Analysis of Total Nitrogen and Total Phosphorus in Environmental Water According to ASTM D8001 by Ion Chromatography

Significance of the Topic

Eutrophication is driven by excess nitrogen and phosphorus in water bodies, leading to algal blooms and ecological disruption. Accurate, simultaneous measurement of total nitrogen (TN) and total phosphorus (TP) is essential for monitoring water quality and informing regulatory measures under goals such as the UN SDGs. The ASTM D8001 method applied to environmental water samples provides a comprehensive approach to nutrient analysis, enhancing environmental protection efforts.

Objectives and Study Overview

This study demonstrates the use of a suppressor ion chromatograph (HIC-ESP) compliant with ASTM D8001 for simultaneous analysis of TN and TP in environmental water. The key objectives are to evaluate method sensitivity, reproducibility, detection limits and spike recoveries following a single alkaline persulfate digestion, and to assess the eco-friendly benefits of an electro-dialysis suppressor in recycle mode.

Methodology and Instrumentation

Samples undergo alkaline persulfate digestion at 120°C for 60 minutes to convert all nitrogen species to nitrate and phosphorus species to phosphate. Following digestion, samples are diluted as required and injected into the ion chromatograph. Mineral separation is achieved on a Shodex SI-52 4E column (250×4.0 mm, 5 µm) with a Shodex SI-92G guard column. A 3.6 mM sodium carbonate mobile phase at 0.8 mL/min and 45°C column temperature is used. Detection is by conductivity after an ICDSTM-40A suppressor in recycle mode.
Instrumentation:

• Pump
• Auto sampler with 200 µL injection volume
• Shodex SI-52 4E analytical column and SI-92G guard column
• ICDSTM-40A electro-dialysis suppressor
• Conductivity detector
• Autoclave for digestion

Main Results and Discussion

• Calibration standards (10–300 µg/L) produced linear curves with r2 ≥ 0.9997 for NO2-N, NO3-N, and PO4-P.
• Reproducibility tests (n=7) at 10 µg/L showed retention time RSD ≤ 0.05% and peak area RSD ≤ 2.2%.
• Method detection limits were calculated as 0.60 µg/L for TN and 1.66 µg/L for TP.
• Mixed digest-check sample spike recoveries averaged 105.8% for TN and 107.8% for TP, confirming digestion efficacy.
• Analysis of a seawater mimic yielded non-detectable TN and TP; spike recovery tests in digested samples showed recoveries of 105.8–106.4%.

Practical Applications and Benefits

The combined digestion and ion chromatography approach simplifies routine environmental monitoring by measuring TN and TP simultaneously in a single run. The use of an electro-dialysis suppressor reduces chemical waste and operational costs, promoting greener laboratory practices with maintained precision and sensitivity.

Future Trends and Possibilities

Advances may include tighter integration with on-line sample preparation, portable ion chromatographs for field analysis, expanded analyte panels for comprehensive nutrient profiling, and further reductions in detection limits through enhanced suppressor technologies and miniaturized systems.

Conclusion

The HIC-ESP system adhering to ASTM D8001 provides a robust, eco-friendly method for simultaneous TN and TP analysis in environmental waters. High linearity, reproducibility and recovery demonstrate its suitability for regular water quality assessment and regulatory compliance.

References

• ASTM D8001, Standard Test Method for Determination of Total Nitrogen, Total Kjeldahl Nitrogen by Calculation, and Total Phosphorus in Water and Wastewater by Ion Chromatography, ASTM International, 2023.