Continuous-addition-of-reagent technique

Figure 4 Experimental setup for implementation of the contin-uous-addition-of-reagent technique. (Reproduced with permission from Marquez M, Silva M, and Perez-Bendito D (1990) Kinetic determination of sulfonamides at the millimolar level by continuous addition of reagent technique. Analytica ChimicaActa 237 353-359 Elsevier.)...

Flow systems, both continuous and discrete, are used in kinetic-based determinations for monitoring fast reactions mainly. To this end (1) the dead time in the mixing system should be several orders of magnitude lower than the half-life of the reaction concerned and (2) nearly the whole kinetic curve must be recorded in order to implement reaction rate-based determinations and perform fundamental kinetic studies (e.g., the determination of reaction orders and rate constants). The advent of stopped-flow mixing and the continuous-addition-of-reagent technique has made noncatalytic reactions competitive with equilibrium methods in practical terms. 

Figure 6 Kinetic profiies provided by continuous-addition-of-reagent technique. (A) Typicai kinetic curve. (B) Recording obtained for a chemicai system invoiving an undesirabie interaction between the reagent and some reaction ingredient. (Reproduced with permission from Siiva M (1993) Recent strategies in automated reaction rate-based determinations. Tutorial Review Analyst 118 681-688.)...

M-i-PT-M-PT Fe-Co, Ni-Co, Cu-Fe Logarithmic-extrapolation and single-point methods Interpolation method used to overcome synergistic effects Use of the continuous-addition-of-reagent technique... 

Type of reaction uncatalyzed chemiluminescence "TS, 3,3, 5-triiodo-L-thyronine T4, 3,3 5,5 -tetraiodo-L-thyronine (i-Thyroxine) CAR, continuous-addition-of-reagent technique LC, liquid chromatography. 

Recently the continuous-addition-of-reagent (CAR) technique [182] was applied for the determination of fluorophores by POCL chemistry [95-99], The applicability of this technique was demonstrated by the determination of natively fluorescent acepromazine in horse plasma [95], the alkaloid harmaline in plasma [96], and other dansylated alkaloids [97], A separation step has also been included and applied to postcolumn detection of PAHs [98] and dansylated P-carboline alkaloids [99],... 

This chapter focuses on analytical CL methodologies, with emphasis on the kinetic connotations of typical approaches such as the stopped-flow, the continuous-addition-of-reagent (a new kinetic methodology) and the pulse perturbation technique developed for oscillating reactions, among others. Recent contributions to kinetic simultaneous determinations of organic substances using CL detection (kinetometric approaches included) are also preferentially considered here. 

Although other commonly used open systems such as the stopped-flow methodology or the continuous-addition-of-reagent (CAR) technique are especially well suited to fast uncatalyzed reactions, they can also be applied to slow reactions. 

In CL techniques, after mixing of the reagents and the sample, the CL reaction starts and the emission intensity is being produced, decreasing once the reactants are consumed. This implies a transient character of the CL emission, the time scale of which depends on the specific reaction, and which can range from a short flash to a continuous glow. This fact is crucial for selection of the most convenient systems of reagent addition. 

Flow-injection methods are quicker, more precise and use less reagents than other techniques in addition, they are very useful where only a Hmited amount of sample is available. The main advantages of the combination of FIA with DCP/OES are the increase in precision in sample handhng, fewer physical interferences, ahigher throughput of samples and versatihty towards physical and chemical properties of reagents. Some minor disadvantages are the loss of sensitivity compared with continuous nehuHzation, and the fact that only one element can he determined at a time. 

Thus, the use of alkyllithium initiation offers the synthetic chemist a tool of enormous flexibility for "tailor-making" polymers of precise structure. Control of molecular weight, molecular-weight distribution, diene structure, branching, monomer-sequence distribution, and functionality can conveniently be achieved by such techniques as incremental or sequential addition of monomer, initiators, or modifier, programming of temperature, continuous polymerization, or the use of multifunctional reagents. 

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