Chromatographic Determination of Analgesics

Abstract

In this experiment, a known sample, phenacetin, and an unknown sample, #201, underwent chromatography to determine the contents of the unknown sample. A drop of each in aqueous form was placed on a silica gel sheet and a developer was used to separate the components for comparison. The unknown contents of a #201 capsule were determined to be acetylsalicylic acid based on the results of another chemistry lab student, Merissa.

Data and Results

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Figure 1: Chromatogram of Phenacetin and an Unknown Sample on Silica Gel Sheet with an Aqueous FeCl3/K3Fe(CN)6 Detector Solution

Table 1: Summary of Chromatographic Data

| Known Sample (Phenacetin) | Unknown Sample Dot 1(#201) | Unknown Sample Dot 2(#201) |

Distance Travelled by Centre of Spot (mm) | 10.0 | 2.0 | 20.0 |

Distance Travelled by Solvent Front (mm) | 59.0 | 53.0 | 59.0 |

Rf Value | 0.169 | 0.037 | 0.339 |

Table 2: Rf Values from Other Students

| Rf Value | Known Sample |

Merissa | 0.37 | Acetylsalicylic Acid |

Zoe Emis | 0.00978 | Caffeine |

Hayley Atkins | 0.647 | Caffeine |

Calculations

Rf Value Calculation Equation: distance travelled by centre of spot/distance travelled by solvent front

Rf Value Calculation for Known Sample: (10.0mm)/(59.0mm) = 0.169

Rf Value Calculation for Unknown Sample Dot 1: (2.0mm)/(53.0mm) = 0.037

Rf Value Calculation for Unknown Sample Dot 2: (20.0mm)/(59.0mm) = 0.339

Discussion

The composition of the unknown sample capsule is thought to be acetylsalicylic acid based on the results of Merissa’s experiment. The second unknown sample dot had an Rf Value of 0.339. This is very close to her value of 0.37 and therefore thought to be the same. As for the first unknown sample dot, the value did not match with the caffeine values, acetylsalicylic value, or the known phenacetin value and therefore no conclusion can be made.

Conclusion

The unknown contents of a #201 capsule were chromatographically determined to be acetylsalicylic...