Chemistry Reference
In-Depth Information
simplicity in operational procedure, robust and easy control of temperature and solutions handling, and low
cost of reagents can be highlighted [56]. A sequential injection system was also recently developed for the
determination of sulfates by using spectrophotometric detection and multivariate curve resolution-alternating
least squares [57]. The proposed flow methodology allowed in-line preparation of the samples, with the
corresponding increase in sampling rate and simplicity analysis. Additionally, the reagent consumption and
waste generation was minimal. In addition, to these excellent SIA applications, this topic has been reviewed
in multiple recently published articles [58-68].
16.4 Lab-on-valve
All current procedures could become environmentally friendly by reducing the amounts of reagents consumed
and it can easily be achieved by downscaling the manifold components and arranging them in a single device.
This concept is known as the micro-total analytical system (
-TAS), which involves arranging all steps of
sample processing in a single device of a few square centimeters [69]. Micro FIA (
μ
-FIA) systems, which
exploit microelectronic techniques to integrate pumps, mixing and reaction chambers as well as detectors in
a single chip provide the so-called lab-on-valve (LOV) concept.
As the third generation of FIA analysis, in the LOV (see Figure 16.3) configuration an integrated
microconduit is placed on top of the selection valve. The microconduit is potentially designed to incorporate
and handle all the necessary unit operations required for a given assay, that is, act as a small laboratory; hence
the name LOV.
Thus, it may contain facilities such as mixing points for the analyte and reagents, appropriate column
reactors packed for instance with immobilized enzymes, or small beads furnished with active groups such as
ion-exchangers, which in themselves might be manipulated within the LOV in exactly the same manner
as liquids, and even detection facilities. For optical assays (e.g., UV/Vis or fluorometry), this can readily be
achieved by use of optical fibers, the ends of which, furthermore, can be used to define the optical path length
μ
Sample
Reagent
Beads
1
6
2
Carrier
Selection valve
.
C1
C2
3
5
Carrier
4
D
Waste
Pump
Carrier
Reagent 2
Figure 16.3
LOV system. The microconduit placed atop the selection valve should ideally act as a small
laboratory. However, when large instrumental detector devices are to be used, it is necessary to employ external
detection as shown in the figure. Besides aspirating liquids, it is also possible to handle small beads (furnished
with active functional groups), which can be used to integrate small packed column reactors.
