title: Autonomous filtration system for portable capillary electrophoresis instruments
Creators: name: Paniagua-Cabarrús, MG
Publisher: name: University of Tasmania
Year: 2022

description: Environmental pollution has become of global concern as the population grows, and industrial and agricultural activities increase. These directly influence human wellbeing, because pollutants are carried by soil, water and air into waters and farms into animals and crops that are consumed by people. These contaminants can also alter atmospheric conditions, the hydrological cycle, and the greenhouse effect. The environment as we know it is prone to changes on a long-term basis, but it is difficult to measure and correlate unless implementing long term monitoring strategies to establish trends and patterns of change. So far this is one of the most complicated topics in science. Amongst these pollutants, there is a special interest in nutrient enrichment which can be correlated with the perception of over fertilization. These can influence the growth of toxic algal blooms along with hypoxia in freshwater and marine environments and human health. Nutrients monitoring currently relies in samples that are taken on the field and transport to the laboratory, making environmental monitoring a laborious, complex, expensive, and slow task. The development of field deployable analytical instrumentation is crucial to overcome this issue. Monitoring strategies should include the analysis of several samples per day, for several months or even years, and be done often in remote locations. In recent decades scientists have dedicated significant time and resources to the study of miniaturized field deployable instruments. The frequent challenges faced while developing these instruments are sample filtration, changes of weather conditions in the field, like temperature and humidity, size and portability of the devices and excessive cost to produce and run the instruments. This thesis is focused on addressing the challenge of continuous sample filtration of liquid samples in order to make a fully autonomous field deployable system capable of monitoring water chemistry. This includes considerations to control the temperature of analysis while on site, power consumption, portability, cost, and versatility of the target analytes. Chapter 1 gives an overview of capillary electrophoresis systems and the path towards automatization and portability. The main challenges encountered while developing field deployable instruments and the invention of microdevices are to overcome the problems of sample preparation, excessive use of reagents, sample incompatibility within detectors and fast response of the systems. In Chapter 2 the aim was to develop a continuous particle removal device as a solution for automated filtration. In this work an H-filter, a passive microdevice, has been considered because it is a simple structure, low cost, easy to replicate and does not consume extra energy compared to active methods. The H-filter was designed, manufactured, and integrated to a portable capillary electrophoresis (pCE) system, developed previously at University of Tasmania. The fabricated microdevice allowed continuous removal of particles over 1 μm size in water samples without the necessity for a membrane filter that requires cleaning or replacement. The integrated system was tested continuously for 6 weeks, using a soil slurry water sample with particulate matter up to 100 μm. The portable capillary electrophoresis (pCE) coupled with a capacitively-coupled contactless conductivity detector (C\(^4\)D), separated, and detected chloride (Cl\(^-\)), nitrate (NO\(_3\)\(^-\)) and sulphate (SO\(_4\)\(^{2-}\)) with detection limits (LOD) from 500 to 1000 ppb, and relative standard deviations (RSD) of 12% for Cl\(^-\), 13% for NO\(_3\)\(^-\) and 14% for SO\(_4\)\(^{2-}\), for a total of 1575 samples analysed. Due to the dimensions of the H-filter particulate matter over 100 μm could not be analysed. In Chapter 3 the aim was to remove particles above this size to allow the analysis of real water samples. To achieve this, a 3D printed mini cyclone was incorporated into the system. The microdevice was printed in a PolyJet printer and connected to a peristaltic pump with a flow rate of 4 mL/min. The mini cyclone has two outlets, the underflow where the bigger particles will follow through and the overflow, where the smaller particles will out. The sample collected from the overflow was analysed by a particle sizer and particles up to 90 μm size were found indicating that particles above this size were completely removed. By connecting the mini cyclone to the H-filter on-line to a portable capillary electrophoresis was demonstrated that all the particles above 1 μm were removed from a water sample. To test the flexibility of the instrument the C4D was switched for an LED detector. The method allowed to detect zinc (Zn\(^{2+}\)) from 10 different environmental water samples, with variable particulate matter contents, with no clogging or blockage of the system. The capillary electrophoresis instrument was tested in an industrial water treatment plant, detecting Zn\(^{2+}\) in real time. The instrument developed was able to produce a clean sample to analyse contaminants in water continuously for several weeks but concerns about portability arose from the field deployment as detailed in Chapter 3. In Chapter 4 the objective was to incorporate all the necessary pieces to perform the separations in a truly portable and autonomous analytical apparatus. First considerations were how to maintain stable and controlled temperature. To achieve this all the electronic parts, microdevices and solutions were placed into an insulated box. A 3D printer was used to produce a platform where the pumps, microdevices, electronics, solutions and even waste containers were mounted to avoid mobile parts. An exterior submersible pump was connected to provide sample from a water stream with a distance over 10 m. The sensitivity of the instrument was tested performing a calibration curve. The limit of quantification (LOQ) was 91 ppb for Cl\(^-\), 403 ppb for NO\(_3\)\(^-\) and 227 ppb for SO\(_4\)\(^{2-}\), and LOD was 30 ppb for Cl\(^-\), 121 ppb for NO\(_3\)\(^-\) and 75 ppb for SO\(_4\)\(^{2-}\). The instrument variability was 10% for Cl\(^-\), 10% for NO\(_3\)\(^-\) and 8% for SO\(_4\)\(^{2-}\), for n=3. Two different field deployments were completed. First, a pond in Margate, Tasmania, Australia where the pCE worked for 10 days, analysing a total of 241 samples, separating, and detecting chloride, nitrate, and sulphate. For a second deployment the pCE was taken to a secure location next to Plenty River in Tasmania, Australia. A total of 974 samples were analysed continuously for 1 month. The insulated box contains all the elements needed to perform analysis from a water stream, including sample intake, sample pre-treatment, separation and detection of various analytes, and data collection. The insulated box is easily transportable by 1 operator and does not needed any maintenance during the time deployed. Current portable instrumentation has been developed and tested for numerous environmental samples, but many of them still perform the sample clean up by filters, membranes, or cartridges that must be replaced constantly. While other on-site instrument like sensors are capable to detect a single analyte at the time. The pCE developed in this work, can detect a mix of different analytes, the detection method can be easily changed, it is truly portable and automated, and able to work for several weeks without the need of maintenance or parts replacement.