Development of an Integrated Syringe-Pump-Based Environmental-Water Analyzer (<i>i</i>SEA) and Application of It for Fully Automated Real-Time Determination of Ammonium in Fresh Water

The development of a multipurpose integrated syringe-pump-based environmental-water analyzer (<i>i</i>SEA) and its application for spectrophotometric determination of ammonium is presented. The <i>i</i>SEA consists of a mini-syringe pump equipped with a selection valve and laboratory-programmed software written by LabVIEW. The chemistry is based on a modified indophenol method using <i>o</i>-phenylphenol. The effect of reagent concentrations and sample temperatures was evaluated. This fully automated analyzer had a detection limit of 0.12 μM with sample throughput of 12 h^–1. Relative standard deviations at different concentrations (0–20 μM) were 0.23–3.36% (<i>n</i> = 3–11) and 1.0% (<i>n</i> = 144, in 24 h of continuous measurement, ∼5 μM). Calibration curves were linear (<i>R</i>² = 0.9998) over the range of 0–20 and 0–70 μM for the detection at 700 and 600 nm, respectively. The <i>i</i>SEA was applied in continuous real-time monitoring of ammonium variations in a river for 24 h and 14 days. A total of 1802 samples were measured, and only 0.4% was outlier data (≥3 sigma residuals). Measurements of reference materials and different aqueous samples (<i>n</i> = 26) showed no significant difference between results obtained by reference and present methods. The system is compact (18 cm × 22 cm × 24 cm), portable (4.8 kg), and robust (high-resolution real-time monitoring in harsh environments) and consumes a small amount of chemicals (20–30 μL/run) and sample/standards (2.9 mL/run)