(a) Extracted component
Register Now for This ACS Short Course!
Capillary Gas Chromatography: Techniques and Problem Solving Monday-Tuesday August 3-4,1987 Cleveland, Ohio This ACS Short Course teaches you the practical and advanced techniques of high-resolution GC. You learn the characteristics of capillary columns, how to recognize good and bad capillary separations—and how to correct poor results. Two renowned experts in the field, Milos Novotny and Stuart Cram, are your instructors for this intensive and vital course. NOTE: Space is Limited. Register Today!
How You'll Benefit from This Course— • Gain comprehensive knowledge of this vital analytical technique • Apply learned techniques to a wide variety of separations • Learn how to facilitate the transition from packed to capillary columns • Be able to improve quantitation methods • Learn troubleshooting and preventative maintenance For full details on this course, write for a free descriptive brochure. Or CALL COLLECT (202) 872-4508. Ask for Karen McIlvaine, our Short Course Registrar.
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
