fibers by Raman spectroscopy Research project

Transcription

1 National Institute for Criminalistics and Criminology Laboratory Fibers and Textiles F. Gason K. De Wael In situ study of cotton dyed fibers by Raman spectroscopy Research project Laurent Lepot University of Liège Laboratory of Analytical Chemistry Professeur B. Gilbert 1

2 Interest in Raman spectroscopy Raman spectroscopy Fast technique No destructive Suitable technique for pigments and dyes Forensic needs Fast technique No destructive Sensitive regarding to the % of dye on fibers Potential of Raman spectroscopy in forensic examination of fibers? 2

3 bjectives of the research project Evaluation of the technique Creation of a spectral library Automatic attribution of unknown spectrum to a chemical class of dye Forensic case studies 3

4 Instrumentation DILR LabRam Confocal microscope pen Electrode CCD detector Lasers : 488, 514.5, and nm BRUCKER FT-Raman Laser : 1064 nm 4

5 Measurement 10 µm 10 µm 5

6 Data processing 6

7 Dye and dyed fiber λ = nm obj. 100x D yed fiber PA fiber C H 3 N N N N C 2 H 5 S 3 H P ure dye W avenum ber (cm -1 ) 7

8 Dye and dyed fiber λ = nm obj. 100x D yed fiber C H 3 N N N N C 2 H 5 S 3 H P ure dye W avenum ber (cm -1 ) 8

9 Study of cotton dyed fibers Selection of mono-dyed cotton fibers from our fibers reference collection on the basis of the Colour Index book 172 samples chemical class chemical constitution Analysis by Raman spectroscopy (514,5 nm) Creation of a spectral library in MNIC software 9

10 Selected chemical classes Azo (56 samples) Anthraquinone, -noïd (62 samples) Indigoïd (11 samples) xazine Phtalocyanine Di-, triphenymethane Stilbene Thiazole Sulphur 10

11 Preliminary results Fluorescence masks Raman signal (20 % samples) Raman spectra quality depends on fluorescence Discrimination is effective Raman spectrum = fingerprint of the molecule Assignment to a class within the spectral library is optimal for very similar dye molecules difficult without similar reference molecules 11

12 Example C orrelation (% ) λ = 514,5 nm bj. 20x 56,9 D ye 8 64,5 D ye 10 65,1 66 Dye 26 D ye 19 72,6 D ye ,5 D ye 9 D ye 17 Q uery spectrum W avenum ber (cm -1 ) 12

13 Example NH 2 S 3 H NH 2 S 3 H 80,5 % NH S 2 Query sample CH 3 64,5 % 72,6 % Dye 9 HN NH 2 S 3 Na Dye ,9 % NH 2 S 3 H NH CH 3 65,1 % 66 % HN S 2 CH 2 CH 2 S 3 Na NH 2 Dye 8 NH 2 HN S 3 H Dye 10 HN NH 2 S 3 H Dye 26 NH N C CH 3 CH 3 Dye 19 NH H 3 C S 3 H 13

14 Case study 1 Comparative study for evidence of contact Cotton dyed fibers from a black trousers Cotton black fibers collected on a car seat 14

15 Case study 1 λ = 514,5 nm bj. 20x Reactive Black 5 Car seat f2 Car seat f1 Trousers f2 Trousers f W avenum ber (cm -1 ) 15

16 Case study 2 Investigative study for evidence of contact Cotton blue dyed fibers collected on victim Blue jeans? 16

17 Case study 2 λ = 514,5 nm bj. 20x Jeans friend Jeans F ather S uspect Jeans 2 S uspect Jeans 1 Indigo pow der W avenum ber (cm -1 ) 17

18 Case study 2 At this stage of Raman investigations Every jeans dyed with indigo is a possible source BUT A particular aspect of the suspect s jeans Undyed PES fibers are used for the weft yarn 18

19 Case study 2 λ = 514,5 nm bj. 20x T rousers cotton blue fiber P A fiber m elted with indigo dye P E S fiber m elted w ith indigo dye T rousers P E S fiber w ith blue portions W avenum ber (cm -1 ) 19

20 Further work Development of statistical tools based on discriminant analysis Interest for poly-dyed cotton fibers Extension of study to wool Daily application to forensic case studies 20

21 Thank you for your attention 21

22 22

23 Laser wavelength 4000 Dyed fiber 11 λ = nm obj. 20x Y Data Dyed fiber 11 λ = nm obj. 100x * PA fiber peaks * * * * * * * * * 1000 Pure dye 11 λ = nm obj. 20x 0 Pure dye 11 λ = nm obj. 20x Wavenumber (cm -1 ) 23

24 Evaluation is positive Raman resonance spectra of dyed fibers higher signal from the dye (minor component) Laser choice Green excitation a little bit more fluorescence Red excitation but a stronger Raman signal several peaks of the fibre in the dye signal 24

25 Commercial catalogue 25

26 Case study 1 λ = 514,5 nm bj. 20x Reactive Black 5 a - in situ b - in resin C ar seat f2 C ar seat f1 T rousers f2 T rousers f W avenum ber (cm -1 ) 26