A modified method of on-line solid phase extraction and fluorometric detection for underway monitoring and onboard analysis of trace ammonium in seawater.

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Publisher: Elsevier B.V.
Document Type: Report
Length: 442 words

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Keywords Ammonium; Flow analysis; Fluorescence detection; Seawater; Matrix blank; Underway determination Highlights * An on-line automated shipboard underway analyzer was developed for continuously monitoring ammonium in seawater. * The modifications included establishing an automated sample loading way, improving the elution mode, optimizing reagent dosage. * Field tests were successfully carried out to prove the practicability. Abstract A sensitive and automated method for underway and onboard analysis of trace ammonium in seawater was established using on-line solid phase extraction and fluorescence detection. Ammonium reacted with o-phthalaldehyde and sulfite to produce isoindole derivative that was concentrated on a hydrophilic lipophilic balanced (HLB) cartridge and then rapidly eluted with ethanol and measured using a fluorescence detector. The work was modified from our previous developed method, where 30 mL of a seawater sample was introduced into a reaction bottle with a 10 mL pipette. In the modified method a 10 mL sample loop was adopted for sample introduction to reduce possible contamination caused by manual operation. More importantly, the present method makes underway monitoring much more automatic. The detection limit was 3.5 nmol L.sup.-1, and the relative standard deviation was 3.52% (n = 12) for a sample spiked with 40 nmol L.sup.-1 ammonium standard. The method was free of the effects of salinity, carry-over and dissolved organic matter, with recoveries between 94.0% and 106.1%. An equation was introduced to correct matrix effects, and pure water and seawater blank were found to be equivalent to ammonium concentration of 8.1 [plus or minus] 2.2 nmol L.sup.-1 and 6.0 [plus or minus] 0.8 nmol L.sup.-1, respectively. The correction method can also be introduced to determination of other trace analytes where matrix effect cannot be neglected. A technique of stopped-flow was adopted and stopped-flow time could be adjusted depending on the concentration of ammonium in the seawater samples. The sample throughput was 7--9 h.sup.-1, and the method permitted the analysis of samples over a wide range of concentrations. The modified method has been successfully applied for shipboard underway determination of ammonium in a coastal area and shipboard determination the ammonium concentration of discrete samples in three vertical profiles during a cruise in the South China Sea. Author Affiliation: (a) College of Ocean and Earth Sciences, Xiamen University, Xiamen, China (b) State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen, China (c) Key Laboratory of Marine Ecosystem and Biogeochemistry, State Oceanic Administration & Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou, China * Corresponding author Article History: Received 21 September 2020; Revised 14 April 2021; Accepted 16 April 2021 Byline: Ting Wang (a,b), Yongming Huang (b), Jin Xu (b), Weidong Guo (a,b), Yong Zhu (c), Dongxing Yuan [yuandx@xmu.edu.cn] (b,*)

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Gale Document Number: GALE|A664259229