Determination of Anions and Carboxylic Acids in Urban Fine Particles (PM2.5 )

Significance of the Topic

The chemical makeup of urban fine particulate matter (PM2.5) directly affects air quality, public health, and environmental policies. Water-soluble anions and low-molecular-weight organic acids in PM2.5 influence atmospheric chemistry, acid deposition, and respiratory risks. Sensitive multi-component analysis supports regulatory compliance and source apportionment studies.

Objectives and Study Overview

This study aimed to establish a high-pressure ion chromatography (HPIC) method capable of simultaneously quantifying 12 target ions—fluoride, acetate, formate, mesylate, chloride, nitrite, nitrate, succinate, malonate, sulfate, oxalate, and phosphate—in urban PM2.5 samples. The work compares the new method’s scope and sensitivity with existing EPA and ASTM protocols.

Methodology

Airborne fine particles were collected on quartz filters over 48 h at 77.5 L/min. Extracts were obtained by ultrasonic agitation in deionized water, cooled, and filtered through 0.45 µm nylon membranes. Calibration standards and working mixes covering 0.02–6 mg/L were prepared from 1 000 mg/L stock solutions of individual analytes. Chromatographic separation used a hydroxide gradient (1–50 mM KOH) at 1.5 mL/min, 30 °C, with 25 µL injections. Suppressed conductivity detection (186 mA) provided quantification. Method precision, linearity, and detection limits were assessed via repeated injections and signal-to-noise criteria (S/N=3).

Used Instrumentation

• Thermo Scientific Dionex ICS-5000+ Reagent-Free HPIC system (DP Dual Pump, EG Eluent Generator, DC Detector/Chromatography Compartment)
• Dionex AS-AP Autosampler
• Dionex AERS 500 Anion Electrolytically Regenerated Suppressor, 4 mm
• Dionex EGC 500 KOH Eluent Generator Cartridge
• Dionex CRD 200 Carbonate Removal Device (optional)
• Chromeleon CDS software, version 7.2
• IonPac AS11-HC Guard and Analytical Columns, 4×50 mm/4×250 mm

Main Results and Discussion

Baseline separation of all 12 analytes was achieved with resolutions >2.0 (except carbonate/malonate at 1.2). Retention time RSDs were ≤0.03 %, and area RSDs ≤0.87 %. Calibration curves exhibited excellent linearity (r2 ≥ 0.9983) over 0.02–6 mg/L. Method detection limits ranged from 0.06 to 18.5 µg/L. Analysis of real PM2.5 samples detected ten ions; highest concentrations were found for nitrate, sulfate, and chloride, with mesylate indicating marine aerosol influence. Spike recoveries of 80–121 % confirmed method accuracy.

Benefits and Practical Applications of the Method

• Expanded analyte coverage beyond standard EPA/ASTM methods
• Low detection limits suitable for trace environmental monitoring
• High precision and robust quantification in complex matrices
• Automated reagent-free eluent generation reduces maintenance
• Applicability to ambient air quality assessment, source apportionment, and regulatory compliance

Future Trends and Potential Applications

Advances in on-line sample preconcentration and coupling with mass spectrometry promise enhanced specificity and lower detection limits. Portable or field-deployable HPIC systems could enable near-real-time monitoring. Extending analyses to ultrafine fractions (PM1) and integrating speciation of trace metals or organic markers will deepen insight into aerosol chemistry and health impacts.

Conclusion

The developed HPIC method with suppressed conductivity detection offers a comprehensive, sensitive, and reliable approach for quantifying key inorganic anions and carboxylic acids in urban PM2.5. It outperforms traditional protocols in scope and analytical performance, supporting more detailed environmental assessment and air quality management.

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