If Griess reaction (predictably) does not help, take a look at the following publication for more sophisticated method:

http://www.ncbi.nlm.nih.gov/pubmed/18967191

For ultimate sensitivity look around if anyone in your institution has "nitric oxide" gas phase chemiluminescence analyzer (NOA 280 from Sievers Instruments; Boulder, CO or similar setup).  This is by far one of the more sensitive methods for detecting low levels of nitrites and nitrates.

Hope it helps.

Standard Methods for the Examination of Water and Wastewater. SM-4500-NO2. Colorimetric method, the de facto method for nitrite in water. You can easily detect 5 ug/L (ppb); if you are careful and have a good UV spectrophotometer you can get detection limits between 1 and 2 ug/L. Simple, fast, precise and cheap.

It is a usual method, known from literature. Even, spectrophotometrical test kits are available: ftp://www.mn-net.com/deutsch/Beipackzettel/NANOCOLOR/985069de.pdf

The simplest is spectrophotometrical test kit that uses tablets. I have used it.

Dear Sir;,The only thing that I can suggest is offering two articles I have published, one in 2005 and the other in 2012. I must add that the LOD in these articles are 1-22 mic.g/mL and 1mic.mol/L respectively. If you think these articles help you I can send them to you.

Hi Mortada

I agree with Crause and Bergmann,

Dear Prof. Tehrani

Could you please send me these articles.

Thank you

Hach instrument is an EPA approved instrument for the determination of most inorganic constituents of water including nitrite. You can search for nitrite method +Hach in google...

We have determined nitrite/ nitrate by spectrophotometer. Our results are published in repute journals and well cited. For best result, the analysis must be performed within few hours ( as early as possible ). And each day new standards have to be prepared and instrument must be calibrated perfectly. Repeatation of analysis increase the confidence level.

Standard Methods for the Examination of Water and Wastewater. SM-4500-NO2. Colorimetric method.

Hi Wael, 

First, Nitrite is not existing in drinking water open to the atmosphere because it is easily oxidized by oxygen and get converted to nitrate NO3. However, you can refer back to standard methods book, but easily you can analyze it using: 

1- HACH spectrophotometeric method with its ready-made reagent. HACH is existing all over the world. 

2- Ion Chromatography with specific columns. 

Regards,

http://www.sciencedirect.com/science/article/pii/S003991400100323X

Detection and determination of Nitrate and nitrite: A review

Please go through this research paper

It is relatively easy and widely described in literature. Test kit producers (Macherey&Lange, and others) offer special chemical kits for spectrophotometrical analysis. Nitrit can be formed in reducing reactions from nitrate (photolysis, photocatalysis and electrolysis). For latter we found it even when oxidizing anodes were used as counterelectrodes.

H1

Wael Mortada

Standard Methods for the Examination of Water and Wastewater. SM-4500-NO2. B .   Colorimetric method..I always work with this method .It measures from 5-1000 micrograms per liter