As pointed out in our post on HPLC pump accuracy uniform and reproducible column retention times are critical when analytes are pumped through a high performance liquid chromatography system. One of the most efficient ways of checking on the accuracy of HPLC pump systems is the Flow Cal 5000 digital liquid flow meter available from Tovatech. But how do you check on the accuracy of the checker – namely the Flow Cal 5000?
Flow Cal 5000 HPLC Flow Meter Accuracy Checks
When received from Tovatech the Flow Cal 5000 is accompanied by a UKAS traceable calibration certificate* good for one year. Standard calibration is 1 ml/min but on request it can be supplied at points from 0.5 to 25 ml/min. Multiple readings are taken at each flow rate then averaged on the calibration certificate.
A recalibration procedure should be scheduled annually or immediately if users think the unit is not operating correctly. Return it to Tovatech for a recalibration procedure that requires an estimated 2-week turnaround time.
The recalibration exercise begins with developing “before” data – that is how the flowmeter performs “as received.” The before data at a flow rate of 1 ml minute is provided on the certificate. (Additional flow data are available on request at an extra cost if users require it.) After the before data are recorded the flow tube is cleaned, repairs performed and the equipment is rechecked and adjusted to bring it into calibration specifications at required flow rates.
As with the initial calibration re-calibration is accomplished gravimetrically using water, not a reference flowmeter. A mass of water is passed through the unit over a recorded period of time then corrected for density. Mass is then converted into volume of water.
Actual flow rates are determined from the volume over time measurements then compared to the flow meter’s displayed readings that are captured and averaged via the RS-232 interface to a PC. The flow meter’s firmware is adjusted until the displayed rate matches the actual flow. This exercise is repeated for all calibration flow rates and the linearity is checked.
The recalibrated Flow Cal 5000 is returned to the user with the recalibration certificate.
For more information on this topic visit the HPLC Flow Meter pages on our website and download a copy of the Buyers’ Guide or call our scientists.
*Equivalent to NIST standards and accepted by the FDA