Evaluation of Automated Solid-Phase Extraction for Nitrosamines Using US EPA Method 521

May 1, 2016
Kevin A. Schug

Kevin A. Schug is a Full Professor and Shimadzu Distinguished Professor of Analytical Chemistry in the Department of Chemistry & Biochemistry at The University of Texas (UT) at Arlington. He joined the faculty at UT Arlington in 2005 after completing a Ph.D. in Chemistry at Virginia Tech under the direction of Prof. Harold M. McNair and a post-doctoral fellowship at the University of Vienna under Prof. Wolfgang Lindner. Research in the Schug group spans fundamental and applied areas of separation science and mass spectrometry. Schug was named the LCGC Emerging Leader in Chromatography in 2009, and most recently has been named the 2012 American Chemical Society Division of Analytical Chemistry Young Investigator in Separation Science awardee.

,
Doug D. Carlton Jr.

,
The University of Texas at Arlington

Special Issues

Special Issues, Special Issues-05-01-2016, Volume 14, Issue 2
Page Number: 57

Disinfection by-products (DBP) are an ever-present nuisance in the efforts to purify drinking water, wastewater, and municipal waters from various sources.

 

Disinfection by-products (DBP) are an ever-present nuisance in the efforts to purify drinking water, wastewater, and municipal waters from various sources. An emerging class of DBP compounds with health effects is nitrosamines which result from chloramination or chlorination if the water is nitrogen-rich. Five of these nitrosamines have been listed on the US EPA’s new Contaminant Candidate List (CCL-3). Of the nitrosamines, the most common and problematic is N-nitrosdimethylamine (NDMA). The maximum admissible levels set by the US EPA are 7 ng/L for NDMA and 2 ng/L for N-nitrosodiethylamine (NDEA).

The US EPA developed method 521 to measure seven nitrosamines in drinking water using solid phase extraction (SPE) and GC–MS-MS with large volume injection and chemical ionization for sensitive analysis. Sample preparation for EPA 521 involves passing 0.5 L of sample water through 6-mL coconut charcoal SPE cartridges. Nitrosamines are then eluted with methylene chloride and further concentrated to 1 mL. Analysis is then performed with tandem mass spectrometry after gas chromatography separation (GC–MS-MS). A large volume injection (LVI) of 8 µL onto the GC column is used to increase sensitivity. Chemical ionization (CI) is used to preserve the molecular ion with minimal adducts. An ion trap or triple quadrupole MS is used for MS-MS. The purpose of this application note is to demonstrate that in addition to modern measurement technology the addition of automated solid phase extraction can improve method performance (1).

Results and Discussion

The chromatography is shown in Figure 1 and shows excellent separation of the desired compounds in a 12-min run, shortened from the suggested separation methods of 32 and 42.5-min in Method 521.

Figure 1: 5-ng/L standard with internal standard and surrogate added. Zoom used to show the detail of peaks. 1. NDMA, 2. NMEA, 3. NDEA, 4. NPYR, 5. NDPA, 6. NPIP, 7. NDBA, SS NDMA-d6, IS NDPA-d14.

 

Precision of the SmartPrep® Extractor and manual SPE were compared by extracting three concentrations, 5, 20, and 50 ng/ mL, with three cartridges each and is shown in Table I. It can be seen that precision between three replicates is better for the automated system rather than the manual system. Although the method very specifically mentions care in not letting the cartridge go dry once the process is started, it is difficult in a multi-step process to be as reproducible as an automated system.

 

Reference

  • D.D. Carlton Jr. and K.A. Schug, “Evaluation of Automated Solid-Phase Extraction for Nitrosamines Using US EPA Method 521,” AN1001504_01, www.horizontechinc.com (2015).

 

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