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Chlorinating drinking water helps reduce pathogens, but it can also form potentially carcinogenic byproducts, e.g., haloacetic acids (HAAs), dalapon, and bromate [1,2]. The US Environmental Protection Agency (EPA) and the EU set a maximum contamination limit for the sum of five HAAs (HAA5: MCAA, MBAA, DCAA, DBAA, TCAA) of 60 parts per billion (60 µg/L) [3]. EPA Method 557 describes their quantification in the μg/L range in a wide variety of water types [4]. Here, the analysis is accomplished with a Metrohm ion chromatograph (IC) coupled to a triple quadrupole Agilent mass spectrometer (MS). This sensitive method requires no sample extraction, and the Metrohm Suppressor Module eliminates any eluent interferences. Analytes are well-resolved from matrix components with the Metrosep A Supp 19 column. Matrix spike recoveries for 1 µg/L of all analytes were between 65–115% even in heavily loaded water samples. Minimum reporting levels (MRL) were 0.025−0.25 µg/L. The presented IC-MS/MS method fulfills all requirements of EPA Method 557.

Water samples included tap water (from eastern Switzerland) and mineral water (Evian containing c(hydrogen carbonate) = 360 mg/L, c(sulfate) = 14 mg/L, c(chloride) = 10 mg/L, and c(nitrate) = 3.8 mg/L). Additionally, the laboratory synthetic sample matrix (LSSM) according to EPA 557 (c(ammonium chloride) = 100 mg/L, c(nitrate) = 20 mg/L, c(hydrogen carbonate) = 150 mg/L, c(chloride) = 250 mg/L, and c(sulfate) = 250 mg/L) was analyzed. Samples were stabilized with 0.1% methanol (v/v) and cooled to 4 °C. Internal standards were added at a concentration of 4 µg/L (here: MCAA-13C and MBA-13C).

Instrument photo, IC, ion chromatography, IC-MS, IC-MS/MS, ESI, mass spectrometry, mass spectrometer, Agilent, mass hunter, hyphenated, coupling, VAR, value added reseller, ion chromatography mass spectrometry, 889, 940, Professional IC Vario, Dosino
Figure 1. Instrumental setup to measure haloacetic acids, dalapon, and bromate including an 889 IC Sample Center – cool (Metrohm), 940 Professional IC Vario (Metrohm), and 6475 Triple Quadrupole LC/MS with Jet Stream Technology Ion Source (Agilent). A Dosino was used for direct infusion to the MS during method optimization.

The hyphenation of HPLC with mass spectrometry has commonly focused on the study of organic molecules. Hyphenating ion chromatography (IC) with mass spectrometry (MS) opens up the field to highly sensitive analysis of ionic and more polar substances in aqueous solutions or salt-containing matrices. Using the 889 IC Sample Center − cool guarantees stable and reproducible sample processing at 4 °C (Figure 1) by preventing the decay of the degradation-sensitive HAAs.

The 948 Continuous IC Module, CEP automatically produces KOH eluent from ultrapure water and a KOH concentrate.
Figure 2. The 948 Continuous IC Module, CEP automatically produces KOH eluent from ultrapure water and a KOH concentrate. The electrochemical eluent production takes place at a membrane in the eluent producer cartridge.

The metal-free microbore ion chromatograph 940 Professional IC Vario with a Metrosep A Supp 19 column, sequential suppression, and an IC Conductivity Detector MB accomplished chromatographic separation without any interferences and a reduced void volume. Sensitive and selective detection of haloacetic acids was carried out with an Agilent 6475 Triple Quadrupole LC/MS equipped with an Agilent Jet Stream Technology Ion Source, operated in dynamic multiple reaction monitoring (dMRM) acquisition mode. Conductivity detection can be used to quantify common anions like fluoride, chloride, nitrate, or sulfate in parallel. An additional Dosino enables direct infusion of standard solutions to the MS for method optimization, i.e., finding the best MS parameters to detect the analytes of interest.

The 948 Continuous IC Module, CEP precisely produces a potassium hydroxide eluent in concentrations from 15−100 mmol/L potassium hydroxide (KOH) (Figure 2). The IC was operated with the software MagIC Net, and the MS by MassHunter software. Synchronization of both instruments was controlled via a remote cable. Table 1 lists the most important instrument settings.

Table 1. This table lists the most important method parameters for haloacetic acid determination with IC-MS/MS.
IC Column Metrosep A Supp 19 - 150/4.0
Eluent/gradient 15−100 mmol/L KOH + 10% methanol
Flow rate 0.5 mL/min
Column temperature 15 °C
Injection volume 100 μL
Suppression sequential
Ion polarity negative
Gas flow 12 L/min
Sheath gas flow 12 L/min
Gas temperature 150 °C
Sheath gas temperature 245 °C
Detection dMRM (dynamic Multiple Reaction Monitoring)

The presented method is capable of determining all relevant haloacetic acids, bromate, and dalapon in drinking water according to EPA 557 (Table 2). Separation on the column Metrosep A Supp 19 - 150/4.0 with a hydroxide eluent was robust and reproducible. This combination enabled sufficient resolution between highly concentrated matrix peaks (i.e., chloride, nitrate, bicarbonate, and sulfate) and the analytes (Figure 3). The matrix was diverted to the waste to avoid ion suppression in the MS. A further advantage of this setup is the solvent-stable suppressor. Using 10% methanol in the eluent helps the transfer from aqueous to gas phase and has no impact on the suppressor. Thus, no further post-column addition of organic solvents with a secondary pump was necessary to improve evaporation of analytes in the MS.

Calibration from 0.1−40 µg/L with quadratic fits resulted in R2 values in the range of 0.996−0.999. Determination of the lowest concentration minimum reporting levels (LCMRL) was done as per EPA 557, chapter 9.2.4 (Table 2). Seven replicates were successfully analyzed for the upper and lower PIR (prediction interval of results) limit (acceptable range 50–150%).

Figure 3. Overlay of a chromatogram of laboratory synthetic sample matrix (LSSM) according to EPA 557 with c(ammonium chloride) = 100 mg/L, c(nitrate) = 20 mg/L, c(hydrogen carbonate) = 150 mg/L, c(chloride) = 250 mg/L, and c(sulfate) = 250 mg/L (light colored lines), and of LSSM spiked with 1 μg/L of all analytes (intensely colored lines). Injection volume was 100 μL.

Water samples were directly analyzed (no dilution needed). Table 3 shows that spiking recoveries of 1 µg/L were in the range of 65−115% (for LSSM), 46−112% (for tap water), and 87−150% (for Evian water). Replicates for tap water (n = 7) were in the range of 0.7−6.8% RSD (relative standard deviation). For mineral water (Evian) (n = 6) and for LSSM (n = 7) RSD values were in the range of 1.6−6.3% and 1.0−36.5%, respectively. Most values were ≤5%, except for TCAA (which elutes close to sulfate).

Critical pairs were DBA/nitrate and TCAA/sulfate. The diverter windows must be accurately set to acquire complete data for the analytes DBAA and TCAA and divert both nitrate and sulfate to the waste. Sample degradation at room temperature was visible after one day and considerable degradation occurred after four to five days. The samples must be measured in a timely manner or a sampler with cooling function must be used (e.g., 889 IC Sample Center – cool). A Metrohm CO2-suppressor (MCS) was used in this setup as it improved the conductivity background and hence reduced the number of interfering ions in the MS.

Table 2. Determination of lowest concentration minimum reporting levels (LCMRL) was done as per EPA 557, chapter 9.2.4 minimum reporting level (MRL) confirmation. Seven replicates were analyzed for the upper and lower PIR (prediction interval of results) limit (acceptable range 50−150%). *Concentrations lower than 0.025 μg/L were not tested, but signal-to-noise ratio was >10 and showed that the minimum limit was not reached.
Analyte Abbreviation Retention time [min] Precursor m/z Product m/z Concentration for minimum reporting level [μg/L]
 PIR limits [%]
Monochloroacetic acid
 MCAA 15.8 93 34.9 0.025* 91−109
Monobromoacetic acid MBAA 17.2 137 79 0.025* 88−112
Bromate BrO3 16.7 127 111 0.025* 84−116
Dichloroacetic acid DCAA 25.6 127 83 0.025 84−116
Dalapon DAL 28.0 141 97 0.025 74−126
Bromochloroacetic acid BCAA 28.0 173 81 0.05 74−126
Dibromoacetic acid DBAA 31.4 217 173 0.025 75−125
Trichloroacetic acid TCAA 37.9 161 117 0.25 62−131
Bromodichloroacetic acid BDCAA 40.2 163 81 0.025 79−121
Chlorodibromoacetic acid CDBAA 43.5 207 79 0.025 52−148
Tribromoacetic acid TBAA 49.1 251 79 0.025 62−138
Table 3. Three types of water samples were spiked with 1 μg/L of all listed analytes and determined with IC-MS/MS. Analytes were not evaluated in the original unspiked samples. They were either not detected or below 0.1 μg/L. Concentration values are averaged over at least six replicates.
Analyte Concentration [μg/L] in samples spiked with 1 μg/L of all analytes
  Tap water (eastern Switzerland) Mineral water (Evian) LSSM (EPA 557)
MCAA 1.12 1.41 1.15
MBAA 1.00 0.97 0.87
BrO3- 0.88 0.86 0.84
DCAA 0.88 1.03 0.80
DAL 0.88 0.93 0.76
BCAA 0.87 0.87 0.71
DBAA 0.88 1.22 0.79
TCAA 0.46 1.50 0.65
BDCAA 0.89 0.91 0.87
CDBAA 0.88 1.00 0.88
TBAA 0.88 1.43 0.84

The presented method fulfills all analytical requirements of US EPA 557 [4]. The robust setup of hyphenating Metrohm IC and Agilent MS guarantees the highest sensitivity and selectivity for all relevant haloacetic acids, dalapon, and bromate, even in complex drinking water matrices. The five representative substances (mono-, di-, and trichloroacetic acid, and mono- and dibromoacetic acid) were precisely quantified in the sub μg/L concentration range for various water samples. The requirements of EPA 557 [4] and the EU directive [5] are met with this method.

  1. Zhao, H.; Yang, L.; Li, Y.; et al. Environmental Occurrence and Risk Assessment of Haloacetic Acids in Swimming Pool Water and Drinking Water. RSC Adv 10 (47), 28267–28276. DOI:10.1039/d0ra02389b
  2. Sinha, R.; Gupta, A. K.; Ghosal, P. S. A Review on Trihalomethanes and Haloacetic Acids in Drinking Water: Global Status, Health Impact, Insights of Control and Removal Technologies. Journal of Environmental Chemical Engineering 2021, 9 (6), 106511. DOI:10.1016/j.jece.2021.106511
  3. US EPA, O. National Primary Drinking Water Regulations. https://www.epa.gov/ground-water-and-drinking-water/national-primary-drinking-water-regulations (accessed 2022-09-19).
  4. United States Environmental Protection Agency. Method 557: Determination of Haloacetic Acids, Bromate, and Dalapon in Drinking Water by Ion Chromatography Electrospray Ionization Tandem Mass Spectrometry (IC-ESI-MS/MS). EPA Document No. 815-B-09-012 2009.
  5. Directive - 2020/2184 - EN - EUR-Lex. https://eur-lex.europa.eu/eli/dir/2020/2184/oj (accessed 2024-03-11).
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