Colorimetric coordinate systems

To represent the color, three different colorimetric coordinate systems can be used for the signals three primary colors (red, green, and blue) hue, saturation, and intensity (H, S, I)... 

In colorimetric terms, color differences are generally characterized by the distance between two colors in one of the color notation systems, most commonly the CIELAB system. The difference determined in this way represents the total color difference. Since a color is characterized by three quantities, a color difference can also be expressed in terms of three difference components (that is, differences in the color coordinates) and thus described in greater detail. Visually equal color differences between almost equal colors may, upon colorimetric measurement, be considered distinct if the colors of one pair differ strongly from those of the other pair. The formulas for color differences are further elaborated in order to remedy this defect. 

In addition to the standard Watson-Crick base pairing it has recently been discovered that thymine can selectively bind to mercuric ion (Hg ) via the formation of a thymine-Hg -thymine (T-Hg -T) complex (72). The presence of the Hg at the thymine-thymine mismatch leads to a significant increase ( 10°C) in the T . Mirkin and coworkers (40) incorporated this T-Hg "-T coordination chemistry in the DNA-AuNP system to design a novel colorimetric assay for detecting Hg " "(Fig. 12.15). In a typical assay, two batches of AuNPs were functionalized with two complementary sequences, respectively, and combined to form aggregates. 

These methods, which include colorimetric methods, are based on the measurement of radiation absorption by molecular species at a specified wavelength. In mineral analysis, the absorbent species are usually compounds, mostly coordination complexes, formed in a reaction between the mineral and a chromogen ligand. These methods are more sensitive and selective than the previously discussed methods. Some of the methods that use ultraviolet (UV)-vis-ible spectrophotometry can be combined with dynamic techniques like flow injection systems or with a previous separation using liquid chromatography,... 

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