General Catalog

Professional IC Systems
Metrohm Inline Ultrafiltration and Dialysis
Metrohm Inline Ultrafiltration
Modern ion chromatography recommends all samples
to be filtered prior to injection. Separation columns
with particle sizes below 10 µm require absolutely
particle-free sample solutions. Unfiltered solutions
can increase pressure on the column which in some
cases can radically reduce the life span of the column.
Manual filtration is usually carried out by means of
disposable filter cartridges with a pore size of 0.45 µm
or less. These become clogged very quickly, particularly
with samples containing very fine particles. Sample
changers with filter caps are used as an alternative.
Their pore size is often larger than that of disposable
filters. However, they are expensive and there is still a
risk of clogging.
With Metrohm Inline Ultrafiltration, which belongs to
the membrane separation techniques, these problems
no longer apply. The samples are placed directly on
the sample rack. When the samples are processed the
sample flow is channelled into the lower chamber of
the ultrafiltration cell and passes along the membrane
and into the waste container. In the upper chamber of
the cell a peristaltic pump creates a vacuum and draws
the sample solution through the ultrafiltration membrane.
The filtered sample solution enters the injection
loop and is then injected. Less than 20% of the original
solution is removed as filtrate, the remainder
flows directly into the waste container. This, together
with the geometrical arrangement of the cell, virtually
eliminates the formation of a filter cake which could
block the membrane. Metrohm Inline Ultrafiltration is
particularly suitable for samples with a light to medium
load, for example drinking water, surface water, wastewater,
digestion solutions, extracts.
Metrohm Inline Dialysis
Highly polluted samples require complex and laborious
sample preparation steps before they can be analyzed.
Metrohm Inline Dialysis provides a considerable rationalization
of the whole process. Samples must meet
just one condition: they must be liquid or be able to be
brought into liquid form and they need to be largely
homogeneous. Larger particles can be removed by
centrifuging, if necessary. The sample solution is then
dialyzed in the dialysis cell according to the method
patented by Metrohm (European Patent 0 820 804, US
Patent 5,861,097). Due to this special «Inline Stopped-
Flow Dialysis» method a virtually complete dialysis is
obtained. This means that the acceptor solution has
the same ionic concentration as the original sample
(equilibrium dialysis). The acceptor solution is then
injected directly into the ion chromatograph where it
is analyzed. Whereas in ultrafiltration the sample solution
is filtered through the membrane as a result of a
difference in pressure, the driving force in dialysis is the
difference in concentration between the two sides. The
ions to be determined diffuse through the membrane,
but no sample solution is forced through the membrane.
This means that no filter cake is formed that could
block the membrane. By means of this technique it
is possible to determine anions and cations even in
cutting oil emulsions, biodiesel, dairy products or body
fluids such as blood and urine.
If the system is programmed so that the next sample is
dialyzed during the current run, the total analysis takes
about the same time as direct injection.
Acceptor solution
Sample
Particle
Membrane
Ion
Membrane
Ion
Particle
Sample
«Stopped flow» method
An equilibrium is achieved between the acceptor solution and the sample
solution
Ultrafiltration
14 — IC