# First and second derivatives of UV/Vis spectra using the Savitsky-Golay method

Three spectra have been obtained, A consisting of pure compound 1, B of a mixture and C of pure compound 2. The data, together with wavelengths, normalised to a constant intensity of 1 are presented below.

wavelength | A | B | C |
---|---|---|---|

220 | 0.891 | 1.000 | 1.000 |

224 | 1.000 | 0.973 | 0.865 |

228 | 0.893 | 0.838 | 0.727 |

232 | 0.592 | 0.575 | 0.534 |

236 | 0.225 | 0.288 | 0.347 |

240 | 0.108 | 0.217 | 0.322 |

244 | 0.100 | 0.244 | 0.370 |

248 | 0.113 | 0.267 | 0.398 |

252 | 0.132 | 0.262 | 0.376 |

256 | 0.158 | 0.244 | 0.324 |

260 | 0.204 | 0.251 | 0.306 |

264 | 0.258 | 0.311 | 0.357 |

268 | 0.334 | 0.414 | 0.466 |

272 | 0.422 | 0.536 | 0.595 |

276 | 0.520 | 0.659 | 0.721 |

280 | 0.621 | 0.762 | 0.814 |

284 | 0.711 | 0.831 | 0.854 |

288 | 0.786 | 0.852 | 0.834 |

292 | 0.830 | 0.829 | 0.763 |

296 | 0.838 | 0.777 | 0.674 |

300 | 0.808 | 0.710 | 0.589 |

304 | 0.725 | 0.636 | 0.529 |

308 | 0.606 | 0.551 | 0.480 |

312 | 0.477 | 0.461 | 0.433 |

316 | 0.342 | 0.359 | 0.372 |

320 | 0.207 | 0.248 | 0.295 |

324 | 0.113 | 0.161 | 0.226 |

328 | 0.072 | 0.107 | 0.170 |

332 | 0.058 | 0.070 | 0.122 |

336 | 0.053 | 0.044 | 0.082 |

340 | 0.051 | 0.026 | 0.056 |

344 | 0.051 | 0.016 | 0.041 |

348 | 0.051 | 0.010 | 0.033 |

#### Questions

- Produce and superimpose the graphs of the raw spectra. Comment.

- Calculate the 5 point Savitsky Golay quadratic first and second
derivative of A. Plot the graphs, and interpret them; compare both first and
second derivatives and discuss the appearance in terms of the number and
positions of the peaks.

- Repeat this for spectrum C. Why is the pattern more complex? Interpret
the graphs.

- Calculate the 5 point Savitsky Golay quadratic second derivatives of all three spectra (note two of these graphs have already been generated) and superimpose the resultant graphs. Repeat for the 7 point derivatives. Which graph is clearer, 5- or 7-point derivatives? Interpret the results for spectrum B. Do the derivatives show it is clearly a mixture? Comment on the appearance of the region between 270 and 310 nm, and compare to the original spectra.