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Liquid Chromatography Flowmeter – Frequently Asked Questions Liquid Chromatography Flowmeter – Frequently Asked Questions



Q: My liquid chromatography flowmeter offers five possible integration times, which should I select?

A: For most HPLC or GPC/SEC applications, selecting 1172 msec integration time ensures that any pump pulsation or transient flow spikes will have minimal impact on your measurement. Using this setting will provide an accurate measurement of the average flow rate providing you with a reliable evaluation of your system’s performance. Shorter integration times should be selected if you are looking to troubleshoot a problem with your liquid chromatography system as it allows you to pinpoint the source of flow fluctuation.

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Q: My HPLC pump indicates that its pressure is very stable but my TESTA flowmeter shows huge pulsations. How is that possible?

A: By design, the pressure displayed by your HPLC pump is heavily smoothed in order to reveal trends and avoid damage to the connected HPLC Columns. However, it is not designed to show short term fluctuations. By comparison, TESTA flowmeters are designed to monitor the flow rate from your HPLC pump in real-time. This useful feature supplies the information about the status of the pump as well as the ‘operational health’ of its seal rings and check valves. In otherwords, the HPLC pump pressure transducer and the TESTA flowmeter fulfill very different tasks.

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Q: I am using a TESTA flowmeter to optimise liquid reagent delivery by my flow chemistry system. I detect huge difference between the flow rate I set on the system pump and the measured value obtained by the flowmeter. Is my flowmeter defective?

A: No, the flowmeter is doing exactly what it was designed for. Most flow chemistry pumps are optimized around a single flowrate value and for a particular solvent. If you deviate far from this optimization point and use a different solvent, this can result in a notable deviation between the real flow rate and the set value. However, this is exactly why a flowmeter is an absolute necessity for improving the reproducibility and yield from your chemical reactions. Our chemistry flowmeter supplies the real current flow rate of liquid reagents being added and shows also what fluctuations occur at a particular setting. Knowledge of this will allow you to optimise your flow chemistry reaction accordingly and even to select pumps better suited for your application.

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Q: Testa Analytical flowmeters are small devices which fit neatly in the palm of a hand. However, in which orientation (vertical or horizontal) is it best to operate the device?

A: The best operating position is undoubtedly upright with the display readable. This is the “designed” orientation. However, TESTA flowmeters will work in any orientation with minimal effect on the measured flow rate. As such, we recommend that you choose an orientation, and keep it constant in order to obtain reproducible results.

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Q: I noticed that my TESTA flowmeter shows negative flow rate values. How is this possible?

A: Our flowmeters are by design bi-directional. This means that they can measure the flow in both directions. If the displayed is negative, then your device is incorrectly connected in reverse to the designed direction of flow. Please note the negative values are valid measurements but not calibrated.

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Q: How often should I solvent flush my refractive index detector (RID)

A: As often as needed is the simple answer. A good practice is every time when solvent is replaced, flush the RID several times and observe the trend of the baseline. Once the baseline stabilizes, only then you can assume the reference is filled with new solvent. On a day-to-day basis, flush your RID a minimum of once a day, preferably at the beginning of the working day and for good measure, flush again at the end of the working day. Following this procedure will help maintain the accuracy and repeatability of your RID measurements.

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Q: Why should I solvent flush my refractive index detector?

A: Here are 4 good reasons to solvent flush your refractive index detector (RID). Firstly, the reference cell in your RID must contain the same solvent as used as in the eluent channel, regular flushing assures this. Secondly, while eluant constantly flows through the sample cell, the reference cell content is static. In time, bubbles may collect in the cell causing an imbalance in the signal. Flushing will remove the bubbles. Thirdly, it is often the case that solvent mixtures change with time. This happens within the reference cell of a RID as well. Flushing makes sure fresh (and representative) solvent is in the reference cell. Finally, upon replacing solvent A with solvent B, you must ensure that your RID reference cell contains only the new solvent. Even the smallest traces of the previous solvent may ruin a measurement.

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