The Importance of Thin Layer Chromatography and UV Microspectrophotometry in the Analysis of Reactive Dyes Released from Wool and Cotton Fibers

Abstract

Samples of reactively-dyed wool and cotton were obtained from a range of dye manufacturers, dye distributors and the Forensic Science Service (FSS) Fibre Data Collection. The wool fibers were red in color and had previously been compared using comparison microscopy (CM), visible range microspectrophotometry (VS) and thin layer chromatography (TLC). The cotton fibers were blue and black in color and had not been previously compared. Red, blue and black fibers were chosen because they are often encountered in casework. The usage of reactive dyes to color fibers has increased over the last 10–15 years and these are often seen in casework. Before techniques were available that allowed reactively-dyed fibers to be compared using TLC only CM and microspectrophotometry were routinely carried out. Many laboratories, who had a microspectrophotometer, only had a visible range instrument. It was therefore important to see which techniques provide additional information, that gives greater individuality to fibers, to that obtained from CM. The color was released from the wool and cotton fibres using alkaline hydrolysis and a cellulase enzyme respectively. Many of the red wool samples were differentiated from each other using CM. More differentiation was found using VS and even more when ultraviolet range microspectrophotometry (UV) or TLC was used. Two samples could only be differentiated using TLC because CM, VS and UV failed to separate them. The black cotton samples were predominately differentiated using CM but VS allowed for further differentiation. With the samples used in this project UV and TLC failed to separate the samples further. The blue cotton samples benefited from the use of CM, VS and either UV or TLC to reduce the number of matching pairs. All techniques aided differentiation although with this set TLC and UV proved to be complementary techniques. Results demonstrate that TLC and UV both yield important information over and above that obtained from CM and VS. Although in some parts of the project TLC and UV are complementary if the concentration of the dye in the fiber is not sufficient for TLC or the scientist doesn't wish to ‘destroy’ the fiber UV would be of more use than TLC.

The Effect of Ionizing Gamma Radiation on Natural and Synthetic Fibers and Its Implications for the Forensic Examination of Fiber Evidence*

“…A closer examination of the spectral region between 1800 and 1000 ⁄ cm was undertaken to assess whether any spectral variations could be attributed to radiation damage. The task was complicated by the fact that the basic dyes used are normally mixtures and the level of fiber dye is low, normally about 1-2% (19). Baseline corrected infrared absorbance spectra for black, blue, and red acrylic fibers before and after 1000 kGy irradiation are shown in Fig.…”

Forensic comparison of synthetic fibers

“…[62] Reactive dyes in wool and cotton can be differentiated by this technique rather than other techniques such as comparison microscopy, visible-range microspectrophotometry, ultraviolet-range microspectrophotometry, and TLC. [67] This technique is nondestructive and has been identified as important for differentiating red wool and blue cotton in particular.…”

Extraction and Analysis of Disperse Dyes from Colored Polyester Single Fibers Using Liquid Chromatography/Linear Ion Trap Tandem Mass Spectrometry

“…1,2 Many studies have been conducted to analyze the dyes in colored fibers using microspectrophotometry, [3][4][5][6][7][8][9][10] TLC, [11][12][13][14][15][16][17][18][19] HPLC, [20][21][22][23][24][25] and LC/MS, [26][27][28][29][30] because these dyes can provide significant information in forensic analyses.…”

“…31 Dye-extractions are performed by heating colored fibers in various solvents and solvent mixtures, [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] including the recommended pyridine/water (4:3, v/v) mixture by the SWGMAT guidelines. 32 We reported a method for extracting a residual surfactant from threads using centrifugal filtration of a methanol solution extracted into a glass capillary.…”