Capillary Electrophoresis (CE) using a Capacitively-Coupled Contactless Conductivity Detector (C⁴D).

tl;dr

• There are no accessible detection systems for taking automated measurements of water quality, particularly nutrient levels
• Enter Capillary Electrophoresis (CE), a simple and accurate technique for separating dissolved solids
• Overcoming the major challenges involved with detecting dissolved solids with Capacitively-Coupled Contactless Conductivity Detection (C⁴D)
• Realising the potential of an open-source C⁴D CE platform for a global community of water researchers

Our C⁴Dapillary project began with some hobbyist Aquaculture after discovering we couldn't find a product to autonomously monitor the nutrient levels in our systems. Aquaculture systems require careful and precise control of a range of nutrients. Although, in these natural systems, the levels of these nutrients tend to vary across the day – making manual techniques cumbersome and fraught with error. Research into detection systems failed to find any products meeting capable of reliable, automated measurement of a range of nutrients. Most available sensors only detect select compounds, which meant no alternatives existed outside expensive laboratory-grade equipment. Our strong background in science drove us to research other analytical techniques that could detect the presence of compounds. We uncovered a powerful technique called Capillary Electrophoresis (CE) which allowed for the repeatable detection of ions with different charges without the need for expensive, closed-source components. Unfortunately affordable (<USD$10k) commercial implementations of CE are relatively non-existent which drove the development of the C⁴Dapillary open-source CE platform. This project will focus on the detection of ions in water, given the vast potential for improving Humanity's quality of life, although the potential applications are innumerable.

Capillary Electrophoresis (CE) works by passing a high voltage current through a solution filling a micron-diameter glass capillary tube. The current passing across the charged ions causes them to migrate from one side of the tube to the other. This causes them to pass the detector at different times allowing them to be mapped onto a chart called an electrophoretogram. This technique was limited in its widespread application as it was often coupled with UV-based optical detectors which are prohibitive due to their expense. Conductivity based detectors offered a cheaper alternative but came into direct contact with the solution, degrading and bio-fouling over time causing spurious measurements. This project uses a detection system that negates the large costs of UV and other spectroscopy based CE implementations by using wireless detection of CE separated ions. This process is superior to Spectroscopy techniques as it removes interaction between ions, a large source of error in separated samples.

You can imagine this like dropping several different coins off the top of a tall enough building. If you stood on the ground you could determine each of them by the time when they hit the ground, with the lowest surface area to mass ratio first. The following GIF shows how the CE process works,

This illustrates the Capillary Electrophoresis (CE) technique using a detection system called Contactless Conductivity Capacitively Coupled Detection (C⁴D). C⁴D functions by applying a high-voltage electrical signal across the capillary and reading the signal as it is attenuated by the solution passing through the capillary. The attenuated signal is converted to a DC voltage signal with peaks as each ion passes through the sensor. As the different ions are separated through CE the time the ion passes the detector can be compared to a standard sample and the ion identified.

The Executive Director of the United Nations Environmental Programme states that the lack of resources for monitoring and assessment make it difficult to obtain a global picture of water quality. The application of the CE-C⁴D to the monitoring of compounds in drinking and sanitary water has the potential to address many of the issues in the resourcing of sustainable water management. The impact of widespread access to an affordable automated nutrient monitoring system is a paradigm shift from our current complicated and onerous measurement processes. Technology such as this in the hands of the average citizen empowers the population with knowledge of their water quality and, with simple cloud based technology, has potential to expand to a global community of water researchers.

From our research it is becoming increasing clear that the potential applications of CE-C⁴D are almost limitless. While nutrient monitoring is critical to human health it is also an important indicator in the health of other natural systems that are critical to human survival. A large proportion of the world relies heavily on seafood as a source of food, while significant research suggest our Ocean’s health is rapidly declining. A fleet of self-sustaining, marine drones equipped with our system could provide the consistent, repeatable and precisely timed measurement of nutrients required to effectively monitor and study the oceans health. The scientific confidence that such an intellectual resource could provide would inform intervention and prevention strategies for minimising harm to our oceans and ultimately the Earth.

We hope you see the same potential in our C⁴Dapillary open CE-C⁴D platform and upcoming water testing prototype. We're excited to be working on something that may just change the world and we look forward to hearing your thoughts as we progress.