Separating materials for linking TLC and FTIR

Details Separating materials for linking TLC and FTIR Separating materials for linking TLC and FTIR

1997-09-18

1999-03-16

Ludlow, Jan

Chemistry: analytical and immunological testing

Including chromatography

Utilizing paper or thin layer plate

73 6154, 2101983, 422 56, 422 70, 422 8205, 422 8209, 436164, 436169, 436178, G01N 3090

Patent

active

058829393

DESCRIPTION:

BRIEF SUMMARY
The invention relates to separating materials for thin-layer chromatography (TLC) which are suitable, in particular, for in situ infrared spectroscopy (IR) and Fourier transform infrared spectroscopy (FTIR).
For some time now research has been carried out on linking TLC to infrared spectroscopy, the objective being to combine TLC, a powerful and economical separation method, with IR, a spectroscopic method acknowledged as being informative (Percival C. J., Griffiths P. R. (1975), Anal. Chem., 45 (1), pp. 154-156). Despite the major effort in fabricating special layers (e.g. silver chloride as the base, with an addition of the perfluorinated hydrocarbon fluorolube to reduce scattering) the detection limit and sensitivity remained inadequate. Moreover, if silica gel was used as the stationary phase, the spectral range important for analytical purposes and known as the "fingerprint range" could not be used, owing to the intrinsic absorption of the silica gel.
Owing to its silanol and siloxane groups, silica gel is one of the strongly absorbing materials. Reflectance spectroscopy with such strongly absorbing materials involves an anomalous profile of the dispersion curve, most of the incident radiation being reflected directionally. This leads to so-called "residual rays" which no longer contain any spectral information. Further problems arise from the fact that the effective penetration depth in the vicinity of absorption bands of the matrix is much less than in spectral ranges without matrix absorption. Instead of silica gel, Danielson et al. (1992) Analyt. Chem. 64, 2183-2186, therefore employed zirconium oxide as the sorbent. While it was possible to measure FTIR spectra of substances adsorbed on this sorbent, many substances which can be separated without any problems on silica gel were impossible to separate on zirconium oxide, since they either remained in the start zone or migrated with the solvent front. This meant that the analytically important range of R.sub.f values between 0.2 and 0.8 could not be attained.
In the wave number range between 1350 and 1000 the strong intrinsic absorption of the silica gel in this range produces a strong interfering band which is superimposed on the DRIFT spectra (diffuse reflectance infrared Fourier transform; reflectance spectra in the medium-infrared range) of adsorbed substances. Consequently, significant portions of the "fingerprint range" can no longer be covered. DRIFT measurements on silica gel layers were first carried out by Fuller and Griffiths (Fuller M. P., Griffiths P. R. (1978), Anal. Chem. 50 (13), pp. 1906-1910; and Fuller M. P., Griffiths P. R. (1980) Appl. Spectrosc., 1980 (34), pp. 533-539). In so doing, spectra of methylene blue could be measured with 1.2 .mu.g of substance.
Given the versatility of the possible applications, in particular of silica gel 60 (pore size 60 Angstroms) as a sorbent in TLC and HPTLC and the quality standard achieved, in particular, for this stationary phase there is a need for the development of suitable precoated layers on the basis of silica gel for linking with IR spectroscopy. It is an object of the invention to provide separating materials for thin-layer chromatography which permit an in situ study by means of FTIR spectroscopy even with small amounts of sample material. This object is achieved by the provision of separating materials for thin-layer chromatography, whose sorbent layer comprises an addition of a reflection enhancer.
The invention relates to separating materials for thin-layer chromatography which comprise a sorbent layer, formed from sorbent particles, on a support, the sorbent layer comprising an addition of at least 10 percent by weight, based on the amount of sorbent, of a reflection enhancer, preferably magnesium tungstate and/or Bi.sub.2 0.sub.3. In preferred embodiments the particle size of the reflection enhancer is 3-5 .mu.m and the amount of the reflection enhancer is from 0.6 to 1.5 times the amount of sorbent. SiO.sub.2 -containing sorbent particles are preferred.
The invention further r

REFERENCES:
patent: 4271021 (1981-06-01), Hauck
Chemical Abstracts CA 117: 123754 Danielson et al., Anal. Chem. (1992), 64(18), 2183-6, 1992.
Chemical Abstracts CA 113: 178964 Yoshioka et al., J. Chromatogr. (1990), 515, 205-12, 1990.
Miller, Chromatography: Concepts and Contrasts. John Wiley & Sons New York: 1988, pp. 236-239.

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