Page 1

Indian J. Arpl. Chem. Vol. 33, No. 6, 11)70.

Differentiation and Identification of Different Brands of Iron-base Writing Ink in Comparative

Examin~tion

of Questioned

Documents by .Thin .Layer Chromatography and

Spectrochemi~al

Analysis*

N. K. Seo and P. C. Gbosb WBST BBNOAL FORBNSIC SCJBNCB LABORATORY, CALCUTTA-12

.

.

I

( Received January 29, 1970 ) Thin layer chromatographic examination of different samples of iron-base writing inks, has been made in consideration of their · forensic importance. It has been found that TLC. examination of inks combined with spectrochemical studies provides a novel method for distinguishing between different brands of same class of writing ink from each other. This may be of immense value to forensic chemists. , ·

Methods are described for the separation and identification of the ink dyestuffs of different brands of iron-base writing ink by thin layer chromatography and determination of the proportion of one or more major constituents· by measuring their optical densities. The nature and amounts of the inorganic cations present in the samples are de~ermined spectrographically. A combined method of thin-layer chromatography with spectrophotometric and spectrographic · analysis can distinguish between different brands of iron-base writing ink and .provides a convincing proof of identity pr otherwise of two or more closely similar iron-base ink in the examina~ion of documents. The analysis of inks often plays an important part in document examination. In literature many articles have been published about the· analysis of the colouring matter of ink by paper chromatography which may serve to show jhat different. dyestuffs are present and sometimes to identify the actual dyestuffs 1 - 0 , 8 , 10 - 18 but very few abou~ TLC-separation of ink dyes. u The chromatography, electrophoresis 7 , 11 and micro-chemical tests often help to determine that a document has been written with a particular class of ink, e.g. iron-ba~e dyestuff or alkaline inks etc. These tests are of particular value in • Presented at the joint Convention of Chemists of C.S.T.R. held at I.I.T. Kharagpur in. December, 1969.

4


N. K..

358

SEN AND P.

C. GHOSH

demonstrating that two different inks have been employed on a single document. But if two brands of ink of the same路class of ink incorporating the same dyestuff have been used in writing certain passages路 or alterations in the text of the document it frequently occurs that no-definite differences are establish~d by the present methods of qualitative chemical and chromatographic analysis. We investigated in our laboratory to what extent' it would be possible to distinguish between the different brands of iron-gallotannate ink from each other by determining the proportion of two or more major constituents of this type of ink by measuring their optical densities. after their separation by TLC and determining spectrographicaiiy the nature and amount of inorganic cations present in different brands of tbe same class of ink. This is a new路 approach to the problem and few publications in this special field are found in literature.

EXPERIMENTAL

Ten samples of writing ink of different colours and brands of iron-base ink in common use were used in a series of experiments and tests were carried out, on a representative selection of popular blue, black and blue-black inks of Indian origin, which are generally used in writing documents. Trial experiments were carried out in the first instance, with the liquid ink taken directly from ink bottles supplied by courtesy of manufacturers.

Examination of fluid it;~ks : Ink dyestuffs were separated from each other and other ink components by thin layer chromatography on Silica Gel G.- Trial experiments .were performed with the followins solvent systems : _ (a)

n-butat;~ol-acetlc

acid-water in the ratio of 4.5 : 1 : 4.5 parts by volume

(b) phenol-water in the ratio of 1 : 4 parts by weight {c) absolute alcohol-water in the ratio of 5 : 1 parts by volume {d) absolute alcohol-water-acetic acid in the following ratios of {i) 120 : 17.2: 0.5 parts .by volume, (ii) 120: 17.2 : 1 parts by volume, {ii) 7: 1 : 0.5 parts by volume (e)

methanol-water in the ratios of (i) 6 : 1 parts by volume, (ii) 7 : 1 parts by. volume

(f)

absolute alcohol-methanol in the ratio of 1 : 1 part by volume

(g) methanol-ethyl acetate-water-acetic acid in the ratio of 10 1 30 : 10; 1.5 parts by volume .

(h) pyridine (i)

tetrahydrofuran

The separation of ink dyestuffs were found best with the solvent systems (a), (d)j and (g). Solvents of analytical reagent grade were used. Silica Gel plates (20 x 7.5 em) of ca 0.25 mm thickness were prepared by spread~ ing a slurry made in the proportion of 1 gm Silica Gel G (E. Merck) to 2 ml distilled


DIFFERENTIATION AND IDENTIFICATION OF DIFFERENT BRANDS

359

water with a specially made thin layer spreader as developed by Stahl• a which takes up the spreading mixture and it is applied uniformly in a thin layer. A layer of 0.25 mm proved s"uitable for analysis of writing inks. The plates were allowed to set in air for 10 min. and baked at 105"C for 45 min. The plates thus prepared were first washed with eluting solvent by ascending technique and then activated for 30 min at 105°C before spotting. The samp.les of ink from th~ ink-bottle were spotted by means of micropipette on five such plates. The chromatogram was developed with 50-100 ml of appropriate solvents for different brands of ink. After the development and drying, each plate was viewed under u.v. light and the Rf values and the fluorescence under u.v. light of· chromatograms were noted (Figs. 1 & 2 and Table 1).

17

0

0

t1

~

~

·1

{j

0::.

c::. 0

Q

0o·

0

0

0-

D

0

0 0

0,...

~

~

0

2

3

4

5

Fig. 1. Thin layer Chromatography of diff.:rent brands of iron-base writing ink on Silica Gel G t. Sulekha Special Royal Blue 2. Sulekha Ordinary Blue 3. Sulekha Executive Blue 4. Parker Qui~k Permanent Blue-Black S. Parker Quink Permanent Blue.

0

~ d

•t:)

' p

0

~ 0 ~

0 0

t;!

Q

7

e

0 0 0

'V

CJ

0

A.

~

-9

10

Fig. 2. Thin layer Cbromatog~;apby of different brands of iron-base writing ink on Silika Gel G 6. Pilot Royal blue 'l. Gdbb Special Blue-Black 8. Delu;~~e Camel Permanent Black 9. Deluxe Camel Permanent Blue 10. Standard writi_ng ink Permanent Blue


N. K. SEN AND P~ C. GHOSH

360 (

TABLE I

Chromatographic analysis of iron-base writing inks by TLC. on Sili~a Gel G Sample Commercial name Brands of the Solvent Number number of the writfng ·ink and their system•. of of ink ink (Iron-base) oris~nal colour .spots . ~ulekha

1 2

'

Sulekha

Main spot

Rrx1oo Minor

spot~

Special Royal Blue

a

3

5.9 (deep blue) 1

Ordinary Blue

a

5

40 (blue)

61.3 (pink) F 46.6 (deep pink) F 22.6 (blue violet) 8 (blue)

20 (light blue) 11.8 (pink)

3

Sulekha

·Executive Blue

a

5

39.4 (deep blue)

61.8 (light pink) F 46.0 (pink) F 22.4 (deep violet) 10.5 (blue)

4

Parker Quln.k

Permanent blue-black

g

5

36.6 · (blue)

66.6 (pink) 22'2 (deep violet) 16.6 (light violet) 5.5 (violet faint)

s

Parker Quink

Permanent blue

g

66 (violet)

73 (pink) 53 (blue violet) 37 (bl~ish violet) 25 " 12

6

Pilot

Royal blue

d (i)

6

13.63 (Pink)

53.63 (bluish violet) F 50.90 (green) 43.63 (light green) 27.27 (violet) 22.72 (greenish)

7

Gribb

Special blue-black

d (iii)

4

40.0 (Blue)

55.0 (pink) F 45 (faint pink) 20 (faint blue)

4

Deluxe Camel

Permanent black

a

9

Deluxe Camel ·

Permanent blue

a

4

10

Standard writing ink

Permanent blue

d (ii)

4

8

30 (red)

12 -(blue)

50 (deep blue)

62.5 (yellow) F 41.2 (green) F 12.6 (pink) 33.0 (pink) F 27.0 Oight pink) 4.0 (liglit blue) 27.27 (lig~t blue) 10.0 (bluish pink) 5.0 (blue)

•a=rr-butanol-acetic acid-water (4.5+ 1 +4.5) d=abs. alcohol-water-acetic acid (i) (120+17.2+0.5), (ii) (120+17.2+1), (iii) (7+1+0.5) g=m~thanol·ethyl acetate-water-acetic acid,( 10+30 + 10+ 1.5) 1=Colours of the major and minor spots are given in ( ) F=Faintly visible


DIFFERENTIATION AND IDENTIFICATION () F DIFFERENT BRANDS

361

路 Examination of ink dyt;tuffs and iron conJe"r of ink samples: (i) The major dye spots were marked and recovered by scrap'pjng off and extracted repeatedly with hot distilled water, filtered through glass wool and the filtrate collected separately. The general analytical properties of the class of dy&tuff&路 present in different. samples were studied with various reagents. (ii) Definite volume of the ink sample LD.Ol ml' was applied on TLC. plate. The chromatogram developed was air-dried and scrapped路 off and extrac_ted with methanol apd the solution was made up to 5 mi. The optical densities of these. solutions were determined colorimetricaUy at wav-e length of maximum absorption belwcen 500-650 mp. in a "Spectro路nic 20'' (Batii.sc:h .and Lamb). In a like manner an unstained portion of the chromatogram was scrapped off and extracted with methanol (E. Merck) filtered and filtrate was used as a control for adjustment of colorimeter. (iii) 5 m~ of each sample was heate.O in a 1()0 ml Pyrex conical flask with a mixture of nitric and sulphuric acids until all th.e organic material was de~troyed. The excess nitric acid was removed by h.eating, the mixture was cooled and a. few drops of 70-72% perchloric acid were added and boi1ed till the sulphurous fumes disappeared and the solution was perfectly water-clear and made up to a definite volume (20 ml).

The iron-content of the different brands of iron-base writing ink was determined colorimetrically at 480 mp. (thiocyanate methcd). Tbe results are shown in Table II.

TABLE [[ Number Original of colour the of sample ink 1 2 3

4

s

6 7 8

9 10

Major dyes~uft' present Class of dyest111f. identified

Blue Carbonium dyestuff Blue " Blue Blue-black " Blue Blue ,, Blue-black Black Blue Blue

.

..

.. ...

.

Quantity of iron in

Absorptiom spectra {)plical Maximum absorption in m.p density 605

ll.035

595

0.057

610

0.052 . ().032 0.091 0.105 0.054 0.022 11.012

6os 615 615

605 560 610 . 605

().C)51

ppm.

'

109.00 0.36 1.36 145.23 57.80 0.45 225.00 27.23 1.726 63.54

The ratio of O.D.of dyestuff to iron in ppm. 0.0005 0.1582 0.3823 0.00022 0.0016 0.2313 . 0.00024 0.8078 0.0070 0.0803

Spectrographic analysis of inorganic cation:s of different brands of iron-base writing ink : 6 ml of ink was slowly evaporated to dryness on a platinum crucibie on a water bath and the residue was ignited at a lo0w temperature until the carbon was comple~ely bum~ off. The ash was subjected ~o ~pe*ographlc analysis in a Hilger E-1


N. K. SEN AND P. C. GHOSH

362

large quartz spectrograph with arc condition, D. C, and pro-arc 3 amp. 5 sec. A weighed quantity of ash was mixed with spectrographically pure· graphi~e and burnt to completion at 8 amp. The line intensities were measured with Hilger non-recording microphotometer and the microphotometric reading between wa~elengtb region 2500 A and 3500 A were converted into intensities with ·the use of Siedel function. The photographic plate used was of Ilford Ordina_ry ( Fig. 3 and Tabl,e III ).

~.

!( ;~,: x;~·; ~~i ~:~~?~

:-

'

3

'

; .

l':"> ];$~'<'>;1 Fig. 3 : Spectrographic analysis of iron-base writing ink of different brands.

TABLE III _Number Name of brands of ink of writing ink sample

2 3

4 5

6 7 8 9

10

Major inorganic elements present io the sample

Sulekha-Special Fe Royal Blue Sulekha-Ordinary Fe Blue Sulekha-Executive Fe Blue Parker-Quink PerFe&Mn manent Blue Parker-Quink PerFe manentBiue Pilot-Roy,al Blue Fe Gribb-Special Blue Fe Deluxe-Camel PerFe rnanent Bla<"k Deluxe-Camel PerFe&Ni rnanent Blue ' Fe •standard Writing ink

Traces of inorganic elements detected in the sample

Remarks

Ca Mn Ni Cu Ag Pb

si

Ca Mn Ni Cu Ag Pb Ca

Mn Ni

Ag

Ni

Ag

Mn

Cu Ag

Mn Mn

Ni Cu. Ag Ni Cu Ag

Mn

Ag

Si Ca Mn

v

Mn

Pb

Cu Ni

Cu Ag

-

•Prepared in the laboratory with known quantities of constituents as a control sample.

DISCUSSION

The ink dyestuffs of different brands of the same class of iron-base ink have been separated by thin layer chromatography, which offers considerable advantages. over chromatography on paper. This technique of separation is better, very fast and


DIFFERENTIATiON AND IDENTiFICATION OF DIFFERENT BRANDS

363

the quantities required in this method are smaller than those needed for the corresponding method on paper. Moreover the dyespots are easily recovered, extracted by scrapp~ng off and qualitatively identified spectrophotometrically and their general analytical properties studied directly on chromatograms. It is clear from the chromatograms as路 shown in Figs. 1 & 2 and Table I that the di~erent

brands of the same class of iron-base writing ink give varying numbers of spots of individual components probably due to the presence of isomeric forms of dye and impurities in the commercial samples of ink tested. However on most chromatograms one or two main spots appear. The Rf value and the- absorption properties of the dye spots are usually sufficient. to characterise the dye. The proportion of the major constituents namely the dyestuff and iron-content of the (-iron-base ) ink samples are determined by measuring their optical densities spectrophotometrically at the point. of their maximum absorption. The ratio between optical density of dyestuff to iron-content in p.p.m. shows a definite difference in the different brands of iron-base writing ink. Further, a new approach to the problem of distinguishing between the brands of the same class of ink is based on identification of the inorganic elements present in the different brands of iron-base writing ink as shown in Fig. 3 and Table III. This combined method of chromatographic separation of ink dyestuffs by TLC. with spectrophotometric and spectrographic analysis of organic dyestuff& and inorganic elements respectively in ink have been of particular value in finding definite difference in the different brands of iron-base writing ink, which could not be distinguished by qualitative chemical and chromatographic analysis. Further work on application of these techniques in the ink writing on document is in progress. ae This .work was supported by grants from the Council of Scientific and Industrial Research, Govt. of India. .Our grateful thanks are due to Dr. S. Chowdhuri, Director of the Forensic Science Laboratory,. Home Department,. Goyt. of West Bengal and to Prof. (Mrs.) A. Chatterjee, University College of Science, Calcutta for their keen interest in the work.

REFERENCES 1. 2. 3. 4. 5. 6.

1. 8.

F. Angermayer, Krimlntillwissenschllft, 1954, 1, 41, Proceeding Kriminalistlk. K. A. Apps, Printing Ink Technology, Leodard Hill, London (1958). A. Bangsgaard, Kriminalistik, 1956, 1, 34. R. J. Block, E. L. Durrum and G. Zweig, A Manu!ll of Paper Chromatography & Pl.l.per Electrophoresis, Academic Press, New York, 1958. K. Bosch and B. Mueller, Arch. Krimlnol., 1960, 126, 15. J. M. Bracket and L. }\rand ford, J. Criminal L11w, Cri~inaf,. Police Sci., 1952, 43, 530, C. Brown and P. L. K1rk. )-, Crimina, Law, Criminal, Pollee Set., 1954, 45, 334. C. Brown and P. L. Kirk, J. Crim~nal Law, Criminal, PCJlice Sci., 1954, 45, 334.

V:路


N. K. SEN AND P. C. GHOSH

364

9,. 10. 11. 12.

13. 14.

IS. 16. 17. 18. 19.

20. 21. 22. 23. 24. 25. 26.

C. Brown and P. Kirk, Mikrochim, Acta, 1956, 1729. B. B. Cl•ldwell; AMly$f, 1955, 80, 68. D. B. Doud, J. Forensic Science, 1958, 3, 486. K. Koopmann, Chein. Weekblad, 1959, 55, 109. C. G, Macris and M. D. Tiganezis, Anal Ghim. A eta, 1955, 13, 129. E. Martin, Int. Crim. Pol. Rev., 1954, 81, 232. E. Martin, Int. Grim. Pol. Rev., 1955, 91, 257. E. Martie, Int. Crim. Pol. Rev., 1958, 114, 18. ~· M:ethyer, Int. Grim. Police Rev, 1961, 148, 130. S. Pougbeon, and z. Molester, Rev. Int. Crim. Pol. Tech .. (Geneva), 1958, 12. 207. P. s. R.aju, R. C. Banerjee and N. K. Iyengar, J. Forensic Sciences, 1968, 8, 268 (Tech. Section). Ch. Sannie and R. Moloster, Rev. Grimin. Pol. Teeh. (Geneva), 1952, 6, 154. A. W. Somerford,!nt. Grim. Pol. Rev., 1952, 59; 170. H. J. ·starclc, Krlminalwi$senchaft, 1954, 1, 85. Tewari, Swarup Narain, Arch. Kriminol, 1960, 1l6, 26. P Wolienweber, J. Gliromatog.,l962, 7, 557. Stahl. Thin-Layer Chromatography-A Laboratory Handbok, 1965, 6. N. K. Sen and 'P. C. Ghosh, J. Indian Acad. Forens Sci, 1910, 9, 54.

1970_Sen, Ghosh - Differentiation and identification of different brands of iron-base writing ink  

Methods are described for the separation and identification of the ink dyestuffs of different brands of iron-base writing ink by thin layer...

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