Chemistry Reference
In-Depth Information
the chromogenic reagent, made the system reversible and the reagents reusable. The method was successively
applied to the assay of lead in high-octane gasoline. Simple FIA has also been adapted for post-analysis
in-line waste detoxification, such as the TiO
2
catalyzed UV mineralization of aromatics [35]. On-line solid-
phase extraction coupled to different detectors using chelating resins and other low-cost adsorbents have been
used to recover metals at trace levels in different matrices [36-42]. The FI-based manifolds have the
advantages of reducing solvent usage and exposure, disposal costs and extraction time for sample preparation.
Consequently, SPE has been successfully used for the separation, preconcentration, and sensitive determination
of metal ions in numerous types of samples.
Despite of the significant advantages of FIA compared to batch assays, adaptation of FI to industrial
environment for process analytical purposes was hindered by the following drawbacks: (1) complicated flow
manifolds, (2) lack of flow stability due to peristaltic pumps do not provide steady flow on 24 h basis operation
and therefore require frequent maintenance increasing this way the cost of the analysis, and (3) the continuous
flow of reagents produces considerable amounts of waste material in the case of 24 h process control
applications. These disadvantages were more or less overcome by the introduction of Sequential Injection
Analysis, which is considered as the second generation of FIA-based techniques.
16.3
Sequential injection analysis
While most FIA-procedures employ continuous, unidirectional pumping of carrier and reagent streams, SIA
is based on using programmable, bidirectional discontinuous flow as precisely coordinated and controlled by
a computer. Sequential injection has shown the ability of performing different determinations without system
reconfiguration (placing different reagents on the ports of the selection valve); as a consequence of the non-
continuous consumption, a reagent saving is promoted [9, 13, 43-45]. A sketch of a typical SIA-manifold is
reproduced in Figure 16.2.
The core of the system is a multi-position selection valve with six ports as it enables the sequential selection
of the various solutions and the subsequent redirection towards the detection system. Most of the characteristics
Reagent 1
Standard
Sample
1
6
2
Carrier
Selection valve
.
Carrier
3
5
4
D
Waste
Carrier
Pump
Reactor
Reagent 2
Figure 16.2
Sequential injection analysis system. Selection valve (SV) and central CC of which randomly can
address each of the six individual ports. Initially, sample and reagent are by means of the syringe pump (SP),
and via the central CL, aspirated into a HC and stacked there as individual zones. Thereafter the zones are
through Port 5 and the reaction coil forwarded to D, which monitors the product formed as the result of the
dispersion of the zones into each other during the transport.
