Method validation is the documented process of proving that an analytical method performs reliably for its intended application. Regulatory agencies such as the ICH, USP, FDA, and ISO require validation for methods used in pharmaceutical release testing, clinical diagnostics, environmental compliance, and food safety. Validation ensures that the method generates defensible, reproducible data within defined acceptance criteria.
Accuracy (trueness) measures how close the measured value is to the true value and is assessed through spike recovery experiments, analysis of certified reference materials (CRMs), or comparison with a reference method. Precision describes the closeness of replicate measurements and is expressed as relative standard deviation (%RSD). Repeatability (within-run precision) is obtained by analyzing replicates under the same conditions on the same day. Reproducibility (between-laboratory precision) assesses performance across different laboratories, analysts, and instruments. Intermediate precision bridges the two, varying factors such as day, analyst, or instrument within a single laboratory.
Specificity (selectivity) demonstrates that the method measures the analyte unequivocally in the presence of interferents — matrix components, degradation products, or related substances. For chromatographic methods, specificity is shown by baseline resolution of all peaks. The detection limit (LOD) and quantitation limit (LOQ) define the method’s low-concentration capability. LOD is the smallest detectable signal (typically S/N ≥ 3 or 3.3σ/S), while LOQ is the lowest concentration that can be quantified with acceptable accuracy and precision (S/N ≥ 10 or 10σ/S).
Linearity is the method’s ability to produce test results proportional to the analyte concentration over a given range, demonstrated by the correlation coefficient (r² ≥ 0.995 or 0.999), y-intercept, and residual analysis. The range is the interval between the upper and lower concentrations where the method has demonstrated acceptable linearity, accuracy, and precision. Robustness measures the method’s resistance to deliberate variations in parameters such as pH, temperature, flow rate, or injection volume. Ruggedness (now often folded into robustness) historically refers to reproducibility under different operational conditions.
System suitability testing (SST) is performed before and during each analytical run to verify that the instrument and method are performing acceptably. SST parameters include resolution, tailing factor, theoretical plates, and precision of replicate injections. A formal validation protocol specifies the experiments, acceptance criteria, and statistical methods in advance. The final validation report documents all results, deviations, and a statement of the method’s intended scope and limitations. Fully validated methods provide the foundation for reliable analytical data across all regulated industries.
