An Autosampler with a Short Transfer Line for Curie Point Pyrolysis Capillary Gas Chromatography Akira Onishi', Makoto Endo, Shigeki Uchino, Naoto Harashima, and Naoki Oguri Japan Analytical Industry Co. Ltd, 208 Musashi, Mizuho, Nishitama, Tokyo 190-1 2, Japan

Key Words: Capillary GC Curie point pyrolysis Multichannel autosampler Polymer analysis

Summary A new multichannel autosampler which can automatically analyze up to twenty samples in sequence has been developed for Curie point pyrolysis - capillary GC. Compared with a previous system [l] the transfer line between the pyroysis unit and chromatograph is shorter, and thus has less dead volume, and can be operated at a higher temperature (300°C). The relative yields of higher boiling point, highly polar, and thermally labile pyrolysates generated from polymers, and the reproduci- bility, were better than those obtained from the previous autosampler. To facilitate rapid operation an additional flow controller is installed on the new device to shorten the time taken to purge air from the sampler.

1 Introduction Curie point pyrolysis - capillary GC is a powerful method for the compositional and structural analysis of non-volatile compounds such as synthetic plastics [2], rubbers [3], and paints [4]

The best prospect for achieving universal reproducibility in analytical pyrolysis GC is in accurate control of variables such a s pyrolysis temperature and the temperature between the pyrolysis chamber and the capillary column (the latter to maintain the pyrolysates in the vapor state), the linear velocity of the carrier gas, and the temperature of the GC column oven [5]. Manual operation, however, presents some difficulties in the normaliza- tion of pyrolysis variables. To achieve the standardization of pyrolysis conditions, we have previously developed the model JPS-220 multichannel autosampler for Curie point pyrolysis GC

The development of the Curie point pyrofoil sampler has been continued by introduction of the model Auto 330 high precision autosampler with a short transfer line; this enables the analysis of higher molecular weight pyrolysates than was possible with the model JPS-220. The Auto 330 can hold up to 20 samples in the sample holder a t ca ambient temperature without any degrada- tion and/or further polymerization during the waiting time before pyrolysis; this has solved a problem observed on another auto- sampler 161 in which thermally labile compounds could degrade or polymerize before pyrolysis (7,8]. The Auto 330 is, moreover, installed on a GC injection port so that the condensation of high boiling point pyrolysates on to the wall of transfer pipe is much reduced in comparison with the JPS-220.

111.

The applications by Auto 330 are illustrated and results from the pyrolysis capillary GC analysis of some synthetic polymers are compared with those obtained from the JPS-220. The paper demonstrates the superiority of the Auto 330.

2 Experimental

2.1 Instrumentation

The configuration of the model Auto 330 automatic pyrolyzer with short transfer line is shown in Figure 1 the model FWC-33 flow controller controls the flow of carrier gas to the model JHP 3 pyrolyzer and transfers the pyrolysates on to the GC column, the model JPS-330 auto-injector continuously feeds up to 20 samples

FWC-33 n A B

C D

rl i Jps-330

Figure 1

Auto 330 autosampler for Curie point pyrolysis: A, stop valve; B, mass flow valve; C, pressure valve; D, solenoid valve; E, RF coil; F, split outlet; G, capillary column; H, FID.

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Autosampler for Curie Point Pyrolysis Capillary GC

to the JHP-3. The cross section of the configuration of the JPS-330 and JHP-3 is shown in Figure 2.

Sample preparation and Auto 330 operation are as follows: samples of known weight are wrapped in pyrofoil in a manner ensuring good contact [9] (a) and placed on the JPS-330 magazine

front of the trap: if the falling of the foil is not detected, the collection and release serial motion C + D + C is repeated twice.

The slide-way is returned to its initial position and a timer installed in the Auto 330 turns on to ensure adequate cooling of the GC column oven before the next analysis. After processing of the first sample and the subsequent cooling period, the magazine is motor-driven to the position where the second pyrofoil- wrapped sample is ready to be dispensed into position B. The process is then repeated.

This entire process is microprocessor-controlled

The FWC-33 flow controller is of importance in ensuring efficient operation of the Auto 330. Purge and replacement of 600 ml of air by carrier gas are required when the JPS-330 magazine is replaced. Use of a GC mass-flow controller for this task requires more than 30 min whereas use of the FWC-33 achieves rapid and complete replacement within 2 min of switching on the solenoid valve. Faster stabilization of the linear velocity of the GC carrier gas is ensured by control of the column inlet pressure by means of a valve in FWC-33.

2.2 Condition for Pyrolysis GC

In this study 0.2 mg samples wrapped in pyrofoil were pyrolyzed at 590 "C for 3 s. The JHP-3 - JPS-330 combination was installed (Figure 1) directly on the injection port of a Hewlett-Packard model 5890 gas chromatograph equipped with split inlector and flame ionization detector. A Hewlett-Packard model 3396 integra- tor was used for data collection and processing. Separations of pyrolysates were performed on a 30 m x 0.25 mm i.d. column coated with 0.25 pm film of polydimethylsiloxane DB-1 (Jaw). The column temperature was maintained at 50 "C for 3 min, then programmed at 10 "/min to 250 "C, which was held for 10 min. Helium was used as carrier gas; a total flow rate of 50 mlimin was split in the ratio 50: 1. The Auto 330 and JPS-220 were held at 300 and 200 "C, respectively. The identification of pyrolysates was performed with a directly coupled model QP2000A quadrupole mass spectrometer (Shimadzu), EI ionization was performed at 70 eV .

Figure 2

Cross section of the JPS-330 - JHP-3 assembly: a, PyrofoiP; b, magazine; c, air plunger; d, injector; e, motor; f , air plunger; g, slide way; h, photo sensor; i, pyrolysis sample tube; j, RFcoil; k, oven; I, heater; m, carrier gas inlet; n, maintenance heater; 0, needle; p, trap.

(b) located at position A Air remaining in the JPS-330 is then purged with carrier gas from the FWC-33 and the first pyrofoil wrapped sample is pushed by a pneumatic inlector (d) down to the pyrolysis chamber (B) where the sample is instantaneously pyrolyzed and the pyrolysates transferred to the GC column for analysis An electromagnet (1) then moves from position C to position D to pick up the used pyrofoil

After the analysis, the magnet and pyrofoil are withdrawn to position C and a slide-way (9) is positioned under the magnet The magnet current is then switched off and the used pyrofoil falls on to the slide-way and thence into the trap (p) The falling of the pyrofoil into the trap is detected by a photo sensor (h) located in

2.3 Samples

Bisphenol A-type epoxy prepolymer (YD-0141, approximate mole- cular weight range 2000, was obtained from Toto Kasei. Toyolac 700 ABS resin, a copolymer of acrylonitrile (23 %), butadiene (13 %), and styrene (64 %), was obtained from Toray Industries. Polystyrene with a weight-average molecular weight of 13000 was obtained from Pressure Chemical Co. (Pittsburgh, PA, USA). Poly-2-hydroxy-3-phenylisopropylacrylate (PHPPA) was synthe- sized by solution polymerization using AIBN as initiator, purified by precipitation in methanol, and then dried.

2.4 Difference Between the JPS-220 and the Auto 300

We have previously described the use of the JPS-220 multichannel autosampler for Curie point pyrolysis GC 111. The JPS-220 can be effectively installed on to any GC instrument, but the tubing through which pyrolysates are transferred to the GC injection port is long (1.3 m). Also, for simplification of operation, the instrument incorporates a 6-port valve to maintain carrier gas flow into GC column: the valve is switched when the pyrolysis chamber is opened for changing a sample. In order to protect the valve seal, however, the temperature limit for this valve is less than 200 "C. Condensation of high boiling or highly polar pyrolysates on the valve or transfer tube is, therefore, possible.

354 VOL. 16, JUNE 1993 Journal of High Resolution Chromatography

Autosampler for Curie Point Pyrolysis Capillary GC

I

A s dn improvement of the JPS-220, the Auto 330 was developed to be coupled to the GC with a shorter (70 mm) length of glass-lined transfer tubing The temperature limit of the Auto 330 has been increased to 300 "C by use of a heat resistant gasket and by elimination of the 6-port valve

3 Results and Discussion

3.1 Comparison of Polystyrene Analyses

For comparative assessment the Auto 330 and JPS-220 were alternately combined with the same GC system and the relative yields of high boiling point pyrolysates of polystyrene were measured. The pyrograms are shown in Figure 3.

A S

I I

SS

sss

I I I

10 20 30 min 0

S ss

B

I I

sss

I I I

0 10 20 30 min Figure 3

Pyrograms of polystyrene: A, analyzed by Auto 330; B, analyzed by JPS-220; S, styrene; SS, styrene dimer; SSS, styrene trimer.

It is well known that polystyrene is thermally decomposed mainly to the monomer (S), the dimer (SS), and the trimer (SSS), and it has been reported that SSS was produced in greater amounts than SS when pyrolysis was performed at ca 600 "C [ 101 When the JPS-220 was used, the peak area of SSS relative to that of SS was 0 69, using the Auto 330 it was 1 70 The lower ratio obtained using the JPS-220 could have resulted from the lower temperature limit of JPS-220 and the deposition of SSS in that instrument's longer transfer line The Auto 330 thus proved be better than the JPS 220 for the analysis of high boiling point pyrolysates obtained from polymers such as polystyrene

A

A

B SSA

I I I I 0 10 20 30 min

B <

A

1 I I I I 0 10 20 30 min

Figure 4

Pyrogram of ABS resin: A, analyzed by Auto 330; B, analyzed by JPS-220; B, butadiene; A, acrylonitrile; S, styrene; AS and SA, hybrid dimers; SS, styrene dimer; ASA, ASS, SSA, and SAS, hybrid trimers.

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Table 1

Comparison of the reproducibility of the peak areas relative to that of styrene, obtained with the Auto 330 and the JPS-220, of the characteristic pyrolysates of an ABS copolymer.

Model Relative peak area Monomer Dimer Trimer B A S AS SA ss ASA ASS SAS

Auto 300 Ave. 3.8 15.4 100 3.6 2.9 2.6 6.6 4.5 8.5 cv % 3.6 3.0 1.5 2.8 3.6 4.0 4.5 4.3 3.1

JPS-220 Ave . 3.0 18.3 100 5.1 4.2 3.5 6.9 3.8 59 cv % 6.7 3.4 1.1 5.0 2.7 7.1 2.8 5.1 3.6

3.2 Comparison of Reproducibility for ABS Resin Analysis

For comparative assessment of reproducibility, a multicomponent sample, tricomponent terpolymer ABS, was quantitatively ana- lyzed, under the same conditions, using the JPS-220 and Auto 330. The pyrograms obtained are shown in Figure 4. Reprodu- cibility and CV % data obtained for five replicate measurements of the relative peak areas of nine characteristic peaks generated from ABS are shown in Table 1, from which it is apparent that six of the nine CV % data measured by the Auto 330 are better than those measured by the JPS-220. All CV % data obtained using the Auto 330 were < 5 %, indicating the suitability of the equipment for quantitative analysis.

Experimental data showed that the relative intensity of the butadiene peak measured by the JPS-220 was less than that measured by the Auto 330. This can be attributed to the adsorption of the pyrolysates in the long transfer line. It is apparent from the pyrogram in Figure 4 and from Table 1 that the relative area of the acrylonitrile peak measured by the JPS-220 is larger than that measured by the Auto 330; the height of the acrylonitrile peak was, however, found to be smaller by the JPS-220. This can be attributed to diffusion in the long transfer line. It has, on the other hand, been reported that the styrene dimer is formed primarily by intermolecular reaction [ll]. The higher relative intensities of dimers measured by JPS-220 could be as a result of secondary reaction being greater than in the Auto 330.

Furthermore, as already mentioned, condensation of higher boiling point pyrolysates takes place on the surfaces of the 6-port valve and the transfer line, so the relative peak areas of trimers (ASS, SSA, and SAS) measured by the JPS-220 were less than those measured by the Auto 330. For same reason the trimer peaks measured by JPS-220 were wider and showed more tailing than those measured by the Auto 330.

3.3 Comparison of Reproducibility for Epoxy Prepolymer

To assess suitability for the analysis of higher boiling point products, a characteristic pyrolysate of YD-014, bisphenol A, was measured using the JPS-220 and Auto 330 under the same conditions The pyrograms are shown in Figure5 Using the Auto 330 the average ratio of the size of the bisphenol A peak to the total for all the peaks was 22 7 %, for the JPS-220, however, the ratio was only 3 8 % The monoglycidyl ether of bisphenol A (MGEBA), one of the characteristic pyrolysates from epoxy prepolymer, could be determined using the Auto 330, but not with the JPS 220 In conclusion, it is proved that the Auto 330 is superior to the JPS-220 for measuring pyrolysates with higher boiling points, such as bisphenol A and its glycidyl ether

A

- I 0

B

1

1

3 2 1

4

I I 10 20

I I 0 10 Figure 5

3

h

4

L - 4 A L u

I 20

5

I

30 min

I 5

I 30 min

Pyrogram of epoxy prepolymer: A, analyzed by Auto 330; 8, analyzed by JPS-220; 1, phenol; 2, cresol; 3, p-isopropylphenol; 4, p-isopro- penylphenol; 5, bisphenol A; 6, monoglycidyl ether of bisphenol A.

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Autosampler for Curie Point Pyrolysis Capillary GC

A

- I 0

B

1

L I

10

2

4 3

I

2 4

3

I

20

I I

0 10 20 Figure 6

A I

30 min

&

30 min I

Pyrogram of poly(1 -phenoxy-2-hydroxypropylacrylate): A, analyzed by Auto 330; 0, analyzed by JPS-220; 1, phenol; 2, l-phenoxy- 2-propanone; 3, 1 -phenoxy-2,3 propanediol; 4, 1 -phenoxy-2- hydroxypropylacrylate.

3.4 Analysis of Highly Polar and Thermally Labile Samples

A major component formed upon pyrolysis of PHPPA is its monomer, 2-hydroxy-3-phenylisopropylacrylate (HPPA), which is highly polar and thermally labile [ 121. The temperature used for

pyrolysis of PHPPA and the maintenance of heating of the transfer line are, therefore, very important for this analysis. The pyrograms of PHPPA obtained by both the Auto 330 and the JPS-220 are shown in Figure 6. Optimum pyrolysis conditions were deter- mined using the Auto 330: the yield of HPPA from PHPPA showed a maximum a t a pyrolysis temperature of 590 "C. The peak height of HPPA relative to that of the secondary pyrolysis product 1-phenoxy-2-propanone (marked as peak no. 2 in Figure 6) decreased from 1.5 to 1.2 when the transfer line temperature was increased from 200 to 220 "C. When the temperature was reduced to 180 "C, on the other hand, the HPPA peak showed tailing. Pyrolysis at 590 "C and a transfer line temperature of 200 "C are, therefore, the most suitable for PHPPA analysis.

The relative peak area of HPPA obtained by the Auto 330 was 1.9 times that obtained by JPS-220; the HPPA and PHPPA peaks (peaks 3 and 4 in pyrogram B of Figure 6 ) , moreover, showed tailing. This could be a result of the adsorption in the long transfer line of the JPS- 220.

It has been demonstrated that suitable pyrolysis and transfer line temperatures are more important when pyrolysis analysis of highly polar and thermally labile samples is performed using a high performance pyrolyzer with a short transfer pipe.

References

111

121 S Tsuge, Chromatogr. Forum. 44 (1986) 1.

I31 N. Nobuhira and S. Hirayanagi, J. SOC. Rubb. Ind. Japan 62 (1989) 77.

141 S. Yamaguchi, J. Hirano, and Y . Isoda. J Anal. Appl. Pyrol 16 (1989) 159.

151 T.P. Wampler and E.J Levy, J. Anal. Appl Pyrol 12 (1987) 75

161 H.R Schulten, W.G. Fischer, and H . J Wallstab, HRC & CC 10 (1987) 467

[71 S. Tsuge, H Ohtani, H Matsubara, and M Ohsawa, J. Anal Appl Pyrol. 11 (1987) 81.

181 H Nakagawa, S Tsuge, and T. Koyarna, J Anal. Appl. Pyrol 12 (1987) 97.

[9] N. Oguri and P. Kim, Internat Lab. 19 (1989) 58

I101 S. Tsuge and H Ohtani, Pyrolysis Gas Chromatography - Fundamen- tal, Data and Atlas, 2nd Edition, Tech. System, Tokyo, (1991).

1111 H. Ohtani, T. Yuyarna, S Tsuge, B. Plage, and H.R. Schulten. Eur. Polym. J. 26 (1990) 893.

(121 N. Oguri and A. Onishi, LC-GC Internat. (in press).

N. OgUrJ, A Onishi, To. Hanai. and X. JJn, HRC 15 (1992) 9

MS received April 3, 1993 Accepted May 25, 1993

Journal of High Resolution Chromatography VOL. 16, JUNE 1993 357