Undercover Chromatography

My kids are really into two things this week.

The first is capillary action. Ever since we did our last experiments on capillary action, Abigail has managed to work the phrase in every single day. Even her My Little Pony train tracks were set up in a dumbbell formation so Abby could say the train was showing the movement of water between cups in capillary action. I’m happy that the idea has stuck with her, so I’d love to reinforce it.

The second is spies. Ever since we watched Spy Kids on family movie night, and got Briana a book that came with secret spy ears and a few other spy toys, it’s all we talk about. We are even planning a spy birthday party for Abigail, even though her birthday is a significant amount of time from now.

So I decided that today, since the kids are off of school for a teacher in service day, I’m going to show the kids how to use chromatography to detect who the bad guy is.

You see, the bad guy has left a note, and it threatens all that is sacred around Valentine’s Day- the candy.

But the bad guy made a mistake. He left behind the pens.

As a secret spy team leader, I know that if we can figure out which green pen was used, then we can dust it for prints and find out who is threatening our precious school loot bags.

Briana suggests an alternative course of action – handwriting analysis. She tells us that they use handwriting analysis at school all of the time to find out who work belongs to if the author forgets to put their name at the top. There is some anxiety about the amount of time my analysis will take with the candy missing. I assure her that the bad guy won’t eat the stolen candy and so she agrees to the chromatography plan.

I tell the kids that every marker has a unique print in the way that the manufacturer makes the dye. We need to find out what print each marker makes and compare it to the print the note will make. They don’t believe me so I quickly show them our experiment on a purple Dora marker. (I’ll show you how we did that in just a second. I won’t eat your explanations! J ) As we waited, I asked them what colors make purple, and sure enough a pink and a blue came out of the purple marker.

CHROMATOGRAPHY

Supplies:

*Prewritten note

*Green Markers left behind by our bad guy (You may want to test ahead of time to make sure that the ones you have will result in a profile different enough for the kids to detect.)

*Three cups

*Water

*Coffee filter or paper towels (I tried it both ways and the coffee filter works better and slightly faster.)

Step 1: Get a coffee filter for each kid. Since we have six pens, each of my girls will get the profiles for three markers and we’ll compare together. Write down where each marker will make its mark in pencil. The pencil won’t bleed so you’ll be able to see it in the end. You want to go about 1-2 inches up from the bottom.

Step 2: Make a dark line with each marker inside the brackets.

  

Step 3: Put a small amount of water in all three cups. You only need a couple of inches of water at most.

  

Step 4: Put your coffee filter into the cup and watch the water creep up to the line and start separating the pigments out. When you put your filter into the water, try to keep the marker lines from touching each other so they don’t bleed onto each other. Also put it in the water such that the water has to climb a bit to get to the marks. Otherwise all of the markers will bleed into the water and a mixture color will creep up. This is why you want your marks a few inches up on the filter.

  

Why does the water defy gravity and creep up the filter?

“Capillary action!” both girls scream simultaneously.

That’s right! Each pigment in the marker will be carried by the water, at a different speed and for a different distance, and that will make a unique profile for each marker. This is called chromatography. (I am so excited because gel electrophoresis is one of my favorite lab techniques to play with and we’re getting closer.)

We put the note in the third cup with water to compare it to the maker profiles. Then we wait for about 15 minutes until the water gets all the way to the top of the filters.

I got the idea to do this part of the experiment here: http://www.exploratorium.edu/science_explorer/black_magic.html

While we wait, we learn how to fingerprint ourselves.

FINGERPRINTING

Supplies: Baking powder (or flour), paint brush, lotion, dark paper, scotch tape.

Step 1:  Lotion up. I lotioned everyone’s hands to make our prints stickier.

Step 2: Get out dark paper and push each of your fingers down in a row. You will not see anything – yet – and that’s what makes this so cool. I used blue paper because that was the darkest I had on hand, but black would work best, though you might see your greasy prints on black paper.

Step 3: Sprinkle the paper with baking powder and lightly(!) dust it with the paintbrush. You still will not see anything.

Step 4: Shake off the excess and…wow!...fingerprints show up out of nowhere.

We print the marker lids. (My secret – I took off all of the marker caps before we used them, telling the kids that the lids would have the bad guys prints since we didn’t have gloves to keep their prints off. I wash the powder off of my hands and relotion. As I take the pencils holding the lids and hand them to the kids, I make sure to get a good thumb on each lid.) The kids find good prints on each lid, and a few partials which is fun.

Step 5: Use scotch tape to lift the print off of the marker. Take the tape and gently push it onto the print. Lift the tape up carefully and put the taped print down on the paper next to the original print to compare.

The kids are already screaming that they know who the bad guy is because they realize that Mommy’s print seems to be on all the markers because the prints are too big for their fingers. Too smart for my own experiments. I tell them that even if they are right, first we have to find out which pen the bad guy used.

The marker profile are done and we take them out of the water to analyze.

It’s a lively debate, but…

…even without letting the message finish its capillary actions, it’s clear that it was the Sharpie Light that was used. The kids are fascinated that the markers that all looked similar in color have such different profiles, all blue and yellow which make green.

The prints match! Mommy is the bad guy! (Isn’t that just always the case.) It was Mommy with the light green Sharpie in the kitchen.

The kids are so excited to have solved a real crime, and gotten their candy back, though we have a small debate about whether chromatography is sleuthing or spy work. Sleuthing, to Briana, is using observations to be a detective. A spy uses gadgets. We can’t decide if chromatography and lab work is observational (sleuth) or a gadget (spy) for a while, but Abby consults her party invitations and realizes that there is a fingerprint image on them. That means that fingerprinting is spy work. Good sleuthing, Abby.

The kids make me promise that we can fingerprint Daddy when he gets home. I see a few more spy related activities in our future. Take cover!

<3 Pedigreed Housewife