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Introduction
Haloacetic acids (HAAs) are formed as disinfection by-
products when water is chlorinated to remove microbial
content. The chlorine reacts with naturally occurring
organic and inorganic matter in the water, such as
decaying vegetation, to produce by-products that include
HAAs. Of the nine species of HAAs, five are currently
regulated by the EPA (HAA5): monochloroacetic acid
(MCAA), dichloroacetic acid (DCAA), trichloroacetic acid
(TCAA), monobromoacetic acid (MBAA), and
dibromoacetic acid (DBAA). The remaining four HAAs
are unregulated: bromochloroacetic acid (BCAA),
bromodichloroacetic acid (BDCAA), dibromochloroacetic
acid (DBCAA), and tribromoacetic acid (TBAA).
According to the U.S. Environmental Protection
Agency (EPA), there might be an increased risk of cancer
associated with long-term consumption of water
containing levels of HAAs that exceed 0.6 mg/L.
1
EPA
Methods 552.1, 552.2, and 552.3, are used to determine
the level of all nine HAAs in drinking water.
2,3,4
These
methods require derivatization and multiple extraction
steps followed by gas chromatography (GC) with electron
capture detection (ECD).
In comparison to the conventional EPA methods using
GC with ECD, the combination of ion chromatography
and mass spectrometry (IC-MS and IC-MS/MS) offers
sensitive and rapid detection without the need for sample
pre-treatment. Ion chromatography is a form of liquid
chromatography that uses ion-exchange resins to separate
atomic and molecular ions. The retention time in the
column is predominantly controlled by the interactions of
the ions of the solute with the resin. Coupling IC with the
highly selective detection of a triple quadrupole mass
spectrometer allows unambiguous identification of
substance peaks. Matrix interference effects are greatly
reduced, which improves the sensitivity and lowers the
detection limits.
In the method described here, water samples can be
injected directly into an ion chromatography system that
is coupled to a Thermo Scientific TSQ Quantum Access
triple stage quadrupole mass spectrometer. The separation
of all nine HAAs addressed in the EPA methods is
achieved with an anion-exchange column using an
electrolytically formed hydroxide gradient.
Goal
To develop a simple, rapid, and sensitive IC-MS/MS
method for analyzing haloacetic acids in water.
Experimental Conditions
Ion Chromatography
IC analysis was performed on a Dionex ICS 3000 system
(Dionex Corporation, Sunnyvale, CA). Samples were
directly injected and no sample pre-treatment was
required. The IC conditions used are shown in Table 1.
Column Set:
Dionex IonPac
®
AG24 (2 × 50 mm),
IonPac AS24 (2 × 250 mm)
Suppressor:
ASRS
®
300, 2 mm
Column Temperature: 15 °C
Injection Volume:
100 µL
Flow Rate:
0.3 mL/min KOH gradient, electrolytically generated
(Table 2)
Table 1. Ion chromatography system conditions
Retention Time (min)
[KOH] mM
0.00
7.0
15.1
7.0
30.8
18.0
31.0
60.0
46.8
60.0
47.0
7.0
Table 2. Electrolytically formed hydroxide gradient details
The separation performed on the IonPac AS24 column
used a hydroxide gradient. It is known that hydroxide is
not a recommended eluent for mass spectrometers. The
addition of an ASRS 300 anion self-regenerating
suppressor is critical. This suppressor is placed in line
after the column and electrolytically converts the
hydroxide into water, making the separation compatible
with mass spectrometric detection. See Figure 1.
Analysis of Haloacetic Acids in Drinking Water
by IC-MS/MS
Charles Yang
1
and Stacy Henday
2
1
Thermo Fisher Scientific, San Jose, CA;
2
Dionex Corporation, Sunnyvale, CA
Key Words
• TSQ Quantum
Access
• EPA
• Ion
chromatography
• Water analysis
Application
Note: 454