Gradient Techniques with Injection of Two or Several Zones

2 Gradient Techniques with Injection of Two or Several Zones 

The method of selectivity measurement is based on the fact that in any chemical procedure for a given species A any interference caused by the presence of an extrinsic species B will always, at least as observed from the detector s point of view, appear as (positive or negative) pseudo A. Therefore, the extent of this interference can be quantified by the selectivity coefficient, kAB, defined for any FIA method by the equation  

However, for both synchronous or asynchronous merging, the precision is critically dependent on maintaining not only the ratio of the two pumping rates, which is simple to achieve with a peristaltic pump, but also their absolute values, which is much more difficult. Thus, a more practical flow system should allow the two species to be injected separately without the need of keeping the pumping rates in separate lines absolutely constant. Such a system is presented in Fig. 4.25a, which 

Ia+b can be deduced, since it will hold (Section 2.5) that 

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