Reverse Modified Griess Test
Nonporous or thick surfaces will not permit the passage of the acetic acid-bearing steam through the reaction layers. These materials (e.g., vinyl, wood, sheet metal, thick leather, carpeting, floor tiles, drywall) are not suitable for the Modified Griess Test since passage of acetic acid steam is critical to the color-producing reaction.
The Modified Griess Test has been altered to accommodate these materials as follows:
- Confirm nitrite sensitivity of test paper.
Tape a piece of filter paper to the back of a piece of nitrite-sensitive test paper. Using a nitrite test swab saturated with 15 percent acetic acid solution, dab the corners of the test paper. Each corner should turn orange, confirming the sensitivity of the paper to nitrite compounds.
- Mark reference points of evidence on test paper.
Arrange the evidence item face up and the treated paper emulsion side face down on the questioned surface. Using a pencil, index any points of reference.
- Apply acetic acid solution to test paper.
Wipe the emulsion-coated side of the test paper with cheesecloth saturated with the acetic acid solution. Lightly apply the solution to the entire surface. (Heavy application may cause indistinct or hazy results.)
- Create layers of reaction items.
Place the test paper emulsion side down on the evidence item. Apply heat using an iron to the back of the treated paper. (The back of the paper is covered by filter paper to prevent the iron from sticking to the treated emulsion-coated paper.)
- Examine and interpret results.
Separate the treated paper from the evidence item. Any orange indications on the paper are the result of a chromophoric reaction chemically specific for the presence of nitrite residues.
- Label and retain test paper.
Mark the previous pencil marks placed on the test paper in ink when the paper is dry. Label with additional data according to laboratory protocol.
Click here to watch a video on the Reverse Modified Griess procedure