Friday, December 17, 2010
A Digital HPLC Flowmeter Makes System Calibration Easier
Meeting tough FDA standards for HPLC system IQ OQ PQ validation as well as ongoing PV (performance verification) calls for properly installed, calibrated, and maintained equipment. A digital liquid hplc flowmeter such as the FlowCal 5000 is proven to be a convenient and accurate tool to calibrate HPLC pump flow rates, simplifying the calibration and validation procedures. Pump flow rates from 25 mL/min down to as low as 0.05 ml/min can be measured with an accuracy of ± 1 % of the flow rate. This type of tool saves time and labor compared with using a timer while manually collecting the effluent for measurement by weight or volume. In addition, the data collected is independent of operator technique and is therefore both more accurate and more precise.
When checking into digital HPLC flow meters laboratory technicians should determine if the models being considered will deliver accurate data at the flow rates typically used and have a traceable calibration certificate. In addition, the flow meter must be compatible with all brands of HPLC systems used in the lab. All wetted parts should be able to safely handle common HPLC solvents. The flow meter should have an appropriate interface such as an RS232 port for connection to a printer or PC for printing and archiving in accordance with good laboratory practices (GLP).
Installation and Maintenance
Although they are highly accurate, digital flow meter performance is adversely affected by improper mounting and poor maintenance. Citing the FlowCal 5000 as an example, several mounting configurations are available and supported by hardware supplied with the unit. Regardless of the mounting method, the unit must be within 10 degrees of vertical and with suitable space available for placing the collection vessel below the flow meter. Wall mounting, free-standing and stack system options are the most commonly used although in some instances an adapter kit can be employed to mount the unit on wide necked reagent bottles.
While GLP requires annual recalibration, flow meter accuracy can quickly deteriorate with improper use.
For example, dirty sensing tubes can trap bubbles and create false readings. In cases where bubbles are observed during operation the quick remedy is turning the meter off and letting it drain, then return it to operation. This suggests that the number one rule is to keep the sensing tube clean using supplied equipment for this important function. Another good practice is to institute a standard operating procedure specifying that flow meters be cleaned every two weeks when they are in constant use. Flow meters such as the FlowCal 5000 are shipped with a cleaning kit and directions for carrying out this function, a procedure that is usually completed within 15 to 30 minutes. If flow meters are not to be used over a week or more they should be flushed with ethanol to prevent algae growth.
One method to archive data in order to properly respond to FDA inquiries involves connecting the flow meter to a PC using the RS-232 interface. This allows operators to record flow meter readings electronically, such as in an Excel document using the Windows HyperTerminal program. The process collects data and displays it using HyperTerminl.exe, copies it on a clipboard and pastes it into Excel for analysis. Step-by-step details for this process are available from FlowCal equipment providers such as Tovatech.