Chromatography is a method of separating out materials from a mixture. Ink is a mixture of several dyes and therefore we can separate those colors from one another using chromatography. When ink is exposed to certain solvents the colors dissolve and can be seperated out. When we expose a piece of paper with ink on it to a solvent, the ink spreads across the paper when the ink dissolves.
Some inks are water-soluble, so you can use water as the solvent. Inks which are not water soluble are often alcohol-soluble and you can use isopropyl alcohol as the solvent to create your chromatograph. Also, you can use acetone.
Different ink pens use different types of ink and this is obvious when you expose the ink to a solvent. Follow the instructions below to discover the pattern of each pen.
Coffee filters/Paper towels/regular copy machine or printer paper can be used.
Another crystal glass to prepare your solvent (if use isopropyl alcohol)
Mini binder clips
Wooden splints or plastic straws
4 different black pens and/or markers
• The Exercise:
Cut the coffee filter paper/Paper towel/printer paper into strips approximately 2 centimeters wide (cm) by 6.5 cm long. Prepare a total of 4 chromatography strips this way.
Take one of the chromatography strips and use a ruler and pencil to draw a line across it horizontally 1 cm from the bottom. This is the origin line. Repeat this step for the 4 chromatography strips.
Use one of the pens/markers, place a small dot of ink at the center of the origin line of a chromatography strip. This is your spotted sample.
Use a pencil to label which pen/marker you spotted on the chromatography strip. Do not use a pen labeling the strips> the ink will run when the solvent passes through the strips.
Repeat this step until you have spotted ink on each chromatography strip.
Prepare your solvent. Make a 45% isopropyl alcohol solution to use as your chromatography solvent.
Pur 20 milliliters (ml) of 90% isopropyl alcohol solution into a crystal glass. Add 20 ml of water to the glass, the final volume is 40 ml. Stir thoroughly with the wooden splint/straw. Cover the glass with plastic wrap, so that the solution does not evaporate.
If you decide to use acetone or water as solvent, you don’t need to dissolve the solvent.
Depending on the glass you use, pour about 2-3 ml of the solvent into the Crystal glass. Depending on the glass, maybe you can run two prepared chromatography strips in the glass.
Clip two of the prepared chromatography strips to a wooden splint or straw. Make sure the two strips do not touch each other and the bottoms align. Rest the splint/straw on top of the beaker so that the strips hang into the glass and do not touch the sides of the glass.
If necessary, add more solvent to the glass. The goal is to have the end of each chromatography strip just touching the surface of the solvent solution but avoiding touching the ink spots. Add solvent as needed to achieve this goal.
Cover the top of the glass with plastic wrap.
Let the solvent rise up the strip (by capillary action) until it is about 0.5 cm from the top, then remove the strip from the solvent. Keep a close eye on your chromatography strip and the solvent front-if you let it run too long the dye may run off the paper and become distorted.
Use a pencil to mark how far the solvent rose.
Take a picture of your TLCs for each pen.
Allow the chromatography strip to dry, then measure (in centimeters) and calculate the Rf for each pen/marker dye component. Record your results in a table like this one for each pen:
Component Color Component Rf value
Total number of components:
• Write a lab report with your findings, as samples include the four types of pen. In your procedure indicate which solvent you use. And if you have to change your solvent, explain in procedures and observations. In results include the pictures of your TLC and tables. Discuss in Results if the inks from the different pens/markers separate differently and justify your answer based on the colors and Rf values.
• Upload as a single pdf your lab report including your pictures.
WRITING CRIME LAB REPORTS
A lab report is a neatly written account of your experiment and procedures, as described below. It should be an impersonal account written in third person. The report should be typed.
All pages should be of the same size with writing on only one side of each sheet, with no ragged edges and paginated. The report should include all information related to the crime lab and the person performed the analysis. The report should include the following information, with headings to begin each section (see the example).
Crime Laboratory, Telephone and Fax
To: the recipient of the lab report (detective)
Lab File Number
Agency Case Number
Evidence Submitted by: Name of the officer
Samples received by Laboratory: Date and time
A short statement giving the objective to be achieved by performing this experiment.
The procedure is an impersonal set of directions on how you perform the analysis. It should include detailed directions.
Some labs require certain observations like if the sample was consumed during the analysis. Such observations should be recorded.
A detailed description of the results of the analysis. It must follow the same order as the procedures and samples received. This section must include tables/graphs and figures and sometimes statistical analysis to improve the understanding of the results.
Itemized summary of the results.
Forensic Scientist Signature and Date
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