OSMOMAT 050 User Guide
Page 7 of 51
Version 1.1 (2011-10-12)
1.2 Application Restrictions of the OSMOMAT 050
The OSMOMAT 050 is not suitable for measuring whole blood samples.
1.3 Measurement Method of the OSMOMAT 050
The measurement principle of the OSMOMAT 050 is based on a measuring cell, consisting of an up-
per and lower half, each with a volume of approx. 10 µL, separated by a semipermeable membrane
(Fig. 1-1)
. The so-called reference cell, located below the membrane, is equipped with a pressure
transducer (pressure converter, measuring bridge). The upper half of the measuring cell, also known
as sample cell, is connected to the automatic rinsing mechanism. In standby state, both cells contain a
solvent
(such as Ringer's solution, isotonic NaCl solution)
to prevent pressure drops and ensure that
the pressure measurement membrane is relaxed.
After adding a sample with a higher colloid osmotic (oncotic) pressure (e.g. serum or plasma) to the
sample cell, permeation of solvent causes underpressure in the reference cell based on the laws of
osmosis (because the membrane is impenetrable to proteins, this can only be achieved by a flow of
solvent). This is measured by a pressure transducer, amplified electronically, and displayed as posi-
tive, direct colloid osmotic pressure (COP value), either in mm Hg (mm of mercury), cm H
2
O, or k-
Pascal. By default, the reading is displayed in mm Hg. The measurement unit can be switched by
pressing the corresponding buttons on the digital display.
Different types of semipermeable membranes with varying permeability ("pore size") can be used for
macro molecules with different molecular weights. This results in a characteristic reference number for
each type of membrane (the so-called "membrane cut-off", indicated in dalton units). Membranes with
a cut-off of 10,000 or 20,000 dalton have proven to be very useful in practical applications.
Sample cell
Semipermeable membrane
Reference cell
Pressure transducer
Amplifier
Display
Figure 1-1: Schematic figure of the measuremet principle
Summary of Contents for OSMOMAT 050
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