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Matec Applied Sciences
56 Hudson St., Northborough, MA 01532 Ph: (508) 393-0155 Fax: (508) 393-5476
www.matec.com
e-mail: [email protected]
FREQUENTLY-ASKED QUESTIONS ABOUT
CHDF OPERATION
1.
How frequently should the CHDF GR500 eluant be replaced?
The CHDF GR500 eluant degrades with time. It should be replaced every two to three days. Check the
conductivity of the eluant in order to determine if it is suitable. The conductivity ranges for the
different GR500 types are as follows (in microSiemens per centimeter): 1X-GR500: 7-10; 2X-GR500:
22-27; 2X-GR500-LA: 14-18; 1X-GR500 pH9: 13-18. The GR500 eluant absorbs Carbon Dioxide
from the ambient which causes its pH to drop, and its conductivity to increase; this results in
measured particle sizes smaller than expected. The 1X-GR500 pH9 eluant is especially sensitive to
CO2 absorption. Bacterial growth also takes place as the GR500 ages.
2.
I obtain smaller than expected CHDF particle size results when I inject calibration standards.
Most likely, your GR500 eluant is either degraded or contaminated. See Question 1 above.
3.
How is the GR500 eluant prepared?
Add 950 ml of deionized water (conductivity should be less than 2 micro Siemens per centimeter) to 50 ml
of GR500 concentrate. Eluant degassing by either sonication or vacuum filtration is recommended.
4.
How long does the GR500 concentrate last, and how should it be stored?
The GR500 lasts about one month. It should be kept refrigerated.
5.
Does the Marker fluid need to be injected at an exact time for every run?
No. In both manual, and auto-sampler operation, the software detects when the marker is injected. The
injection time is recorded; the marker elution time is calculated as the marker exit time minus the
injection time. A marker delay time of zero seconds is recommended for auto-sampler operation (this
is set under the current method file).
6.
How should the marker fluid be prepared?
The marker fluid consists of a solution of sodium benzoate in deionized water. Its concentration varies
depending on the type of fractionation cartridge used. Typical concentrations are in the range 0.1% to
0.5%. This concentration should be adjusted in order to obtain a reasonable marker peak height
(displayed on the CHDF software Raw Data graph) upon marker injection into the CHDF. Marker
peaks heights of 10 to 40 mAU’s (milli Absorbance Units) for the CHDF-2000 instrument, and 5,000
to 15,000 counts for the CHDF-1100 are acceptable.
7.
Why is the pump pressure fluctuating more than 200 psi during a run?
Air bubbles are lodged in the pump pistons. Stop the pump; open the pump purge valve (located on the
lower right- hand corner of the CHDF-2000; or on the CHDF-1100 pump front panel); insert a 5-ml
plastic syringe into the purge valve, and slowly draw fluid. Air bubbles in the pump and pump-inlet
tubing should be removed. Tighten the purge valve and start the pump. If the air bubbles re-appear,
the Whatman de-gassing filter on the pump-inlet tubing should be replaced. This filter lasts about one
month. Cavitation, which results in air bubble generation, occurs if the Whatman filter needs
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