I am relatively new to the self-driving lab domain and am working on setting up a platform to automate chemical reactions. For my first experiment, I’m attempting a colour-matching experiment similar to what @sgbaird demonstrated here.
My setup involves a controllable peristaltic pump to deliver liquid reagents into a reactor, followed by an inline UV-Vis spectrophotometer to capture the spectrum of the mixture.
I am currently facing an issue with efficiently triggering the spectrophotometer. Right now, I am asking the pump to take a fixed volume of solution (that I have experimentally determined through trial and error) which brings the mixture into the spectrophotometer’s probe volume. However, this method feels extremely imprecise, and I believe there must be a more reliable way to trigger the spectrum acquisition exactly when the sample reaches the probe.
Is the main idea that you’re trying to correlate the material with the time of acquisition? (i.e., in the flow chemistry setup, the composition of the material at a given position changes as a function of time, and you want to correlate that with the spectrophotometer’s readings at a fixed position as a function of time)
At the moment, I want to use the UV-Vis spectrophotometer to monitor the extent of a reaction.
So, after mixing the solutions in the reactor and allowing them to react (e.g., 10 mins), I want to pass the mixture through the UV-Vis spectrophotometer and acquire the spectrum only when the sample reaches the probe.
Once the measurement is done, I clean the reactor, and no spectra should be taken during that time. I then repeat the process with new compositions.
I don’t know if I clarified what I want to do and the problem better.
As I understand you are trying to do sample positioning/detection, right? Two methods come to mind:
Use a liquid-vapor sensor. These can be had for about $30 off digikey. I am currently implementing a sample positioning system that relies on these sensors for sample detection, and they work really well. Basically you run your tubing through the detector and hook the board up to a DAQ like a labjack or a Pi or arduino and read the voltage - it will switch from high to low depending on if air or liquid is present in the tubing. Here is one example, it comes in different sizes for different tubing diameters: https://www.digikey.com/en/products/detail/tt-electronics-optek-technology/OCB350L062Z/1942310?s=N4IgTCBcDaIPIGEBCBmArABgDIYGxgC0ACkAXQF8g. This assumes you are flushing your sample out with air or at least have an air gap on before your sample.
Implement some sort of computer vision based edge detection to detect sample presence. I’ve used a system that uses this method and it can be finicky. I haven’t built one myself so I’m not sure where to point you here - I would imagine there are some good off the shelf solutions for doing this.
