Challenges analyzing perchloroethylene in water samples

Objective: To explore the temperature and holding time constraints of water quality samples outlined in EPA Method 524.2. Methods: Prepare 160 water samples representative of a municipal water source with a pH of 7.2 Spike with Perchloroethylene (PERC) to achieve a concentration of 5 ppm (v/v). Hold samples at four temperatures: 3℃, 5℃, 20℃, and 25℃ for 27 days. Samples were analyzed every three days for 27 days using Inficon’s HAPSITEⓇ ER. An additional analysis of 32 samples was conducted to identify proper mixing time for PERC in water. A regression model with a quadratic function was performed to determine statistically significant differences between concentration and time; concentration and time with temperature combined. A One Way Analysis of Variance (ANOVA) test was performed to identify statistically significant differences between concentration and temperature. A coefficient of variation was used to determine adequate mixing time. Results: There is an indication of an effect in the concentration of PERC attributed to time and temperature. Ideal mixing time to achieve a 5ppm concentration under ambient conditions was identified to be within 1.5 to 2.5 hours. Conclusion: Complexity of PERC’s solubility and volatility during analysis was not anticipated. Using a phosphate buffer solution creates a “salting out effect” where it disrupts the distribution of PERC in water. Physical properties, although incorporated as part of the challenges, became a crucial factor in the variation of PERC concentration.