Page 23 - An Inky Lead Questioned Documents

6. On the Data Collection sheet, assign the first not to let the sample dots come into direct
digit in the value the label ‘A’, the second the contact with the solvent.
label ‘B’, and so on.
16. Place the lid back on the development chamber.
7. For each digit in the value of the receipt, cut out Do not disturb the set-up until ready to remove
an approximately 0.5 cm2 square from an ink- the plate.
dense area. Closely trim off any excess paper
around each sample. 17. Allow the solvent to travel up the plate for 10
minutes. The longer it runs, the more separation
8. Place each sample on a glass microscope will occur, but do not allow the solvent to reach
slide in the same order as they appear on the the top of the plate.
receipt. Make sure the pieces are at least 1 cm
apart. 18. Take the plate out of the development
chamber. With a pencil, immediately draw
9. Cut out a small ink-dense piece from the end a line across the plate to mark how far the
or beginning of the signature. Try to be as solvent traveled.
nondestructive of the signature as possible.
19. repeat steps 1 18 with the second receipt, using
10. Place the signature sample at the end of the a new TLC plate and microscope slide.
glass slide.
20. Allow the solvent to evaporate from the plates
11. Put one drop of solvent onto the first sample. completely. Follow steps 21 24 for each plate.
Make certain that the solvent does not touch
any of the other samples. 21. Inspect each ink lane to determine the
component colors. For each color, gently mark
12. Press the end of a fresh microcap onto the first the bottom of its band with a pencil.
digit. The rubber bulb is not needed simply hold
the glass microcap carefully and the inksolvent 22. Measure the distance in cm between the
mixture should rise up the pipette. bottom line and the top line for the solvent.
Record this distance as the Total Distance
13. Position the microcap over the first dot on the Traveled by Solvent (DS).
TLC plate. Gently press the tip of the microcap
onto the dot and allow all of the sample to 23. For each sample, measure and record the
spread out onto the plate. distances between the bottom line and the
bottom of each distinct color band in that
14. Using a fresh microcap, repeat steps eleven sample’s lane, and record the color of each band
through thirteen with the remaining digits and (DC1-C3).
the signature sample.
24. Finally, for each spot, calculate and record the
15. Open the lid on the development chamber, and retention factor (Rf)— the ratio of the distance
insert the TLC plate so that the samples are traveled by that spot (DC1-C3)) to the total
toward the bottom of the chamber. Be careful distance the solvent traveled )DS).

THE MYSTERY OF LYLE AND LOUISE 23