Coffee Filter Chromatography, Crime Science Lab
Paper Chromatography Pigment "Forensic Lab" Science Inquiry Tools
Oct 5, 2009
Scientific inquiry involves critical thinking and experimentation, and provides opportunities for new insights and discoveries. Marker dyes and pigments are useful for these coffee filter paper chromatography studies.
Paper Chromatography Principles, Uses and Value
Here is a quick perspective. Paper chromatography
- is one of the earliest molecular separation techniques. (Morgan and Wilson, An Early Description of Paper Chromatography? , Chromatographia 60: 135-136).
- is inexpensive, rapid and provides clear results.
- was developed and promoted by Tswett (early 1900s) to separate visibly-pigmented compounds (chlorophyll, hemes, cytochromes) by powder-in-column and paper methods.
- uses suspended paper strips or sheets (with chemical added and dried at the paper's bottom) to wick a suitable solvent through the paper and to the top.
- upon the end of the run, the paper is dried, and visible compounds are recorded and identified by comparison with known standards.
- can reveal uncolored compounds by specific chemical reagents sprayed onto the paper to detect distinct compounds: amino acids, sugars, lipids and nucleic acids.
Forensic Investigation of Pigmented Markers Using Coffee Filter Paper Chromatography
This simple experiment takes about 30 minutes. Experimenters learn paper chromatography, characteristics of dyes, pigments, solvents and paper interactions. This is a "who-did-it?" approach to criminology and forensics.
The graffiti artists' case:
- Recently, some people were detained and accused of being graffiti artists.
- Graffiti markers were seized for Crime Lab analysis. Samples from the crime scene walls were also obtained.
Investigators may be "deputized" as CSI lab investigators – to qualify them to perform an analysis of markers from the crime scene. The objective is to compare the seized evidence - the potentially incriminating markers - to the data and evidence previously removed and identified from the graffitied walls.
Materials and Methods for CSI Crime Scene Investigator by Coffee Filter Paper Chromatography
Materials needed include:
- Fine tipped markers (10-12), both water-soluble and permanent markers.
- Coffee Filters. Cheap varieties work well (Dollar store, Kroger, Publix brands). Kroger filters were used here.
- Clear glass containers, or 250 ml beakers, for water and filter placement.
- Pencils to mark the filter paper bottom circle with date, time, class and marker code.
- Notebooks, or Lab Sheets, for CSI notes.
Methods:
- Draw a pencil line approximately 20 mm above and all around the bottom edge of each filter (see photos below).
- Label each marker by a number, or letter code, for marker identification. Mark a single dot at the filter paper line.Separate each dot 15-20 mm apart to permit clear, separate lanes.
- Carefully add 20-30 ml of water, or 70 % isopropyl rubbing alcohol, to cover bottom of glass chamber to a depth of 10-15 mm. Do not splash or wet the glass walls. Walls must be dry.
- Carefully bend marked filter into "V" (cone shape) and insert dotted filter into the chamber.
- Run begins immediately when this happens. When the solvent reaches the top edge of the paper, remove the paper to end the run.
- Place filter on a dry paper towel.
- Measure the solvent migration distance (origin at spot line to top of filter) = denominator in mm for Rf value.
- Measure the distance of top edge of each dye to origin at spot-line = numerator. Rf values = mm dye run/ mm solvent run.
- All dye values will read 1.0 or less. If a dye does not move, the Rf value = 0.
Results of Paper Chromatography and Interpretations
The CSI investigation concludes as follows:
- Any RF value less than 0.1 is evidence of a crime marker match for graffiti guilt.
- Do any markers show absolute purity of color? Which ones, and what does this mean?
- Do all colors have the same Rf values? Explain.
- Can other interesting experiments be done with this technique? Explain.
- See principles and plant pigments for more chromatography ideas.
Great science occurs with CSI agents and their labs. Consider a career in Law and Order, Forensics (CSI), or any of the sciences, including medicine and allied health fields.
Resources
Bioinstrumentation, Tools for Understanding Life. 1996. Wandersee, J.H., et al. eds. National Assoc. Biol. Teachers, Reston, Va. 329 pp
Paper Chromatography. 1976. 15th ed., Micropaedia of Encyclopedia Brittanica. Chicago, Illinois
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