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2
Experimental
Sample Preparation
Preparation of standards
A methyl tertiary-butyl ether (MTBE) solution combining
four types of haloacetic acids [monochloroacetic acid
(MCAA), dichloroacetic acid (DCAA), trichloroacetic acid
(TCAA), and monobromoacetic acid (MBAA), 100 mg/L
of each, Kanto Kagaku] was used for the haloacetic acid
standard solution. The solution was diluted in ultrapure
water and used to prepare the calibration curve.
Preparation of laboratory fortified matrix
The following anions were added to a final concentration
as shown: Cl
-
, 35 mg/L; SO
4
2
-
, 35 mg/L; NO
3
-
, 50 mg/L.
Ascorbic acid was added at 10 mg/L level.
Preparation of the sample
After sampling the tap water, ascorbic acid was added at
the level of 10 mg/L for residual chlorine removal.
Liquid Chromatography
Equipment:
Thermo Scientific
™
Dionex
™
UltiMate
™
3000 RSLC system, which included
the LPG-3400RS Quaternary Rapid
Separation Pump, WPS-3000TRS Rapid
Separation Thermostatted Wellplate Sampler,
and TCC-3000RS Rapid Separation
Thermostatted Column Compartment
Column:
Acclaim HAA column
(2.1 x 50 mm, 3 µm), P/N SP6917
Mobile phase A:
Water (LC/MS grade)
Mobile phase B:
200 mM aqueous ammonium sulfate solution
Mobile phase C:
Acetonitrile
Gradient:
Refer to Figure 1
Flow rate:
0.3 mL/min
Operating temperature: 25.0 °C
Injection volume:
50 µL
Figure 1. LC gradient
To extend the life of the columns, they should be stored
in a 100 mM acetic ammonium (pH 5.0)/acetonitrile
(1:4 v/v) solution.
Mass Spectrometry
Equipment:
Thermo Scientific
™
TSQ Quantum Ultra
™
triple-stage quadrupole MS
Ionization method:
Negative ESI
Spray voltage:
500 V
Sheath gas:
60 arbitrary units
Aux gas:
10 arbitrary units
Capillary temperature:
250 °C
Vaporizer temperature: 400 °C
Skimmer offset:
10 V
Collision gas pressure: Ar, 0.8 mTorr
Cycle time:
2 ms
Mass resolution:
Q1: 1.5 Da (SRM mode)
SRM transitions:
Refer to Table 1
Results and Discussion
Separation of Matrix Ions
When optimizing separation conditions, it is important to
adequately separate matrix ions and haloacetic acids.
However, further care is required to separate chloride ions
and MCAA. Detection close to the MCAA retention time
was confirmed using accurate mass MS.
1
Cl
-
(
m/z
35) is
detected as fragment ions from NaCl
2
-
(
m/z
93) using
CID. It is therefore detected in the same transition as
MCAA. If the retention mechanism is unclear, or if
separation of MCAA and chloride cannot be confirmed,
false quantification could result, depending on the
behavior of the chloride ions. This is why processing to
remove chloride ions is recommended in analysis systems
using ODS columns.
In this investigation for the Acclaim HAA column, the
resolution of HAAs from interfering anions in a synthetic
sample matrix spiked with HAAs is demonstrated
(Figure 2).
Compound
Name
Precursor
(
m/z
)
Product
(
m/z
)
CE
(eV)
MCAA quantitation ion
93
35
10
MCAA qualifying ion
95
37
10
DCAA quantitation ion
127
83
10
DCAA qualifying ion
129
85
10
TCAA quantitation ion
161
117
10
TCAA qualifying ion
163
119
10
Table 1. SRM transitions