Haloacetic Acids Analysis
Haloacetic acids and their regulations
Haloacetic acids (HAAs), which are found to increase the risk for cancer, are disinfection byproducts (DBPs) generated during the water chlorination process. During this disinfection process, chlorine reacts with naturally occurring organic and inorganic matter in the water to produce DBPs including HAAs, trihalomethanes (THMs), and chlorate.
Of the nine known species of HAAs (HAA9) found in the treated water, five (HAA5) are currently regulated at the total level of 60µg/L by the US EPA:
- Monochloroacetic acid (MCAA)
- Dichloroacetic acid (DCAA)
- Trichloroacetic acid (TCAA)
- Monobromoacetic acid (MBAA)
- Dibromoacetic acid (DBAA)
The remaining four HAAs (bromochloroacetic acid (BCAA), bromodichloroacetic acid (BDCAA), dibromochloroacetic acid (DBCAA), and tribromoacetic acid (TBAA)) are not currently regulated, but are on the Unregulated Contaminant Monitoring Rule (UCMR) 4 list for monitoring by public water systems between 2018 and 2020.
In Japan, MCAA, DCAA, and TCAA are regulated in drinking water at 0.02 ppb, 0.04 ppb, and 0.2 ppb, respectively, while China regulates DCAA and TCAA at 0.05 ppb and 0.1 ppb, respectively.
HAAs analysis using gas chromatography
Gas chromatography is most commonly used for analyzing HAAs. EPA Methods 552.1, 552.2, 552.3, and Standard Method 6251 are approved by the U.S. EPA. These methods use: methyl tert-butyl ether (MTBE) or anion exchange resins to extract HAAs from water samples (liquid-liquid microextraction); diazomethane or acidic methanol (derivatization) to convert HAAs into methyl esters, and analysis by gas chromatography-electron capture detection (GC/ECD).
Although these methods are gold standards for regulatory compliance for analysis of HAAs, they all share the disadvantages:
- Low sensitivity detection for monochloroacetic acids (MCAA)
- Susceptible to chromatographic interference, especially for MCAA
- Identification problems due to drifting in retention time
- Long GC run time
HAAs analysis using IC-MS/MS
EPA Methods 552.1, 552.2, and 552.3 use gas chromatography with electron capture detection (GC-ECD) to determine the level of HAAs in drinking water. The drawback of these methods is the use of derivatization and multiple extraction steps which can take a total 30 hours to complete the analysis. EPA Method 557 uses ion chromatography (IC) coupled with mass spectrometry (IC-MS/MS), providing sensitive and rapid detection without sample pretreatment.
Here are some of the advantages of using the IC-MS/MS method:
- Direct injection
- Matrix diversion setup
- No tedious liquid-liquid extraction/sample pretreatment/derivatization
- Fully automated
- High recovery (>90%)
In addition to the US, the United Kingdom also uses EPA Method 557 for analysis of HAA5 and HAA9. Because the method is rapid and simultaneous, it is gaining more popularity for routine analysis and investigative surveys for HAAs analysis in drinking water.
For more information
HAAs analysis using two-dimensional ion chromatography
Although currently not approved by the EPA, haloacetic acids can also be analyzed using two-dimensional ion chromatography (2-D IC). When using a single dimension for anion exchange separation, the HAAs are not well resolved from the common matrix anions, resulting in co-elution. However, if 2-D IC is used, the fractions containing HAAs from first dimension are captured on a concentrator column and then transferred to a smaller inside diameter (i.d.) second dimension column with different surface chemistry where the HAAs are then well separated.
There are several reasons why 2-D IC is able to achieve low detection limits for HAAs:
- In the first dimension, sensitivity is increased by loading a larger sample volume than typical, and the effect of the sample matrix is eliminated as the analyte ions are sent to the second dimension.
- In the second dimension, the low concentrations of the analyte are concentrated, thereby increasing sensitivity, and are confirmed by using a column with different selectivity than used on the first dimension.
For more information on HAA analysis by 2-D IC
HAAs analysis in UCMR 4
In the newly developed UCMR 4 (unregulated contaminants monitoring rule 4), the EPA requires public water systems to monitor three groups of brominated HAAs (HAA5, HAA6Br, and HAA9) using EPA Methods EPA 552.3 or 557. HAA5, which is already regulated, is included in the monitoring to get better understanding of co-occurrence of HAA5 with other unregulated HAAs. As indicators, TOC (total organic carbon) and bromide samples are also collected at the same time as HAA samples are taken and analyzed using the approved EPA methods.