Forensic S&ence International, 53 (1992) 51- 60 Elsevier Scientific Publishers Ireland Ltd.

51

THIN LAYER CHROMATOGRAPHY OF COMPUTER PRINTER RIBBON INKS

NAVNEET KAURa, OM PRAKASH JASUJAa and ATUL K. SINGLAb

aDepartmat of Forensti Science, Punjabi Unive-rsity, bForensic Science Consultant, Patiala-147 002 (India)

(Received August Z’th, 1991) (Revision received November lOth, 1991) (Accepted December 30th, 1991)

Summary

Twenty-five computer printer ribbons, al1 black in colour, were analysed by thin layer chroma- tography. With the use of proper solvent solutions al1 different brands were differentiated on the basis of colour spots and their RF values.

Key words: Computer crimes; Questioned documents; Thin layer chromatography

Introduction

Computer printed documents (computer printouts) make a distinctive group of documents. Occasional problems may arise about the source and authenticity of these printouts. The print quality, print style, alignment and other unique identi- fying characteristics may be helpful in the examination of these documents using methods for conventional typescript examinations. In addition thin layer chro- matography of the inks from these printouts may provide an additional alter- native for comparing two printouts or to establish the identity of the printer in cases where the printer ribbon may not have been yet changed.

Thin layer chromatography is probably the most widely used technique to dif- ferentiate between similar coloured inks and almost every type of ink available has been analysed with the help of this method [l - 91. While reviewing the literature, the authors could not find any reference to thin layer chromatography of computer printer ribbon inks, and it would seem no work has been reported so far on this problem.

In the present study, various computer printer ribbon inks have been differen- tiated with the help of thin layer chromatography.

Correspondence to: O.P. Jasuja, Lecturer in Forensic Science, Punjabi University, Patiala 147-002, India.

0379-0738/92/$05.00 0 1992 Elsevier Scientific Publishers Ireland Ltd. Printed and Published in Ireland

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Materials and Methods

Twenty-five computer printer ribbon inks of different brands were collected from various computer centers. Al1 the ribbons appeared black in colour. A smal1 sample of about 0.5 cm2 was cut from each ribbon and extracted in 1 ml pyridine for 30 min. The colour of each extract was noted and stains of these ex- tracts were prepared on a white sheet of paper. Also a few lines were drawn by writing some strokes with the ribbon pressed against the paper. Round plugs (8 - 10) were punched from these strokes with a modified hypodermic needle and then extracted with pyridine. The number of plugs used depended on the intensi- ty of the stroke. The ribbons, extracted stains and writing strokes were exam- ined under ultraviolet radiation for any flourescence. The colour of these extracts, stains and writing strokes were noted. Al1 the samples were divided

TABLE 1

COLOR OF STAINS OF SAMPLES (IN DAYLIGHT)

Specimen no. Brand of ribben

2 T.L. System’ 4 Gold Line’ 6 Ink Link’ 8 Full Mark 9 Uni Products

11 Diablo ’ 19 Uni Products

Cokw of stain

Blue-black Blue-black Blue-black Light blue-black Blue-black Blue-black Blue-black

code no.

A B C D E F G

1 Klear Point 12 Trent 16 Epson LX 80 17 Full Mark 23 L and T 24 Universal

Black Black Black Black Black Black

3 Data Products 5 Peng Gone 7 Kores

10 Universal 15 Kores 13 Gold Line 14 Kores

Violet-black Violet-black Violet-black Violet-black Violet-black Violet-black Violet-black

18 Data Products 20 TVSE 21 Ink Line 22 Matrix 25 Honeywell

Violet-black Violet-black Violet-black Violet-black Violet-black

U V W X Y

‘Plastic ribbons: al1 other are cloth ribbons.

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TABLE 2

BLUE-BLACK COLORED INKS

Solvent front run: 9.8 cm; temperature: room temperature (32°C).

Sample na.

A

spots

No. of spots

8

color of spots

Blue Torquoise blue Purple Blue Violet Purple

RF Values

0.041 0.071 0.194 0.316 0.449 0.755

C

D

E

11

Violet 0.918 Torquoise blue 0.973 Torquoise blue 0.041 Torquoise blue 0.071 Pink 0.194 Pink 0.214 Blue 0.326 Violet 0.439 Purple 0.765 Violet 0.928 Torquoise blue 0.973

Blue 0.041 Torquoise blue 0.071 Pink 0.184 Purple 0.204 Pink 0.234 Blue 0.326 Violet 0.449 Pink 0.653 Purple 0.765 Violet 0.918 Torquoise blue 0.975 Pink 0.347 Purple 0.367 Torquoise blue 0.428 Torquoise blue 0.459 Black 0.541 Torquoise blue 0.561 Skyblue 0.938

Pink 0.357 Purple 0.367 Torquoise blue 0.459 Black 0.531 Torquoise blue 0.561 Skyblue 0.959

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TABLE 2 (continwd)

Sample no. spots

No. of spots colm of spots

RF Valws

F 14 Purple 0.031 Blue 0.061 Pink 0.092 Purple 0.204 Blue 0.306 Pink 0.367 Torquoise blue 0.398 Skyblue 0.428 Blue 0.459 Skyblue 0.50 Pink 0.643 Purple 0.785 Violet 0.918 Torquoise blue 0.969

11 Pink 0.367 Purple 0.388 Violet 0.479 Blue 0.49 Purple 0.50 Black 0.52 Purple 0.531 Torquoise blue 0.551 Pink 0.888 Purple 0.939 Pink 1.0

into three groups based on the colour of the extracts and stains (Table 1). Thin layer chromatography of each sample was performed on precoated Silica Gel-60 glass plates of 0.25 mm layer thickness showing no flourescence (Merck, Darn- stadt, Germany). Three standard size spots from each sample (i.e. one each from ribbon extract, stain and written stroke) were applied with disposable capillaries. In the cases of dilute extracts, extracts were applied repeatedly to the same spot. After drying the spots, the plates were kept in a saturated developing chamber containing a solvent system for 35 min at room temperature (31 f 2°C). After development, the plate was taken out of the chamber and the solvent front was marked. The developed plates were allowed to dry in the open.

They were then examined in daylight as wel1 as under ultraviolet radiation for any additional spot or fluorescente of the spots.

Results and Discussion

Al1 twenty-five ribbon samples, which appeared black in daylight could not be

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TABLE 3

BLACK COLORED SAMPLES

Solvent front run: 10 cm; temperature: room temperature (31°C).

Sample no. spots RF values

H

No. of spots

4

color of spots

Black Pink

Sky Pink

0.04 0.13 0.79 0.99

1 7 Pink 0.26 Pink 0.33 Pink 0.51 Sky 0.79 Blue 0.98 Pink 0.99 Brown 1.00

J

K

L 7

Skyblue 0.8 Blue 0.98 Pink 0.99

Black 0.14 Violet 0.21 Pink 0.24 Blue 0.26 Torquoise blue 0.30 Black 0.32 Skyblue 0.79 Green 0.98 Pink 0.99

Purple 0.24 Pink 0.26 Torquoise blue 0.33 Skyblue 0.81 Blue 0.97 Pink 0.99 Brown 1.0

M 5 Pink 0.18 Pink 0.24 Skyblue 0.81 Skyblue 0.98 Pink 0.99

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TABLE 4

VIOLET-BLACK COLORED INKS

Solvent front run: 7.5 cm; temperature: room temperature (32°C).

Sample 120. spots

No. of spots cobr of spots

RF Values

N 6 Violet 0.466 Purple 0.615 Light purple 0.626 Pink 0.720 Deep blue 0.92 Black 0.973

Violet 0.360 Blue 0.493 Purple 0.533 Light purple 0.613 Pink 0.693 Blue 0.933 Black 0.986

Violet 0.333 Blue 0.507 Purple 0.889 Light purple 0.613 Pink 0.693 Brown 0.88 Green 0.933 Brown 0.986

Violet 0.40 Violet 0.466 Purple 0.533 Light purple 0.626 Pink 0.693 Green 0.933 Brown 0.986 Violet 0.44 Violet 0.48 Purple 0.533 Light purple 0.613 Pink 0.933 Blue 0.986 Brown 1.0

Violet 0.36 Purple 0.52 Light purple 0.613 Pink 0.693 Brown 0.907 Green 0.933 Brown 0.987

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Table 4 (Cmtinud)

Sample no. spots RF Values

No. of spots cokn” ofspots

T 7 Violet 0.36 Purple 0.507 Light purple 0.613 Pink 0.693 Brown 0.893 Green 0.933 Brown 0.973

U

W

7

8

5

7

Violet 0.36 Purple 0.533 Light purple 0.627 Pink 0.720 Pink 0.733 Deep blue 0.933 Black 1.0

Violet 0.306 Violet 0.360 Purple 0.40 Purple 0.533 Light purple 0.613 Pink 0.707 Blue 0.96 Brown 0.986 Purple 0.52 Grey 0.613 Black 0.786 Deep blue 0.946 Black 1.0

Violet 0.32 Violet 0.386 Purple 0.533 Light purple 0.626 Pink 0.72 Blue 0.933 Brown 0.986

Y 4 Violet 0.386 Purple 0.52 Pink 0.626 Blue 0.92

differentiated under ultraviolet radiation as none of the samples showed any fluorescente.

It was interesting to note that while al1 the ribbons and their strokes were black, this was not the case of their extracts and stains. Of the twenty-five

58

samples, extracts of ‘7 were blue-black, 6 were black and 12 were violet-black. In this way the twenty-five samples could be subdivided into three groups (Table 1).

Within the three sets no differente in RF values or number of spots were developed. There were differences in the intensity of the shades of the spots. The spots developed from written strokes were less intense, while they were darker in the case of stains and ribbon extracts.

Tables 2-4 record the developed spots and their RF values for the ink samples. Figures 1 - 3 are diagrammatic representations. It is evident from the Tables that the inks of the three subgroups display different colours and dif- ferent RF values.

For the separation of the various inks a number of solvent systems reported in the literature were tried. It was found that the violet-black group could be separated and differentiated effectively with the solvent suggested by Brunelle et al. [8] for TLC of conventional typewriter inks (butanol:ethanol:distilled water 50:10:5). This solvent was not effective for the black and blue-black subgroups.

AP B C D E F G

Fig. 1. Diagramatic representation of thin layer chromatograms of blue-black inks. Spot colours iden- tified as: 1, blue; 2, black; 5, torquoise blue; 9, pink; 10, purple; 11, sky blue; 12, violet. See Table 2 for RF values. See Discussion for solvent.

59

09 02 ??s & i : 09

.i2 010 09

eg ??2 eg

??2

0 0 0 0 . 0 I* I

H I J K L M I idRlGl#

0 3

0 . . . . . . . . . . ??w- N I P 0 s R T LI V w X r

Fig. 2. Diagramatic representation of thin layer chromatograms of black inks. Spot colour identified as; 1, blue; 2, black; 3, brown; 5, torquoise blue; 9, pink, 10, purple; 11, sky blue; 12, violet. See Table 3 for RF values. See Discussion for solvent.

Fig. 3. Diagramatic representation of thin layer chromatograms of violet -black inks. Spot colours identified as; 1, blue, 2, black, 3, brown, 4, deep blue; 6, green; 7, grey; 8, light purple; 9, pink; 10, purple; 12, violet. See Table 4 for RF values. See Discussion for solvent.

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For these latter inks a series of tests was made with solvents based on polarity [lol. These experiments led to a solvent formula (butanol:ethyl acetate:chloro- form 1:1:2) for black inks. A solvent formula (ethyl acetate:ethanol:chloro- benzene:methanol:ammonia 2:3:10:3:0.5) was the most suitable for blue-black inks.

Conclusion

The computer printer ribbons, which were al1 black in colour, could be divided into three subgroups on the basis of the colour of their extract in pyridine. The inks of each sub-group and using a different solvent could be further successfully differentiated from each other by thin layer chromatography, except in the case of samples no. 14 and 15, both of which are the same brand (Kores).

Acknowledgment

The authors thank Mr. J. S. Juneja, Incharge, Computer Center, Punjabi University, Patiala, for providing the samples of computer printer ribbons.

References

1 S.N. Tiwari and N. Bhat, Thin-layer chromatography of fountain pen inks. Int. Grim. Police Rev., 260 (1972) 201- 203.

2

3

4

5

6

7

8

9

G.R. Nakamura and S.C. Shimoda, Examination of microquantities of bal1 point pen inks from documents by thin layer chromatography. J. Grim. Luw, Crim&oZ. PoZti Sci., 56 (1965) 280. R.S. Verma, K.N. Prasad and G.J. Mishra, Thin layer chromatographic analysis of fibre tip pen inks. For& Sci. Int., 13 (1979) 65-70. O.P. Jasuja and A.K. SingIa, Thin layer chromatographic analysis of fibre tip and hi tec point pen inks. Zndtin J. Forensic EX., 4(4) (1990) 167 - 170. R.S. Verma, K.N. Prasad and G.J. Mishra, TLC examination of dyes used in some Indian red coloured pencils. J. India Acad. Forensic Sci., 17 (1978) 69- 70. R. Jindal, O.P. Jasuja and R.M. Sharma, Thin layer chromatographic analysis of some coloured pencils. Zn&an J. Fwensic Sh., 4 (4) (1990) 191-202. O.P. Jasuja, A.K. SingIa and Seema B.L., Thin layer chromatographic analysis of Indian stamp pad inks. Forensic Sci. Int., 42 (1989) 255-262. R.L. Brunelle, J.F. Negri, A.A. Cantu and A.H. Lyter 111, Comparison of typewriter ribbon inks by thin layer chromatography. J. Fortic Sc%., 22 (1977) 807. E.A. Davis, and A.H. Lyter 111, Comparison of typewritten carbon paper impressions. J. Foren- sic Sci., 27 [2] (1982) 424-427.

10 J.M. Bobbit, Thin Luyer Chromatogruphy, Reinhold, New York, 1963.