摘要:

The relaxation of excited molecular states is often followed by the emission of light. Molecular excited states are related to the orbital, vibrational, and rotational levels of the orbital electrons. In addition, the electron spin determines the singlet and triplet states. In the singlet state the spin of an electron is paired, whereas in the triplet state the spin is not paired. When a molecule is excited to an upper singlet energy level, such as S2(Figure 1), it can rapidly (10−10sec) go to the lowest excited state S1without emission of light. From S1the molecule may go to any of the rotational and vibrational levels of the ground electronic state S0. This happens either by fluorescence emission or by nonradiative internal processes, referred to as intersystem crossing. From T1, the molecule can return to S0by nonradiative processes or by a radiative process called phosphorescence. Under suitable conditions S1and T1can also transfer their excitation energy to other molecules.

ISSN:0007-8980    

DOI:10.1080/10408348708542802

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Voltammetric techniques of analysis, i.e., those based on the measurement of current resulting from an oxidation or reduction at an electrode surface following the application of a potential difference to an electrochemical cell,1have assumed an important place in the armory of analytical techniques for the identification and determination of trace concentrations (i.e., 102to 10-4ppm) of many organic, organometallic, and inorganic molecules of environmental significance. Techniques such as normal and differential pulse polarography (NPP and DPP), anodic and cathodic stripping voltammetry (ASV and CSV), adsorptive stripping voltammetry and electrochemical detection (ED) coupled with flow injection analysis (FIA - ED), ion chromatography (IC -ED), and high performance liquid chromatography (HPLC - ED) are particularly notable in this respect. Organic and organometallic molecules of environmental importance as pollutants, drugs of abuse, food additives and contaminants, agrochemicals, etc., as they are contained in a variety of complex biological matrices such as air, plasma, tissue, and soil, can be determined by these voltammetric techniques at trace concentrations usually after the application of sample pretreatment procedures and certain separation techniques.

ISSN:0007-8980    

DOI:10.1080/10408348708542803

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor