ninhydrin

Question 1

visualisation of latent prints using ninhydrin

Answer 1

1910 – Siegfried Ruhemann synthesizes 1,2,3-indanetrione by accident
1911 – Ruhemann gets a violet product with ammonia
1913 – Aberhalden and Schmidt note that the compound reacts with sweat (first to call it ninhydrin)
1954 – Oden and von Hofsten use a 0.2% ninhydrin/acetone solution to develop LP

Question 2

ninhydrin

Answer 2

• reacts with amino acid in sweat to give a purple colour
• has a high affinity for cellulose
• prints can be developed after a long period of time

Question 3

ninhydrin characteristic

Answer 3

rystalline solid, soluble in water and polar solvents, turns red in sunlight on heating, must be stored in a cool place

Question 4

formulation of ninhydrin reagent

Answer 4

Originally made up with acetone or ether (fire risk) as solvent. Conc acetic acid added to improve sensitivity

1974 – Morris and Goode introduce the first non-flammable formulation–
Does not dissolve ink BUT gives coloured background on banknotes and rag based writing papers.
-Banned in 1997 by the Montreal protocol “ozone layer”

1987 – Vienna Convention for the Protection of the Ozone Layer issues its Montreal Protocol, which phases out CFCs
1995 – UK HO PSDB recommends use of CFC replacements

Question 5

processing conditions

Answer 5

• Heating accelerates the development of fingerprints (up to 100 degrees)
• Relative humidity of 65% is needed as water catalyses the reaction
• exposure time is ~3 minutes, need a specially adapted humidity oven
• Marks developed using ninhydrin fade

Question 6

1981

Answer 6

complexes of Ruhemann’s purple with metal salts can be formed

Question 7

ninhydrin analogues

Answer 7

DFO
1950 – Druey and Schmidt synthesize diazafluoren-9-one
1990 – Pounds et al. report the first use of DFO to develop fluorescent prints

-DFO was the most sensitive AA reagent until the early 21st century
1993 – Frank et al. report the synthesis of DFO analogs – none were found to be superior to DFO

Question 8

main uses of DFO

Answer 8

-Latent and Bloodmarks on semi-Porous and Porous surfacesDFO (like ninhydrin) reacts with the amino acids present in fingerprints.
-The areas of application are the same: porous surfaces like paper, unpainted wood etc.
A fingerprint developed with DFO is less visible in white light than after treatment with ninhydrin but with green light (about 530 nm), it fluoresces strongly.

The fluorescence is viewed and photographed through orange or red filter (goggles).

Question 9

formulations of DFO

Answer 9

There are 3 formulations for DFO but the one using fluorisol allows other visualisation procedures to take place.

Can be developed at room temperature but takes longer.

Question 10

comparison between ninhydrin and DFO

Answer 10

• Ninhydrin, produces an intensely coloured product ‘Ruhemann’s purple’.
• DFO a pale pink extremely fluorescent product.

-Ruhemann’s purple fluoresces by complexing with metal salts but this additional process is still not as
sensitive as DFO.

-DFO requires heat for the reaction to proceed while ninhydrin will react at room temperature provided moisture is available

Question 11

IND

Answer 11

1958 – Cava et al. synthesize 1,2-indanedione
1996 – 5-methylthio-1,2-indanedione was the first analog prepared and evaluated
1996 – The parent compound was prepared and evaluated in September
1998 – IND and Zn mixing experiments initiated (not successful due to 1:1 mix)
2007 – Stoilovic et al. publish the first successful mixed IND-Zn reagent
Currently the most sensitive AA reagent

Question 12

1,2-indanedione

Answer 12

• like DFO It produces a weak initial print (pale pink) but has strong fluorescent detail when viewed under green light
• fluorescence stronger after treatment with zinc chloride

Question 13

IND disadvantages

Answer 13

• relatively short life as a working solution

- less likely to develop prints on low quality paper than DFO