Evaluation of Various Anion-Exchange Chemistries for the Analysis of Haloacetic Acids in Drinking Water Using 2-D Matrix Elimination Ion Chromatography and Suppressed Conductivity DetectionKannan Srinivasan, Rong Lin, and Christopher Pohl Thermo Fisher Scientific, Sunnyvale, CA, USA

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Executive SummaryHaloacetic acids (HAAs) are drinking water disinfection byproducts that are regulated due to their potential carcinogenicity. Analysis of trace levels of HAAs in high ionic strength drinking water matrices is challenging. Traditional GC methods require laborious and time-consuming sample preparation and derivatization steps prior to analysis. Direct injection IC-MS-based methods are highly sensitive and selective, and obviate the need for extensive sample pretreatment and derivatization, but ESI-MS instrumentation may not be readily available in routine monitoring laboratories. Two-dimensional matrix elimination IC (MEIC) with suppressed conductivity detection is a simple and cost-effective alternative for sensitive and selective quantitative determination of ppb levels of HAAs in drinking water samples. Optimization of anion-exchange chemistry is critical for maximum method performance.

AbstractDisinfecting water is an important step when processing drinking water. However, commonly used disinfectants, such as chlorine, chlorine dioxide, chloramine, and ozone, react with naturally occurring organic and inorganic matter in the source water to form disinfectant byproducts that are potentially harmful to humans. The U.S. EPA has regulated five haloacetic acids referred to as HAA5, which include monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, mono-bromoacetic acid, and dibromoacetic acid. Stage 1 Disinfectants/Disinfection Byproducts Rule regulates the HAA5 at 60 μg/L annual average.

U.S. EPA Methods 552.1, 552.2, and 552.3 are presently used for analyzing the HAAs. These methods are labor intensive and require multiple extraction and derivatization steps. Recently, a direct injection IC-MS and IC-MS-MS method that uses a high capacity Thermo Scientific™ Dionex™ IonPac™ AS24 anion-exchange column showed excellent separation of nine HAAs and bromate with greater than 90% recovery in the presence of high concentrations of matrix ions such as chloride and sulfate. In this analysis, we evaluated a direct injection suppressed conductivity detection method for analyzing HAAs. Additionally, we evaluated the use of two-dimensional MEIC in conjunction with various column chemistries such as Dionex IonPac AS11-HC, AS16, AS19, and AS24.

Keywords Haloacetic acids, Water analysis, 2-D ion chromatography, ICS-3000

Acid Abbreviation Chemical Formula pKa Boiling

Point °C

Monochloroacetic Acid MCAA* ClCH2CO

2H 2.86 187.8

Dichloroacetic Acid DCAA* Cl2CHCO

2H 1.25 194

Trichloroacetic Acid TCAA* Cl3CCO

2H 0.63 197.5

Monobromoacetic Acid MBAA* BrCH2CO

2H 2.87 208

Dibromoacetic Acid DBAA* Br2CHCO

2H N/A 195

Tribromoacetic Acid TBAA Br3CCO

2H 0.66 245

Bromochloroacetic Acid BCAA BrClCHCO2H N/A 103.5

Dibromochloroacetic Acid DBCAA Br2ClCCO

2H N/A N/A

Dichlorobromoacetic Acid DCBAA Cl2ClCCO

2H N/A N/A

* MCAA, DCAA, TCAA, MBAA, and DBAA are collectively referred to as HAA5.

Table 1. What Are HAAs?

2

Drinking Water MatrixSulfate in drinking water currently has a secondary maximum contaminant level (SMCL) of 250 mg/L, based on aesthetic effects (i.e., taste and odor). This regulation is not a federally enforceable standard, but is provided as a guideline for states and public water systems. U.S. EPA estimates that about 3% of the public drinking water systems in the country may have sulfate levels of 250 mg/L or greater.

• Chloride 250 mg/L

• Nitrate 20 mg/L

• Ammonium chloride 100 mg/L

Current Methods• U.S. EPA 552.1, 552.2, and 552.3

Liquid-liquid microextraction, derivatization, and gas chromatography with:

(a) Electron capture detection(b) Mass spectrometry detection

• Suppressed ion chromatography with MS or MS-MS detection:

– Direct injection method– Matrix diversion setup– No need for liquid-liquid extraction or sample pretreatment– No need for derivatization– Fully automated– Coelution not an issue since MS is a selective detector– Recovery >90%

U.S. EPA RegulationCurrent: Stage 2 Disinfection Byproducts Rule (DBPR)• Monitoring of HAA5 at all plants that disinfect with chlorine

– Total MCAA, MBAA, DCAA, DBAA, and TCAA– Maximum contamination level (MCL) = 60 µg/L annual average

• Maximum contamination level goal (MCLG)

– DCAA should not be present– TCAA less than 30 µg/L

• Bromate

– MCL = 10 µg/L – MCLG = not present

Column Functionality Capacity µeqv/Column Hydrohobicity

Dionex IonPac AS16, 4 × 250 mm Alkanol quaternary ammonium 170 Ultralow

Dionex IonPac AS19, 4 × 250 mm Alkanol quaternary ammonium 240 Low

Dionex IonPac AS20, 4 × 250 mm Alkanol quaternary ammonium 310 Low

Dionex IonPac AS24, 2 × 250 mm Alkanol quaternary ammonium 140 Ultralow

Table 2. Column chemistry details.

3

Figure 1. Analysis of HAA5 in the presence of inorganic matrix ions using a Dionex IonPac AS16 column at 30 ºC. HAA5 is poorly resolved or coelutes with matrix ions as shown above (colored labels).

0 2.5 5.0 7.5 10.0 12.5 15.0 17.5 20.0 22.5 25.0 27.5 30.0

1.5

µS

Minutes

Concentration: 4.00 mM

10.00

55.00

3

10

14

8,95

4 12

11

1315

1

2

6

7

0.3

Peak Identi�cation:1. Fluoride2. Acetate3. MCAA4. Bromate5. Chloride6. MBAA7. Nitrite8. Nitrate

25584

9. Bromide10. DCAA11. Chlorate12. DBAA13. Carbonate14. TCAA15. Sulfate

Figure 2. Analysis of HAA5 in the presence of inorganic matrix ions using a Dionex IonPac AS19 column at 15 ºC. HAA5 is poorly resolved or coelutes with matrix ions as shown above (colored labels).

0 4 8 12 16 20 24 28 32 35–1

10

Concentration: 6.00 mM 10.00

65.00

3

58

9

15

4

11

14

17

7

6

18

13

12

10

16

12

µS

Minutes

Peak Identi�cation:1. Fluoride2. Acetate3. MCAA4. Chlorite5. MBAA6. Bromate7. Chloride8. DCAA9. DBAA10. Nitrite

25585

11. Chlorate12. Benzoate13. Bromide14. Nitrate15. TCAA16. Carbonate17. Sulfate18. Phosphate

Figure 3. Analysis of HAA5 in the presence of inorganic matrix ions using a Dionex IonPac AS20 column at 15 ºC. HAA5 is poorly resolved or coelutes with matrix ions as shown above (colored labels).

0.0 2.5 5.0 7.5 10.0 12.5 15.0 17.5 20.0 22.5 25.0 27.5 30.00

7

Concentration: 7.00 mM

16.90

3

5 8

14

4

11

13

76

12

10

15

91,2

µS

Minutes

Peak Identi�cation:1. Fluoride2. Acetate3. MCAA4. Chlorite5. MBAA6. Bromate7. Chloride8. DCAA

25586

9. DBAA10. Nitrite11. Chlorate12. Bromide13. Nitrate14. TCAA15. Carbonate

3

58

9

15

4

11

14

7

6

10

12

0 4 8 12 16 20 24 28 32 36 40 44 470

4

Concentration: 7.00 mM

18.00

65.00

1,2

13

Peak Identi�cation:1. Fluoride2. Acetate3. MCAA4. Chlorite5. MBAA6. Bromate7. Chloride8. DCAA9. DBAA10. Nitrite

µS

Minutes25587

11. Chlorate12. Carbonate13. Bromide14. Nitrate15. TCAA

Figure 4. Analysis of HAA5 in the presence of inorganic matrix ions using a Dionex IonPac AS24 column at 15 ºC. HAA5 is poorly resolved or coelutes with matrix ions as shown above (colored labels).

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Figure 5. Analysis of HAA5 in the presence of inorganic matrix ions using a new prototype anion-exchange chemistry at 15 ºC. Excellent resolution of all HAA5 was achieved in the presence of matrix ions.

0 10 20 30 40 50 60 70 750.1

2.2

Concentration: 20.00 mM

50.00

65.00

75.00

4

5

11

18

17

6

14

31

2

7–9

1516

10 12

13

µS

Minutes

Peak Identi�cation:1. Fluoride2. Acetate3. Chlorite3. MCAA5. MBAA6. Bromate7. Carbonate8. Chloride9. Sulfate

25588

10. Phosphate11. DCAA 12. Nitrite13. Benzoate14. DBAA15. Bromide16. Chlorate17. Nitrate18. TCAA

Matrix Elimination Ion ChromatographyFeatures• Allows for large loop injection in the first dimension (4 mm column):

– Possible to inject a larger loop than the standard approach since the capacity and selectivity of the analytical column in the first dimension dictates the recovery, and the analyte of interest is analyzed in the second dimension

• Focus the ions of interest in a concentrator column after suppression in the first dimension:

– Hydroxide eluent suppressed to deionized (DI) water, thus providing an ideal environment for focusing or concentrating the ions of interest

• Pursue analysis in the second dimension using a smaller column format with a smaller cross-sectional area, leading to sensitivity enhancement that is proportional to the flow rate ratio:

– For example, for a 4 mm column operated in the first dimension at 1 mL/min and a 1 mm column operated in the second dimension at 0.05 mL/min, the enhancement factor is 20

• Pursue analysis in the second dimension using a different chemistry:

– Enhanced selectivity

• Easy implementation on the Thermo Scientific Dionex ICS-3000 system

Figure 6. Diagram of an MEIC 2-D system setup.

Pump

Injection Valve 1

Suppressor 1

CD 1

Injection Valve 2

Autosampler 1

LoadInject

Transfer to 2-D Load Concentrator

Large Loop

1st DimensionColumn (4 mm) 2nd Dimension Column (2 mm)

Suppressor 2

CD 2

ConcentratorColumn

(UTAC-ULP1)

1111111

EG

1st Dimension 2nd Dimension

CRD 1

CRD 2External Water

Waste

Waste

Waste

External Water

Waste

Waste

Pump EG

Diverter Valve Waste

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5Figure 7 shows analysis of HAA5 in reagent water (DI water). The top chromatogram shows the analysis in the first dimension of the MEIC setup using a 4 mm Dionex IonPac AS19 column. Excellent resolution of HAA5 can be inferred. The bottom chromatogram shows the analysis in the second dimension of the MEIC setup using a 2 mm Dionex IonPac AS19 column.

In Figure 8, conditions are similar to Figure 7, except the sample is high-ionic-strength water (HIW). Under these conditions, the matrix ions overwhelm the analytes, as shown in the top chromatogram. The bottom chromatogram shows the analysis in the second dimension using the MEIC setup. Performance is similar to what was shown in Figure 7B. The above example demon-strates the utility of the MEIC methodology for this work.

30 40 50 60 65–0.2

1.2

1

24 5

EGC_2.Concentration: 7.00 mM

12.00

65.00

0 10 20 30 35–0.05

0.35

1

3

4 5

EGC_1.Concentration: 8.00 mM12.00

65.00

2

3

A. First Dimension: 10 ppb HAA5 in RW

B. Second Dimension: 10 ppb HAA5 in RW

Columns: 1. Dionex IonPac AG19, AS19, 4 mm 2. Dionex IonPac AG19, AS19, 2 mmFlow Rate: 1. 1.0 mL/min 2. 0.25 mL/minSuppressor: 1. Thermo Scienti�c™ Dionex™

ASRS™ ULTRA II 4 mm 2. Dionex ASRS ULTRA II 2 mm Current: 1. 161 mA 2. 41 mAInj. Volume: 1000 µLConcentrator: UTAC-LP1Temperature: 30 °CSamples: 1) MCAA 2) MBAA 3) DCAA 4) DBAA 5) TCAA

µS

Minutes

µS

Minutes 25590

Time Gradient Gradient (mM) (mM) 0 8 6510 8 65 10.1 12 728 12 728.1 65 735 65 742 65 742.1 65 1260 65 1260.1 65 6565 65 65

Figure 7. MEIC analysis of HAA5 in reagent water (deionized water).

30 40 50 60 65–0.2

1.2

EGC_2.Concentration: 7.00 mM

12.00

65.00

0 10 20 30 35–200

1800

EGC_1.Concentration: 8.00 mM

12.00

65.00

NO3

Cl

SO4

PO4CO3

1

24 5

3µS

Minutes

µS

Minutes

A. First Dimension: 10 ppb HAA5 in HIW

B. Second Dimension: 10 ppb HAA5 in HIW

Columns: 1. Dionex IonPac AG19, AS19, 4 mm 2. Dionex IonPac AG19, AS19, 2 mmFlow Rate: 1. 1.0 mL/min 2. 0.25 mL/minSuppressor: 1. Dionex ASRS ULTRA II 4 mm 2. Dionex ASRS ULTRA II 2 mm Current: 1. 161 mA 2. 41 mALoop: 1000 µLConcentrator: UTAC-LP1Oven: 30 °CSamples: 1) MCAA 2) MBAA 3) DCAA 4) DBAA 5) TCAA

25591

Time Gradient Gradient (mM) (mM) 0 8 6510 8 6510.1 12 728 12 728.1 65 735 65 742 65 742.1 65 1260 65 1260.1 65 6565 65 65

Figure 8. MEIC analysis of HAA5 in HIW (high ionic strength water).

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Conclusion An MEIC method was developed for the analysis of HAAs in drinking water matrices. HAA5 were detected at low ppb levels in reagent water and in high-ionic-strength water. Several column chemistries were evaluated and a new high capacity stationary phase was found to optimize separation selectivity and method performance. MEIC is a (potentially) simple and economical alternative to current GC- and IC-MS techniques for routine monitoring of HAAs in drinking water.

WP70423_E 12/12S