Why is purging the injector in HPLC considered a necessity?

Purge Injector in HPLC: A Necessity

Understanding the HPLC System

Before diving into the role of a purge injector, let’s briefly revisit the core components of a High-Performance Liquid Chromatography (HPLC) system:

basic HPLC system, including pump, injector, column, detector, and waste

• Pump: Delivers the mobile phase (solvent) at a constant flow rate.
• Injector: Introduces the sample into the mobile phase stream.
• Column: Separates the components of the sample based on their interactions with the stationary phase.
• Detector: Detects the separated components as they elute from the column.
• Waste: Collects the effluent from the detector.

The Role of the Purge Injector

A purge injector is a critical component in HPLC systems that ensures accurate and reproducible sample injection. Its primary function is to eliminate any residual sample or solvent from the injection loop before the next injection.

purge injector, showing the injection loop and purge valve

• Injection Loop: A fixed volume loop where the sample is loaded.
• Purge Valve: A valve that allows the mobile phase to flow through the injection loop, cleaning it.

The Purge Process

1. Sample Loading: The sample is loaded into the injection loop using a syringe or autosampler.
2. Injection: The injection valve is switched, injecting the sample into the mobile phase stream.
3. Purge: The purge valve is activated, allowing the mobile phase to flow through the injection loop, removing any residual sample.

Why is Purging Essential?

• Accuracy: Residual sample in the injection loop can lead to carryover, affecting the accuracy of subsequent analyses.
• Precision: Consistent purging ensures reproducible injection volumes.
• Peak Shape: Carryover can distort peak shapes, compromising data quality.
• Sensitivity: Removing residual sample improves the signal-to-noise ratio.

Types of Purge Injectors

• Manual Purge Injectors: Require manual operation of the purge valve.
• Automated Purge Injectors: Integrated into autosamplers for automated purging.

Conclusion

The purge injector is an indispensable component in HPLC systems. By effectively removing residual sample from the injection loop, it contributes significantly to the accuracy, precision, and overall performance of the analysis.