J.R. Morris, G.C. Goode. Police Res. Bull. No. 24 (1974), 45-53 45

NFN - An Improved Ninhydrin Reagentfor Detection of Latent FingerprintsJ R Morris and G C Goode, AWRE, Aldermaston,Berks.

A previous article in this bulletin1 described someaspects of the research programme being carried outat AWRE Aldermaston under contract to PSDB onchemical methods for the detection of latent fingerprintson porous surfaces with particular reference to newreagents and techniques. This programme also includesan evaluation of reagents already in current police use.The mos t impor tan t o f these i s n inhydr in . Therecommended formulations and development conditionsfor this reagent vary widely and are often not optimumfor achieving maximum detection efficiency. This articlebriefly describes a new formulation for the ninhydrinreagent (N.F.N.) which offers important advantages insensitivity, low toxicity, non-flammability and good non-ink-running properties. It has been successfully testedunder operational conditions and is being recommendedby PSDB fo r genera l po l i ce use . Some typ ica lapplications of the new reagent are discussed.

Review of Ninhydrin Reagents

Ninhydrin was first used for fingerprint detection nearly20 years ago and since that time has established itselfas the reagent universally used for the detection of printson porous surfaces such as paper. It provides a means

of detecting, with high sensitivity the amino acid andammonia components of fingerprints and is relativelyclean and simple to apply. The chemical reactionsinvolved however are complex and its effectivenessdepends on the reactant concentrat ions and thedevelopment conditions in terms of temperature andt ime, the lat ter being of par t icu lar importance incontrolling the background colouration effects whicharise for many substrates. The first reported reagent wasby Oden2 in 1957 who recommended an acetonesolution of ninhydrin, acetic acid being added to maintaina high sensit ivi ty. Since that t ime many claims toimproved reagents have been made based on changesof composition, solvent and development conditions asshown in Table 1, but in general, little or no improvementover the original formulation was achieved. One of thesereagents described by Crown5, in which petroleum etherhas been used as solvent, has made a signif icantcontribution to the examination of documents by itsimproved non ink-running properties but the reagentappears to give poor sensitivity with some types ofpaper. This however, appears to be considerablyimproved by the addition of 1% acetic acid as illustratedin Figure 1.

J.R. Morris, G.C. Goode. Police Res. Bull. No. 24 (1974), 45-53 46

Fig 1 The effect of the addition of 1% acetic acid on the “Crown” ninhydrin reagent

J.R. Morris, G.C. Goode. Police Res. Bull. No. 24 (1974), 45-53 47

Improved Ninhydrin Reagent N.F.N.

In considering possible modif icat ions to ninhydrinreagents attention has been paid to safety, both in termsof toxicity and flammability since these are of particularimportance operationally where laboratory facilities areoften somewhat inadequate. All the solvents used incurrent reagents are highly flammable e.g. acetone ore ther and under some cond i t i ons a re po ten t ia lexplosives. Ignition by common electrical sources suchas switches, fluorescent fittings or other contacts canreadily occur and fires have been reported in fingerprintp rocess ing env i ronments . The so lven t t r i f l uo ro-trichloroethane (Fluorisol) which is essentially non-toxic,non-flammable and has little effect on most types ofprinting inks has been exploited as a suitable substitute.Further investigation revealed that ninhydrin is insolublein this solvent but a solution can be prepared if a smallvolume of ethyl alcohol and acetic acid is first usedfollowed by dilution with FluorisoI. The amount of thealcohol used must be kept to a minimum if the non ink-running properties and non-flammability of the Fluorisolare to be maintained. The formulation shown in Table 2was devised to give a general purpose reagent capableof achieving consistent results with a wide variety ofpaper substrates with minimal background effect.Recently a post-development treatment of the resultingfingerprint marks to give alternative colours or possiblya fluorescent image has been investigated. This in noway changes the sensitivity or properties of the NFNreagent and should prove useful tor coloured surfaces.The technique is at present undergoing operationalevaluation.

TABLE 1

SOME PUBLISHED NINHYDRIN REAGENT FORMULATIONS

Acetic

Author Solvent Acid Ninhydrin Remarks

Conc. Conc.

J. Oden2 Ether or acetone 4% 0.2% Highest sensitivity for amino acids

H A Speak3 Ethyl alcohol None 1.5%

N.S.Y.4 Acetone None 0.4% Acetic acid omitted to avoid diffusion

of chloride

D A Crown5 Petroleum ether None less than Good non ink-running properties.

0.7% Highly flammable

H Fritz and H Jordan6 Acetone/water 0.3% 1% Sample exposed to UV irradiation

before treatment

A J Brooks Jn.7 Ethyl alcohol None 1.5% Review article

D G Moony8 Ethyl ether None 0.5% Highly dangerous in untrained hands

New Ninspray Iso propyl alcohol Conc. 1.2% Proprietary aerosol pack

unknown

TABLE 2

PREPARATION OF NFN REAGENT

It is essential that all glassware used for preparing solution

should be thoroughly clean and dry.

1 Stock Solution

Mix:- 25g ninhydrin crystals

50 ml glacial acetic acid

100 ml absolute ethyl alcohol (ethanol)

Dissolve the ninhydrin in the alcohol, adding the acid

slowly and stirring until the solution is mixed. Filter and

store in well stoppered bottles in the dark.

2 Working Solution

Mix 30 ml of stock solution with 1000 ml of Fluorisol

(dried over molecular sieve type 3A) with stirring, allow

to stand for 30 minutes and filter if necessary.

It must be noted that whilst the working solution is

virtually non-flammable ethyl alcohol itself is highly

flammable and strict fire precautions must be taken

when making the stock solution. Additionally, with

prolonged use the working solution will tend to lose

Fluorisol by evaporation and hence the fire safety

margin is reduced. Therefore solutions should not be

left exposed to the air for long periods.

J.R. Morris, G.C. Goode. Police Res. Bull. No. 24 (1974), 45-53 48

Fig 2 A comparison of N.F.N. with “Ninspray” using a palm print on a split Embassy Cigarette packet

J.R. Morris, G.C. Goode. Police Res. Bull. No. 24 (1974), 45-53 49

Key to strips

A. Control strip. Not processed.B. Processes with Ninhydrin in Acetone.C. Processed with “Ninspray”D. Processed with Ninhydrin/Petroleum ether/

Acetic AcidE. Processed with the N.F.N. Reagent.

Key to ink lines1 and 2. Writing inks.3, 4 and 5. BaIl point pens.6, 7, 8 and 9. Fibre marker pens.10, 11, 12 and 13. Felt marker pens.

Fig 3 A comparison of non ink-running properties for ninhydrin reagents

J.R. Morris, G.C. Goode. Police Res. Bull. No. 24 (1974), 45-53 50

Fig 4 Application of N.F.N. to detection of fingerprints on the gummed surface of postage stamps

J.R. Morris, G.C. Goode. Police Res. Bull. No. 24 (1974), 45-53 51

Fig 5 A comparison of freshly prepared N.F.N. with 6 months old reagent

J.R. Morris, G.C. Goode. Police Res. Bull. No. 24 (1974), 45-53 52

Method

To achieve best development of the latent impressionthe sample is simply dipped in the NFN working solutionuntil fully wetted (5-10 secs) and the solvent is allowedto evaporate at ambient temperature (or 2 mins).Brushing is an alternative technique but difficulties areencountered when spraying as an aerosol. The samplemay then be heated for a short period, the duration ofwhich depends upon the temperature e.g. 20 minutesat 60°C or 2 minutes at 120°C. The developed imagecan be viewed after 1 hour, though some marginalimprovement is sometimes obtained after a further 48hours. The optimum development conditions for anyninhydr in reagent depend to some extent on thepar t i cu la r subs t ra te invo lved s ince the ra te o fdevelopment of the background colouration, due to thepresence of ninhydrin positive materials if different fromthat of the print itself. In general the development offingerprint marks with the NFN reagent is more rapidthan with other formulations described. For substrateswhich give rise to background difficulties e.g. sometypes of surface coated papers including cigarettepackets, high quality note paper and some postal ordersthe best results are achieved without heating, samplesbeing s imply s tored in the dark for 24 hours, oroccasionally up to 72 hours. With any of the abovedevelopment conditions the most permanent image isobtained if samples are stored in sealed polythene bagsin the dark.

Results

Under laboratory conditions using low background paperthe sensitivity of NFN has been shown to be as high asany other ninhydrin formulations. However for surfacesexhibiting background colouration problems, the newreagent offers significant improvements as illustratedby a comparison with a commercial ninhydrin aerosolspray applied to Embassy cigarette packet in Figure 2.The effect of the reagent on most common types ofprinting inks is minimal as shown by comparison withother reagents in Figure 3. It has also been found to beeffective for detection of prints on gummed surfaces e.g.sheets of postage stamps as illustrated in Figure 4.

Operational Experience

The NFN reagent has been evaluated under operationalconditions by eight regional police forces over a periodof 6 months. At a recent meeting organised by PSDBfingerprint experts were unanimous in their acceptance

of NFN as an excellent general purpose fingerprintreagent and concluded that i ts use had led to asignificant improvement in detection efficiency with anoverall reduction in processing time. They also reportedfavourably on the non ink-running properties in theexamination of documents and on the safety aspects.The shelf life of the reagent has been established to benot less than 6 months and no apparent difference hasbeen observed using reagent stored for that periodcompared with fresh material (Figure 5).

In spite of the success of the new reagent it must notbe concluded that this or any other formulation ofninhydrin will be universally applicable. Many absorbentsurfaces remain which react so strongly with the reagentthat the background colouration precludes its use forf ingerpr in t detect ion. These inc lude papers wi thpart icular surface coatings e.g. bank notes, somecheques and postal orders, rag based writing papersand surfaces which have been exposed to high humidityconditions. It has not been successfully applied to non-absorbent surfaces such as plastics or ceramics forwh ich a l te rna t i ve chemica l methods a re underinvestigation.

Conclusions

The NFN is one of a suite of chemical reagents whichshould offer significant advantages in operational policeuse. This new formulation is being recommended byPSDB as a replacement for other ninhydrin reagents incurrent use and the continuing feedback of commentsresulting from its adoption is to be encouraged if futureproblem areas are to be effect ively ident i f ied. Asresearch continues on the evaluation of new reagentsfor fingerprint detection it becomes more apparent thatno single chemical system is likely to be applicable toall cases and that the future trend wil l be towardsdefining appropriate reagent selection criteria so thatthe most effective use can be made of new reagents asthey become available.

Acknowledgments

The work is being undertaken under contract to thePolice Scientific Development Branch, Home OfficeThanks are due to Dr A M Knowles (PSDB) for hisinterest in this work and for useful comments anddiscussions. The authors wish to acknowledge Mr. J RGoodchild for his technical assistance.

J.R. Morris, G.C. Goode. Police Res. Bull. No. 24 (1974), 45-53 53

References

1 J R Morris, G C Goode and J W Godsell. PoliceResearch Bulletin No. 21 1973.

2 S Oden. B.S. Patent 767,341. January 30 1957.

3 H Speak. ldentification News. March 1964.

4 New Scotland Yard data sheet

5 D A Crown. J Criminal Law, Crimonology and PoliceScience 1969, 60, 258.

6 H Fritz and H Jorden. Arch Fur Kriminoligie.May 1970.

7 A J Brooks. Fingerprint and Identification Maga-zine November 1972.

8 D G Mooney. Identification News September1973 9.