Abstract
Pentacyanidoferrate(II) complexes of aromatic N-heterocycles, such as 4-cyanopyridine, exhibit characteristic colors and strong metallochromism associated with the donor-acceptor interactions of the metal ions with the cyanide ligands. In the presence of transition metal ions insoluble polymeric complexes are formed, displaying bright yellow, red, brown and green colors with zinc(II), nickel(II), copper(II) and iron(III) ions, respectively. Such metallochromic response is better observed on filter paper, allowing applications in analytical spot tests. The effects can be explored visually and probed by means of modern instrumental facilities, including spectrophotometric and resonance Raman techniques. In this way, by using the cyanopyridinepentacyanidoferrates, the Prussian Blue test for ferric ions can be extended to the entire row of transition metal elements, providing a new and modern insight of such classical Feigl's spot tests.
Highlights
Colorimetric reagents have been extensively explored in analytical chemistry since the beginning of the last century, after the outstanding work of Fritz Feigl on spot tests (Feigl and Anger 972)
The limits of the visual detection of the spot tests can be extended with the aid of modern instrumental facilities, encompassing for instance, fiber optics spectrophotometry and Raman techniques
Such instrumental detection can be directly applied on spot test plates and filter paper, providing more than just a positive or negative response, allowing to access the chemical nature of the analytes by means of their electronic and vibrational features
Summary
Colorimetric reagents have been extensively explored in analytical chemistry since the beginning of the last century, after the outstanding work of Fritz Feigl on spot tests (Feigl and Anger 972) Because of their simple use, spot tests became a common practice in Chemistry and Forensics, allowing rapid and practical detection of analytes, including representative, lanthanide and transition metal ions. They are usually performed using spot test plates or filter paper, allowing many interesting variations, for instance, by combining solvent elution and rapid evaporation procedures as in the so called “ring oven” technique (Riyazuddin 1994, Cortez and Pasquini 2013). Such instrumental detection can be directly applied on spot test plates and filter paper, providing more than just a positive or negative response, allowing to access the chemical nature of the analytes by means of their electronic and vibrational features
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