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General Test Procedure (GTP) for Identification by IR

PURPOSE
To lay down the procedure for identification by IR

APPARATUS
  • FTIR (Perkin Elmer, Model: Spectrum One or Equivalent)
  • Hydraulic / pellet press capable of applying pressure up to 15 ton
  • Agate mortar and pestle
  • Plates transparent to Infrared region (NaCl or AgCl)
  • Pellet holder
  • 13 mm Die
  • Desiccator containing activated silica gel

REAGENTS
Potassium bromide (KBr): Spectroscopy grade
Potassium chloride (KCl): Spectroscopy grade
Mineral oil (Nujol / Paraffin): Spectroscopy grade
Specified solvents: Spectroscopy grade

PROCEDURE

Method –I (For solids as Disc)
  • Transfer about 300 to 400 mg of KBr or KCl (previously dried at 105°C at a pressure not exceeding 20 mm Hg for 12 hrs) or as specified, into a clean and dry mortar. Triturate to fine powder with a clean and dry pestle.
  • Spread evenly in the die and compress at a pressure of about 10 to 12 tons using a pellet press.
  • Remove the pellet carefully from the die. The disc should be clear. If the visual inspection shows that the disc is opaque, it should be discarded and a new one should be prepared.
  • Place the disc in the pellet holder and in turn place in the instrument.
  • Record the background spectrum.
  • Transfer about 1 to 2 mg of sample along with 300 to 400 mg of KBr or KCl into a clean and dry mortar. Triturate to a fine powder with a clean and dry pestle.
  • Repeat steps 1 to 4.
  • Record the sample spectrum.

Method-II (For solids as Mull)
  • Spread evenly one or two drops of mineral oil between the plates. Fix the plates in the holder and in turn place them inside the instrument.
  • Record the background spectrum.
  • Prepare a mull by triturating 5 to 10 mg of a sample with a minimum quantity of mineral oil in a mortar.
  • Place a small amount of mull between the plates and spread uniformly.
  • Fix the plates in the holder and in turn place them inside the instrument.
  • Record the sample spectrum.


Method-III (For liquids as Neat thin film)
  • Fix the plates in the holder and in turn place them inside the instrument.
  • Record the background spectrum.
  • Place a drop of a sample using a capillary tube at one corner of the plate.
  • Spread the drop as a thin film between two plates uniformly.
  • Fix the plates in the holder and in turn place them inside the instrument.
  • Record the sample spectrum.

Method-IV (For solutions)
  • Prepare either as specified or 1% to 10% w/v or v/v solution in a suitable solvent.
  • Fill a liquid sampling cell (of known path length, usually 0.5 to 0.1 mm) with a neat solvent used for making the solution and recording the background spectrum.
  • Replace the solvent with the sample solution in the cell.
  • Record the sample spectrum.

REFERENCES
USP, BP and EP.

Notes:
  1. All spectra, including the background must be recorded in the region 4000 cm-1 to 650 cm-1, unless otherwise specified in the individual monograph.
  2. Each of the recorded spectrum is an average of minimum of 8 scans.
  3. In case of requirement for comparison with the standard,
  • Compare with the similarly recorded spectrum of the reference sample.
  • If the spectra do not match, record the spectrum of sample and reference sample concomitantly and compare. In case of solid samples, if the spectra do not match even after concomitant recording, dissolve the sample and reference sample in a suitable solvent, evaporate to dryness and record the spectra with residues and compare.

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