[Dkh7234]

Good Afternoon All,

I am doing scientific research in the agriculture field. I am testing various fertilizers and have been exploring my options as far as quantification of nitrogen in a sample.

Total Nitrogen = (1) organically bound nitrogen + (2) ammonia nitrogen + (3) nitrate nitrogen + (4) nitrite nitrogen

I've combed through various posts when I used the search feature for kjeldahl nitrogen. While there has been a wealth of knowledge, I am still missing a few pieces of information. I hope to take my understanding of this subject to the next level. I would like to perform TKN analysis at my facility.

I am aware that TKN (Total Kjeldahl Nitrogen) is organically bound nitrogen + ammonia nitrogen. I am in the process of putting together the necessary laboratory equipment to conduct a TKN test. There are a few uncertainties on my behalf that I would like to clear up.
1. First, I am extremely safety conscientious. All procedures will be conducted under a fume hood with all prophylactic mechanisms in place.
2. The digestion process requires expensive hotplates and heating blocks.  I would like to perform the process via an open flame. What is the general consensus on this? It would dramatically reduce my capital expenses if I could just use simple bunsen burners.
3. Can I pretreat my samples in such a way that nitrite and nitrate will be summed up in my final titration calculation?
4. Are selective ion probes applicable for quantification of nitrite and nitrate?
5. Here is a link to the Kjeldahl appartus I would like to put together. Recommendations? http://www.capitolscientific.com/Corning-3340-500-PYREX-500mL-Kjeldahl-Nitrogen-Distilling-Apparatus-Includes-Flask-Graham-Con?gclid=CPv8uovj0rgCFcmf4AodfDAAWw

Looking forward to the replies and information. Thank you kindly. Upon completion of this task, I will certainly compile all the information into a neat easy to read PDF for future inquires.

[Arkcon]

If you don't want to buy a heating block or steam plate, then I guess you don't have to.  You can use a Bunsen burner, heck, Wikipedia uses their pictures in its diagrams: http://en.wikipedia.org/wiki/Kjeldahl_method#Method  You'll want a good ring stand, and a wire gauze diffuser to protect the flask from too much heat.  And you'll have to be careful.  In my high school days, they were just phasing out the asbestos coated gauze for fiberglass coated gauze, but you still need it to protect the flask from the flame.  Its funny 'tho, you have a fume hood, and you can't spring for an electric heating mantle?  You're not lying about the fume hood and other precautions, are you?

[Arkcon]

Although, I'm not sure you need the Kjeldahl Nitrogen procedure.  Your analyates are already "digested" as it were.  I don't know if the respective nitrate and nitrite selective ion electrodes cross react with each other.  But, although its expensive, and crany to work with, ion chromatography can quickly give accurate quantitation of nitrate and nitrite.

[marquis]

Kjeldahl can be touchy to run.  Be careful on the titration.

I've only seen the test done with electrical heaters. Never seen Bunsen burners used.

We ran the test to determine the amount of nitrate in solutions. 


Good luck.

[Dkh7234]

Thank you all thus far for the information.

I have a fume hood and a bare bones laboratory. We have slowly been piecing equipment together.

A little research has yielded a protocol that uses salicylic acid in order to "recover" the nitrate and nitrite in the final titration. Does this sound familiar?

I'm going to need to run about 6 tests a day. I'm planning on purchasing 3 kjeldahl apparatus units. This way I can run a known standard and 2 tests at a time.

For titration, I'm going to pick up a 25mL Class A buret. They boast .1mL intervals.

I'm having second thoughts on using the bunsen burner. Might just pick up a digestion unit used somewhere.

Does anyone have any protocols? Specifically for fertilizer analysis. Always looking to read and see what other methods are out there.

[marquis]

With nitrates, it's probably a good idea to stick with electric. We had an eight station
electric heater for kjeldahl.  It worked, but needed some finesse.

Many agricultural companies have switched to Near Infra-red (NIR) for nitrogen analysis.
We investigated NIR for some pharmaceutical uses.  Ran into some validation
issues that prohibited it's use.

Don't know if NIR would work for your application, but it wouldn't hurt to check.