Stormwater Testing

Crispim, C. P., Nogueira, R. F., Ometto, J. P., & Campos, M. L. A. (2018). Atmospheric Environment, 191, 525-531.

The significance of accounting for organic nitrogen (ON) in atmospheric nitrogen deposition estimates has long been recognized. However, global data on ON concentrations in rainwater remain limited, primarily due to the challenges and uncertainties associated with existing analytical techniques.

This study introduces a simple, cost-effective, and reliable method for ON determination in rainwater, utilizing the photo-Fenton process under UV irradiation. The method’s recovery efficiency was assessed using solutions of individual compounds—urea, serine, glycine, histidine—and a mixture of these, including arginine. Near-complete ON recoveries (~100%) were achieved for solutions containing 50 μmol N L^-1, using 50 μmol L^-1 Fe²⁺, 2.0 mmol L^-1 H₂O₂, and adjusting the pH to ~2.5, followed by 90 minutes of UV irradiation. The average reagent blank was less than 2.0 μmol N L^-1.

The setup employed a homemade reactor with a 400 W high-pressure mercury lamp, manually modified by removing the external bulb. Controlled ventilation maintained the reactor temperature at approximately 85°C. The method demonstrated precision between 1.3% and 5.7% for ON recovery.

Rainwater samples collected on an event basis revealed ON concentrations ranging from 4.1 to 34.3 μmol N L^-1 (n = 18), contributing 13–45% of the total nitrogen, with an average of 33%. Analytical precision for rainwater ON measurements was ≤7.0%, highlighting the method's reliability for environmental monitoring.

Vieira, Vítor D., et al. Talanta 235 (2021): 122820.‌

This study introduces Outer Plug Standardization (OPS), an innovative technique that serves as an alternative to traditional internal standardization in capillary zone electrophoresis (CZE). OPS was successfully applied to develop a high-throughput method for determining chloride (Cl^-), nitrate (NO₃^-), and sulfate (SO₄^2-) in rainwater samples.

Injection accuracy was evaluated and found to contribute minimally to error, with an average relative standard deviation (RSD) of 1.26%. The OPS technique significantly enhanced the precision of the method, improving intra-day and inter-day precision by 32.5% and 24.7%, respectively. Using a capillary with an effective length of 23.5 cm, the separation of the three inorganic anions was achieved in under 1 minute. The method demonstrated detection limits of 0.05 mg/L for chloride, 0.09 mg/L for nitrate, and 0.11 mg/L for sulfate.

To validate the method, a statistical t-test compared the results of 82 rainwater samples analyzed using both the newly developed method and the official APHA 4140 method. No significant differences were observed at a 95% confidence level, confirming the accuracy and reliability of the proposed technique for routine environmental analysis.