CORRESPONDENCE
Gas Chromatographic Analysis of Polycyclic Aromatic Hydrocarbons in Soot Samples SIR:We refer to the article of Chakraborty and Long (1967) in which Figure 7 shows comparative spectra for a pyrene standard and an unknown from the gas chromatograph. Although, in the text, they do not claim coincidence, the figure may leave some readers with this impression. We would like to suggest that the spectrum for the unknown shown in Figure 7 is actually either 1- or 3-methylpyrene or a mixture of the two. The table below gives important wavelength positions for 1-, 3-, and Cmethylpyrene and pyrene as determined in this laboratory with a Cary 14 spectrophotometer. These are compared with the values given by Chakraborty and Long for pyrene and the GLC unknown.
Pyrene 371.2 361.3 356.6 351 .O 335.3 319.3 305.0 278.6 262.1 252.0 240.6 231.5 a
wavelength^ Positions for Pyrenes 3-Methyl- 1-Methyl- 4-Methyl- Pyrene pyrene pyrene pyrene Std.
Fraction B
378
SIR:We have considered the comments of Thomas and Monkman on Figure 7 of our paper (Chakraborty and Long, 1967). We hoped it was clear that, although there is a striking resemblance in the absorption maxima of the substan&) responsible for fraction B corresponding to peak 9 in the gas chromatogram to those of pyrene, there is a bathochromk shift of the maxima. We concluded that the p.c.a.h. responsible for this spectrum "is a derivative of pyrene" but we could not identify it. The resemblance between the important wavelength positions for 1-, 3-, and 4- methylpyrene reported by Thomas and Monkman and those of the GLC unknown is of interest and supports our view that this is a pyrene derivative. However, we have evidence that GLC peak 7 corresponds to a mixture of the methylpyrenes. The absorption spectrum corresponding to this GLC peak is compared with that of a mixture of 1methylpyrene and 4-methylpyrene in Figure 1 of this letter.
358 343.3 326.7 312.5 275.8 265.0 255.0 242.5 233.0
343.4 326.6 312.5 275.9 264.5 253.5 244.7 234.6
337.0 321.0 306.7 275.9 265.0 255.0 244.5 234.0
334 319 307 372 262 252 240 231
346 330 316 277 267 257 244 236
M4t
i-
Wavelengths in mp.
The bands shown for fraction B at 378 and 358 mp are a mystery. The log E values for pyrene and methylpyrene are very similar for corresponding absorption bands : Pyrene
MP
WAVELENGTH (MILLIMICRONS)
log e
371.2 361.3 356.6
2.30 2.73 2.76
*a
335.3
4.74
*P
Figure 1. Ultraviolet absorption spectra of a mixture of l-methylpyrene and Cmethylpyrene and that of gas chromatographic peak 7 in Figure 1 of the origiaal paper
- - GLC peakand7 4-methylpyrene -Mixture of -1-methylpyrene
If the bands shown in the spectrum for fraction B in the positions 378 and 358 mp belong to the methyl derivative of pyrene as we assume, then these bands should not appear in this spectrum. The ratio of the absorbances of the a band at 378 and the p band at 346 is about 1 to 100. Notice the lack of a structure in the standard pyrene spectrum. Allowing for slight instrumental variations of wavelengths between laboratories, it is clear that the unknown is not pyrene.
(This was not published in our paper in the interests of brevity.) It can be seen that there is close agreement between the absorption maxima. Consequently, if GLC peak 7 corresponds to a mixture of the methylpyrenes, then peak 9, with longer retention time, might be expected to correspond to a mixture of substances, including the unidentified pyrene derivative, of higher molecular weight than the methylpyrenes.
Literature Cited
Literature Cited
Chakraborty, B. B., Long, Ronald, ENVIRON. SCI.TECHNOL. 1, 828 (1967).
Chakraborty, B. B., Long, Ronald, ENVIRON. SCI. TECHNOL. 1 , 828 (1967).
R. Long B. B. Chakraborty
R. S. Thomas J, L. Monkman Department of National Health and Welfare Ottawa, Ontario, Canada
The University of Birmingham Birmingham, England Volume 2, Number 3, March 1968 217
