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

摘要

The development of a multipurpose integrated syringe-pump-based environmental-water analyzer (iSEA) and its application for spectrophotometric determination of ammonium is presented. The iSEA 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 o-phenylphenol. The effect of reagent concentrations and sample temperatures was evaluated. This fully automated analyzer had a detection limit of 0.12 mu M with sample throughput of 12 h(-1). Relative standard deviations at different concentrations (0-20 mu M) were 0.23-3.36% (n = 3-11) and 1.0% (n = 144, in 24 h of continuous measurement, similar to 5 mu M). Calibration curves were linear (R-2 = 0.9998) over the range of 0-20 and 0-70 mu M for the detection at 700 and 600 nm, respectively. The iSEA 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 (n = 26) showed no significant difference between results obtained by reference and present methods. The system is compact (18 cm x 22 cm x 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 mu L/run) and sample/standards (2.9 mL/run).