Griess reagent was first developed in 1879 by Peter Griess. It is used to determine the level of nitrites, chemicals that contain two oxygen molecules bound to a nitrogen molecule (O-N-O), in solutions. In the presence of nitrites, the reagent causes the solution to change color, to a deep pink. Nitrites are present in food and water, and high concentrations can be toxic to humans.
Peter Griess was a pioneer within the field of organic chemistry. He was the first to describe the Griess diazotization reaction, the basis for the Griess test, which detects nitrite molecules. This diazotization reaction describes the change of nitrite into a diazo compound, a compound that contains two nitrogen atoms linked together at the end of a molecule.
Griess reagent is made up of one part of a 1% solution of sulfanilamide in 5% phosphoric acid and 0.1% naphthylethylenediamine dihycrochloride in distilled water. Sulfanilamide is also known as sulfanilic acid and is normally a solid that dissolves in acidic liquid solutions. When in contact with nitrites, it forms a diazo compound. The napthyleneethylenediamine then turns the diazo compounds to a pinkish color.
The more nitrites in a solution, the more color that is produced by the addition of the Griess reagent. This entire chemical process forms the chemical basis for the Griess test. The color produced from the addition of Griess reagent is read off of a spectrophotometer, a machine that measures light transmittance or absorbance. The darker the color, the more nitrites are present.
There are many different contexts in which the measurement of nitrites is important. In forensics, the Griess test is used to test for nitroglycerine, an explosive compound. Griess reagent is used to test nitrite levels in food products, particularly meats. Nitrites are found in human blood as well, where high concentrations can be dangerous.
In the blood, nitrites react with hemoglobin and change it into methemoglobin. Hemoglobin is a protein found in the blood that carries oxygen from the lungs to cells throughout the body. Methoglobin cannot carry oxygen to cells; when hemoglobin is changed to methoglobin, it results less oxygen being transported through the body. Griess reagent is used to determine nitrite levels in blood plasma, the liquid that contains red blood cells. At high concentrations, nitrites are toxic and can cause death, so determining nitrite levels in the body is necessary for diagnosis of certain diseases and may be required during an autopsy.
