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May 30, 2012 - Register Now for This ACS. Anal. Chem. , 1987, 59 (11), pp 786A–786A. DOI: 10.1021/ac00138a761. Publication Date: June 1987. Copyrigh...
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(a) Extracted component

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107

100

f

I

80 60 40 20

65

77

239

9 1

,

116

132

207

ψ

0

X

(b) Mass spectral library N,W'-di-otolylguanidine

I I

107

100 5065

77

91

11fi

224

133

(c) Authentic Λ/,ΛΡ-di-o-tolylguanidine

239

ΝΗ — C — Ν Η

107

100

CH3

80-

Ice 20Η

NH

CH3

239 65

77

50

V

116

133 .

224

100

150

200

250

m/z Figure 3. Direct probe, El mass spectra of the extracted component and Λ/,Λ/'-di-otolylguanidine.

molecular weight indicated a nitrogencontaining moiety. This was consistent with the previous chromatographic and solubility observations. High-res­ olution MS provided an exact mass for the molecular ion of this compound, 239.1444 u. Two possible elemental compositions, C16H17ON and C15H17N3, were postulated, as were several likely structures, each contain­ ing phenyl and methyl groups. Al­ though we still were plagued with the same problem of insufficient sample, we found that Fourier transform infra­ red (FT-IR) absorption spectroscopy of the unidentified component led to similar projections about its molecular structure. We conducted a comprehensive com­ puterized literature search based on the functional nature of the unknown component. Using key words such as aerosol, nebulizer, extractables, de­ composition, degradation, rubber, and seals, Chemical Abstracts (1967-85) yielded 107 relevant papers. Unfortu­ nately, none of these shed any light on the identity of the component. Howev­ er, reference to the Kirk-Othmer En­ cyclopedia of Chemical Technology and the CRC Handbook of Chemistry and Physics proved to be much more

786 A · ANALYTICAL CHEMISTRY, VOL. 59, NO. 11, JUNE 1, 1987

fruitful when we considered the tenta­ tive structural assignments. In the en­ cyclopedia, we focused on compounds commonly used in rubber processing that contained phenyl, methyl, and ni­ trogen functions; in the CRC text, we concentrated on the hypothesized mo­ lecular weight of 239.1 and formula of C15H17N3. Both texts yielded listings for the same compound, N,N'-di-otolylguanidine. Corroboration of identity and chemical structure

Our literature searches produced a via­ ble candidate for the component. At the same time, we solved the problem of limited quantity of extracted sample by extracting a much larger number of diaphragm seals (several hundred) and by using a semipreparative, reversedphase HPLC column. As a result, ap­ proximately 15 mg of material was iso­ lated, providing an adequate supply of sample for unambiguous structure elu­ cidation. For example, direct probe EIMS yielded a spectrum (Figure 3a) free from the high level of background in­ terference previously encountered. Ions indicative of molecular weight m/z = 239, phenyl m/z 91, 77, 65, and