Multichannel Autosampler for Curie-Point Pyrolysis Capillary
Gas Chromatography
Naoki Oguri＊ and Akira Onishi
Japan Analytical Industry Co. Ltd, 208 Musashi. Mizuho, Nishitama,Tokyo 190-12, Japan
Toshihiko Hanai
Int. Inst. of Technol. Anal., Health Res. Fond., Inst. Pasteur de Kyoto 5F. Sakyo-ku. Kyoto 60, Japan
Xigao Jin
Institute of Chemistry, Chinese Academy of Sciences. Peking. 100080 China

Key Words:
Capillary GC
Curie-point pyrolysis
GC-MS
Multichannel autosampler
Summary
A multichannel autosampler which can automatically analyze
up to 20 samples h sequence has been developed for on-line
Curie-pout pyrolysis - capillary GC. The results obtained fromthe system show that the analysis of thermally labile samples
could be performed without either thermal degradation orreaction during the waiting time before the final pyrolysis. The
reproducibilities of the relative peak areas and retention timesof the characteristic pyrolysates of a tricomponent copolymer
were significantly better than those obtained by manual sample
manipulation.
1 Introduction
Pyrolysis is used as a means of sample introduction for the gas
chromatographic analysis of high molecular weight compounds:
the technique uses high temperatures to degrade the compounds
to a characteristic mixture of volatile monomers. oligomers, andother pyrolysates. Curie-point pyrolysis - capillary GC is a
powerful method for analysis of the composition and structure ofsuch non-volatile compounds as syntheticplastics [1]. rubbers [2].
and paints [3].
In previous work. liquid, solid, and powder samples have beenhandled by wrapping in 50μm thick Pyrofoil@, placed in a speciallydeveloped. magnetic. metal foil holder. and inserted into thepyrolyzer [4. 5]. Because pyrolysis can be effected by a number ofexperimental parameters. it should be performed as reproduciblyas possible. especially for quantitative analysis. For this reason
we have developed a multichannel autosampler which can handle
up to 20 samples without causing any degradation and/or further
polymerization inside the sample holder during the waiting time
before final pyrolysis. This has solved a problem observed withanother autosampler [6] in which thermally labile compounds
could be degraded or polymerized before pyrolysis [7. 8].
The results from quantitative analysis of multi-component polymers has shown that as a result of the standardization of experimental conditions the reproducibility obtained using the autosampler is much improved in comparison with manual sample
manipulation.

2

Experimental

2.1 Instrumentation
A schematic diagram of the model JPS-220 multichannel autosampler and JHP-22 pyrolyzer is shown in Figure 1. Samples areweighed and individually wrapped in Pyrofoil@ in a manner
ensuring good contact. The Pyrofoil@-wrapped samples (A) areplaced on a magazine (B). the purge valve (C) opened to replace
the air inside the equipment with carrier gas. and, after 1 min. thesix-port valve (D) turned to the sampling position. The first sample
is pushed by the injector (E) down to a pyrolysis chamber (F)where it is instantaneously pyrolyzed. The pyrolyzates aretransferred, through (D), to a on-line GC column for chromatography.
A magnet (G) is then lowered to retrieve the spent sample andreturned to the upper position. A slide-way (I) is placed below themagnet and when the electricity supply to the magnet is switched
off the used sample (H) slides into the trap (J). The slide is thenreturned to its initial position. The instrument is controlled byunit (K).
When gas chromatographic analysis of the first sample is complete. the foil magazine is moved forward. the second sample
dispensed into the pyrolysis chamber by the plunger. and thesecond processing begins automatically. This sample introduction method is repeated up to 20 times from one magazine.
In order to keep the carrier gas flow rate constant. during
operation the inlet gas pressure is controlled by a pressurebalancer (L). Without this pressure controller. it took more than
30 min to obtain the stable gas pressure which is important for
production of reproducible pyrograms.
2.2 Condition for Pyrolysis GC
About 0.2 mg of a sample. wrapped in Pyrofoil, was heated at590℃ for 3 s The sample introduction and pyrolysis system were
coupled directly to a model HP 5890A gas chromatograph(Hewllet-Packard) equipped with a model D-2520 integrator(Hitachi). The GC system was equipped with name ionization
detection and fitted with a 30 m x 0.25 mm id. fused silica

3 Results and Discussioncapillary column coated with a 0.25 μm film of immobilized
polydimethylsiloxane (DB1: J&W. Folsom. CA. USA).
Following pyrolysis, the column temperature was maintained at50℃ for 3 min and then programmed at 10°/min to 250℃ which
was held for 10 min. Helium was used as carder gas: a total flowrate of 50 ml/min was split in the ratio 50 : 1. The identification of
the pyrolysates was performed with a directly coupled model
QP 2000 A quadrupole mass spectrometer (Shimadzu): ionization
was by EI at 70 ev.
2.3 Samples
A commercial bisphenol A type epoxy prepolymer and modified
polyamide hardener were obtained from Konishi. A Toyolac 700
ABS resin. a copolymer of acrylonitrile (23 %). butadiene (13 %).
and styrene (64 %). was obtained from Toray lndustries.

The multichannel autosampler coupled on-line with the Curiepoint pyrolyzer and the capillary GC system may be used not only
for time-saving automatic measurements on a large number ofsamples, but also for the highly accurate quantitative analysis ofthermally labile samples.
3.1 Anarysis of a Thermally Labile Sample
Conventional autosamplers for pyrolysis GC are usually provided
with auxiliary heating in order to maintain the sample holder at atemperature sufficient to prevent condensation of pyrolysates on
its inner wall [6]. Because uncured epoxy resins are susceptible tofurther curing. even at low temperatures. when such samples aremounted in a conventional pyrolyzer they are often exposed totemperatures which cause further curing during the waiting
period before final pyrolysis: the degree of reaction depends on
the temperature, the waiting time. and the size of the sample.
etc.: these are. in turn. reflected in the specificity and thereproducibility of the resulting pyrograms [8].
Since the sample magazine of JPS-220 is designed to be located
far from the pyrolysis chamber. such heating is not necessary.
This enables thermally labile samples to be analyzed reproduci-pyrogram from the uncured resin some of the monophenol
pyrolysate peaks had increased in size whereas that of bisphenol
A had, in contrast. decreased. These differences obviously
reflected the curing reactions of the epoxy resin with amidehardener.
3.2 Reproducibllity
The reproducibility of PY-GC analysis is influenced by each of aseries of steps: one of the most critical is the sample handlingtechnique [9]. As already mentioned. the use of an autosampler
enables reproducible sampling handling: because of this anenhancement of the reproducibility and standardization of quantitative analysis would be expected.
A tricomponent copolymer, art ABS resin. was analyzed quantitatively using both automated and manual sample introduction
systems. Figure 3 shows the pyrogram of the ABS resin: theintensities of the monomer (A. B. and S). dirner (AS. SA, and SS)
and trimer (ASA. ASS. and SAS) peal(s represent the structural
specificity and composition of the copolymer.

bly. Figure 2A shows the pyrogram obtained from a sample ofthe epoxy resin mixed with amide hardener (1:1) at room
temperature. No changes were observed in the pyrograms whensamples were stored in the sample magazine from 1 to 60 min.
which indicates that the JPS-220 is suitable tor the analysis ofthermally labile samples. The pyrogram of the epoxy resin cured
at 150℃ for 60 min is shown in Figure 2B: compared with theThe relative peak areas and retention times of the specificpyrolysates are summarized in Tables1 and 2. respectively The
relative standard deviations (CV%) of the peak areas and retention
times (tr) are also listed in the tables and (in part) presented
schematically Figure 4. The CV% and tr data show that theexperimental reproducibility obtained using the autosampler
were as much as 1.3 and 2.3 times better, respectively. than thoseobtained by manual sample introduction under the same conditions.
We consider that in addition to the completely uniform sample
introduction, pyrolysis. and chromatographic processing effectedby the autosampler control. there is another reason for thisimprovement: the removal of air by purging the pyrolyzer withcarrier gas. During manual sample introduction, air enters the