Waters Dextro-Pak Cartridge - Manual (Page 4)

[ Care and Use ManUal ]
Dextro-Pak Cartridge 4
Iv. sample fIlterIng
1. Filter all samples through a 0.45 µm membrane filter just
before injection to remove particulates. Suitable replacement
filters are provided in the Waters Aqueous Sample
Clarification Kit, P/N WAT026865. Suitable disposable filters
with a larger surface area are also available.
2. Use an (in-line Precolumn Filter (P/N WAT084560) immedi-
ately before the column to protect it from any particulate matter
in the sample or mobile phase.
3. Sugar samples often contain polysaccharides or other high
molecular weight materials, such as proteins, which will adsorb
to the cartridge packing and become difficult or impossible to
remove. Use guard columns packed with C
18
for all samples,
except very pure sugar solutions, to avoid contamination of the
cartridge packing material.
4. Place the insert inside the inlet of the Dextro-Pak cartridge.
5. The Guard-Pak TM inserts are supplied dry and must be wetted
before use. To wet, place a few inserts under methanol in a
Buchner flask and draw a vacuum of 635 mm (25-inch) for a
few minutes, breaking the vacuum a couple of times, to ensure
that all air is sucked from the inserts. The inserts can be stored
in methanol in a small jar until needed. When the insert in use
becomes plugged, simple remove it and replace it with a fresh,
wetted insert and restart the flow. Flush the methanol from the
system for about 15 minutes.
a. Removal of Lipids and Polymeric Materials
Use the following procedure to extract lipids and polymeric material
from your sample:
1. Fill a 10 mL syringe with 5 mL methanol and slowly flush
the methanol through a Waters SepPak ® C
18
cartridge (P/N
WAT020515) to activate the packing material.
2. Wash the methanol from the cartridge with two 5 mL portions of
pure water.
3. Blow excess water from the cartridge with the syringe.
4. Slowly pass the sample through the Sep-Pak C
18
cartridge, reject
the first 2 mL, and collect the next few milliliters for analysis.
b. Removal of Salts and Acids
Do not expose silica bonded phase packing to a pH of greater than 8
or less than 2. If samples are strongly acidic or alkaline, neutralize
prior to injection.
Many organic acids and salts elute at or near the void volume. Some
larger organic acids may be retained long enough to interfere with
the analysis of the sugars. Remove these materials by using ion
exchange resins.
• Pass the sample containing the ionizable compounds through a
small open column (such as a Pasteur pipette) filled with resin.
• Alternately, add a small amount of resin to the sample and
shake.
When using ion-exchange resins, keep in mind that the resins are
supplied in a wetted condition and that this water may dilute the
sample to a significant degree.
Some sugars may be adsorbed by the resin and must be washed
out for full recovery. Certain resins may contain a strongly acidic
functionality causing inversion of sugars, such as sucrose that are
prone to hydrolysis.
A mixed bed, ion-exchange resin that has been used successfully for
sample cleanup is Amberlite MB-i
® . Amberlite MB-i ® is available
from Sigma Chemical Company, St. Louis, MO (Catalogue Number A
7393).
v. test CondItIons
Waters cartridges are thoroughly tested for adherence to our
specifications. However slight variations in your results may occur
depending on the equipment used. Therefore before attempting
the first analysis, test sample makeup, equipment settings and
condition, perform the test sample run given here for your new
cartridge and record the results (retention time and the settings
used). Use these results for comparison throughout the life of
your cartridge.