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Fast and low-cost determination of anions in municipal drinking water

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Hua Yang and Jeffrey Rohrer

Thermo Fisher Scientific, Sunnyvale, CA, USA

Introduction

Ion chromatography (IC) is a well-accepted technique for monitoring inorganic anions in water, including surface, ground, drinking and waste waters. In the United States, water quality is regulated through the Safe Drinking Water Act (SDWA) and the Clean Water Act (CWA) and enforced through the United States Environmental Protection Agency (US EPA).1 IC methods have been approved by the US EPA for compliance monitoring of inorganic anions in drinking water since the 1980s through US EPA Method 300.0 that was updated in 1997 to US EPA Method 300.1.2 Various IC methods for water analysis have been demonstrated in Thermo Scientific™ Dionex™ application notes using standard or microbore flow rate columns with both carbonate/bicarbonate and hydroxide eluents.3

This work demonstrates the determination of inorganic anions in drinking water by IC using a Thermo Scientific™ Dionex™ IonPac™ AS22-Fast-4µm column4 set on a Thermo Scientific™ Dionex™ Easion™ Ion Chromatography System in Displacement Chemical Regeneration (DCR) mode. Figure 1 shows a diagram of the setup. The Dionex Easion IC system is an integrated, single-channel low-cost system designed for isocratic applications with suppressed conductivity detection. Coupled to the Thermo Scientific™ Dionex™ AS-DV Autosampler, it provides a fast and low-cost choice for routine water analysis.

Figure 1. Illustration of an IC system in DCR mode.

Equipment and consumables

  • Dionex Easion IC system
  • Dionex AS-DV autosampler
  • Thermo Scientific™ Dionex™ Chromeleon™ 7.2.10 MuA Chromatography Workstation
  • Consumables in Table 1

Table 1. Consumables.

Product name

Part no.

Thermo Scientific™ Dionex™ DCR Installation Kit for 4 mm column

056884

Thermo Scientific™ Dionex™ ACRS 500 Anion Chemically Regenerated Suppressor (4 mm)

085090

Thermo Scientific™ Dionex™ IonPac™ AS22-Fast-4µm Guard Column (4 × 30 mm)

088487

Thermo Scientific™ Dionex™ IonPac™ AS22-Fast-4µm Analytical Column (4 × 150 mm)

088486

Thermo Scientific™ Dionex™ Displacement Chemical Regeneration (DCR) Reagents

057559

Thermo Scientific™ Dionex™ AS22 Eluent Concentrate (100×)

063965

Thermo Scientific™ Dionex™ AS-DV Autosampler PolyVial (5 mL) with filter cap (20 µm), 250 pack

038141

Experimental

All reagents (eluent, regeneration solution and standard) were prepared with degassed deionised (DI) water with 18 MΩ-cm resistance or better.

Individual anion standard stock solutions (1000 mg L–1) were prepared by dissolving sodium or potassium salts (ACS reagent grade or better) in DI water. Aliquots of these standards were combined and diluted with DI water to prepare mixed calibration standards (Table 2).

Table 2. Calibration standards (mg L–1).

Level

1

2

3

4

5

6

7

Fluoride

0.1

1

5

10

20

0

0

Chloride

0.2

2

10

20

40

50

100

Nitrite-N

0.1

1

5

10

20

0

0

Bromide

0.1

1

5

10

20

0

0

Nitrate-N

0.1

1

5

10

20

0

0

Phosphate-P

0.2

2

10

20

40

25

50

Sulfate

0.2

2

10

20

40

50

100

A drinking water sample was collected locally. No filtration was needed as filter caps were used on the Dionex AS-DV autosampler vials.

The chromatography conditions are listed in Figures 2 and 3.

Figure 2. Separation of inorganic anions using the Dionex IonPac AS22-Fast-4µm column.

Results and discussion

Figure 2 shows a separation of inorganic anions within 10 min using the Dionex IonPac AS22-Fast-4µm column. As this figure shows, seven inorganic anions are well resolved. The Dionex IonPac AS22-Fast-4µm column can be used for compliance monitoring of inorganic anions in water. Compared to the 15 min method using Dionex IonPac AS22 column, this method is fast and saves per injection, allowing two additional samples to be run every hour.

Figure 3. Analysis of municipal drinking water using the Dionex IonPac AS22-Fast-4μm columns.

Figure 3 shows the determination of inorganic anions in a drinking water sample. Among the common anions, fluoride, nitrate and nitrite are regulated with the Maximum Contaminant Level (MCL) for fluoride at 4 mg L–1, nitrite at 1 mg L–1 and nitrate at 10 mg L–1. The results show that the drinking water sample contains chloride (3.84 mg L–1), sulfate (1.96 mg L–1) with less than 1 mg L–1 of fluoride (0.54 mg L–1), nitrite (0.01 mg L–1) and nitrate (0.06 mg L–1), which meet the safety criteria.

Linearity

Table 3 shows the calibrations are linear for the inorganic anions with r2 from 0.995 to 1.

Table 3. Linearity obtained using the Dionex IonPac AS22-Fast-4μm column with a 25.0 μL ­injection.

Analyte

Range (mg L–1)

Coefficient of determinationa (r2)

Fluoride

0.1–20

1.000

Chloride

0.2–100

0.999

Nitrite-N

0.1–20

1.000

Bromide

0.1–20

0.999

Nitrate-N

0.1–20

0.996

Phosphate-P

0.2–50

0.995

Sulfate

0.2–100

0.997

aCalibration type is linear and forced through the origin

Conclusion

This work shows the determination of inorganic anions in a drinking water sample using the Dionex Easion IC system in DCR mode. The integrated Dionex Easion IC system coupled with AS-DV autosampler and the Dionex IonPac AS22-Fast-4µm columns provides a fast, simple, and low-cost instrument setup for routine determination of inorganic anions in drinking water.

References

  1. National Primary Drinking Water Regulations. https://www.epa.gov/ground-water-and-drinking-water/national-primary-drinking-water-regulations [accessed 27 May 2020].
  2. Method 300.1. The Determination of Inorganic Anions in Water by Ion Chromatography; rev 1.0. US EPA, Office of Water, Cincinnati, OH (1997). https://www.epa.gov/sites/production/files/2015-06/documents/epa-300.1.pdf [accessed 27 May 2020].
  3. Inorganic anions Analysis by EPA 300.0 & 300.1. https://www.thermofisher.com/us/en/home/industrial/environmental/environmental-learning-center/contaminant-analysis-information/anion-analysis/common-anions-analysis-epa-300-0-300-1.html [accessed 27 May 2020].
  4. The Dionex IonPac AS22-Fast-4µm IC columns. https://www.thermofisher.com/order/catalog/product/088489?SID=srch-hj-088489#/088489?SID=srch-hj-088489 [accessed 10 June 2020].
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