II-9
Matec Applied Sciences
56 Hudson St., Northborough, MA 01532 Ph: (508) 393-0155 Fax: (508) 393-5476
www.matec.com
e-mail: [email protected]
microelectrophoresis or electro-acoustic ESA analysis. Problems may occur when diluting systems
stabilized with cationic surfactants. For specific information regarding specific sample systems, please
contact Matec Applied Sciences directly.
Most samples will need to be sonicated before analysis. For many samples prepared by the dilution of a
concentrate, placing the sample container in an ultrasonic bath will be sufficient. For dispersing powders
into liquids or when dealing with materials which may have a strong tendency to form aggregates, it will
be necessary to use an ultrasonic probe immersed in the sample itself. In both cases, the objective is to
prepare a uniform dispersion in which the particles exist in the actual state of dispersion that you wish to
characterize.
The CHDF 2000 requires that the sample be injected by syringe through an injection valve, or the sample
may be injected using an autosampler. In many cases it is necessary to filter the sample before injection to
remove coagulum or outsize particles. Five-micron filters which attach directly to the end of the syringe
are recommended. These filters are available from Matec Applied Sciences.
2.8 ELUANT
The standard eluant supplied for use with the CHDF 2000 is designated GR-500 and is for anionic
systems. Most materials will be anionic when dispersed in GR-500. The eluant consists of surface active
agents in de-ionized water. GR-500 is supplied in the form of a concentrate which must be diluted 10:1
for use, e.g., 900 ml de-ionized water to 100 ml GR500 concentrate. GR-500 should be diluted with de-
ionized water and the final solution should be filtered under vacuum through either a 0.1 or 0.2 µm pore
size filter. The purpose of this filtration under vacuum is to remove any particulate matter and also to de-
gas the GR-500. Care should always be taken when handling the GR-500 to avoid contamination. The
eluant should be used within 3 days of preparation. The GR-500 concentrate should be used within one
month of receipt. It should be kept refrigerated.
Matec supplies three types of GR-500 eluant: 1X-GR500, 2X-GR500, and 2X-GR500-LA. The appropriate
conductivity ranges (µSiemens/cm) of final eluant solutions are 6-9 for 1X-GR500, 14-19 for 2X-GR500-
LA, and 22-27 for 2X-GR500. Each of these eluants can be used with any of the three types of cartridges
available. Most commonly, 2X-GR500 is used in conjunction with a C-202 cartridge.
Both 2X- eluants produce the same resolution and use the same calibration curves. The 2X-GR500
contains 10 milligrams/l sodium azide biocide; the 2X-GR500-LA eluant contains only 0.5 milligram/l
sodium azide. As a result, the 2X-GR500-LA eluant degrades faster due to bacterial growth. The shelf-life
for these eluants is three days for the 2X-GR500-LA, and one week for the 2X-GR500. The 2X-GR500
cannot be used at 200 nm UV-detection because of the high UV-absorption by sodium azide.
The 1X-GR500 provides higher particle resolution efficiency than the 2X- formulas. The upper particle
size limit is lower with 1X-GR500. The 1X-GR500 contains 0.5 milligrams/l sodium azide. Its shelf life is
three days.
NOTE:
The CHDF 2000 and the fractionation cartridge have been specifically calibrated for use with GR-500
eluant. The use of any other eluant will give erroneous results and voids the CHDF 2000 warranty.
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