: No single system covers the full range from nL to mL; specialized injectors are required.