Zinc v. Cadmium Reduction Method for Nitrate

[Dana Riddle]

Hi Randy,
I currently use the cadmium reduction method for testing nitrate with a correction for water salt content. Is the zinc-based test as accurate?

 

[Randy Holmes-Farley]

I'm not really sure on the relative accuracy of different methods, but zinc-cadmium together is a very common method.

https://www.nature.com/articles/srep20165?WT.feed_name=subjects_environmental-monitoring

The well-known zinc-cadmium reduction method is frequently used for determination of nitrate. However, this method is seldom to be applied on field research of nitrate due to the long time consuming and large sample volume demand. Here, we reported a modified zinc-cadmium reduction method (MZCRM) for measurement of nitrate at natural-abundance level in both seawater and freshwater. The main improvements of MZCRM include using small volume disposable tubes for reaction, a vortex apparatus for shaking to increase reduction rate, and a microplate reader for high-throughput spectrophotometric measurements.

and

spectrophotometric methods are by far the most widely used for nitrate determination based on the utilization of metallic granules, such as zinc16,17, cadmium18,19, vanadium20, hydrazine-copper21,22, and copperised cadmium23. Under the singe or combined action of metallic granules, nitrate can be reduced to nitrite for further detection based on the formation of a pink-colored azo dye derived from diazotizing nitrite with sulfanilamide and coupling with N-1-naphthylethylenediamine dihydrochloride24,25. Among them, the well-known zinc-cadmium reduction method is most widely used for nitrate determination in seawater due to its low cost and easy operation without using expensive instruments.

 

[Dana Riddle]

Just wondering. There was a comment about using the Red Sea nitrate kit. I've never used it but am familiar with the Hach cadmium reduction method. Thanks!

 

[RonK1911]

Dana, what correction factor do you use for your nitrate tests in saltwater?

 

[Dana Riddle]

Dana, what correction factor do you use for your nitrate tests in saltwater?

I ran samples of freshwater and saltwater spiked with a Hach nitrate standard, and looked at absorption over a concentration range. I have an Excel file. Somewhere.