Does anyone detect the 'salt effect' when determining ammona in seawater, highly saline water or brine?
How does the time of colouration change when using the indophenol blue reaction in salt water according to your experience?
Article A novel ammonium-free seawater preparation method for determ...
http://www.publish.csiro.au/en/EN07032
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.530.4693&rep=rep1&type=pdf
From our SOPs for foeld measurement of nutrients, the following note about ammonium measurement in hypersaline waters:
”Preparation of sample for ammonium testing: High salt levels interfere with colour development of the method reagents, so dilution may necessary. Similarly, very high ammonium levels, beyond the range of the test, may interfere with proper colour development. If dilution is required follow the instructions in Table One. Use a 1:2 dilution for most hypersaline samples (not fresh or seawater). Reserve higher dilutions for testing samples where a 1:2 dilution results in a turquoise colouration developing.
Dear Peri, thank you! This is consistent with our practical experience. In addition, high concentrations of ammonium are most common in hypersaline lakes. Dilution reduces the salt effect and decreases the sample concentration to the working range of determination.
I am sure that the combination of:
- method of additions;
- use blank based on salt matrix;
- and the dilution,
is the most correct way to measure ammonium in hypersalne water.
High-salt analytical chemistry is much more complicated than freshwater chemistry and I’m really interested in how our colleagues work.
When adjusting a standard method for hypersaline brines, I often find very little information in the method textbooks. Possibly because few people are testing hypersaline lakes. However, reviewing the package inserts put out by Merck for their tests (available online) is often informative, whether you use their product or not. Their interference table contains information on NaCl, but also other ions. In most hypersaline waters you need to consider the Ca, Mg, and SO4 concentrations as well. An example based on a blue indophenol reaction: http://www.merckmillipore.com/INTERSHOP/web/WFS/Merck-AU-Site/en_US/-/USD/ShowDocument-File?ProductSKU=MDA_CHEM-100683&DocumentId=201310.231.ProNet&DocumentUID=43001453&DocumentType=PI&Language=EN&Country=NF&Origin=PDP
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