Dialysis can solve the problem of the precipitation of proteins by separation of low-molecular sugars from the high-molecular proteins
In food chemistry the determination of sugars in dairy products is of the utmost importance.
When carrying out direct ion chromatographic determinations the precipitation of protein constituents on the column is a recurring problem.
Instead of demanding precipitation procedures, the dialysis technique can be used to separate the interfering protein matrix.
The use of dialysis as an inline sample preparation step results in a rapid automated analysis system.
The sugar constituents are determined by means of pulsed amperometric detection.
The problem.
Sugar analysis plays an important role in food control.
In many cases, as the low-molecular sugar constituents are readily soluble, sample preparation is straightforward and rapid.
However, the analysis of protein-containing samples can pose severe problems. Precipitation of the proteins affects the column and ultimately destroys it.
This can be prevented if demanding precipitation procedures (eg, Carrez precipitation) are carried out before the analysis.
However, such sample preparation steps may lead to co-precipitation, inclusion, or even decomposition of the sugars to be determined.
Solution outline.
Dialysis can solve the above problem.
The separation of the low-molecular sugars from the high-molecular proteins is determined exclusively by the osmotic pressure at the membrane.
This means that, due to the concentration difference existing across the cellulose membrane, the sugars migrate from the sample stream into the acceptor solution (eg, ultrapure water) whereas the high-molecular protein constituents stay on the sample side of the membrane.
This sample preparation step occurs inline and can therefore be completely automated.
The time needed is negligible as the dialysis is performed during the recording of the previous sample's chromatogram.
The instrumental setup is the 817 Bioscan and dialysis.
In dialysis the analytes pass from the sample solution into the acceptor solution by diffusion through a dialysis membrane.
After only a short time a concentration equilibrium is established between the sample solution and the acceptor solution.
The number of analytes in the sample solution is not reduced as these are constantly being resupplied.
Whereas the mono-, di- and oligosaccharides can pass through the membrane almost without any hindrance, polysaccharides or larger particles - the matrix - are simply transported past the dialysis membrane. Matrix effects are therefore reduced to an absolute minimum. Automated sample preparation is becoming more and more an integral part of a high-performance IC system.
With the introduction of the patented dialysis method, Metrohm believes it has placed a new milestone on the way towards this goal.
