We demonstrate how to make a reliable and useful scientific instrument called a "Fraction collector" for use with column chromatography applications or educational science projects.
We used the free downloadable "Scratch" graphical programming language and the Lego WeDo robotics kit to make this Auto Sampler/Fraction collector. The only cost is for the Lego WeDo robotics components and the Lego pieces used for the apparatus. We have taken the system through hundreds of cycles and it works reliably. In a nutshell, the scratch program gets input from a sensor and controls a servo motor. The motor turns a sample wheel that holds empty tubes until the sensor "detects" a tube in front of it. It then tells the program to stop the motor for a certain amount of time, then repeat the process for the next empty tube. Each tube stops under a sample outflow to collect a few drops then moves on to the next empty tube to collect the next sample.
The program that we wrote to control the Servo Motor and Sensor is also downloadable from the Scratch Website and you can easily change it for your own use.
We'll explain what a fraction collector does and how its used with column chromatography.
To start with, If you wanted to sample the outflow from something over time or collect timed samples then you might want to use a fraction collector. It stops a sample bottle or vial for a given amount of time to collect some drips from an outflow tube and then moves the next empty sample container into position. Another variation on this theme would be to start with sample containers that had something in it, for example "algae" and stop in a magnetic field (between two magnets) for specific amounts of time or in front of an LED to give the sample different amount of light at a specific wavelength. You can stop the sample for a constant amount of time or program the sampler to stop at the magnets, fro example, for increasing or decreasing amounts of time for each sample. It would do this for 1-40 samples. This project can be easily reconfigured to include a proximity switch and light sensor with an LED circuit. You can even have multiple sites contributing sample to the containers as they stop and start at different positions.
OK, back to the project, a Fraction collector can cost 4,000-15,000K$, ours cost less than 150$ and has a "build time" of less than 30 minutes (if you have the Lego and WeDo parts and you download our program script from the "Scratch" website).
Out apparatus can accept from 1-40 small sample vials or up to 10 larger sample bottles. The prototype is so easy to work with that you can do much more than we've described.
Here are a few websites for reference as we go along.
Scratch graphical programming website: scratch.mit.edu
Bionicle website: http://bionicle.lego.com/en-US/default.aspx
WeDo website: www1.lego.com/education/search/default.asp
If you have a child who likes Lego or you have a friend with kids who like Lego then just ask them to put this together for you.
The main Lego parts (aside from the WeDo kit are: the gear box, 3 axles, generic building pieces and some Bionicle joints.