Grantee Research Project Results
1999 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, 1998 through October 31, 1999
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 by-product (DBP) molecular weight profiles by using tandem mass spectrometry (MS/MS) techniques. The work that has been done to date is an introduction to the final experimental design.Progress Summary:
Optimization of Size Exclusion Chromatography (SEC). (1) Reproducibility studies show that repeated SEC-UV absorbance (UVA) chromatograms under the same conditions with NH4HCO3 as eluent were almost completely superimposed. Chromatograms with NaCl as eluent could not be reproduced. Peak height increased with each successive run when using NaCl as eluent, implying problems with stabilization of the solid phase matrix. (2) SEC-UVA chromatograms with different eluents show that MilliQ-water is not satisfactory as an eluent. While NaCl gave slightly better separation than NH4HCO3, its lack of reproducibility and non-volatility was considered negative. (3) SEC-UVA chromatograms under different eluent concentrations indicate that the chromatograms became extended with increase in ionic strength. An increase in ionic strength will favor a more coiled conformation due to a shielding of charges, which decreases molecular size. An eluent of 0.03 M NH4HCO3 seems to be the best choice for separation. (4) SEC-UVA chromatograms of Suwannee River fulvic acid (SRFA) and chlorinated SRFA show that chlorination of SRFA caused its UV absorbance to decrease substantially. This has been suggested by other researchers as a result of alteration or destruction of aromatic chromophores in SRFA. (5) SEC chromatograms with UV 254 and 272 nm show that the two chromatograms had very similar shapes and retention times for the large peak and the first small shoulder peak, but had different retention times for the second small shoulder peak. This difference likely results from different absorbance bands from different functional groups. (6) SEC-UVA/TOC chromatograms with NH4HCO3 as eluent show that the inorganic carbon interfered the TOC analysis severely even under the addition of strong acid and sparging. SEC-UVA/TOC chromatograms with NaCl eluent and a loop of 100 ml (50 mg SRFA) show that the concentration of TOC in the SEC fractions was near the method detection limit and could not produce a reliable chromatogram. SEC-UVA/TOC chromatograms with NaCl eluent and a loop of 500 ml (250 mg SRFA) yields satisfactory response levels. (7) Chromatograms of SEC-UVA/TOX were compared. TOX seems to be distributed evenly but UVA decreased greatly with retention time, which indicates that chlorinated compounds were produced with a wide range of molecular size.
Preliminary MS of SEC Fractions. (1) Chlorinated SRFA samples were prepared by adding a dose of 500 mg/L Cl2 into 500 mg/L SRFA with a reaction time of 5 days. The eluent of 0.03 M NH4HCO3 was degassed just before use. SEC was carried out with a copolymer SEC column. The flow rate was 0.80 ml/min. The SEC elute passed a UV detector, then was collected by a fraction collector at a rate of one fraction per 2 minutes. The fractionated samples were either used directly (the first set) or concentrated through the bubbling of pure nitrogen gas (the second set). 0.25 ml of each sample was diluted with 0.25 ml of methanol. Micromass AutoSpec-oaTOF mass spectrometer was used in the electrospray (ESI) positive ion mode with a magnetic sector analyzer. (2) For the first set of samples, the ion peaks of almost all the fractions were very low in intensity, and it is difficult to distinguish them from noise peaks. The chlorine isotope pattern was ambiguous because of the low sensitivity. The only exception was the last peak of the SEC chromatogram; even though the UV absorbance of the peak was very weak, the MS sensitivity was much higher compared to other fractions. But none of these peaks demonstrates clear chlorine isotopic patterns. There are three possible reasons for the low responses: the concentrations of the samples were too low; low ionization efficiency of some components in ESI positive ion mode; and depression of ionization due to the presence of NH4HCO3. (3) For the second set of samples, the combination of the 10-fold concentration and the removal of NH4HCO3 provided much improved sensitivities of the ion peaks for all fractions. TIC of all the fractions showed normal peak shapes. There are ion peaks at every mass unit, but some of the peaks can be distinguished from noise spikes using peak width as an indication. A common phenomenon is the occurrence of some ion peaks in group 2 mass units apart, which may suggest chlorination patterns. The relative intensities within the group, however, did not fit into that pattern, but this may be the results of the same ion peak intensity coming from different sources. MS/MS analysis of one of the fractions show that the signal to noise ratio was only ~2:1, and it is difficult to determine these peaks on the MS/MS spectrum as real peaks.
Future Activities:
Research plans for the next reporting period include the concentration of SEC fractions, the full examination of SEC-TOX pattern, the exploration of electrospray conditions and chlorine fragmentation, the monitoring of neutral loss experiments, and the screening of standards for chlorination potentials.Journal Articles:
No journal articles submitted with this report: View all 25 publications for this projectSupplemental Keywords:
drinking water, disinfection by-products, molecular weight, HPLC, SEC, MS/MS., RFA, Scientific Discipline, Waste, Water, Chemical Engineering, Physics, Environmental Chemistry, Chemistry, chemical mixtures, Analytical Chemistry, Drinking Water, monitoring, alternative disinfection methods, public water systems, complex mixtures, human health effects, molecular weight separation, exposure and effects, chemical byproducts, disinfection byproducts (DPBs), exposure, community water system, HPLC, treatment, tandem mass spectrometry, toxicity, DBP risk management, water quality, 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.