Detection of Chlorinated and Brominated Byproducts of Drinking Water Disinfection Using Electrospray Ionization−High-Field Asymmetric Waveform Ion Mobility Spectrometry−Mass Spectrometry

Abstract

The lower limit of detection for low molecular weight polar and ionic analytes using electrospray ionization-mass spectrometry (ESI-MS) is often severely compromised by an intense background that obscures ions of trace components in solution. Recently, a new technique, referred to as high-field asymmetric waveform ion mobility spectrometry (FAIMS), has been shown to separate gas-phase ions at atmospheric pressure and room temperature. A FAIMS instrument is an ion filter that may be tuned, by control of electrical voltages, to continuously transmit selected ions from a complex mixture. This capability offers significant advantages when FAIMS is coupled with ESI, a source that generates a wide variety of ions, including solvent clusters and salt adducts. In this report, the tandem arrangement of ESI-FAIMS-MS is used for the analysis of haloacetic acids, a class of disinfection byproducts regulated by the US EPA. FAIMS is shown to effectively discriminate against background ions resulting from the electrospray of tap water solutions containing the haloacetic acids. Consequently, mass spectra are simplified, the selectivity of the method is improved, and the limits of detection are lowered compared with conventional ESI-MS. The detection limits of ESI-FAIMS-MS for six haloacetic acids ranged between 0.5 and 4 ng/mL in 9:1 methanol/tap water (5 and 40 ng/mL in the original tap water samples) with no preconcentration, derivatization, or chromatographic separation prior to analysis.

Modeling the resolution and sensitivity of FAIMS analyses

“…Whether this was the case for published work is difficult to ascertain. While the ESI source current was estimated [26,32,37,38] as 30 -60 nA, its fraction for the analyte of interest, the extent of desolvation prior to FAIMS injection, and the transmission efficiency of ESI/FAIMS pinhole interface are unknown. Second, no other ions may be injected concurrently with the ion of interest: those will initially fill a part of the charge capacity, even if subsequently lost to the FAIMS filtering action.…”

“…Typical targets are small halogen-containing molecules that are common groundwater contaminants, such as haloacetic acids [37,56] and (per)halogenates [24 -26] [25] peaks in CV spectra are compared in Figure 8a. The FWHM calculated at saturation is about half that at I in 3 0, because of powerful Coulomb repulsion at very high ion currents: I sat ϳ290 pA is attained at I in ϳ420 pA.…”

Assessing exposure in epidemiologic studies to disinfection by-products in drinking water: report from an international workshop.

“…Analyses of polar DBPs, like the HAAs, have required expensive, complex, and time-consuming (about 20 samples/24 hr) preparative analytical procedures. Some promising new techniques such as electrospray ionizationmass spectrometry (ESI-MS) alone (17) or in combination with high-field asymmetric waveform ion mobility spectrometry (ESI-FAIMS-MS) (18,19) offer prospects for substantial improvements for polar DBPs like that seen with HAAs. ESI-MS and ESI-FAIMS-MS can reduce the time required for analysis to less than 5 min/sample.…”

“…New methods may substantially reduce the cost and time required to measure biomarkers [e.g., solid-phase microextraction followed by fast gas chromatography with either electron capture detection or mass spectometry can substantially reduce sample volume requirements and analysis time for biological samples (40)]. The emerging technology of ESI-MS and ESI-FAIMS-MS shows early promise for rapid analyses of HAAs (18,19), which may eventually make such biomarkers more feasible, although considerable method development and validation are required.…”

Determination of bromate and chlorinated haloacetic acids in bottled drinking water with chromatographic methods

“…Generally, techniques such as ion chromatography (Weinberg, 1994;Jackson et al, 1998;Echigo et al, 2001), MS-based methods (Charles and Pepin, 1996;Magnuson, 1998;Creed and Brockhoff, 1999) could be used for the determination of bromate in drinking water. HAAs in drinking water could be detected with gas chromatography (Munch et al, 1995), capillary electrophoresis (Martinez et al, 1999), ion chromatography (Nair et al, 1994;Lopez-Avila et al, 1999) and MSbased techniques (Ells et al, 1999;Roehl et al, 2002).…”