Chromatography
Studying the Impact of Dissolved and Undissolved Gas
on the Performance of Peristaltic Pumps Carlo Dessy, Testa Analytical Solutions eK
Peristaltic pumps are fl uid delivery tools widely used in laboratory techniques including HPLC, GPC/SEC, Flow Chemistry and Liquid Dosing. It is widely acknowledged that dissolved gas can have an impact on the performance of peristaltic pumps. A common solution to address this problem with HPLC systems, is to utilise a vacuum degasser on the inlet side of the pump. A vacuum degasser is fundamentally a chamber kept under vacuum pressure that contains a length of gas-permeable tubing leading the solvent to the pump. Using this technology, any gas dissolved in the solvent will be extracted in the vacuum chamber before it can reach the pump. Vacuum degassers have been shown to be very effi cient for removing dissolved gas, they do however fail completely if any undissolved gas bubbles are transported along the tubing.
In this scenario, undissolved gas bubbles pass the degassing device largely unaffected by the vacuum and will unfortunately reach your HPLC pump leading to unreliability and the consequent errors in analytical results. This led to the question as to what effect dissolved gas might have on the performance of peristaltic pumps.
In this study we fi rst investigated whether dissolved gas might also have an impact on peristaltic pumps and be the source of inequalities seen in the performance of dual cartridge systems [1]. In further investigations, we demonstrate the effect of undissolved gas bubbles on pump performance and introduce a novel solvent line monitoring device that provides a simple way of eliminating the problems resulting from this effect.
Experimental
In this study, we used a dual cartridge peristaltic pump (Ismatec, Germany) equipped with two new lengths of Tygon tubing with a nominal ID of 0.76mm designed to deliver fl ow rates between 0.1 and 5 mL/min. Flow rate was measured using two Liquid Chromatography Flowmeters (Testa Analytical, Germany) to precisely measure real-time fl ow rates of 0.01 to 5 mL/min. Deionised water was used as the experimental test liquid for our experiments.
After conditioning the peristaltic pump at a nominal fl ow rate of 1 mL/min for several minutes, we started a ramp experiment with incremental increases in steps of 0,5 mL/min from 0,5 mL/ min to 5,0 mL/min nominal fl ow rate. Data was acquired on each step for about 120 seconds. Between steps, the fl ow rate was set to zero gain to ensure the same conditions for the whole ramping experiment.
Figure 1. Comparison of fl ow rate by dual cartridge peristaltic pump.
The results from our fi rst experiment revealed that the two peristaltic pump channels, thought to be identical as they are driven by a common shaft and equipped with the exact same length of tubing, performed quite differently with a notable increasing difference of real fl ow between the 2 channels.
Our experiments were designed to investigate the different impact of dissolved gases and undissolved gas bubbles associated with dual channel peristaltic pumping of a liquid to a fl ow chemistry system or similar applications.
Our fi rst experiment investigated the comparative fl ow from the two channels of the peristaltic pump at different fl ow rates (Figure 1).
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