Mulls preparation

Note Viscous, odorless, moderately combustible liquid used for mull preparation relatively low toxicity soluble in benzene, chloroform, carbon disulfide, ethers incompatible with oxidizing materials and amines. Synonyms mineral oil, adepsine oil, lignite oil. 

A number of experimental alternatives to traditional IR transmission spectroscopy are suitable for overcoming some of these complicating experimental factors. In the technique of diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) (Hartauer et al. 1992 Neville et al. 1992) the sample is dispersed in a matrix of powdered alkali halide, a procedure which is less likely to lead to polymorphic transformations or loss of solvent than the more aggressive grinding necessary for mull preparation or pressure required to make a pellet (Roston et al. 1993). For these reasons, Threlfall (1995) suggests that DRIFTS should be the method of choice for the initial IR examination of polymorphs. He has also discussed the possible use of attenuated total reflection (ATR) methods in the examination of polymorphs and provided a comparison and discussion of the results obtained on sulphathiazole polymorphs from spectra run on KBr disks, Nujol mulls and ATR. 

A quantitative IR absorption for the two polymorphs of the developmental compound (2R,3S)-2-( (lR)-l-[3,5-feis(trifluoromethyl)phenyl] ethyl oxy)-3-(4-fluorophenyl) morpholine hydrochloride was reported in which the measurements were made in mineral oil mull preparations.58... 

Another classical sampling technique for solids is the mineral oil mull preparation (18). In this technique, a small amount of sample ( 1 mg) is placed into an agate mortar. To this, a small amount of mineral oil is added and the sample and oil mixed to an even consistency. The mixture is then placed onto an IR optical window and sampled by the IR spectrophotometer. One advantage to this tech-... 

Infrared spectra were run of Nujol mulls prepared in a glove box and sealed between salt plates. Samples could then be transferred to a Perkin-Elmer Model 283 spectrometer without decomposition. Visible spectra were run in stoppered glass cells on a Cary 118 spectrometer. NMR spectra were run at 180 MHz on a FT instrument. 

Too little sample and there will be no sign of the sample in the spectrum. Too much sample and a thick paste will be produced, with no radiation being transmitted, A rough guide to mull preparation is to use a microspatula tip of sample to 2-3 drops of mulling agent. 

Developments in MIR spectrometers, particularly Fourier-transform (FT) techniques, have enabled the use of a variety of solid sampling techniques which overcome the disadvantages of classic IR-sampling techniques. Classic sampling techniques [30], such as alkali halide pellet preparation (with KBr or KCl) or mineral oil mull preparations, require a mechanical treatment of the sample and may thus induce solid-solid transformations or desolvations. 

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