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Quantifying sampling contribution to measurement uncertainty in microbiological groundwater analysis
Obradović, Vesna
Vučković, Tanja
Perović, Marija
Sampling is often an underestimated source of measurement uncertainty in microbiological water quality assessment. This study quantifies the contribution of groundwater sampling to overall measurement uncertainty using a balanced split-level design and statistical approaches recommended by ISO 29201 (Annex H) and EURACHEM (Annex D). Groundwater samples were collected during 2023–2024 across different seasons following the EN ISO 19458 sampling protocol. Ten duplicate samples were taken under reproducible field conditions by two operators at the same location within a short time interval. Each sample and its replica were analyzed in duplicate for aerobic mesophilic bacteria (CFU·mL⁻¹) using Standard Method 9215B. Data were processed using range statistics (split level design), classical one-way ANOVA, and robust ANOVA (RANOVA) after logarithmic transformation. Results showed that the relative standard uncertainty of sampling (23.35–24.45%) was almost twice the analytical uncertainty (12.53%) and approached the total measurement uncertainty (26.50%). The expanded sampling uncertainty (k=2.95% confidence) reached 46.7%, demonstrating that sampling is a dominant contributor to uncertainty in microbiological groundwater assessment. Although EN ISO 19458 showed acceptable performance (RSD < 30%), the results reveal that sampling uncertainty is frequently underestimated and should be routinely included in ISO/IEC 17025 uncertainty evaluations for microbiological groundwater analysis.
engleski
2026
Ovo delo je licencirano pod uslovima licence
Creative Commons CC BY-NC-ND 4.0 - Creative Commons Autorstvo - Nekomercijalno - Bez prerada 4.0 International License.
http://creativecommons.org/licenses/by-nc-nd/4.0/legalcode
groundwater sampling, measurement uncertainty, microbiological analysis, sampling uncertainty