I could be wrong, but I don't think Hach has an EPA approved method for testing Nitrate on the spectrophotometer. If so your nitrate results should not be used for permit reporting. Nitrite by TNT is compliant though. Check your manual, Hach catalog or call Hach.
David

There is a colorimetric method for both nitrate and nitrite. The nitrite is SM 4500 NO2, SM 4500 NO3, the nitrite method is very simple while nitrate one needs some preparation in water bath.

You may do nitrate by electrode if you get an electrode and ISE meter.

The last time I checked 40 CFR 136 I only saw Cadmium reduction, ISE probe, or IC methods approved for reporting. Maybe I overlooked a method so let me know.

I would like to see some other methods such as the UV method approved so that nitrate would be easier to analyze.

Nitrate is a significant pollutant in streams so more dischargers need to monitor so that the impact on the environment can be assesed.

Hey Victor;

Readily admitting up front that HACH is my competitor and looking at the regulatory docs for (N) measurements per method 352.1 EPA NPDES permit specs allows for Spectrophotometers to measure (N).

The WTW 6100/6600 Spectrophotometers will perform the measurement to EPA specs.  

So as you correctly point out one must be careful when going by the HACH claims of compliance.  Yes, they have EPA compliant meters, but one must read fully at WHAT LEVEL of compliance does their meter work.

Dallas

Making a manual Cd reduction column is approved for regulatory analysis.  You just have to make sure you prep your Cd properly.  The biggest problem with doing it that way is ensuring consistent flow/contact times with your samples.

I think the Cd reduction method is probably the easiest way to go because determining nitrite is quick and easy.  I had been using a non-EPA approved Merck NO3 method where NO3 reacts with a "benzoic acid deriviative" in conc sulphuric to form a red nitro compound.  I used this for non regulatory work but I do not like working with conc sulphuric nor dealing with the hot temperatures involved when the sample is added.  It was also subject to salt interference.

I am planning to get TN and TP approved using Merck kits because they work very well but the NO3 has been the stumbling block for us.  Cd reduction looks like the goods, and you can re-activate too.

Greg.

There's also hydrazine sulfate reduction. Though the N2H4 is pretty toxic it's also quite easy to oxidize with chlorine, or whatever; no heavy metals issue.

The Systea Easy method is included in the newly signed 17 April 2012 Methods Update Rule--it has not been published to the Federal Register as of yet:

http://water.epa.gov/scitech/methods/cwa/update_index.cfm

What kinds of discrepancies do you see? Give us a little more information before we can formulate any thoughts.

If you could provide some Hach test method numbers or the part numbers for the reagent kits you are using that would help.  I couldn't find anything that referenced those ranges that you gave. I'll try and give some helpful general advice.

First the nitrite testing. I would definitely go with the lower range testing kit. You can easily dilute your samples by 2x or 5x to get them within the test range. The standard you are using is very close to the detection limit and as you noted the results you get are pretty good for that level. Just out of curiosity, why are you using silver nitrite as the standard solution? If I recall correctly, silver will actually precipitate out with these reagents and the test conditions. Try using a potassium or sodium nitrite salt. Also, make sure you have the standard concentration calculated as nitrite not as silver nitrite.

For the nitrate test, what is the standard made of? Again, try to go with the sodium or potassium salt. Be sure you are following the timing exactly right on this. The cadmium reduction is time sensitive. The color development stage also must be allowed to proceed to completion. Measuring too early will lead to low recovery.

This is what I am using:

HACH nitrate method 8039 cadmium reduction method HR (0.3 - 30 mg/L NO3 --N) using NitraVer® 5 Nitrate Reagent Powder Pillow
and
HACH nitrite method 8153 ferrous sulfate method HR (2-250 mg/L NO2-)
using NitriVer® 2 Nitrite Reagent Powder Pillows

Sorry for the confusion, initially, I used Sodium nitrite at 10 mg/L and detected around 5 and 8 mg/L using HACH method. ( 10mg/L is used because that is approx what is detected in my experiments)

Then I saw that standard method uses 200mg/L sodium nitrite as accuracy check but I measured 110-115 mg/L which is nowhere close.

I will probably use the dilution method and use lower concentration testing method by HACH.

For nitrate, I am using the Nitrogen-Nitrate Standard Solution, 10 mg/L as NO₃-N ;Product #:30749

@david.S.: Is color development stage the reaction time? I have followed the timing as written in the instruction..

@Dedalus: Is the Cd column the one mentioned here? http://www.umass.edu/tei/mwwp/acrobat/sm4500NO3e.PDF
seems like a lot of work involved; so I can use the HACH powders, but with that column instead of the bottles? Currently, I am considering using probe by HACH to detect nitrate in an attempt to save myself from even more trouble.

Hi jeffryy
I used Cd reduction method in determination of NO3
this method is not really Repeatable method it is very dependent on how you shake it!!! you have to shake your cell very vigorously and very reproducible.