Chromatography is used by the 'Horse Racing Forensic Laboratory' to test for the presence of illegal drugs in racehorses. A concentrated sample of urine is spotted onto chromatography paper on the start line. Alongside this, known drugs are spotted. The chromatogram is run using methanol as the solvent. When finished, the paper is read by placing under ultra-violet light. A chromatogram of urine from four racehorses is shown.
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a) The results for known drugs are given as '$$R_f$$ values'. $$R_f\ \text{value} = \frac{\text{distance travelled by the substance}}{\text{distance travelled by the solvent}}$$<br>Calculate the $$R_f$$ value for caffeine.<br>b) Explain the meaning of the word 'solvent'.<br>c) State two factors which determine the distance a substance travels up the paper.<br>d) From the results the sample from one horse contains an illegal substance.<br>i) State the horse, and the drug present.<br>ii) Give a reason for the use of this drug.