A novel ammonium-free seawater preparation method for determination of trace quantities of ammonium in seawater

摘要

A novel method for preparation of ammonium-free seawater, which is used as a carrier solution and matrix for standard solutions, was designed. These standard solutions are used for calibration curve in flow analysis to detect trace quantities of ammonium in seawater. The system, which consisted of only a peristaltic pump and a hydrophilic-lipophilic balance (HLB) cartridge, was simple, convenient, and easy to operate. The original seawater used in the method could be collected from the coastal regions. And appropriate quantities of ophthaldialdehyde (OPA) and sulfite solution were added to the original seawater (The molar proportions of ammonium : OPA : sulfite were 1 : 200 : 80). After allowing it to set for more than 16 h, the seawater was pumped through the HLB cartridge. The reaction product of ammonium (present in the matrix), OPA and sulfite was retained by the HLB column and the solution coming out of the cartridge was ammonium-free seawater. The ammonium in the original seawater was efficiently removed and also its concentration in the ammonium-free seawater prepared by this method was much lower than that of the seawater collected from the surface of the South China Sea. The difference in the salinity of the seawater before and after the process was negligible, and also the pH was slightly increased. Moreover, ammonium-free seawater could be prepared whenever required, and contamination due to transportation and storage could be prevented.