Grantee Research Project Results
2000 Progress Report: Molecular Weight Separation and HPLC/MS/MS Characterization of Previously Unidentified Drinking Water Disinfection By-Products
EPA Grant Number: R826834Title: Molecular Weight Separation and HPLC/MS/MS Characterization of Previously Unidentified Drinking Water Disinfection By-Products
Investigators: Minear, Roger A. , Barrett, Sylvia
Institution: University of Illinois Urbana-Champaign , Metropolitan Water District of Southern California
EPA Project Officer: Hahn, Intaek
Project Period: November 1, 1998 through October 31, 2001
Project Period Covered by this Report: November 1, 1999 through October 31, 2000
Project Amount: $363,591
RFA: Drinking Water (1998) RFA Text | Recipients Lists
Research Category: Drinking Water , Water
Objective:
The overall goal of this project is the development of new approaches for better characterizing disinfection byproduct (DBP) molecular weight profiles by using tandem mass spectrometry (MS/MS) techniques. A prerequisite to making such procedures meaningful is development of preseparation procedures that will simplify the mass spectral data. The objectives of the reporting period were to: (1) investigate both electrospray positive and negative ion modes. Use of electrospray ionization (ESI) in the negative-ion mode may emphasize certain compound groups such as carboxylic acids and phenolic compounds. It also may give direct information on the chlorine content of certain ion peaks in the form of chloride ions when MS/MS is used; (2) investigate and optimize experimental conditions to obtain the lowest background noise and the highest ion intensities using model compounds; (3) study the effects of chlorination conditions (e.g., the ratio of chlorine to total organic carbon [Cl:TOC], chlorination pH and contact time) on the product formation patterns; and (4) study the MS/MS of chlorinated Suwannee River fulvic acid (SRFA) samples.Progress Summary:
During the past period, we have focused on the identification of chlorinated disinfection byproducts in drinking water through optimizing electrospray/MS/MS. Information has been developed on determining levels of halogenated natural organic matter (NOM) required to obtain measurable mass spectra in both stages of the MS system using surrogate compounds and their mixtures and chlorinated NOM represented by SRFA and a hydrophylic NOM. Studies have been conducted on two instruments, Micromass AutoSpe-oa time-of-flight (TOF) mass spectrometer at MWDSC and a TSQ 7000 ESI quadrapole ion trap mass spectrometer at Kyoto University. From these studies, we have found information on optimal solvent composition, flow rates, and scan rates for quality spectra. Using individual known compounds, their mixtures, and chlorinated SRFA, variables for the second stage MS were examined as to the balance between obtaining spectral finger prints and demonstrating the presence of chlorine in the mass selected.The MWDSC group focused on: (1) optimization of experiment parameters; (2) MS analysis of chlorinated SRFA solutions and the fractions of SRFA from size exclusion chromatography (SEC); and (3) MS/MS studies of dichloroacetic acid (DCAA), dichloro-2-propanone (DCP), and chlorinated SRFA. Seven solvents were evaluated in the ESI negative ion mode through direct infusion into the ESI source: (1) water (H2O); (2) acetonitrile (CH3CN); (3) methanol (MeOH); (4) 1:1 CH3CN:H2O; (5) 1:1 CH3CN:H2O with 1 percent NH4OH; (6) 1:1 MeOH:H2O; and (7) 1:1 isopropanol:H2O.
Experimental parameters were investigated and optimized for the analysis of the chlorinated SRFA samples on the AutoSpec-oaTOF mass spectrometer using ESI negative ion mode. The optimized conditions were found to be 1:1 CH3CN:H2O as the mobile phase, flow rate of the mobile phase at 40 µL/min, and scan rate at 5 sec/decade. The presence of DCP was suggested by the mass spectra of the chlorinated SRFA samples, but not by the mass spectra of the chlorinated SRFA samples subjected to SEC. This implied possible strong interactions between DCP and the column stationary phase employed for the SEC separations. Chlorination conditions, such as the ratio of Cl:TOC (w/w), pH of chlorination, and contact time, affected the ion peak distribution of the mass spectra of chlorinated SRFA samples.
The MWDSC instrument was capable of producing the MS/MS spectra of DCAA at 0.1 ppm, and capable of identifying DCP as one of the chlorinated products of SRFA. These results suggest that the instrument has demonstrated potential of identifying unknown chlorinated constituents from a complex mixture, using MS/MS as a powerful tool.
Using the Kyoto University instrument, the UIUC group looked at optimization of the quadrapole instrument by examining the formation of chloride ions in the second stage MS with several known chlorine-containing compounds, including dichloroacetic acid, 2,4,6-trichlorophenol and chlorophenol red sodium salt. Also, we searched for appropriate MS conditions for use in finding specific structural information. The parameters examined included carrier fluid flow rate, collision induced dissociation (CID) gas pressure, CID energy. The results show that:
- Carrier fluid flow rate had a strong influence on the efficiency of electrospray ionization. The appropriate carrier fluid flow rates were in the range of 10-100 L/min.
- CID energy dramatically affected the formation of Cl ion for the second MS. The appropriate CID energy was in the range of 35-45 eV.
- CID gas pressure had a significant effect on the formation of Cl- in the second MS. The appropriate CID gas pressure was in the range of 2.5-3.5 mT.
- The formation of chloride ions in the second stage MS requires strong fragmentation, but obtaining structural information requires light fragmentation to varying degrees.
- For the type of instrument used, the appropriate ESI/MS/MS conditions for the formation of chloride ion in the second MS are: carrier fluid flow rate, 10-100 L/min; CID energy, 35-45 eV; and CID gas pressure, 2.5-3.5 mT. The appropriate ESI/MS/MS conditions for seeking structural information of the unknown chlorinated DBPs are: carrier fluid flow rate, 10-100 µL/min; CID gas pressure, 0.5-1.0 mT; and gradually increase CID energy.
- The conditions obtained were demonstrated to be effective in identifying chlorinated compounds in a simple simulated mixture with relatively low concentrations of each component and in a chlorinated SRFA sample.
Future Activities:
The next steps in this research project will include:- Fractionation of chlorinated natural organic matter samples by ultrafiltration membranes will be conducted to obtain chlorine profiles on size exclusion columns (SEC) and other HPLC columns by using radioisotope 36Cl, and characterization of the chlorine-containing SEC fractions by electrospray/MS/MS.
- The effects of chlorination conditions, such as Cl:TOC ratios, chlorination pH, chlorination reagents and contact time, will be investigated in more detail.
- Using a mixture of standards, high resolution ESI will be investigated, which may provide accurate mass determination at the first stage (Dm=0.1 for m/z 500 at 5,000 resolution) and better definition of parent ions for MS/MS.
- Solid-phase extraction will be explored as a preconcentration step prior to mass spectrometry analysis.
Journal Articles:
No journal articles submitted with this report: View all 25 publications for this projectSupplemental Keywords:
drinking water, disinfection byproducts, molecular weight, HPLC, SEC, MS/MS., RFA, Scientific Discipline, Water, Waste, Chemical Engineering, Physics, Environmental Chemistry, Chemistry, chemical mixtures, Analytical Chemistry, Drinking Water, alternative disinfection methods, complex mixtures, monitoring, public water systems, human health effects, molecular weight separation, exposure and effects, chemical byproducts, disinfection byproducts (DPBs), exposure, community water system, HPLC, toxicity, treatment, tandem mass spectrometry, water quality, DBP risk management, drinking water contaminants, drinking water treatment, other - risk managementProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.