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The extraction and analysis of fibre dyes using LC-PDA-Orbitrap-MS

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The extraction and analysis of fibre dyes using LC-PDA-Orbitrap-MS

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Samenvatting

At the Netherlands Forensic Institute (NFI), there has been an intensive study into the analysis of fibre dyes using one single method with liquid chromatography mass spectrometry (LC-MS) for all dye classes. This project has accomplished many goals so far apart from the analysis of some dye classes and the choice of a suitable database. Two of these dye classes are vat and sulphur dyes. This are very non-polar fibre dyes applied to cotton fibres by reducing the dyes to an ionised form. For vat dyes this is achieved by reducing a ketone and for sulphur dyes a disulphide bond. From the measurements there will be a UV/Visible spectrum, a retention time and an accurate mass of the dye molecule. Ideally these three factors will be combined in one database. Since this is not readily available software of different databases has to be tested to compare and find the most suitable database. This comparison is done for disperse, direct, acid and basic dyes.
Derivatisation of the ketones was achieved using semicarbazide and ammonium hydroxyl chloride for conversion to an imine form. Also the Lawesson reagent was used to derivatise the oxygen atom to a sulphur atom. This sulphur atom is oxidised using Oxone making it more polar.
For the sulphur dyes a oxidation is carried out using nitric acid to created sulfonate groups at the disulphide bond.
For the database a group of 6 to 8 dyes in each tested dye class is completely processed according to the database preferences. A group of prepared fibre dyes is run in this database to read out which dyes might be present. This group is prepared by another person to remove any form of confirmation bias. ToxID and a Matlab programmed database were compared with each other.
Results show that the conversion of the imine form of the vat dyes do not influence or decrease the solubility of the dyes in the fibres. This negative effect is the opposite of the goal of this project so these derivatisation reactions should not be operated. The use of the Lawesson reagent however showed increased extraction and different MS signal than expected with the normal dye.
The extraction of the sulphur dyes with nitric acid completely discoloured the fibre but also degraded the fibre. This degradation of the fibre makes it impossible for good analysis using LC-MS making this method unfavourable. A conversion with chloroactetic acid is suggested to make a good derivatisation but some practicalities have yet to be overcome to use this method.
The comparison of the ToxID and Matlab database showed some differences. From the ToxID database only 1 of the 17 (6%) dyes was not identified in contrast to 4 of the 17 (24%) dyes using the Matlab database. With the Matlab database one of these 4 was identified wrongly giving a false positive result. Using the paired t-test to compare whether or not these differences are significant no true significant difference was measured. However the fact that one false positive is given using the Matlab database might not correctly be represented in this test.
The results show that derivatisation of the vat dyes is very difficult but can be achieved using the Lawesson reagent. This increases the extraction of the vat dyes and chromatographic separation appears to be different compared to the dyes in their normal state. Optimisation of the extraction is still necessary. The extraction of sulphur dyes with nitric acid has not proven to be feasible for the LC-MS analysis. Future work must prove however if a chloroacetic acid acidification gives reasonable results and if this method can be successfully applied using the LC-MS analysis.
Database comparison showed that ToxID is the most suitable database for the dye identification if no adaptations are made to the Matlab database. Hence the ToxID database is the database of choice for future database processing.

Toon meer
OrganisatieAvans Hogeschool
OpleidingBiologie en Medisch Laboratoriumonderzoek-Breda
AfdelingATGM Academie voor de technologie van Gezondheid en Milieu
PartnersNederlands Forensisch Instituut
Datum2013-06-03
TypeBachelorscriptie
TaalEngels

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