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Title: Microfluidic stopped-flow measurement of reaction kinetics.
Author: Braddock, Gareth Rhys
ISNI:       0000 0004 2743 305X
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2011
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In recent decades microfluidic analytical devices have become an increasingly popular re- search topic because of the advantages they confer over their macro-scale counterparts. These include inherent low sample hold up volume, rapid response times and flexible operation. These benefits as well as their predisposition to automation make them ideal for use in high throughput analytical systems. The work presented in this thesis is concerned with the underpinning technical issues of per- forming a microfluidic stopped-flow reaction kinetics measurement test. These are concentrated on the ability of a syringe pump system to control the flows on-chip. The issues of particular interest are the measurement of the relaxation flow due to mechanical deformation in the syringe drive. the flushing of sample and delivery volumes on-chip and the interplay between the sample volume and delivered volume. A previous kinetics device [1) using an alternative flow control method exhibited poor performance in the sample capture process due to a breakdown in the flow control. This led to a large deviation in the measured sample volume of up to 85 %, and as a result unreliable reaction data was obtained, For this reason the flow control method was changed to syringe pump system. The ability to hold a reaction mixture in place for the duration of the reaction period is a key requirement of the stopped-flow method. Continued flow due to mechanical deformation in the syringe drive had the potential to make this impossible. The relaxation volume of a 250 ilL syringe used was measured at 10-15 nL at 1.5 bar rising to 105-130 nL at 6 bar, depending on the volume of liquid in the syringe. To protect the reagent mixture in the reactor a syringe pressure limit of 3 bar was implemented. An analytical model was derived relating the relaxation volume to the pressure, syringe liquid volume, drive velocity and syringe size which had a good agreement with the data giving an RMS fit of 7.4 nL. The syringe pump flow control method was shown to deliver consistent operation which was evident in the repeatability of steady state processes like the initial mixture composition, which had a mixture accuracy of 0.5 % and a repeatahilty of 0.3 %, and transient processes like the sample capture processes, which displayed a captured volume repeatability of 2.2 %. As the concentration measurement was performed off-chip a study to characterise the sample capture behaviour was performed. The sample loop size was found to have no effect on the sampling process however, the loop material was found to exhibit a small effect with a PEEK loop giving a slower loop filling compared to a steel loop. The understanding gained from this work has enabled the construction of a device capable of producing reliable reaction data. The device was applied to an example reaction and data were taken over a range of reaction temperatures. Using a second-order kinetic model an activation energy of 50.65 kJ mol-1 and a pre-exponential factor of 3.24 x 1010 L mol-1 were found. The kinetic model gave a good fit to the data with an RMS error of 4.5 %.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available