Name _________________________________________ Pd ____ Date ___________________ CSI: Chromatography Lab v2 WHAT YOU NEED TO KNOW... Chromatography is a method for analyzing mixtures by separating them into the chemicals from which they are made. It can be used to separate mixtures like ink, blood, gasoline, and lipstick. In ink chromatography, you are separating the colored pigments that make up the color of the pen. Even though a pen will only write in one color, the ink is actually made from a mixture of different colored pigments. In criminal investigations, forensic scientist use chromatography to correctly identify types of ink used on a document in question. With sophisticated lab equipment it can be used to determine the chemical composition of ink. Our chromatography lab is not that sophisticated, but we will be able to calculate an Rf value, which will help us identify which suspect wrote the note left at the crime scene. Objective – To identify which suspect’s pen was used to write the note at the crime scene. Follow the procedure below to calculate the Rf values for the five suspects’ pens and the ink from the crime scene note. Procedure 1. Pour about 10 ml of water/solvent into a beaker or small cup. 2. Cut a strip of filter paper to form a point at one end. All strips should be the same length. 3. Test one of the suspects’ pens. Use the pen to make a good-­‐sized dot of color (like the size of a grain of rice) about 1.5 cm up from the pointed end of the paper. (Assign the marker a letter or code so you remember which marker is which.) 4. Use a pencil and make a mark on the paper strip beside the ink dot! 5. Lower the pointed end of the paper into the solvent BUT make sure the color dot stays above the solvent level. Carefully attach the strip to a pencil using a binder clip and place the pencil across the top of the beaker so the strip is at just the right level in the beaker or cup. 6. The solvent should immediately start moving up the paper strip carrying the ink pigments with it. While waiting for the solvent to rise toward the top of the paper, set up your other beakers and test the other markers. 7. When the solvent has finished moving up the paper strip, you can remove the paper from the cup and immediately mark with a pencil the highest point the solvent traveled up the paper strip. 8. Let the strip dry, tape it on your Reference Page and label the sample. 9. Continue testing all of the suspects’ pens and the crime scene note. CALCULATING Rf VALUES AND DESCRIBING YOUR INK SAMPLES 1.) Look closely at each marker’s chromatography strip. Record the Total Number of Colors present for each ink sample on your Reference Sheet. 2.) Each color represents a different pigment present in the ink. Record the colors you observe on your Reference Sheet (Colored Pigment #1 = pink color, colored Pigment #2 = orange color, etc.) 3.) Measure each color strip in each sample in millimeters. 4.) Calculate the Rf value for each colored pigment using the simple formula below: 𝑅! 𝑉𝑎𝑙𝑢𝑒 = 𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑡𝑟𝑎𝑣𝑒𝑙𝑒𝑑 𝑏𝑦 𝑠𝑜𝑙𝑢𝑡𝑒 (𝑝𝑖𝑔𝑚𝑒𝑛𝑡𝑠 𝑖𝑛 𝑖𝑛𝑘)
𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑡𝑟𝑎𝑣𝑒𝑙𝑒𝑑 𝑏𝑦 𝑠𝑜𝑙𝑣𝑒𝑛𝑡 (𝑤𝑎𝑡𝑒𝑟)
5.) Record the Rf values for each colored pigment in the ink on your Reference Sheet and tape the chromatography paper at the bottom of page 3. 6.) Repeat these measurements and Rf calculations for each of the samples tested. POST LAB QUESTIONS: 1. What do the Rf values tell us about the ink? 2. In this experiment, what is the purpose of the water and solvent? 3. Based on your analysis, which suspect wrote the note found at the crime scene? Explain why. 4. Do you think this would be enough evidence to convict the suspect? Why or why not? 5. List some problems that you encountered with this lab. Chromatography Reference Sheet Suspect’s Pen: # of Colors: Solvent Distance (mm): Color #1 Name: Distance (mm): Rf Value: Color #2 Name: Distance (mm): Rf Value: Color #3 Name: Distance (mm): Rf Value: Suspect’s Pen: # of Colors: Solvent Distance (mm): Color #1 Name: Distance (mm): Rf Value: Color #2 Name: Distance (mm): Rf Value: Color #3 Name: Distance (mm): Rf Value: Suspect’s Pen: # of Colors: Solvent Distance (mm): Color #1 Name: Distance (mm): Rf Value: Color #2 Name: Distance (mm): Rf Value: Color #3 Name: Distance (mm): Rf Value: Suspect’s Pen: # of Colors: Solvent Distance (mm): Color #1 Name: Distance (mm): Rf Value: Color #2 Name: Distance (mm): Rf Value: Color #3 Name: Distance (mm): Rf Value: Suspect’s Pen: # of Colors: Solvent Distance (mm): Color #1 Name: Distance (mm): Rf Value: Color #2 Name: Distance (mm): Rf Value: Color #3 Name: Distance (mm): Rf Value: Crime Scene Note # of Colors: Solvent Distance (mm): Color #1 Name: Distance (mm): Rf Value: Color #2 Name: Distance (mm): Rf Value: Color #3 Name: Distance (mm): Rf Value: