Identification of essential oil components by gas chromatography/quadrupole mass spectroscopy

In the Preface to Identification of Essential Oil Components by Gas Chromatography/Quadrupole Mass Spectroscopy [sic], Robert P. Adams, the author, states that he began research on essential oils in 1966. This may account for the reason that he persistently uses the term mass spectroscopy rather than mass spectrometry (Robert, there are no light bulbs inside those mass spectrometers). Again, as was the case with the second edition, there is no indication that this is a third edition; but, as in the second edition, the author clearly acknowledges this fact in the Preface. This edition has spectra for 1606 compounds. Adams takes some liberty in saying that this is 400 more than the previous edition, which actually had spectra for 1252 compounds. Because the spectra were acquired on an HP 5970 Mass Selective Detector (spectra in the previous editions were acquired using a Finnigan ITD800 internal ionization quadrupole ion trap instrument), the display format of the spectra corresponds to that of the Agilent (formerly Hewlett-Packard) ChemStation mass spectral display rather than the Finnigan ITD-800 (now Thermo Electron). The ChemStation has the ordinate of the spectrum labeled in ion abundance rather than percent abundance or relative percent intensity. One of the curiosities of these spectra is that all exhibit exactly the same maximum abundance. As with the previous edition, each spectrum has a structure showing chirality were appropriate, retention time on a DB-5 column, and Kovat’s index. Details are provided about the GC column and the operating conditions of the GC as well as the sample injected into the GC (volume, split ratio, and the internal standard used for retention time). The only important parameter missing from the operation of the mass spectrometer is the rate at which the data are acquired (the number of spectra per second). Another important factor would be the identification of the ChemStation version used. ChemStation has two very different versions of Autotune, and the only way to distinguish between which version was used is by the ChemStation version number. Adams states that data were acquired after using the instrument’s “Autotune” to set the operating conditions. As was criticized in the review of the second edition, this book has some significant shortcomings in the brief text portion. They go beyond the criticism of calling a mass spectral peak an ion. In the discussion of whether or not mass spectra acquired with a quadrupole ion trap (QIT) and a transmission quadrupole are comparable, the author displays what he says are spectra of 3-methyl4-heptone obtained on both instruments. The spectrum displayed that was reported to have been obtained on the transmission quadrupole is not that of 3-methyl-4heptone but that of 2-methyl-4-heptone. The telltale peak at m/z 58, which is 30% of the intensity of the peak at m/z 57 (the base peak), is the giveaway. This m/z 58 peak is obviously missing in the spectrum obtained with the QIT and is also missing from a spectrum for 3-methyl-4-heptone obtained on a transmission quadrupole that appeared in the second edition. Another area exhibiting a limited understanding of electron ionization mass spectrometry is the comparison of spectra of tricyclene. The author points to the fact that the peak at m/z 77 is 102% of the intensity of the peak at m/z 79 in the spectrum obtained with the QIT, whereas the peak at m/z 77 is 98% of the peak at m/z 79 in the spectrum obtained with the transmission quadrupole. These relative intensity differences are insignificant, especially when the intensity of the peak at m/z 77 relative to the intensity of the base peak is about the same in both spectra ( 40%). More effort could have been put into the proofing of these few pages of text. It is stated that a compound is represented by a chromatographic peak that has a retention-time range of 5.589 to 5.67. Then, in an attempt to show how the recorded retention time is determined using the equation “5.89 min 0.03 min 5.62 min” is presented, it is obvious the “5.89” in the equation should have been “5.589”, but this should have been caught in the proofing stage. The references to journal articles would be more valuable if they included titles, which is now the requirement for the Journal of the American Society for Mass Spectrometry. This is especially true for the M. P. Clay reference that cites an unnamed article that appeared in Mass Spec Source, an obscure organ published by Scientific Instrument Services in Ringoes, NJ (http://www.sisweb.com). As was the case with the second edition, the “Appendices” consist of an alphabetical listing of compounds (mostly common names) with their retention times and Kovat’s index on a DB-5 capillary GC column Published online September 28, 2005