Evaluating Duplicate Results Demonstrates Differences Between Direct and Canister Sampling Methods

Abstract Field duplicates of environmental samples are collected to evaluate field and laboratory precision. This study used field duplicate results to assess whether samples analyzed for volatile organic compounds collected using reusable summa canisters exhibit carryover contamination when compared to results for samples collected using direct sampling methods (e.g., soil gas collected by mobile laboratories via dedicated tubing and syringes or groundwater collected using disposable vials). This study utilized data sets of groundwater, soil gas, and indoor air from samples collected between 2000 and 2024 from multiple project sites and analyzed by different analytical laboratories. Volatile organic compound data were evaluated by sampling method (direct or reusable canister), analytical method, and medium following a similar approach to the one described in a prior study by McHugh et al. (2018). This evaluation included assessing the magnitude of the differences between primary and duplicate sample results by calculating percent differences and comparing the number of single‐detect pairs versus non‐detect pairs, which could be an indication of carryover contamination. Results showed that water samples collected using disposable vials and soil gas samples collected using direct sampling methods had greater precision (i.e., lower percent differences) and lower occurrences of single‐detect pairs compared to soil gas or indoor air samples collected using evacuated canisters; confirming that reusable canisters may contain carryover contamination. Other factors contributing to uncertainty (i.e., low detected concentrations, sampling equipment certification process, quality control procedures, and laboratory best practices) were also considered to explain the discrepancies identified in this study.