Micro-Diffuse Reflectance and Matrix Isolation Fourier Transform Infrared Techniques for the Identification of Tetrachlorodibenzodioxins

Abstract

Micro-diffuse reflectance Fourier transform infrared (DRIFT) and matrix isolation (MI) Fourier transform infrared spectra of the 22 tetrachlorodibenzodioxin (TCDD) isomers have been recorded. The DRIFT and MI techniques required about four minutes and one-half minute, respectively, of signal averaging to produce high signal-to-noise (S/N) spectra on low-nanogram-level samples. Spectral subtraction was employed to remove DRIFT solvent impurity interferences. The validity of the DRIFT subtraction technique was demonstrated by comparison of the corrected DRIFT, with the chromatographically pure, MI spectra. The reproducibility of DRIFT frequencies and intensities was tested by comparison of the 1,3,7,8-TCDD spectra from samples independently prepared by two analysts. The MI technique successfully identified 2,3,7,8 in environmental samples. MI spectral subtraction was applied to one sample to remove a coeluting impurity. The DRIFT and MI spectral techniques, used in conjunction with modern chromatographic separation and spectral subtraction, are very promising for the on-line or off-line differentiation of low-level toxic isomeric compounds.

Optical spectra and photophysical properties of polychlorinated dibenzo-p-dioxin derivatives

“…In particular, the spectra of 22 isomers of tetrachloro-substituted DD in an argon matrix and in the vapour phase were recorded. 33 The attention was focused on the IR spectra of the most toxic b-TCDD. 2, 32 ± 34 The IR spectrum of this compound in a KBr pellet was measured 2 in a wider frequency range (4000 ± 375 cm 71 ) than the spectra of other tetrachloro-substituted DD.…”

“…100 In this case, the isomers separated by chromatography were present in an argon matrix at 12 K; this decreases the line halfwidth and, correspondingly, increases the peak intensity of lines. The IR spectra of all the 22 isomers of tetrachloro-substituted dioxin were recorded by this method, 33,35,36 including the spectra of b-TCDD and its completely isotope-substituted analogue ([ 13 C] b-TCDD), in which all the 12 C atoms have been replaced by 13 C. This technique is suitable for the analysis of samples with contents of tetrachloro-substituted DD of the order of hundreds of picograms. 36,100,101 For example, the use of [ 13 C] b-TCDD as the internal standard permitted determination of b-TCDD in a concentration of 15 ± 45 pg per g in an extract from a fish tissue.…”

“…37 To identify dioxins on the basis of their IR spectra, several characteristic bands in the range of 1600 ± 800 cm 71 are used. 24,33,35 Figure 15 presents the IR spectrum of the extract from a fish tissue containing b-TCDD and an internal standard admixed. Generally, the positions of bands in the spectrum recorded by the GC-MI-FTIR method coincide with the positions of the corresponding bands in the spectrum of b-TCDD in a KBr pellet (see Fig.…”

Application of gas chromatography/matrix-isolation/Fourier transform infrared spectrometry to dioxin determinations

“…For such studies scanning type instruments have the disadvantage that even a nonvolatile sample must be continuously consumed in ionization, while the ions measured at any one time represent only a very narrow mass window; the resolution and scan range required for larger molecules exacerbate this problem. The time-of-flight (TOF) mass spectrometer used in plasma desorption studies (2,3,11) can measure ions of all masses produced in a pulsed ionization event, but here resolution has been limited to 1000-2000 because of the Registry No. 2,3,7,8-Tetrachlorodibenzo-p-dioxin, 1746-01-6; 2,3,7,8-tetrachlorodibenzo-p-dioxin-13C12, 76523-40-5.…”

“…That infrared spectrometry is an isomer-specific technique has been very well-documented. In fact, the infrared spectra of all 22 TCDD isomers have been shown to be unique and distinguishable (2,3) both by micro-diffuse reflectance infrared Fourier transform spectrometry (micro-DRIFTS) and by gas chromatography/ matrix isolation/Fourier transform infrared spectrometry (GC/MI/FTIR).…”