one or several hundred degrees below that of the filament. Furthermore, violent convection currents may be noted inside the sample which means that the sample temperature is not homogeneous. Thus, in the practical conditions in which pyrolysis-gas chromatography can be carried out, the polymer decomposition is controlled b y the heating rate of the filament and b y heat transfer to the sample, not b y the equilibrium temperature of the filament. The heat transfer from the filament to the sample is very complicated. For very small samples (less than 1 pg) evenly coated on the surface of a filament, there may be a small difference between the sample temperature and the temperature of the filament surface, although the pyrolysis reaction is endothermic. In this case, the calculation made above will apply. Consequently, in order to achieve good reproducibility, it is necessary to control the heating rate as much as possible, contrary to common practice. In view of the various technological requirements, it seems probable that this control could be achieved more easily by using induction heating (6) rather than the more conventional pyrolysis coils. For large samples (about 1 mg) which are still commonly used, the heat transfer is controlling the pyrolysis. High heat transfer coefficients can rarely be obtained, especially with these conditions where the pyrolyzed samples gathered into a droplet which is suspended in the coiled filament by calefaction (IO). In this case, pyrolysis of the sample is completed long after the filament has reached its equilibrium tem-
perature. However, the sample temperature remains much lower because of the small heat transfer coefficients observed when calefaction takes place. The use of hydrogen instead of argon as a carrier gas leads to a shorter duration of pyrolysis, although the equilibrium temperature of the coil is lower (IO). Thus, in order to achieve good reproducibility, it is necessary to control the heating rate and the equilibrium temperature. This is not sufficient however. Good reproducibility of the heat transfer coefficient is ensured by the use of samples with the same dimensions, located always at the same place on the filament. Furthermore, calefaction and convective heat transfer can be largely influenced by random fluctuations. It is not surprising that in these conditions, the results obtained when using large samples often have poor reproducibility ( I ) , and that in most cases, the pyrolysis of a given well defined polymer results in largely different yields of the various pyrolysis products when it is carried out in different laboratories.
FRANCISCO FARR&RIUS GEORGES GUIOCHON Laboratoire du Professeur L. Jacqu6 Ecole Polytechnique, Paris, France RECEIVED for review October 4, 1967. Accepted December 15, 1967. F.F.R. acknowledges support from a research grant from the Foundation Juan March (Spain).
Detection of Meta-Stable Peaks by Mattauch-Herzog Mass Spectrometer SIR: The observation of meta-stable ions is very important in the study of fragmentation of mass spectra. I n MattauchHerzog geometry, however, a daughter ion from a metastable ion produced between the object slit and the electrostatic field have insufficient kinetic energy and so cannot pass through the electrostatic field (I); therefore, none of these daughter ions can be detected on the photo plate. In the case of a decomposition of ml+ + m2+ (ml - m2) which shows meta-stable ion formation, the energy of the ion ml+, at the accelerating voltage V , is distributed as follows:
+
m/e
mi
m2
.mt
Figure 1. Daughter ions from meta-stable ions detected on photo plate by the shift of accelerating voltage (V-V’)
The ion m2+ cannot pass the electrostatic field because it has an energy of only m2/ml.eV. So, if the accelerating voltage is increased to V‘ = ml/mz. V , the energy of ion mz+ produced between the object slit and the electrostatic field will be as follows: ml - eV‘ m2
3
=IV): e([
ml
= eV
+
the object slit and the electrostatic field) can be detected at the same place as the ion m2+ (produced in the ionisation chamber just as ml+, at the accelerating voltage of by varying the accelerating voltage from V to V’. (Figure 1) Figure 2 shows the actual example of noteworthy daughter ions from meta-stable ions which have been detected in 3,4epoxymenthane (2, 3) by this method. The observed and calculated daughter ions from meta-stable ions and possible
v>
(2)
This energy of eV for the ion m2+ (produced between the object slit and the electrostatic field), in the case of accelerating voltage V’, is the same as that of ml+ at an accelerating voltage V. In other words, the ion m2+ (produced between (1) M. Barber and R. M. Elliot, 12th Ann. Meeting, ASTM E-14, Montreal (1964). ANALYTICAL CHEMISTRY
(a) a daughter ion from meta-stable ion presenting the transition of ml+ -* mz (b)m2+-,mi + (c)ml+-.mi+ (d)mz++mj+ (e) ml++ mj+
~~
(2) Y . Itagaki, T. Kurokawa, H. Moriyama, S. Sasaki, and Y . Watanabe, Chem. Ind. (London),1965, 1654. (3) S. Sasaki, Y . Itagaki, H. Moriyama, K. Nakanishi, E. Watanabe, and T. Aoyama, Tetrahedron Left., 623 (1966).
7,O -
785
8l
6,5-
8
Q
6aO-
c .-
5.5 -
d .
f
I
I
4
5.0-
9 4.5-
Kv 4.0
0---calcd.
-
Figure 2. Daughter ions from meta-stable ions of 3,Cepoxymenthane detected on photo plate by the shift of accelerating voltage (3.5 kV-7.6 kV)
Table I. Possible Breakdown Reactions of 3,CEpoxymenthane Deduced from the Daughter Ions from Meta-Stable Ions (See Figure 2) Obsd - Calcd V'IV V' V'IV V' Transition 1.11 3.88 1.11 3.88 154++ 139+ 15 1
?L
1.40 1.58 2.17
A
A1
4.90 5.53 7.59
+ 154+-+I l l + + 43 154++ 99+ + 55 154++ 71+ + 83
1
