Dyestuffs analytical methods

Since workers can be exposed to these compounds during their manufacture and use, it is important to have reliable analytical methods for determining the degree of exposure through body fluid analysis. Additionally, since these compounds can be present at significant levels in commercial products (derived from them) it is desirable to monitor their level in such products (e.g. dyestuffs) as well. Furthermore, many of the commercial products can be metabolized to the original chemical (e.g. benzidine based dyes can be metabolized to benzidine) making it desirable to monitor the body fluids of workers exposed to the commercial products. 

Solubility data of the dyestuffs are of interest for the optimization of this particular dyeing technique. Therefore an apparatus was developed for the determination of the solubilities in supercritical solvents at temperatures from 250 to 500 K and pressures up to 250 MPa according to the static analytical method [6, 7]. In particular, investigations on the solubility of some selected anthraquinone dyes in supercritical C02 and N20 and more recently of P-carotene in supercritical C02 and CC1F, were performed as a function of temperature and pressure (see section 4.). For the l,4-bis-(n-alkylamino)-9,10-anthraquinones the alkyl chains were systematically varied in the homologous series in order to study the effects of molecular size and polarity on the solubility phenomena [6-10]. 

Extraction or rather leaching of colourants is the first and a very important step in the analytical procedure for the analysis of natural dyes. The chemical composition of extracts from historical materials depends on many factors, such as the source of natural dyes, the technological procedure of their production, storage conditions over the centuries, ageing processes and extraction conditions. The choice of the extraction method depends on the properties of the components and the matrix from which they are isolated, as well as on the mechanism of dyeing with the particular dyestuff. In this regard, they are usually divided into three groups direct, vat and mordant dyestuffs. 

Background and principles UV spectroscopic analysis was one of the first applications of spectroscopy in an analytical context. While a powerful technique of yesteryear, this method is now rather restricted in its use in a modem bioanalytical laboratory. However, UV/visible spectroscopy is still used in specific biochemical analyses, such as dyestuffs in forensic applications. Despite these limitations, a bench spectrophotometer that measures UV/visible absorbance is commonly found in both teaching and research laboratories. In order to better understand the underlying principles it is necessary to consider the excitation of electrons, electronic transition and how this is related to energy and absorbance. 

The simplest use of pervaporation is for the separation and subsequent determination of a single analyte as a result, most reported methods using this technique involve individual determinations. The determination of acetaldehyde in semi-solid and solid food samples is one salient example of single-analyte determinations where pervaporation avoids time-consuming sample preparation steps such as filtration, removal of dyestuffs and turbidity from the Carrez solution, and centrifugation [175]. One other example is the determination of trimethylamine (an objective parameter for fish quality evaluation that correlates well with sensory evaluation) [176]. The method is based on pervaporation of the analyte and monitoring of the colour change in Bromothymol Blue caused by the basic character of the amine the results are consistent with those provided by the official method for trimethylamine. 

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