A. Rygula and P. Miskowiec
284
very famous indigoid dye is 6, 6’-dibromoindigo also known as tyrian or Royal
purple. It is one of the oldest known and the most expensive dye. the colour is obtained from marine shellfish of the muricidae and thasidae families [26].
10.2 Techniques Used for Dye Analysis
10.2.1 Vibrational Spectroscopy Techniques
Raman spectroscopy can obey the restrictions and terms related to the analysis of
natural dyes and pigments. the main problem is very low amount of the analyte in
a sample and in consequence, the necessity of applying very sensitive techniques.
the second difficulty is the absorption of the visible light, which is a characteristic
feature of the chromophores. this phenomenon is responsible for the fluorescence,
which perturbs and overlaps the weak Raman signal. moreover, the fluorescence of
the remains pollutants of the biological components of the sample is also possible.
to avoid the latter, the near infrared wavelength lasers are applied (Ft techniques)
[11, 27, 28].
the absorption is responsible also for the resonance or pre-resonance effect applied in the Resonance Raman spectroscopy (RRS). It is observed when the incident
laser light occurs in the range of an electronic absorption band of the analysed compound. As a consequence, the Raman signal of absorbing compound is enhanced by
the factor of 10
6
[29] that allows to detect the analyte despite its very low concentration. taking into account that the most popular lasers provide an excitation in the
visible or NIR range, it is clear that this effect could be observed frequently in the
dye analysis.
Several advantages in dye analysis provides the Surface Enhance Raman Spectroscopy (SERS). this method requires an interaction of the sample with metal
nanoparticles, usually the silver colloid. According to the theory [29, 30], this interaction causes the chemical and electromagnetic enhancement of the Raman signal
up to 10
15
times and consequently, an intensification of the Raman spectra. SERS is
a popular method in a dye analysis especially in the field of art conservation. there
is a few reports with the application of this technique for the analysis of natural dyes
in textiles [31–34]. the use of SERS to the in situ analyses of natural samples is still
discussed and developed [35].
to sum up, it is worth to underline that during analysis of dyes it is a good
practice to work with different wavelengths of lasers both for avoiding of the fluorescence and taking the advantage of the resonance Raman effect. however the
techniques described above are useless when the Raman signals of pigments are too
weak and/or are overlapped by other biological components of sample. In this situation, the chemometric methods can significantly expand the scope of applicability
of the method.
284
very famous indigoid dye is 6, 6’-dibromoindigo also known as tyrian or Royal
purple. It is one of the oldest known and the most expensive dye. the colour is obtained from marine shellfish of the muricidae and thasidae families [26].
10.2 Techniques Used for Dye Analysis
10.2.1 Vibrational Spectroscopy Techniques
Raman spectroscopy can obey the restrictions and terms related to the analysis of
natural dyes and pigments. the main problem is very low amount of the analyte in
a sample and in consequence, the necessity of applying very sensitive techniques.
the second difficulty is the absorption of the visible light, which is a characteristic
feature of the chromophores. this phenomenon is responsible for the fluorescence,
which perturbs and overlaps the weak Raman signal. moreover, the fluorescence of
the remains pollutants of the biological components of the sample is also possible.
to avoid the latter, the near infrared wavelength lasers are applied (Ft techniques)
[11, 27, 28].
the absorption is responsible also for the resonance or pre-resonance effect applied in the Resonance Raman spectroscopy (RRS). It is observed when the incident
laser light occurs in the range of an electronic absorption band of the analysed compound. As a consequence, the Raman signal of absorbing compound is enhanced by
the factor of 10
6
[29] that allows to detect the analyte despite its very low concentration. taking into account that the most popular lasers provide an excitation in the
visible or NIR range, it is clear that this effect could be observed frequently in the
dye analysis.
Several advantages in dye analysis provides the Surface Enhance Raman Spectroscopy (SERS). this method requires an interaction of the sample with metal
nanoparticles, usually the silver colloid. According to the theory [29, 30], this interaction causes the chemical and electromagnetic enhancement of the Raman signal
up to 10
15
times and consequently, an intensification of the Raman spectra. SERS is
a popular method in a dye analysis especially in the field of art conservation. there
is a few reports with the application of this technique for the analysis of natural dyes
in textiles [31–34]. the use of SERS to the in situ analyses of natural samples is still
discussed and developed [35].
to sum up, it is worth to underline that during analysis of dyes it is a good
practice to work with different wavelengths of lasers both for avoiding of the fluorescence and taking the advantage of the resonance Raman effect. however the
techniques described above are useless when the Raman signals of pigments are too
weak and/or are overlapped by other biological components of sample. In this situation, the chemometric methods can significantly expand the scope of applicability
of the method.