Fast, accurate calibration of flow rates used in HPLC flow systems can be compromised if the flow meter is not maintained. While GLP (good laboratory practices) call for annual flow meter recalibration by the manufacturer, improper use of these precision instruments can soon render them inaccurate.
A serious error is introducing in immediate succession two immiscible liquids into the flow meter. Either allow the first liquid to completely evaporate or introduce a third solvent in which the other two are miscible.
Dirty sensing tubes in FlowCal 5000 HPLC flow meters may cause bubbles to become entrapped. This can create falsely high readings. If bubbles are observed, a quick fix is to turn the unit off, wait approximately 2 seconds to allow it to drain, then switch it on. Contaminated tubes will also result in an “Error 4” reading denoting either the flow meter is not draining or the sensing tube is contaminated.
Another good practice is flushing the flow meter with methanol if it is not to be used for a week or more. This prevents algae growth in the tube.
Recommended Cleaning Procedures
To maintain the accuracy of the FlowCal 5000 flow meter it is essential to keep the sensing flow tube clean. A cleaning kit is supplied for this vital function, which does not entail disassembly of the sensing tube. Be advised that disassembly will invalidate factory calibration.
Flow meters in constant use should be cleaned every two weeks in an operation that normally takes about 15 minutes. Erratic readings are also a sign that cleaning is required.
Following manufacturers instructions disconnect tubing connected to the inlet pipe at the bottom of the vertically mounted flow meter, then power up the unit. Then wrap a small tissue or clean cloth around the flow tube protruding from the top of the meter to prevent cleaning fluid from entering the flow meter via the nearby power and RS-232 sockets.
Check the cleaning brush to be sure it is clean and is free of loose bristles or fiber, then dip it into the cleaning fluid, insert it carefully into the flow tube and push it down until resistance is felt. Gently rotate the brush while moving it up and down in the tube, collecting any foam in the tissue.
After removing the brush, fill the supplied 20-ml syringe with clean warm water and connect the supplied blunt-ended Luer needle. Connect the small bore tubing to the blunt end needle then carefully push the tubing 20 mm into the top of the flow tube and slowly inject the warm water. Water will pass through the flow tube and out the overflow pipe at the bottom of the instrument. The FlowCal 5000 flow meter may report “Error 2” or “Error 4” and the valve may be heard to open and water drain through the drain outlet during operation. This is normal.
Refill the syringe with warm water and repeat this step.
The following step should be repeated two times (a total of three) to ensure all cleaning fluid has been flushed from the flow meter and that the sensor head has cooled to room temperature:
Fill the syringe with clean cold water and connect it to the inlet pipe at the bottom of the flow meter. Place your finger over the top of the flow tube at the top of the flow meter. Very slowly inject the cold water. Water will flow through the flow tube and out the overflow and drain outlet at the bottom. Error readings and valve open and closure may occur and likewise can be ignored.
Clean up any spillage, re-connect the FlowCal 5000 flow meter to the pump and eluent, etc. Allow the eluent to flow for several minutes to flush out any water before taking readings.
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