Ultraviolet/visible spectrophotometry principles

This article provides some general remarks on detection requirements for FIA and related techniques and outlines the basic features of the most commonly used detection principles, including optical methods (namely, ultraviolet (UV)-visible spectrophotometry, spectrofluorimetry, chemiluminescence (CL), infrared (IR) spectroscopy, and atomic absorption/emission spectrometry) and electrochemical techniques such as potentiometry, amperometry, voltammetry, and stripping analysis methods. Very few flowing stream applications involve other detection techniques. In this respect, measurement of physical properties such as the refractive index, surface tension, and optical rotation, as well as the a-, //-, or y-emission of radionuclides, should be underlined. Piezoelectric quartz crystal detectors, thermal lens spectroscopy, photoacoustic spectroscopy, surface-enhanced Raman spectroscopy, and conductometric detection have also been coupled to flow systems, with notable advantages in terms of automation, precision, and sampling rate in comparison with the manual counterparts. 

The most commonly-used detectors are those based on spectrophotometry in the region 184-400nm, visible ultraviolet spectroscopy in the region 185-900nm, post-column derivativisation with fluorescence detection (see below), conductivity and those based on the relatively new technique of multiple wavelength ultraviolet detectors using a diode array system detector (described below). Other types of detectors available are those based on electrochemical principles, refractive index, differential viscosity and mass detection. 

Solution spectrophotometry in the visible and ultraviolet can he used to determine the nature of dyes used to color textiles of archaeological or historical importance. The curves obtained are compared with those from solutions of known materials. The method requires dyeings made with known natural dyes from the region of interest. Collections of such materials have been obtained from Peru, The principle red dyes of Peru can be identified by means of a single solution curve. Blue, from indigo, can easily be distinguished from the purple dibromoindigo obtained from marine molluscs. Yellow dyes are more difficult to identify and require, in most cases, curves in more than one solvent. 

Sommer L., Analytical Absorption Spectrophotometry in the Visible and Ultraviolet. The Principles, Elsevier, Amsterdam 1989. 

L. Sommer, Analytical absorption spectrophotometry in the visible and ultraviolet. The principles, in E. Pungor, W. Simon, H. Malissa, J. Inczedy (Eds.), Studies in Analytical Chemistry, vol. 8, Elsevier, Amsterdam, 1989. 

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