Comparison Microscopy Research Articles

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

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.