Applied Statistical Validation of GC–FID Acetaldehyde Determination in Extra-Neutral Alcohol Using Recovery, Relative Bias, and Factorial Analysis of Variance

Acetaldehyde is routinely monitored in neutral alcohol, but pooled precision summaries can obscure changes in performance across the working range. This study evaluated 446 valid GC–FID verification results obtained by three anonymized analysts on two gas chromatographic systems (GC 8890 and GC 7890B) at 0.6, 2.5, and 9.0 mg L−1. The analysis included measured concentration, recovery, relative bias, relative standard deviation (RSD), confidence intervals, and fixed-effect factorial analysis of variance (ANOVA). Mean recoveries for the GC 8890 and GC 7890B systems were 48.7% and 157.2% at 0.6 mg L−1, 92.1% and 124.8% at 2.5 mg L−1, and 92.0% and 103.1% at 9.0 mg L−1, respectively. Recovery RSD decreased from 47.8% and 18.4% at the lowest level to 4.2% and 3.0% at the highest level. Type III ANOVA identified significant verification-level, analyst, GC-system, and interaction effects. A contextual comparison with concentration-matched AOAC Appendix F targets classified both systems as outside the recovery and RSD benchmarks at the lowest level, showed system-specific partial conformity at the middle level, and placed both systems within the screening benchmarks at the highest level. The contribution of the study is an integrated decision framework in which predefined recovery and RSD targets are interpreted together with factorial interactions to determine when results may be pooled and when level- or system-specific control is required.