Materials Included In Kit
Cups, polypropylene, 30-mL, 30
Filter paper, 12.5-cm diameter, 100 sheets
Markers, water-soluble, set of 8
Page of color photos of sample art chromatograms
Additional Materials Required
Paper clip (optional)
Water soluble black pens or markers, additional (optional)
This activity will require about 2 hours of teacher preparation time the day before the lab to test the pens or markers and to create the art chromatograms for the chromatography challenge. See the included page for color photos of the art of radial chromatography. Three examples are shown in Figure 3, along with the pens and the ink patterns used to create them. Note: Manufacturers may change ink formulations without notice—please test the pens or markers beforehand.
Black ink codes:
- Liquid Expresso™
- Dixon® Vis-aid® Overhead Projection Marker
- Mr. Sketch® Scented Water Color Marker
- Paper Mate®
Although the materials in this activity are considered nonhazardous, please observe all normal laboratory safety guidelines. Remind students to wash their hands thoroughly with soap and water before leaving the laboratory.
Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. All of the materials may be disposed of in the solid trash according to Flinn Suggested Disposal Method #26a.
- Enough materials are provided in this kit for 30 students working in pairs or for 15 groups of students to each make five radial chromatograms. One hundred filter paper circles are provided—75 for student chromatograms, 15 to make wicks and 10 for teacher samples.
- This laboratory activity can reasonably be completed in two 45- to 50-minute class periods. The prelaboratory assignment may be completed before coming to lab. One class period is usually needed to identify the pigments present in different inks and to determine the effects produced by different types of ink “spots” (e.g., dots, lines, arcs). The second class period may then be devoted to duplicating the art chromatogram produced by the teacher.
- Experiment with a variety of water-soluble black markers or felt tip pens to determine the composition of each. Many different brands are commonly available at local stores. Some of the brands we have tested include Expresso, Prang, Vis-Aid, Mr. Sketch, LePen, Paper Mate Flair, Vis-à-Vis, Dick Blic and EF. The specific brands of pens included in the kit may vary depending on availability. Test the pens and markers beforehand to determine how the inks will separate using water as the solvent.
- Manufacturers may change ink formulations without notice. Do not assume that the sample art chromatograms described in the Prelab Preparation section and shown on the color photo page can be duplicated without prior testing. Two Paper Mate Flair pens were tested for this activity with vastly different results. One showed (from least mobile to most mobile) purple, gray, yellow, blue and lavender, the other showed lavender, pink, turquoise, green and yellow.
- Number or code the markers in some way and place them in a central area for students to share.
- Coffee filters are a suitable substitute for the filter paper. The ruffled sides of the coffee filter should be removed with scissors and can be used as “wicks.” Water, however, is more quickly absorbed by coffee filters than by filter paper. This will reduce the separation and resolution of the ink pigments.
- If a chromatogram is running too slowly or not at all, check to make sure that the wick has been inserted snugly into the hole and that there is good contact between the wick and the inside edge of the hole. Typical running times for the chromatograms are 15–17 minutes.
- Avoid excessive handling of the filter paper. Oils from the skin can interfere with capillary action that draws the water through the paper.
- Laminating the sample teacher art chromatograms will increase their durability and protect them from spills during the student procedure. These can be saved for future classes.
- To save laboratory time, wicks may be cut by the teacher in advance, using only 10 filter paper circles. This would leave 5 extra pieces of filter paper for the teacher to experiment with.
- If an ultraviolet (UV or “black”) light is available, shine it on the art chromatograms. Some pigments will fluoresce under UV light.
- The following student laboratory kits can be use to further study the technique of chromatography: AP4503—Introduction to Paper Chromatography Kit, AP5992—Chromatography Centrifuge Kit and FB0586—Plant Pigment Chromatography Kit.
Correlation to Next Generation Science Standards (NGSS)†
Science & Engineering Practices
Asking questions and defining problems
Analyzing and interpreting data
Disciplinary Core Ideas
MS-PS1.A: Structure and Properties of Matter
MS-PS2.B: Types of Interactions
HS-PS1.A: Structure and Properties of Matter
HS-PS2.B: Types of Interactions
Cause and effect
Answers to Prelab Questions
- What will be the adsorbent in this activity? What will be the solvent?
The filter paper will be the adsorbent and water will be the solvent.
- Why is it important that only the wick and not the filter paper circle be in contact with the water in the cup?
If the filter paper is in direct contact with the water in the cup, some of the inks on the paper may dissolve in the water. This will dilute the ink spot on the paper and may change the composition of the ink spot that remains. The separation (resolution) of the pigments on the paper may also be affected—the chromatogram may appear “muddy.”
- What are some of the variables that will affect the pattern of colors produced on the filter paper?
Some of the variables that will affect the pattern of colors produced on the filter paper are (a) the pen brand and the ink composition in each pen, (b) the type of ink spot that is marked on the paper, (c) the thickness or absorbency of the filter paper, (d) the purity of the water solvent, (e) the length of time that the chromatogram is allowed to develop, (f) the distance away from the center hole where each ink spot is placed and (g) the thickness or heaviness of the ink spot.
- Working with a partner, write a general outline describing an “action plan” to reproduce the art chromatogram created by the teacher.
Note: Ask to see the students’ plans. In the first round of this experiment, students should identify the pigments that are in each ink and determine the radial band patterns that will result from different types of ink spots (e.g., dots, lines, arcs, wedges) Trial and error will then be required to discover where the ink spots must be placed, relative to the wick in the center of the paper, to duplicate the art chromatogram created by the teacher.
This is a guided-inquiry activity requiring original art chromatograms prepared by the teacher. See the color photo page for ideas and the Prelab Preparation section for instructions for preparing the chromatograms. The pens tested in this experiment and their ink compositions are described in the Answers to Post-Lab Questions.
Answers to Questions
- List the brand of each pen tested in this activity and record the colors observed in each radial band pattern. Fore each pen, list the colors (pigments) from least mobile (greatest attraction to the paper—closest to the center) to most mobile (least attraction for the paper—closest to the outer edge).
Colors shown in parentheses may be indistinct or blend in with other pigments. Some colors are only seen when the chromatogram is allowed to run longer than 15 minutes. Remember, manufacturers may change formulations and pigments.
Dick Blick: Black, gray, (green) blue, violet, lavender, yellow, pink
EF: Lavender, pink, yellow, turquoise
Le Pen: Brown, (yellow) purple, aqua
Liquid Expresso: Dark midnight blue, gray, dark gray
Mr. Sketch: Yellow, orange, rose, pink, turquoise
Paper Mate: Purple, gray (yellow), blue, lavender
Vis Aid: Gray, yellow-green, blue, lavender, purple
Vis-à-Vis: Yellow-green, rose, purple, turquoise
- Why does an ink separate into different pigment bands? Each ink is composed of different compounds.
Each compound (pigment) has characteristic physical properties that will determine its relative attraction for the adsorbent (paper) versus the solvent (water) in this chromatography experiment.
- Do any of the pens or markers appear to contain common pigments? How can you tell if similar-colored pigments from different pens are actually the same compound? Do any similar-colored pigments appear to be different compounds?
Several of the pens and markers appear to contain similar pigments. The turquoise in the Vis-à-Vis, Mr. Sketch, and EF pens may be the same compound because they seem to have the same mobility—this pigment traveled the farthest in all three pens. The blue pigment in the Paper Mate, Vis Aid and Dick Blick also may be the same compound with moderate mobility. The yellow in the EF pen is quite mobile whereas the yellow in the Mr. Sketch pen has much greater attraction to the paper—these pigments are most likely different compounds.
- Why were only water-soluble markers or pens used in this activity? How could the experiment be modified to separate the pigments in “permanent” markers or pens?
The ink must dissolve in the water in order to migrate with the water through the paper. If the ink does not dissolve, the ink spot will remain at the origin and will not separate into different color bands. The experiment may be modified to separate the pigments in permanent markers by running the chromatograms with different solvents, for example, an alcohol solvent.
This activity was adapted from Flinn ChemTopic™ Labs, Vol. 2, Elements, Compounds and Mixtures; Cesa, I., Editor; Flinn Scientific, Inc; Batavia, IL (2006).