LC Technology key terms

A unitless measure of how long a compound stays in the stationary phase relative to the mobile phase, calculated as (retention time minus void time) divided by void time. Values ideally fall between 1 and 10.

The volume of mobile phase needed to sweep an unretained solute through the column. It marks the earliest possible elution time and serves as the baseline for calculating retention factor and plate count.

The ratio of two retention factors for adjacent peaks, describing how well the stationary and mobile phases distinguish two compounds. A value near 1.0 signals poor separation regardless of efficiency.

A number expressing how completely two peaks are separated, based on the difference in their retention times divided by the average peak width. A value of 1.5 or greater generally means baseline separation.

A measure of column efficiency derived from retention time and peak width, indicating how many equilibration steps a column provides. Higher values give narrower peaks and better separation of closely eluting compounds.

A model describing how linear velocity of the mobile phase affects plate height through eddy diffusion, longitudinal diffusion, and mass-transfer resistance. It explains why flow rate must be optimized for efficient separations.

The speed at which mobile phase travels through the column, usually expressed in millimeters per second. It is distinct from volumetric flow rate and is the variable plotted in Van Deemter curves.

A technique in which mobile phase composition changes during the run, usually increasing organic solvent strength. It compresses broad retention ranges, sharpens peaks, and is common for complex mixtures in reversed-phase separations.

A separation mode in which mobile phase composition stays constant throughout the run. It is simple and reproducible but limited when samples contain compounds with widely different polarities.

The liquid that carries the sample through the column. Its composition, pH, and additives control retention, selectivity, and peak shape, making it a primary tool for method development.

The packed material inside the column that interacts with analytes and slows their movement. Its chemistry, particle size, and pore structure determine selectivity, efficiency, and backpressure.

A chemical treatment that blocks unreacted silanol groups on silica-based stationary phases. It reduces secondary interactions with basic compounds, improving peak shape and reducing tailing.

The nominal diameter of packing particles, commonly 1.7 to 5 micrometers. Smaller particles improve efficiency and speed but raise backpressure, requiring instruments rated for ultra-high-pressure operation.

The pressure required to push mobile phase through the flow path and column. It rises with flow rate, viscosity, and smaller particles, and abnormal increases often signal a blockage or column problem.

A short, inexpensive column placed before the analytical column to trap particulates and strongly retained contaminants. It protects the main column and is replaced periodically to extend column life.

A porous filter disc at the ends of a column or in-line filter that holds packing in place and blocks particles. A clogged frit is a frequent cause of rising pressure or flow loss.

The volume between the point where solvents mix and the head of the column. It delays the arrival of gradient changes and must be considered when transferring methods between instruments.

A component that meters each solvent into the pump so the programmed mobile phase ratio is delivered. Faulty valves cause retention shifts, baseline noise, or erratic composition during gradients.

A piston-driven device that delivers mobile phase at a controlled flow rate. Stable, pulse-free flow is essential for reproducible retention times and reliable quantitation.

An instrument module that draws sample from vials and injects a precise volume onto the column. It controls injection volume, needle wash, and sample temperature, all of which affect reproducibility.

The amount of sample solution introduced onto the column, typically microliters. Larger volumes increase sensitivity but can distort peaks, especially with weak solvents or small-diameter columns.

Contamination of a later injection by residue from an earlier, highly concentrated sample. It causes false peaks or inflated results and is controlled with needle washes and blank injections.

A solvent rinse of the injection needle and loop between samples to prevent carryover. Choosing a wash solvent that dissolves the analytes without harming the sample is important.

The elution power of the liquid in which the sample is dissolved. A solvent stronger than the mobile phase can cause peak distortion or splitting, so weaker solvents are often preferred.

A sample cleanup technique in which analytes are retained on a sorbent, washed, and then eluted. It removes matrix interferences, concentrates samples, and improves selectivity before chromatography.

A cleanup step that adds acid, salt, or organic solvent to biological samples so proteins denature and settle out. The supernatant is then injected, reducing column fouling and matrix interference.

A change in analyte response caused by other components in the sample, often suppressing or enhancing ionization or detection. It can bias results and is assessed with post-column infusion or spiked matrices.

A compound added at a fixed amount to every sample and calibration standard to correct for injection variability and matrix effects. It should be chemically similar to the analyte but absent from the sample.

A quantitation approach that compares sample peak responses to a calibration curve prepared from known standards. It assumes consistent injection volume and detector response across samples.

A plot of detector response versus known analyte concentration used to quantify unknowns. Its linear range, slope, and residuals determine the working concentration range of the method.

The lowest analyte amount that can be reliably distinguished from noise, often estimated as three times the signal-to-noise ratio. It indicates method sensitivity but not quantitation accuracy.

The lowest concentration that can be measured with acceptable precision and accuracy, commonly taken as ten times the signal-to-noise ratio. It defines the lower end of the validated range.

The height of an analyte peak compared with the variation of the baseline noise. It guides detection and quantitation limits and helps judge whether small peaks are real.

Random fluctuation in the detector signal when no analyte is eluting. High noise reduces sensitivity and can come from the lamp, mobile phase degassing, or electrical interference.

Removal of dissolved gases from the mobile phase using vacuum, helium sparging, or inline membranes. Without it, bubbles form in the pump and detector, causing pressure spikes and noisy baselines.

Asymmetric peak shape with a trailing edge, often caused by secondary interactions, extra-column volume, or column aging. It reduces resolution and can distort integration results.

The width of a peak measured at half its maximum height, used to calculate plate count and resolution. It is less sensitive to baseline noise than measurements taken at the peak base.

The process of defining peak start, apex, and end so the software can calculate area or height. Consistent integration parameters are essential for reproducible quantitation across a batch.

A solution that resists pH change, commonly used in mobile phases to control ionization of analytes and silanols. Proper pH improves peak shape and retention reproducibility.

The documented process of proving a method is suitable for its purpose by testing accuracy, precision, specificity, linearity, range, detection limits, and robustness. It supports regulatory acceptance and routine use.

Checks run before or during an analytical batch to confirm the instrument and method perform as expected. Typical criteria include resolution, tailing factor, plate count, and retention time precision.

A quality system of regulations and practices governing nonclinical laboratory studies, covering organization, facilities, equipment, and record keeping. It ensures data are reliable, traceable, and defensible.

A secure, time-stamped record of all changes made to data or methods in a chromatography data system. It supports data integrity and is required under regulated laboratory compliance frameworks.

Digitally stored analytical data and signatures that must be protected, attributable, and retrievable under data-integrity rules. Controls include access permissions, audit trails, and backup procedures.

A document summarizing a chemical's hazards, handling precautions, exposure limits, and first-aid measures. It is a core reference for safe laboratory work and emergency response.

Barrier gear such as gloves, goggles, and lab coats worn to protect against chemical splashes, vapors, and contact. Selection depends on the hazards of the solvents and samples in use.

A ventilated enclosure that draws vapors and aerosols away from the operator. It is used when handling volatile solvents, preparing mobile phases, and working with toxic samples.

The compliant collection, labeling, and removal of spent solvents and sample residues. Segregating incompatible streams and following local regulations prevent environmental release and safety incidents.