Uncertainty evaluation of an ammonia-nitrogen automatic monitoring instrument using the minimal-sample method

In water environment monitoring, ammonia nitrogen（NH₃—N） automatic analyzers are widely used for online determination of NH₃—N concentrations in surface water. However, in practical verification and routine operation, limited repeated measurements due to time and efficiency constraints often result in insufficient sample sizes, posing challenges to uncertainty evaluation. This study applies an improved extremely small-sample grey uncertainty evaluation method to analyze the measurement uncertainty of indication errors of an ammonia nitrogen automatic analyzer, and compares the results with those obtained using the traditional Bessel formula. The proposed method significantly enhances the stability and reliability of uncertainty evaluation under small-sample conditions, providing important support for improving data quality and optimizing verification efficiency in ammonia nitrogen automatic monitoring.