NDMA – Optimizing Sample Recovery: The Impact of Pressure, Temperature, and Flow

Drinking Water
Poster Presentation

Prepared by E. Turcios, C. Carroll, L. Sanchez, P. Parmar
Orange County Water District, 18700 Ward Street, Fountain Valley, CA, 92708, United States


Contact Information: [email protected]; (714) 378-3342

ABSTRACT

The Orange County Water District (OCWD) currently utilizes an in-house-developed method for monitoring N-Nitrosodimethylamine (NDMA), N-Nitrosodiethylamine (NDEA), N-Nitrosodi-n-propylamine (NDPA), and N-Nitrosomorpholine (NMOR) in drinking water, groundwater, recycled water, surface water, and wastewater using an Isotopic Dilution Analogue (IDA) technique with an automated Solid Phase Extraction (SPE) system.

Utilizing an IDA technique for analyzing nitrosamines presents issues in trying to maintain comparable recovery of the IDA standard between directly prepared calibration standards and extracted samples. OCWD utilizes an automated extraction system to perform sample preparation and has continued to modify the technique to optimize these IDA recoveries. In troubleshooting inconsistent IDA recoveries in samples, OCWD identified several key components that significantly affect the recoveries of these relatively unstable isotopic compounds, including the pressure setting of the automated extraction system, the temperature of sample extract concentration, and the flow rate of the nitrogen gas used to perform extract concentration.

Improvements were also implemented to the nitrosamines calibration standard preparation to further improve method performance. While EPA 521 uses separate primary dilution standards (PDS) for the calibration standard preparation (methylene chloride) and for the sample extraction (water), OCWD converted to preparing calibration PDS and IDA PDS in methanol, allowing to use a single PDS for both direct calibration standard preparation and sample extraction.