Application of UV-Visible Spectrophotometry to Differentiate Inkjet Printer Inks Extracted from Printed Matter

Rashmi Sharma¹, T.R. Baggi², A.K. Gupta³

¹Senior Scientific Assistant, Forensic Science Laboratory, Rohini, GNCT of Delhi-110085

²Academic Coordinator, Forensic Science Unit, Department of Chemistry, University College of Science, Osmania University, Hyderabad, A.P. 500007

³Head, Department of Forensic Science, SHIATS, Allahabad, U.P.-211007

*Corresponding Author E-mail: rrashmi_amity@yahoo.com

ABSTRACT:

The UV- Visible absorbance profile of cyan, magenta, yellow and black coloured inkjet printer inks for the differentiation and comparison was obtained by scanning the ink extracts under the wavelength range of 200-800 nm. The various parameters of absorption studies of extracts of different components of printer ink formulations in the visible and UV region enables to differentiate and distinguish different colour print document samples of distinct composition by their characteristic absorbance spectra and profile pattern.

KEYWORDS: UV- Vis Spectroscopy, Inkjet printer inks, Cyan, Magenta, Yellow, Black

INTRODUCTION:

UV-Visible Spectrometry is a technique used to identify the components of various inks as many of them show absorbance in UV or visible or in both the regions. The UV-Vis Spectrophotometric analysis of ink can provide valuable data to differentiate inks of different compositions whether they belong to same source or different one. The analysis involves scanning of extracted ink solutions in UV and visible range and to record the absorbance spectra. Some inks fluoresce on exposure to ultraviolet, light while some others become invisible. Each ink would give a distinct absorbance spectrum and therefore the same can be compared with the spectra of standard inks or admitted / specimen documents.

Ultraviolet–Visible spectrophotometry in this context can be carried out in absorption mode or reflectance mode. The absorption or reflectance in the UV-visible range directly affects the perceived colour of the chemicals involved. In this region of the electromagnetic spectrum, molecules undergo electronic transitions.

The UV-Visible spectrometer works on the ability of UV Visible radiation to promote an electron to a higher energy level. The basic principle of UV-Visible absorption is that the molecules containing π-electrons or non-bonding electrons (n-electrons) can absorb the energy in the form of ultraviolet or visible light to excite these electrons to higher anti-bonding molecular orbital. The more easily excited the electrons (i.e. lower energy gap between the highest occupied molecular orbital, HOMO and the, lowest occupied molecular orbital, LUMO), the longer the wavelength of light it can absorb. The molar absorption coefficient is a constant for every substance and is a measure of the amount of radiation absorbed per unit concentration of a substance.

The microspectrophotometry of UV-visible range has been a mainstay of ink analysis for several years.  However, very little work has been done to analyze the UV-visible characteristics of printer inks and papers.  The characteristic and specific wavelength at which the absorbance takes place, both in the UV and visible range are useful in identifying printer inks.

This study was undertaken to provide a profile of inkjet printer ink using UV-Visible spectrophotometry in order to assist document examiners in their routine casework especially when it relates to the comparison of ink with that of a seized cartridge or suspected inkjet printer. In this work an attempt has been made for the differentiation and comparison of inkjet ink using UV-visible spectrophotometry.

EXPERIMENTAL:

Sampling:

32 coloured documents each containing rectangular blocks of Cyan, Magenta, Yellow and Black colour were printed from inkjet printers of four leading manufacturers. White paper of A4 size from the same company was used to print all the samples. The colours were selected by following RGB model. All four printed colour i.e. Cyan, Magenta, Yellow and Black from each printout i.e. total of 32 x 4=128 samples were analyzed and interpreted.

The four leading brands were marked as A, B, C and D and their different models were marked as 1, 2, 3 and so on. The samples were given marking as 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 26, 27, 28, 30, 31, 32 for different models of brand ‘A’ , 16, 18, 19, 23, 24, 29 for different models of brand ‘B’_, 12, 13, 20, 21 for different models of brand ‘C’ and 14, 15, 17, 22, 25 for different models of brand ‘D’.

Sample Preparation and Scanning:

The samples for analysis were prepared by cutting a coloured squared block of 3X3 cm into pieces. The pieces were then transferred to 15 ml beaker and triturated with 10ml of methanol ^14. The sample was then allowed to be extracted at room temperature with intermittent shaking. The methanol extract was then transferred to 10 ml volumetric flasks after filtering through a Whatman No.1 filter paper. 1 ml of methanol extract was taken and made up to volume of 10 ml. The same procedure was followed for all samples for Cyan, Magenta, Yellow and Black inks. In order to avoid any interference and to record the response of background i.e. paper and the reagent i.e. methanol towards UV-Vis, the blank samples of paper and reagent were also prepared following the same procedure. The four blank samples of paper were prepared by taking the paper from different areas.

A Chemito Spectroscan UV 2600 double beam spectrophotometer from Thermofisher Scientific, India with an attached computer system with installed spectrum 6.89.8 software was used to analyze ink extracts.

RESULT AND DISCUSSION:

The methanolic ink extracts of Cyan, Magenta, Yellow and Black colours were used for UV-Vis analysis with methanol as a blank. Four blank samples of paper extract were also scanned. The UV-Vis spectrum was recorded in the wavelength range of 200 nm – 800 nm in absorbance mode¹² .The obtained spectra were then compared with the others of respective colour with regard to the maximum wavelength and relative absorbance of the components.

Processed Ink Analysis:

The Inkjet inks of four different popular brands taken from printed paper were examined by UV- Vis spectrophotometry in the wavelength range from 200 - 800 nm and summarized in table no. 1 to 4 (portrayed at page no. 4,6,8 & 10 respectively) awhich shows the absorbance data for Cyan, Magenta, Yellow and Black processed ink.

The different analyzed ink samples can be differentiated either on the basis of presence or absence of certain conjugated and non conjugated compounds. The conjugated compound shows the UV peaks in the wave lengths (nm) range as given below¹⁰:

Wavelength (in nm) for Cyan Ink-

204-209, 261, 266, 270-274, 325-326.

Wavelength (in nm) for Magenta Ink-

206-210, 245, 252, 256-258, 270–285, 290, 310, 320- 324, 347- 349.

Wavelength (in nm) for Yellow Ink-

205-210, 248, 252- 259, 268, 275-276, 321-327.

Wavelength (in nm) for Black Ink-

205-210, 253-257, 265, 271-274, 311-315, 323-324, 347.

C-32

M-32

Y-32

K-5

Figure 1: The UV peak at 205, 207, 210 and 254, 209 shows conjugated compounds in Cyan, Magenta, Yellow and Black.

Figure 2: The graph shows peak at 206 nm for conjugated compounds whereas peak at 271 nm for non-conjugated compound in Cyan coloured printer ink of sample no.C-13.

Table 5-8 allows the discrimination of Cyan, Magenta, Yellow and Black colour printing inks of Brand ‘A’ under ultra violet and visible region. Figure no.3-6 represents the characteristics pattern of compounds which shows absorbance under ultra violet and visible region for Cyan, Magenta, Yellow and Black colour Inkjet inks. The distinct pattern for different colour of Brand ‘A’ can be observed which shows discrimination in different colours of Brand ‘A’ itself. Likewise same pattern can be followed to obtain pattern for different colour of other brands.

Table:-1 UV-Vis absorbance profile for Cyan processed ink sample extracts (Absorbance and λ_max

Sample No.1		Sample No.2		Sample No.3		Sample No.4		Sample No.5		Sample No.6		Sample No.7
λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs
209 274 407 626	2.240 .407 .103 .860	206 626	1.092 .275	209 273 406 626	206 407 626	.911 .048 .408	207626	1.489 .181	206 219 339 625 661	1.438 1.294 .166 .336 .292	2.456 .525 .112 .890	205 343 407 626 656	.624 .022 .007 .096 .057

Sample No.8		Sample No.9			Sample No.10				Sample No.11		Sample No.12			Sample No.13				Sample No.14
λmax (in nm)	Abs		λmax (in nm)	Abs		λmax (in nm)	Abs	λmax (in nm)		Abs		λmax (in nm)	Abs		λmax (in nm)	Abs	λmax (in nm)		Abs
208 341 406 626 659	1.941 .334 .092 .856 .631		206 407 626	1.131 .061 .459		205 219 625 661	.480 .324 .087 .068	205 219 626 657		205 219 626 657		206 408 626	1.17 .049 .358		206 271 325 571	1.556 .403 .151 .032	--		--

Sample No.15		Sample No.16		Sample No.17		Sample No.18		Sample No.19		Sample No. 20		Sample No.21
λmax (in nm)	λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs	Abs
204 407 626 --	206 219 261 337 618 662	1.281 1.189 .416 .336 .265 .315	205 219 328 623 661	1.210 .865 .081 .103 .084	204 219 261 337 600 664	.450 .450 .138 .073 .036 .110	207 340 621 665	1.63 .348 .227 .458	207 272 407 626	1.707 .178 .062 .433	204 219 271	.761 .466 .109	-- .633 .044 .171

Sample No.22		Sample No.23		Sample No. 24		Sample No. 25		Sample No. 26		Sample No. 27		Sample No. 28
λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs
206 266 326 665	1.668 .504 .210 .056	206 625	1.090 .226	206 408 625	1.358 .136 .701	206 407 625	1.04 .068 .594	206 270 407 625	1.34 .147 .046 .395	206 306 407 626	1.366 .153 .122 1.051	207 266 333 663.5	1.921 .580 .298 .163

Sample No. 29			Sample No. 30		Sample No. 31			Sample No. 32
λmax (in nm)	Abs	λmax (in nm)		Abs	λmax (in nm)	Abs	λmax (in nm)		Abs
205 220 273	1.09 .944 .177	206		205 342 405.5 625.5 661	1.213 .203 .056 .506 .394	1.34	207 343 602 665		1.822 .309 .192 .619

Table 2: Brand wise discrimination of Cyan colour Inkjet computer printing inks.

Wavelength (λmax) in nm
Brand	UV Region	Visible Region
A	207, 219, 272, 306, 339, 342	407, 602, 626, 660
B	206, 219, 271, 325	407, 571, 626
C	205, 219, 266, 327	408, 625, 665
D	206, 219, 273, 263, 336	619, 600, 656

Figure 3: Characteristic pattern for components detected in the UV Range for Cyan colour ink of Brand ‘A’.

Table:-2 UV-Vis absorbance profile for Magenta processed ink sample extracts (Absorbance and λ_ma

Sample No.1		Sample No.2		Sample No.3		Sample No.4		Sample No.5		Sample No.6		Sample No.7
λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs
209 274 554	2.41 .674 .549	206 256 303 352 555	1.31 .303 .143 .090 .502	208 257 276 554	2.18 .564 .540 .404	207 555	1.70 .387	208 306 553	2.07 .342 1.01	207 285 554	1.20 .204 .404	207 555	1.48 .211

Sample No.8		Sample No.9			Sample No.10				Sample No.11		Sample No.12			Sample No.13				Sample No.14
λmax (in nm)	Abs		λmax (in nm)	Abs		λmax (in nm)	Abs	λmax (in nm)		Abs		λmax (in nm)	Abs		λmax (in nm)	Abs	λmax (in nm)		Abs
207 256 305 333 351 392 553 626	1.85 .812 .408 .292 .229 .127 1.38 .302		208 252 304 333 349 552	2.27 .615 .272 .190 .156 .849		207 245 304 347 512	1.23 .579 .381 .233 .210	206 219 272 553 626		1.65 1.61 .354 .393 .087		208 281 522 551	2.34 .507 .235 .288		208 280 524 554	2.30 .794 .327 .371	207 276 625		1.67 .582 .368

Sample No.15		Sample No.16		Sample No.17		Sample No.18		Sample No.19		Sample No. 20		Sample No.21
λmax (in nm)	λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs	Abs
206 553 626	1.43 .083 .087	210 274 310 324 366 515 542 662	2.40 1.28 .676 .653 .353 1.05 1.07 .045	206 517 546	1.66 .095 .110	207 272 310 324 515 542	1.74 .660 .337 .319 1.05 1.07	206 272 512 540 662	1.50 .328 .111 .116 .051	208 257 276 335 351 554	2.08 .576 .398 .120 .128 1.05	208 282 545	2.22 .781 .173

Sample No.22		Sample No.23		Sample No. 24		Sample No. 25		Sample No. 26		Sample No. 27		Sample No. 28
λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs
207 271 323 522 548	1.93 .635 .281 .195 .210	207 275 324 516 543	1.99 .842 .400 .447 .460	208 275 324 516 542	2.01 .758 .327 .297 .313	206 290 405 519 553 625	1.57 .458 .104 .204 .254 .487	209 258 275 555	2.39 .611 .586 .480	208 239 303 346 542	2.00 .991 .637 .356 .445	205 255 276 553	1.10 .166 .121 .292

Sample No. 29				Sample No. 30			Sample No. 31			Sample No. 32
λmax (in nm)		Abs	λmax (in nm)			Abs	λmax (in nm)	Abs	λmax (in nm)			Abs
271 278 320 363 522 553	.425 .419 .207 .129 .388 .469		206 270 551		1.46 .189 .107		204 257 280 304 352 555	.921 .294 .169 .139 .068 .523	207 249 280 351 555		1.894 .369 .183 .079 .523

Table 6: Brand wise discrimination of Magenta colour Inkjet computer printing inks. The intra brand variation in absorbance peaks can be seen clearly.

Wavelength (λmax) in nm
Brand	UV Region	Visible Region
A	204, 206, 208, 219, 239, 247, 256, 275, 304, 333, 350, 392	512, 542, 554, 626
B	208, 257, 276, 281, 335, 351	523, 545, 555
C	206, 290, 323	405, 518, 522, 547, 553, 625
D	207, 210, 274, 310, 323, 364	516, 542, 553, 662

Figure 4: Characteristic pattern for components detected in the UV Range for Magenta colour ink of Brand ‘A’.

Table 3: UV-Vis absorbance profile for Yellow processed ink sample extracts (Absorbance and λ_max).

Sample No.1		Sample No.2		Sample No.3		Sample No.4		Sample No.5		Sample No.6		Sample No.7
λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs
209 327 416 568	2.21 .178 .088 .027	206 248 391	.973 .183 .082	207 259 431	1.68 .171 .071	209 248 396	2.17 .233 .203	208 259 419	2.11 .769 .612	209 252 417	2.32 .336 .164	208 396	1.86 .136

Sample No.8		Sample No.9			Sample No.10				Sample No.11		Sample No.12			Sample No.13				Sample No.14
λmax (in nm)	Abs		λmax (in nm)	Abs		λmax (in nm)	Abs	λmax (in nm)		Abs		λmax (in nm)	Abs		λmax (in nm)	Abs	λmax (in nm)		Abs
205 251 395	.505 .158 .197		208 253 403	1.96 .410 .215		210 254 390	2.39 1.36 .651	205 258 410		1.15 .348 .190		209 254 391	1.80 1.02 .507		207 268 322	1.82.501 .224	207 394		1.81 .834

Sample No.15		Sample No.16		Sample No.17		Sample No.18		Sample No.19		Sample No. 20		Sample No.21
λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs
208 395	2.30 1.14	207 253 398	1.85 .718 .653	207 258 401	1.69 .634 .469	205257 398	.991 .370 .365	207395	1.81 .890	206327 430	1.48 .029 .042	208 395	2.46 1.10

Sample No.22		Sample No.23		Sample No. 24		Sample No. 25		Sample No. 26		Sample No. 27		Sample No. 28
λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs
208 328 577	2.12 .323 .048	208 259 395	2.31 .994 .659	207 258 393 576	1.89 .794 .550 .033	207 259 425	2.129 1.562 1.203	206 275 321 441 570	1.26 .279 .155 .171 .018	209 255 403	2.294 .853 .373	208 436 584	2.100 .115 .058

Sample No. 29				Sample No. 30			Sample No. 31			Sample No. 32
λmax (in nm)		Abs	λmax (in nm)			Abs	λmax (in nm)	Abs	λmax (in nm)			Abs
208 276 322 441	2.280 .606 .360 .462		206 259 424		1.575 .904 .591		208 254 390	2.373 1.729 .884	208 254 399		2.448 1.143 1.595

Table 7: Variable absorbance peaks in visible region as well as UV region can prove to be useful for the discrimination of Yellow colour computer printing inks of different brands.

Wavelength (λmax) in nm
Brand	UV Region	Visible Region
A	208, 251, 257, 275, 324, 394	405, 417, 430, 441, 568, 570, 584
B	207, 254, 268, 324, 393	430
C	207, 259, 328, 394	401, 425, 577
D	207, 257, 276, 322, 396	441

Figure 5: Characteristic pattern for components detected in the UV Range for Yellow colour ink of Brand ‘A’.

Table 4: UV-Vis absorbance profile for Black processed ink sample extracts (Absorbance and λ_max)

Sample No.1		Sample No.2		Sample No.3		Sample No.4		Sample No.5		Sample No.6		Sample No.7
λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs
210 272 323 579	2.425 .382 .140 .048	209 274 558 624	2.33 .247 .076 .045	209 255 556 625	2.318 .506 .143 .147	210 403 556 625	2.477 .115 .192 .178	209 553 625	2.419 .353 .269	210 255 304 407 556 625	2.430 .338 .142 .211 .498 .620	208 339 555 665	2.08 .259 .312 .278

Sample No.8		Sample No.9			Sample No.10				Sample No.11		Sample No.12			Sample No.13				Sample No.14
λmax (in nm)	Abs		λmax (in nm)	Abs		λmax (in nm)	Abs	λmax (in nm)		Abs		λmax (in nm)	Abs		λmax (in nm)	Abs	λmax (in nm)		Abs
207 253 351 556 625	1.968 .609 .130 .830 .317		208 406 554 625	2.137 .130 .432 .392		207 301 347 528	1.752 .222 .134 .104	208		2.041		209 274	2.44 .368		209 272 323 579	2.44 .550 .196 .060	205 226 314 402 470 586		1.041 .787 .606 .284 .339 .464

Sample No.15		Sample No.16		Sample No.17		Sample No.18		Sample No.19		Sample No. 20		Sample No.21
λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs
207 312 427 561	1.727 .197 .139 .095	209 313 423 583	2.349 .675 .536 .383	207 313 448 586	1.906 .448 .230 .156	208 311 416 577	2.115 .253 .277 .137	207 413	1.869 .477	207	1.816	207 271	1.955 .299

Sample No.22		Sample No.23		Sample No. 24		Sample No. 25		Sample No. 26		Sample No. 27		Sample No. 28
λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs
207 272 321 581	1.738 .416 .177 .056	209 274 315 402 434 582	2.257 .782 .687 .364 .404 .296	207 315 402 581	1.821 .454 .450 .317	414 592 663	.972 .310 .161	206 257 406 562 625	1.385 .291 .078 .160 .476	210 247 304 350 402 544 625	2.433 .891 .507 .277 .179 .354 .414	209 252 303 407 558 626	2.271 .463 .231 .215 .597 1.071

Sample No. 29			Sample No. 30		Sample No. 31		Sample No. 32
λmax (in nm)		Abs	λmax (in nm)	Abs	λmax (in nm)	Abs	λmax (in nm)	Abs
265 324	.397 .151		206 438 627	1.624 .051 .72	208 338 402 557 613 659	2.059 .181 .210 .493 .424 .422	209 257 351 402 557 626	2.291 .308 .040 .073 .587 .288

Table 8: Brand wise discrimination of Black colour computer printing inks. The multiple absorbance peaks in the inks of HP brand can be differentiated it with others.

Wavelength (λmax) in nm
Brand	UV Region	Visible Region
A	208, 247, 255, 273, 303, 323, 338, 350	440, 528, 554, 556, 579, 613, 625, 659
B	208, 272, 323	579
C	206, 226, 272, 313, 321	402, 414, 427, 448, 470, 584, 561, 592, 663
D	208, 265, 274, 313, 324	402, 414, 423, 434, 577, 582

Figure 6: Characteristic pattern for components detected in the UV Range for Black colour ink of Brand ‘A’.

Inter colour variations can be depict from figure 8 to 11 which shows variations within different samples of same colour ink whether they belong to same brand or not. Variations between absorbance at respective wavelength differentiate one colour ink from the other coloured inks

Figure 7: A typical scan of Magenta, Cyan, Yellow and Black colour Inkjet ink of sample A-1 in the UV and visible range.

The Figure 7 shows UV-Vis absorbance spectra for Cyan, Magenta, Yellow and Black colour of Sample A-1.

igure 8: A typical scan of sample number A-12 to A-17 of Cyan colour Inkjet ink.

Figure 9: A typical scan of sample number A-1,A-12,A-14,A-16 of Black colour Inkjet ink.

Figure 10: A typical scan of sample number A-16,B-18,B-19,C-23,C-24,D-29 of Magenta colour Inkjet ink.

Figure 11: A typical scan of Sample number A- 6,A-14,A-16, B- 20 of Yellow colour Inkjet ink.

Figure 8-11 allows the simultaneous comparison of samples analyzed for the primary colour i.e. Cyan, Magenta, Yellow and Black for four leading brands of printer inks. When the same brand samples were examined by the proposed method batch to batch variation was found, necessitating use of control sample of the same batch for the comparison. Further if the industry producing these cartridges adheres to rigid process and quality control these variations could be minimized but not eliminated completely.

CONCLUSION:

The absorbance profile of inkjet ink for the differentiation and comparison analysis was obtained by scanning the ink extracts under the wavelength range of 200-800 nm using the UV-Visible Spectrophotometer. The various parameters of absorption studies of different components of printer ink formulation in the visible and UV region, after the extraction process enables us to differentiate and distinguish different document sample of distinct composition by their characteristic absorbance spectra and profile pattern. The proposed methodology can be used for examination of routine cases involving variety of printing inks. In normal document examination practice the proposed method would be valuable to arrive at an opinion based on the comparison of the questioned printing with that of the admitted printing of the same period.

REFERENCES:

1. Adam, C.D., Sherratt, S.L., Zholobenko, V.L., 'Classification and individualisation of black ballpoint pen inks using principal component analysis of UV-Vis absorption spectra,' Forensic Science International. 174 pp. 16-25, 2008 

2. Adam, C. D., 'In situ luminescence spectroscopy with multivariate analysis for the discrimination of black ballpoint pen ink-lines on paper,' Fors Sci Int'l, 182, pp. 27-34, 2008 

3. Brezova, V., Pigosova, J., Havlinova, B., Dvoranova, D., Durovic, M., 'EPR study of photochemical transformations of triarylmethane dyes,' Dyes and Pigments, 61, pp.177-198, 2004. 

4. Cardoso, J-F., 'High-order contrasts for independent component analysis, Neural Comp,' 11(1), 157-192, Jan 99. 

5. Choi, S., Cichocki, A., Park, H.M., Lee, S.Y., Blind source separation and independent component analysis: A review. Neu Info Proc. - Letters and Reviews, vol. 6 (1), pp. 1 - 57, 2005. 

6. Hyvärinen, A., 'Fast and Robust Fixed-Point Algorithms for Independent Component Analysis', IEEE Trans. on Neural Networks, 10(3), 626-634, 1999. 

7. Kher, A., Mulholland M, Green E, Reedy B, Forensic classification of ballpoint pen inks using high performance liquid chromatography and infrared spectroscopy with principal component analysis and linear discriminant analysis, Vibrational Spectroscopy. 40 (2006) 270-277.

8. Lam, K.P., and Emery, R, 'Image Pixel Guided Tours: A Software Platform for Non-Destructive X-Ray Imaging', Procs SPIE-IS&T, Vol 7425, p74250N1-10, 2009.

9. Lennon M, Mercier G, Mouchot M.C., and Hubert-Moy L., Independent component analysis as a tool for the dimensionality reduction and the representation of hyperspectral images. SPIE Remote Sensing, volume 4541, pp. 2893-2895, France, 2001.

10. Sharma, Y.R. (2007). Elementary Organic Spectroscopy. S. Chand & Company Ltd.

11. Stone, J. V., 'Independent Component Analysis. A Tutorial Introduction', MIT Press, London, England 2004. 

12. Teknomo, K., K-Mean Clustering, available online at: http://people. revoledu.com/kardi/tutorial/kMean/matlab-kMeans. htm Last accessed 19/11/2009. 

13. Thanasoulias, N.C., Parisis, N.A. and Evmiridis, N.P. (2003). Multivariate chemometrics for the forensic discrimination of blue ball-point pen inks based on their vis spectra, Forensic Science International,138 (1-3):75-84.

14. Weyermann, C., Kirsch, D., Vera, C. C., Spengler, B., 'Evaluation of the Photodegradation of Crystal Violet upon Light Exposure by Mass Spectrometric and Spectroscopic Methods,' Journal of Forensic Sciences, 54(2), pp. 339-345, 2009.

15. Xu, Y., Wang, J., and Yao L.(2006).Dating the writing age of black roller and gel inks by Gas Chromatography and UV-Visible Spectrophotometry. Forensic Science International.162:140-143.

Received on 14.03.2016 Modified on 28.04.2016

Accepted on 20.05.2016 © AJRC All right reserved

Asian J. Research Chem. 9(6): June 2016; Page 245-254.

DOI: 10.5958/0974-4150.2016.00041.9