Effect of added inorganic salts to a pyrolysis foil on pyrolysis
of benzylamine by Curie-point
pyrolysis-gas chromatography
Minemasa Hida a, Toshiyuki Mitsui a’*, Yukio Minami b
and Yoshikazu Fujimura c
Criminal Science Laboratory, Aichi Prefecture, 2-1-1 Sannomaru, Naku-ku,
Nagoya 460 (Japan)bScientific Investigation Research Laboratory, Osaka Prefectural Police, 9, Otemaeno-cho,Higashi-ku, Osaka-shi, Osaka 540 (Japan)c
Department of Industrial Chemistry, Faculty of Engineering, University of Chubu,
1200 Matsumoto-cho, Kasugai 487 (Japan)(Received April 26, 1991; accepted in final form August 23, 1991)
aABSTRACTThe relationship between the pyrolysis products of benzylamine and the decomposition
temperatures or dehydration temperatures (D temp) of several inorganic salts was investigated by means of multivariate analysis. The inorganic salts were mixed with chromium
powder mounted in a pyrolysis foil. The apparent pyrolysis temperatures were calculatedwith multiregression analysis using the D temp of the salts. The ratio of the peak area ofbenzene to the total area correlated with the D temp of the salts. However, that of toluene
tended to decrease with Dtemp. This indicated that the inorganic salts had an effect on thepyrolysis temperature of benzylamine.
Benzylamine; gas chromatography; inorganic salt; multivariate analysis; pyrolysis.

INTRODUCTION

Pyrolysis-gas chromatography (Py-GC) has been used for studying themicrostructure, degradation mechanisms and thermal stabilities of various
polymers [1]. However, many pyrolysis procedures are difficult to apply toquantitative analysis because the sample is not heated with sufficient
reproducibility and precision. In a series of articles we have describedanalytical results for medicines [2,3], agrochemicals [4,5] and other chemicals [6,7] by Curie-point Py-GC in which a sample was pyrolyzcd in thepresence of a mixture of a metal powder and an inorganic salt on apyrolysis foil (pyrofoil). This technique was used for quantitative analysis,
with relative standard deviations of less than 3%, using several microgramof the sample. In a previous work [7], we showed that the metal powder
influenced the pyrolysis temperature and that the inorganic salt served as asample supporting material. In addition, inorganic salts effected the ratioof pyrolysis products. In the present paper, the effect of the added
inorganic salts on the pyrolysis products is investigated in detail using
benzylamine as a sample, and benzene and toluene as the main pyrolysis
products. Multivariate analysis was used to study the relationship between
the pyrolysis products and such thermal properties of inorganic salts as
decomposition temperature, melting point and heat content.
APPARATUS AND REAGENTS
A Curie-point pyrolyzer (model JHP-2, Japan Analytical Industry Co.
Ltd) was directly coupled to a gas chromatograph (Shimadzu GC-14A)
equipped with a flame ionization detector (FID). The temperatures of thepyrolyzer unit and the tube connecting the pyrolyzer to the gas chromatograph were maintained at 150°C and 200°C respectively. The analyticalcolumn was a fused silica capillary column CBP-20 (12 m X 0.53 m (innerdiameter)). The GC oven was heated from 50° to 250°C at a rate of 5°C
min-1, and the detector temperature was 250°C. The FID signals wereprocessed with a Shimadzu Chromatopac C-R4A data processor.
The thermal behaviour of the inorganic salts was measured by differential thermal analysis (model TG-TDA/H Rigaku Co.) using about 12 mg of
the sample under a nitrogen atmosphere (50 ml min-1). The mixtures
added to the pyrofoil were analyzed before and after the sample waspyrolyzed, using an X-ray diffractometer (model RINT 1100, Rigaku) with
Cu Ká radiation.
Inorganic salts, listed in Table 1, and chromium powder purchased from
Wako Pure Chemical Industries (Osaka, Japan), were used without furtherpurification. Benzylamine was obtained from Tokyo Kasei Industries.
(Tokyo, Japan) and reacted with hydrochloric acid to form its hydrogenchloride salt. The amine was used in its aqueous solution.
EXPERIMENTAL
The Py-GC procedure was as follows. Equal weights of chromium
powder and the inorganic salt were mixed thoroughly in an agate mortar.
To a piece of pyrofoil whose Curie point was 590°C (dimensions of about 9mm X 22 mm and thickness of 0.05 mm) 30 mg of the mixture was addedusing a microspatula. 10 µl of the sample solution containing 5 µg of
benzylamine hydrochloride was then added to it with a microsyringe. Thesolvent on the pyrofoil was evaporated to dryness on a hot plate at about

150°C for 5 min. The pyrofoil was then loaded into the pyrolyser after it
was carefully folded.

RESULTS AND DISCUSSION
The results of differential thermal analysis (DTA) and X-ray diffractometry (XRD) are summarized in Table 1. The data show that most of thesulphates and carbonates decomposed prior to the pyrolysis of benzylamine
at 590°C. Sodium and calcium salts, and some chlorides did not decompose, and others became dehydrated.
Data analysis
The obtained pyrograms were transformed into computer-readable formin order to perform calculations with a personal computer. The data matrix
is summarized in Table 2, and a typical pyrogram is shown in Fig. 1. There
were two reasons to include in the data matrix both peak areas and heights.
Firstly, it was not clear whether peak areas or peak heights would give
better results. Secondly, a more reliable calculation was obtained using alarger-dimension data matrix. Data analysis was performed with multivariate analysis from a program written in basic using a personal computer(NEC PC-9801VX). This program was developed in our laboratory.

Cluster analysis

Figure 2 presents the dendrogram obtained by applying Ward’s method
to the whole samples. This dendrogram indicates four groups (clusters) as
follows: class 1, nos. 1, 3,4, 6, 14, 16, 19, 20; class 2, nos. 2,5, 7, 8, 9, 13;class 3, nos. 10, 12, 18 and class 4, nos. 11, 15, 17. In class 4, the benzene
peak overlapped with some decomposition products of the inorganic salt on
the pyrogram, because all of the pyrolysis products were introduced to theseparation column to avoid poor reproducibility. Therefore the class 4 salts

were not used to study their effect on pyrolysis. Furthermore, the class 3
salts were similar to class 4.
Multiple regression analysis and canonical correlation analysis
From multiple regression analysis, the pyrolysis products were correlatedwith the decomposition temperatures or dehydration temperatures (D temp )of inorganic salts rather than with the melting points and heat contents.
The multiple regression equation obtained from 14 samples is represented
in eqn. (1)
Y= -2190X 1 , 4- 5370X 2 - 4260X 2 – 626X 4 + 46.3X 5 + 2350X 6 + 725X 7-336(1)where Y is a calculated D temp and Xi(i= 1, 2,...,7) are the data defined
as follows: X 1 is the ratio of peak area of benzene to toluene; X 2 is theratio of peak area of benzene to total; X 3 is the ratio of peak area oftoluene to total; X 4 is the ratio of peak height of benzene to toluene; X5 isthe ratio of peak height of benzene to total; X6 is the ratio of peak height
oftoluene to total and X 7 is the ratio oftotal peak area detected from 0-4
min to total. The multiple correlation coefficient and the coefficient ofdetermination were 0.863 and 0.745 respectively. Table 3 shows the calculated D temp for the salts using this equation. As can be seen in Table 3,
several D temp values were greater than that of the pyrofoil utilized (590°C),

so that multiple regression analysis was performed using the decomposition
temperatures obtained by DTA. Manganese chloride, nickel chloride,sodium chloride, calcium carbonate and sodium carbonate decomposed attemperatures higher than 590°C, as summarized in Table 1. These datasuggest that pyrolysis temperatures in this technique vary depending on theD temp of tne inorganic salts. The coefficients of X 2 and X 3 were larger
than the other coefficients. This means that the ratio of the peak area ofbenzene to total (X 2 ) and toluene to total (X 3 ) are very important inanalyzing the pyrolysis profiles. In addition, X2 is a useful factor resulting
from the canonical correlation analysis (correlation coefficients with equalvariances were used for the calculations). The canonical correlation coefficient was 0.863, and the structure vectors of X 2 and X 5 were 0.640 and
0.793 respectively. Figure 3 illustrates the relationship between Dtemp of
the salts and the relative peak intensities of benzene (solid line) andtoluene (broken line) against the total peak area on the pyrograms. The
ratios of peak area of benzene to total area increased with an increase in
Dtemp of the inorganic salts, and that of toluene tended to decrease. Theseresults are consistent with the bond dissociation energy of the carboncarbon bond, which is generally larger than that of the carbon-nitrogenbond [8]. It is therefore reasonable to conclude that the inorganic salts
effected the pyrolysis products. It is reasonable that this phenomenon
should occur with variation in the pyrolysis temperature in the presence ofinorganic salts.
CONCLUSION
It can also be concluded from this study that the pyrolysis products weredependent upon the Dtemp of the inorganic salts. In the presence of salts

which decomposed at lower temperatures, a smaller amount of benzene
and a larger amount of toluene were produced. In particular, the formationof benzene was favoured using salts which decomposed at higher temperatures. This phenomenon suggests that the pyrolysis temperature is influenced by the inorganic salt.

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