Abstract: The application of flow injection analysis to the simultaneous spectrophotometric determination of two metals in a sample is described and a novel phototransducer which improved peak detection is discussed. Thus, an aqueous HCl sample containing Pb(II) and V(V) at pH 2 was injected into a stream 10^-3 M in 4-(2-pyridylazo)resorcinol (I) buffered in NH3 at pH 9.9. The changes with time in the peaks owing to the V-I complex, formed at pH 2, and the Pb-I complex, formed at pH 9, were observed Pb was determined with 1-2% relative standard deviation in the presence of varying amounts of V but V could be determined with only limited precision in the presence of a constant amt. of Pb. The use of refractometry to measure peaks in flow injection analysis was also discussed with reference to some examples with aqueous NaCl. With the phototransducer, 100 ppb Co(II) could be detected with a relative standard deviation of ~1%.

Abstract: A kinetic model is utilized for a detailed mathematical treatment and experimental evaluation of single-channel and dual-channel flow injection systems that include a gradient chamber. The kinetic model includes three distinct stages in the process, namely clearing reactant from the gradient chamber by first portions of sample, continued entry of sample into the gradient chamber, and decrease of determinant concentration in the gradient chamber via dilution and reaction with reagent. Equations predict entirely different behavioral patterns for different conditions and these predictions are verified experimentally for a wide range of conditions. The data show that the variable-time kinetic model is superior to the titration models previously utilized to describe these flow systems. The principal limitation of the kinetic equations involves an assumption of plug flow that is not completely valid. The extent of deviations from ideal behavior depend on conditions, but are negligible at low concentrations (0-50 mmol l-1) and can be 10% or larger at higher concentrations (100 mmol l-1). While equations are not exact, they are useful in predicting performance characteristics for a variety of conditions and experimental approaches.

Abstract: A variable-time kinetic model is used to evaluate a single-channel flow-injection system with gradient chamber that has been identified as a continuous-flow titration. A physical model, mathematical equations, computed concentration vs. time profiles, experimental data, and formal definitions are used to identify qualitative and quantitative features of the method that have not been apparent from the titration model for the system. It is shown that determinations can be performed with and without reactant in the flow stream and when reactant is in the flow stream, with and without reactant in the gradient chamber when the sample is introduced. It is shown that lowest concentrations with shortest cycle times can be achieved when determinations are performed without reagent in the gradient chamber initially. Characteristics unique to each of three different data processing options are used to evaluate the validity of equations presented. It is suggested that some methods previously identified as continuous-flow titrations are most accurately identified as variable-time kinetic methods, and it is shown that this semantic differentiation can provide improved insight into the methods and can expand the scope of the methods by suggesting new experimental approaches with potential advantages relative to previously described procedures.