Abstract
The analysis of dyes in cultural heritage samples is a well-known challenging task, due to their inherent high tinting strength and consequent low concentration in the carrying matrix a fact that severely limits the number of analytical techniques that can be efficiently and micro-destructively employed for their detection and unambiguous identification. In the present study, an advanced and alternative SEIRA based analytical protocol for the analysis of small quantities of synthetic colorants has been proposed. The method has been set up for the identification of Acid Orange 7 (AO7) using Au nanoparticles obtained by laser ablation in solution (LASiS). Analyses have been performed applying a drop containing a mixture between the colorant and the Au colloidal solution in its unaggregated state on a gold coated glass slide for RAS (Reflection Absorption Spectroscopy) analysis. The first results showed that, thanks to the enhancement produced by the nanoparticles, it is possible to analyze small amount of diluted solutions containing the colorant. Thus, the method has been successfully applied for the analysis of few pieces of dyed wool, after the development of a suitable micro extraction procedure.
Highlights
In 1980 Harstein et al [1] discovered that when a molecule was absorbed on metal surfaces, its infrared absorptions appeared more intense than what would be expected for traditional measurements
Characterization of the colorant In order to obtain a reference spectra, 1 μL of the 10−3 M Acid Orange 7 (AO7) solution was spotted on a gold coated glass slide and RAS measurements were performed on the external profile of the drop (Figure 2, band assignment is reported in Table 2 [29,30,31,32])
This paper shows that Surface–Enhanced Infrared Absorption (SEIRA) can be used as an analytical method to analyze small quantities of colorants
Summary
In 1980 Harstein et al [1] discovered that when a molecule was absorbed on metal surfaces, its infrared absorptions appeared more intense than what would be expected for traditional measurements. This effect was named Surface–Enhanced Infrared Absorption (SEIRA), to recall the analogy with SERS (Surface Enhanced Raman Spectroscopy), which was already known since the beginning of 70th [2,3]. Enhanced infrared spectra can be obtained in transmission, ATR (attenuated total reflection), external reflection and diffuse reflection mode [5] and mainly depend on the morphology of the metal surface. Depending on the type of support, different configurations such as sample-metal, metalsample and metal-sample-metal have been successfully adopted
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