Instructables

Fraction Collector for Chromatography (Lego Wedo and "Scratch")

Picture of Fraction Collector for Chromatography (Lego Wedo and
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Siderits R, Swift M, Lecorchick W, Ouattara O, Siderits I, Malik F.

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

PicoBoard: www.picocricket.com/order-picoboard.php

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.

 
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cool2003 years ago
A truly ingenious application of WeDo and Scratch I have seen. Very creative. Keep up the good work. Thanks for sharing.
lemonie4 years ago
I like the Lego-build.
I'm slightly concerned that for normal-phase chromatography, the plastic is going to suffer from the solvents though - your thoughts?

L
siderits (author)  lemonie4 years ago
Excellent point!

Methylene chloride, for example, "welds" plastic.  Although this fraction collector has many uses that don't require plastic-melting solvents, we do have a few interesting options, if need be.

Both the sample disc and the "trigger" tubes for the IR sensor would be at risk.  We used non reactive tubes for our sensor trigger but you could use glass tubes and put a sticker on the outer surface to reflect the IR signal from the sensor. 

Here are a few thoughts on protecting the disc:

1) cover the plastic disc with a sheet of aluminum foil and poke holes. 
2) design a cut out (groove)  with a few wrapped supports so that any solvent that comes through during a momentary bottle rotation would drip straight down into a waste container. 
3) cut the sample holder plate out of thin aluminum sheeting.
4) use wire spokes with a central hub instead of a flat disk with holes
5) add a solenoid to cut off (pinch) the sample flow during rotation.  This would require a quick 5 minute modification in the scratch program, a battery, a magnetic switch and a solenoid.
6) Cut the sample disc out of wood (I know its hard to think of scientific instruments made out of wood but it is cheap and usable)
7) Use a glass plate and set the bottles in "glued on rings" to hold them in place (E600 glue is magic for this) while the underlying disc rotates a new tube into place.
8) tie the tubes to the outside of a shallow central metal can / drum (line the outside)
9) line the inside of a shallow can / drum with tubes for the upper deck plate
10) spray-paint the disc with a non-reactive or rubberized surface

BTW, Thanks very much for your comment.

R
lieuwe siderits4 years ago
 instead of using a ir sensor it might be easier to use a micro-switch, they come with a lever most of the time, so the only problem would be positioning the switch...
siderits (author)  lieuwe4 years ago
Great idea, the motor could trigger the microswitch, or the tube could do it directly, or we could use a magnetic proximity switch that would trigger a solenoid at the same time!  Excellent thinking.
There's some good thinking.
Ye-olde "DCM" is vicious nasty-stuff...
But I do like the Lego.

L
siderits (author)  lemonie4 years ago
Thanks.  I'm doing a rack feed version now.