Chemical reaction detector , liquid

A schematic diagram of the demonstrator chemical analysis system is given in Fig. 24. The MCB comprises three in/outlets, two micro-pumps, two flow sensors and an optical absorption detector module. The purpose is to measure chemical reaction products by detection of the (spectral) absorption intensity. Sample and reagent liquids are mixed in the appropriate amounts on-board (currently the actual mixing takes place during the propagation in channels) and the optical absorption is measured at the detector side. 

Liquid phase chemiluminescence detectors usually consist of a postcolumn reactor (section 5.8) connected to a fluorescence detector with its source disabled [104,137,138,143-145]. The column eluent is combined with one or several reagents that initiates the desired chemiluminescence reaction. The intensity of light emission depends on the rate of the chemical reaction, the efficiency of production of the excited state, and the efficiency of light emission from the excited state. The chemiluminescence intensity is sensitive to environmental factors such as temperature, pH, ionic strength, and solution composition. In addition, the detection system has to be designed to accommodate the time dependence of the chemiluminescence signal to ensure that adequate and representative emission occurs in the detector flow cell. 

Flow injection is a method using on-line discrimination chemical reactions. Direct selective preconcentration is performed on microcolumns, the analytes being concentrated up to three to four orders of magnitude and injected into the detector. Usually as separation techniques ion-exchange, liquid-liquid extraction, gas diffusion are used. Flow injection systems are connected either to ETA AS or ICP-AES detection systems. These methods have been used for determinations of redox species such as Crflll)/ Cr(IV), Fe(II)/Fe(III), As(III)/As(V), Se(IV)/Se(VI) in soil extracts and water samples. 

Selective detectors are much more useful for the selective quantitation of a small number of chemicals known to be present in a complex matrix than they are for identification purposes. The use of on-line chemical reactions can be very selective for certain chemical families (e.g.. amino acids, sugars). This technique has become widespread in column chromatography, both gas and liquid, and is even the principle underlying many detection schemes in thin layer chromatography [64]. The identification of an unknown presupposes methods supplying far more information and consistent with the ready association of elements of this information with structural details of the corresponding compound. 

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