Kinetics, chemical spectrophotometric methods

A kinetic spectrophotometric method has been developed for the simultaneous quantitative determination of acetaminophen and phenobarbital in pharmaceutical preparations. The basis of the method was the different kinetic rates of the analytes in a two-step chemical procedure first the oxidative coupling reaction with 3-methylbenzothiazolin-2-one hydrazone in hydrochloric acid medium and then using Fe(III) as oxidant and continuous absorbance monitoring. An artificial neural network (ANN) coupled with PCA (PC-ANN) has been used to simulate this method. 

FIA systems are used to investigate the kinetics of homogeneous chemical reactions and for the analytical determination of many components by means of spectrophotometric detection, amongst other applications. In the latter method, a certain concentration of reagent (component forming a coloured complex with the component to be determined) is added (injection), to a constant liquid flow of the solution in which the component to be determined is situated (flow).The resulting solution subsequently passes a reaction chamber, after which detection occurs by means of a spectrophotometer (analysis). 

Several methods that do not require chemical separation are available for measuring uranium in urine (in units of total mass or total activity). These methods include spectrophotometric (total mass), fluorometric (total mass), kinetic phosphorescence analysis (KPA) (total mass), and gross alpha (total activity) analyses (Wessman 1984). The most widely used methods for routine uranium analysis are a-spectrometry and liquid scintillation spectrometry. These methods utilize the natural radioactivity of uranium and are sensitive and require little sample preparation. Photometric techniques such as fluorometry and phosphorometry are less widely used, but kinetic phosphorescence analysis is becoming more widely used. Measurements of total uranium do not provide the relative isotopic abundance of the uranium isotopes, but this may only be important when converting between activity and mass when the isotopic ratios are uncertain. 

Physical methods rely on the measurement of a property of the reaction mixture that can be related to the concentration of a reactant or product species. Properties that have been widely used are pressure (in the case of gas-phase reactions), spectrophotometric absorption and electrical conductivity. Spectroscopic methods such as nuclear magnetic resonance (NMR) and infrared (IR) may also be used to analyse a mixture as the reaction progresses. From the point of view of slow reactions, the time required to make a measurement for any of these physical methods, that is the response time, is minimal. Physical methods of analysis are now widely used in chemical kinetic investigations. 

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