Multisyringe Flow Injection Analysis for Environmental Monitoring: Applications and Recent Trends

Abstract

Multisyringe flow injection analysis (MSFIA) was introduced by Victor Cerda and coworkers in 1999 (Cerda et al., 1999) as a robust alternative to its predecessor flow injection techniques, combining the multi-channel operation of flow injection analysis (Ruzicka & Hansen, 1975) with the possibility of flow reversal and selection of the exact volume of sample and reagent required for analysis as presented in sequential injection analysis (Ruzicka & Marshall, 1990). Generally, flow injection systems are automation tools where, in opposition to batch conventional assays, physico-chemical equilibrium is not attained prior to determination. Hence, flow injection analysis is based in three principles: (1) reproducible sample injection or insertion in a flowing carrier stream; (2) controlled dispersion of the sample zone; and (3) reproducible timing of its movement from the injector point to the detection system. Since its inception, MSFIA has been the basis for automation of more than 120 different assays, reviewed in several publications (Almeida et al., 2011; Magalhaes et al., 2009; Maya et al., 2009; Segundo & Magalhaes, 2006). This type of automatic flow injection systems is based on the utilization of a multisyringe burette, depicted schematically in Fig. 1A and 1B. It is a multiple channel piston pump, containing up to four syringes, driven by a single motor of a usual automatic burette and controlled by computer software through a serial port. A two-way commutation valve is connected to the head of each syringe, allowing optional coupling to the manifold lines or to the solution reservoir. Because the four syringes are driven by the same motor, all pistons move at once in the same direction either delivering (dispense operation) or loading the syringes (pickup operation) with liquids. Considering that the commutation valves can be placed in two positions, there are four possibilities for flow management as depicted in Fig. 1C. Hence, when the pistons are moving upwards, it is possible to dispense liquid into the flow system or send it back to its reservoir. This feature enables that only the necessary amount of reagent solution is introduced into the flow system. Furthermore, when the pistons are moving downwards, it is possible to refill the syringes with solutions present in the respective vessel or to aspirate solutions from the system in order to perform the sampling operation.