The determination of low-level ammonium in seawaters suffers from low sensitivity and high contamination; therefore, it is desirable to develop highly sensitive methods for automatic measurements. A highly sensitive and automated flow technique system for nanomolar level ammonium measurement is described. Reagents for Berthelot reaction were automatically added into seawater samples. After a 10 min reaction at 40°C, the formed indophenol blue compound was on-line extracted onto an Hydrophilic-Lipophilic Balance (HLB) cartridge. The enriched compound was rinsed with water and ethanol solution (30%, v/v) and, in turn, eluted with an eluent containing 30% (v/v) ethanol and 5.0 mM of NaOH, and determined with a spectrophotometer at 640 nm. Parameter, including extraction conditions, reagent concentrations, pH, temperature, and reaction time, were optimized. Under the optimized conditions, the detection limit was 3.5 nM and the linear range was 0–428 nM. The relative standard deviations were 5.7% (n = 8) for 44.6 nM standard solution and less than 6.0% (n = 3–5) for samples within concentrations of about 52.4–288.7 nM; the recovery was in the range 93.6 to 108.5%. The sample throughput was 3 h⁻¹. The proposed method provides a simple, cheap, and automatic way to determine ammonium in seawater samples without complicated sample treatment.

Item Type:	Refereed Article
Keywords:	ammonium, seawater, sequential injection, solid phase extraction
Research Division:	Chemical Sciences
Research Group:	Analytical chemistry
Research Field:	Flow analysis
Objective Division:	Environmental Management
Objective Group:	Marine systems and management
Objective Field:	Measurement and assessment of marine water quality and condition
UTAS Author:	Zhang, M (Dr Min Zhang)
ID Code:	104697
Year Published:	2011
Web of Science® Times Cited:	25
Deposited By:	Chemistry
Deposited On:	2015-11-18
Last Modified:	2018-03-17
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