Griess

The Griess test, or Griess reaction, is a colorimetric assay used to detect nitrite ions in a sample. It was developed in the 19th century by German chemist Peter Griess and has since become a standard method in chemistry, medicine, and environmental testing. The assay relies on a diazotization–azo coupling reaction that produces a colored compound.

In the procedure, nitrite reacts with sulfanilamide under acidic conditions to form a diazonium salt. This intermediate then couples with N-(1-naphthyl)ethylenediamine to yield a pink to red azo dye. The intensity of the resulting color is proportional to the nitrite concentration within a specific range, allowing quantification by spectrophotometry or visual comparison.

Applications of the Griess test are broad. In clinical settings, it is used for rapid screening of urinary tract infections, since many bacteria reduce nitrate to nitrite, yielding a positive test in urine samples. In environmental analysis, it serves to monitor nitrite levels in drinking water, surface water, and wastewater. In food and beverage testing, it helps detect nitrite as a preservative. The method also underpins the Griess assay for measuring nitric oxide metabolites in biological samples, typically after a nitrate-to-nitrite reduction step to assess total NOx.

Reagents commonly involved include sulfanilamide in acid and N-(1-naphthyl)ethylenediamine dihydrochloride. The assay can be affected by interferences such as reducing agents, turbidity, or colored matrices, and nitrate determination requires a prior reduction step to convert nitrate to nitrite.