2. Principles Of Automatic Analysis
Segmented Flow Analysis (SFA), Flow Injection Analysis
(FIA) an Selective Ion Analysis (SIA) are complementary but separate
automatic analytical techniques for measuring many determinands
from Ammonia to Zinc.
Segmented Flow Analysis (SFA)
The principle behind the instrumentation used in
the Segmented Flow Continuous Analysis technique was introduced
by Dr L Skeggs of the University of California in 1957. The technique
involves mixing a liquid sample with reagents pumped in a continuously
flowing stream and segmented with air bubbles. The sample and reagents
are mixed by passing through glass coils and also through a temperature
controlled heating coil if heat is required to speed development
of the colour complex before detection using a colorimeter, fluorimeter
or other suitable detector in the UV and visible wavelength ranges.
In the initial work, it was found that in some analyses the high
molecular weight components contained in samples were interfering
with the chemical reactions. This problem was ingeniously overcome
by the use of a cellophane dialysis membrane to remove them.
Today, the technique has become one of the most reliable
and widely used methods for automatic chemical analysis in routine
and research analytical laboratories. As a technique for measuring
large batches of samples for up to 16 determinands simultaneously
at speeds of up to 120 samples per hour it is unrivalled.
Burkard Scientific is an international leader in
the design and manufacture of segmented flow and flow injection
analysers and has been responsible for many of the recent major
new developments in instrumentation and applications.
Flow Injection Analysis (FIA)
First used by Ruzicka and Hansen in 1975, FIA involves
the injection of a liquid sample into a moving non-segmented continuous
carrier stream of a suitable liquid (usually the colour reagent).
A high precision peristaltic pump is used to pump samples and reagents.
The injected sample forms a zone which is then passed through mixing
coils and carried to a flowcell in the detector - usually a colorimeter,
fluorimeter or flame photometer - for measurement of the optical
activity or emission. One or more channels (determinands) can be
set up to run simultaneously.
The advantages of FIA are: precise sample introduction
(either manual or automatic), small sample volumes (typical 10-50ml)
low reagent consumption and fast sample throughput .
Selective Ion Analysis (SIA)
Developed by Burkard Scientific SIA uses an Ion Selective
Electrode for detection. The method is similar to FIA but the ISE
detector is simpler and allows for certain chemistries that cannot
be catered for by either SFA or FIA and because the system is simpler
it makes it more affordable for low batch size analysis.
Continuous Flow Analysis (CFA)
Less sophisticated then either FIA, SFA or SIA in
not requiring either an injection valve or air segmentation, CFA
is the fourth automatic flow method. An example application of
CFA is the simultaneous determination of bitterness and colour
using the Series 2000 Beer-Malt analyser.
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