Elimination of salt effect for the determination of nitrate in estuarine waters
Date Issued
2008
Date
2008
Author(s)
Ning, Ai-Hua
Abstract
The precision and accuracy of the copper-cadmium reduction method for nitrate determination have been evaluated for estuarine waters, and the interference induced by salinity has been studied. An erratic decay trend on the efficiency of the reduction column was found as salinity increases. Further study indicates that the efficiency is closely related to the concentration and pH of the complexing reagents ( NH4Cl or EDTA ) add prior to allowing the sample to pass through the column. Application of a combination of 4% w/v NH4Cl and 0.5% w/v EDTA gives more stable results than using either reagent alone. However, for estuarine samples with a wide salinity, the raw readings still need correction. Empirical formulae are proposed for this purpose: ( S ) = a‧S + E ( DDW std ) = ( E ( SW std ) - E ( DDW std ) ) /ΔS NO3- ] = { ( Abs total / k NO2- ) - [ NO2- ] } / E (S) here E, a, S, k represent efficiency of the column, slope, salinity, and slope for nitrite respectively. The above equation set provides a more accurate and convenient way to calculate the concentration of nitrate in estuarine environment with salinity ranging from 0 to 35.
Subjects
nitrate
Cd-Cu reduction method
salt effect
Type
thesis
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