Curie-point pyrolyzer

Figure 8.45 Apparatus for pyrolysis gas chromatography. A, filament or ribbon-type pyrolyzer and B, Curie-point pyrolyzer. (Reproduced with perm.i ion from ref. 848. Copyright American Chemical society).

Curie-point pyrolyzer (high frequency inductive heating of a ferromagnetic carrier). 

Curie-point pyrolysis employs high-frequency (HF) inductive heating of a ferromagnetic wire (d 1 mm). A diagram of a Curie-point pyrolyzer designed for Py-GC is shown in Fig. 4.7.2. 

Fig. 4.7.2. Schematic diagram of a Curie-point pyrolyzer (Fischer, Germany). Note the possible modifications of the wire tip (a, b, and c) for solid samples. Pyrolysis glass injector (/), ferromagnetic wire (2), carrier gas inlet (3), impulse cable from power generator (4), induction coil (5), aluminum box (6), adapter for GC injector (7), GC inlet (8), GC septum (9), GC oven (10)...

Several Curie-point pyrolyzers are obtainable from Fischer (Germany), Scientific Glass Engineering (Australia), Horizon Instruments (England) and Japan Analytical Industries. In addition, laboratory-constructed models have been described in the literature (Saiz-Jimenez and De Leeuw 1984, 1986, Boon et al. 1987, Genuit et al. 1987, Pouwels and Boon 1987, Saiz-Jimenez et al. 1987). 

Pyrolysis involves the thermal decomposition, degradation, or cracking of a large molecule into smaller fragments. Pyrolysis GC is an excellent technique for identifying certain types of compounds which cannot be analyzed by derivatization, e.g., polymers. The pyrolysis temperamre is typically between 400°C and 1000°C. A number of analytical pyrolyzers have been introduced and are commercially available. The devices consist of platinum resistively heated and Curie point pyrolyzers. The carrier gas is directed through the system, and the platinum wire is heated to a certain temperature. The material decomposes, and the fragmentation products are analyzed. ... 

Radio-frequency induction heated wires (Curie-point pyrolyzers)... 

Commonly used RF frequencies in Curie point pyrolyzers are 400 to 1000 kHz, and the power outputs range from 100 to 1500 watts. The rate of temperature rise depends on the conductor mass and specific heat, as well as on the power consumption of the ferromagnetic conductor. This power consumption per unit surface is related to the amount of heat generated by the conductor and implicitly to the temperature. More detailed descriptions of the parameters implicated in the heating of a ferromagnetic conductor located inside a high frequency induction coil are found in literature [5, 10]. 

Different practical constructions of a Curie point pyrolyzer are commercially available. In these systems, the sample is put in direct contact with the ferromagnetic alloy, which is usually in the shape of a ribbon that can be folded over the sample forming a sample holder. The sample and its holder are maintained in a stream of inert gas in a similar way as for resistively heated filaments. The housing where the sample and its ferromagnetic holder are introduced is also heated to avoid the condensation of the pyrolysate but without decomposing the sample before pyrolysis. Autosample capabilities for Curie point pyrolyzers are also commercially available (e.g. DyChrom modelJPS-330) [11, 12]. 

As an example, in the study done on Kraton 1107 [16], the decomposition was found linear for the oven temperature and the ratio of two monomers (styrene and dipentene) only in a temperature range from 450° C to 625° C, which is narrower compared to that found for a filament or Curie point pyrolyzer. 

The reproducibility of the results for heated filament pyrolyzers and Curie point pyrolyzers as well as the comparison between the two systems was reported for a number of materials [41], The reproducibility of the analysis was evaluated both qualitatively and quantitatively. It was found that for most samples the results are obtained with very good reproducibility for the same instrument. However, differences in the instrumentation may play an important role regarding the dissimilarity of the results, even when they are operated at comparable parameters. These differences are typically less pronounced between filament pyrolyzers and Curie point pyrolyzers. Also, microfurnace pyrolyzers are closer to filament pyrolyzers than large furnace ones. On the other hand, laser micropyrolyzers or sealed vessel furnace pyrolyzers may lead to quite different results. 

The humic substances and soils were pyrolyzed in a type 0316 Curie-point pyrolyzer (Fischer, 53340 Meckenheim, Germany). The samples were not pretreated except drying and milling. The final pyrolysis temperatures employed were 573 K, 773 K and 973 K, respectively. The total heating time was varied between 3 and 9. 9 s. 

Infrared spectra were obtained using Hitachi 260-10 and 270-30 spectrometers and a Digilab FTS-IMX FT-IR. The El (70 ev) and Cl (isobutane) mass spectra were obtained employing a JEOL JMS-D300 GC mass spectrophotometer connected with a JAI JHP-2 Curie Point Pyrolyzer (injector temperature-250"C pyrolyzer... 

The dissemination of GC-MS after 1965 strongly accelerated the development of Py-GC. til 1966, Simon and co-workers reported the first directly coupled Py-GC/MS system using a Curie-point pyrolyzer, a metal capillary column GC, and a rapid scanning MS." In 1968, huddemage and Hummel introduced field ionization MS(FI-MS) to simplify the mass spectra resulting from Py-MS. This technique dramatically improved the effectiveness of direct Py-MS, because of the simpler fragmentation in FI-MS. 

In a Curie-point pyrolyzer, an oscillating current is induced into the pyrolysis filament by means of a high-frequency coil. It is essential that this induction coil be powerful enough to permit heating the wire to its specific Curie-point temperature quickly. In such systems, the filament temperature is said to be self-limiting, since the final or pyrolysis temperature is selected by the composition of the wire itself, and not by some selection made in the electronics of the instrument. Properly powered, a Curie-point system can heat a filament to pyrolysis temperature in milliseconds. Providing that wires of the same alloy composition are used each time, the final temperature is well characterized and reproducible. 

Curie-point pyrolyzers are generally not used in this stepwise fashion, since they are limited to one temperature per sample because of the way heating is controlled. Microfumaces, however, have been designed with a separate desorption zone, so that a sample may be manually lowered into a low-temperature zone for a first run, retrieved, and then lowered into the pyrolysis zone for a second run. Filament pyrolyzers are now available with a low-mass, programmable interface zone along... 

Among the definite advantages of the Pyroprobe over Curie-point pyrolyzers are the absence of solvent and grinding for sample introduction, ease in weighing the sample, and freedom of temperature choice. It is also hard to overestimate the possibilities provided by CDS Pyroprobe to carry out so-called sequential pyrolyses i.e., the pyrolysis temperature and time are chosen in a way that each pyrolysis affords only fractional decomposition of the sample. This additional capability of the CDS instrumentation was successfully used to identify the provenance of amber artifact from Hasanlu. ... 

Similar complications were observed for Curie-point pyrolyzers. In a recent review, the author complained that ... 

The sample preparation procedures were similar for both of these studies. Smoke aerosols of the materials of interest were produced in the laboratory under either nonflaming or flaming combustion conditions, and the material produced collected on glass fiber filters. The volatile organic fraction was removed from the collected material by gentle heating (50 to 55°C) under vacuum for 24 to 48 h. A portion of the nonvolatile material was then subjected to analysis by Py-MS using a Curie-point pyrolyzer (510°C) interfaced to a quadrupole mass spectrometer via an expansion chamber. 

Analysis was performed by desorbing the organics from the traps with a Curie-point pyrolyzer unit in series with a quadrupole mass spectrometer. The data produced were similar to Py-MS data, although, quite likely, thermal desorption was taking place rather than pyrolysis. The typical mass spectrum obtained from the contaminated areas was dominated by the major ions of PCE. Table 7.5 shows the various compounds that were identified in spectra obtained from the 25 samples spaced around the contaminated area. Table 7.6 shows the compounds identified by static trapping from a particular location and by purge-and-trap GC/MS analysis of water from an adjacent well. 

Curie-point pyrolysis involves placing the sample wire into a radio frequency field that induces eddy currents in the ferromagnetic material and causes a temperature rise. When the wire reaches the Curie-point temperature, it becomes paramagnetic and stops inducting power. The temperature at which the wire stabilizes (the Curie point) is a function of the type of metal. For example, the Curie points of cobalt, iron, and nickel are 1128, 770, and 358°C, respectively. Wires made from alloys of these metals produce intermediate temperatures. For example, the commonly used nickel-iron wire has a Curie point of 510°C. Differences between filament and Curie-point pyrolyzers depend on the pyrolysates examined and may be obscured by other instrumental differences, including the design of the transmission system to the detector. 

Samples of a single S. aureus strain were pyrolyzed in an air atmosphere tube furnace and in a vacuum Curie-point pyrolyzer connected to a triple-quadrupole mass spectrometer. Pyrograms of S. aureus were distinguishable from those of E. coli and Bacillus strains. Peaks related to fatty acids were identified in the mass pyrograms. 

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