Determination of inorganic anions in wastewater using a capillary ion chromatography system

Význam tématu

Determining inorganic anions such as fluoride, chloride, nitrite, bromide, sulfate, nitrate, and phosphate in water is essential for environmental monitoring, regulatory compliance under the Safe Drinking Water Act and Clean Water Act, and protecting public health. Capillary ion chromatography offers reduced reagent consumption and waste, enabling continuous operation and rapid response.

Cíle a přehled studie / článku

This study demonstrates a capillary ion chromatography method using a Thermo Scientific Dionex ICS-4000 system equipped with a Dionex IonPac AS18-4μm capillary column and a 100 nL injection valve. The goal is to achieve fast (13 min), sensitive, and accurate determination of inorganic anions in drinking water, raw water, treated water, and municipal wastewater without extensive sample dilution.

Použitá metodika a instrumentace

Eluent: 26 mM KOH generated electrolytically; flow rate 0.012 mL/min; column temperature 35 °C; injection volume 100 nL; run time 13 min. Suppressed conductivity detection with an ACES 300 capillary suppressor in recycle mode at 8 mA.

• Thermo Scientific Dionex ICS-4000 Integrated Capillary HPIC System with RFIC-EG
• Dionex IonPac AG18-4μm guard column (0.4×35 mm) and AS18-4μm analytical column (0.4×150 mm)
• EGC KOH eluent generator cartridge, CR-ATC trap column, HP degasser
• ACES 300 capillary suppressor, 100 nL injection valve, AS-AP autosampler
• Chromeleon CDS software, version 7.2 SR4

Sample preparation included 0.2 µm filtration, optional five-fold dilution, and reversed-phase cartridge cleanup for wastewater to remove hydrophobic interferences.

Hlavní výsledky a diskuse

The Dionex IonPac AS18-4μm column achieved baseline separation of seven inorganic anions within 13 minutes. Calibration was linear over broad ranges (e.g., 0.2–300 mg/L for chloride; narrower ranges for fluoride and nitrite). Method detection limits ranged from 1.4 to 34.2 µg/L. Retention time precision was excellent (<0.05% RSD); peak area precision was 2–3% RSD. Comparative analysis of undiluted and five-fold diluted samples yielded equivalent concentrations, eliminating the need for routine dilution. Spike recovery experiments in various water matrices showed 86–106% recovery for most anions; lower bromide recovery (66–83%) was observed at low spike levels in high-carbonate samples.

Přínosy a praktické využití metody

The capillary IC method offers low eluent consumption (approximately 15 mL/day), minimal waste, continuous readiness without lengthy startup, and extended eluent cartridge life (up to 18 months), reducing operational costs. Direct analysis of undiluted samples streamlines laboratory workflow, supporting routine QA/QC and regulatory compliance in drinking water and wastewater laboratories.

Budoucí trendy a možnosti využití

Future developments may include coupling capillary IC with mass spectrometry for enhanced selectivity, further miniaturization of flow paths, automated online monitoring and data processing, and expansion of the technique to emerging ionic contaminants and more complex matrices.

Závěr

A capillary ion chromatography method using a Dionex IonPac AS18-4μm column and a 100 nL injection valve provides a rapid, sensitive, and robust approach for inorganic anion analysis in diverse water samples. The technique meets stringent detection and precision requirements, reduces reagent use and waste, and facilitates direct analysis of undiluted samples, making it well suited for environmental monitoring and compliance testing.

Reference

1. U.S. EPA. Method 300.0, The Determination of Inorganic Anions in Water by Ion Chromatography; Office of Water, 1993.
2. U.S. EPA. Method 300.1, The Determination of Inorganic Anions in Water by Ion Chromatography; Office of Water, 1997.
3. U.S. EPA. National Pollutant Discharge Elimination System (NPDES).
4. Greenberg A.E.; Clesceri L.S.; Eaton A.D. Standard Methods for the Examination of Water and Wastewater, 18th ed.; APHA, 1992.
5. ASTM D4327-97. Standard Test Methods for Anions in Water by Chemically Suppressed Ion Chromatography.
6. Thermo Scientific Application Note 135: Determination of Inorganic Anions in Wastewater by Ion Chromatography, 2012.
7. Thermo Scientific Application Note 154: Determination of Inorganic Anions in Environmental Waters, 2003.
8. Thermo Scientific Application Update 197: Anion Determinations in Municipal Wastewater Samples Using EPA Method 300.1 (A), 2016.
9. Thermo Scientific Technical Note 132: Determination of Inorganic Anions in Municipal Water Using High-Pressure Capillary IC, 2016.