Pyrolysis injection system

Figure 11.1 shows the pyrogram of lead white pigmented linseed oil paint obtained at 610 °C with a Curie-point pyrolyser, with on-line methylation using 2.5% methanolic TMAH. The pyrolyser was a Curie-point pyrolysis system FOM 5-LX, specifically developed at FOM Amolf Institute (Amsterdam, the Netherlands), to reduce cold spots to a minimum. This means that the sample can be flushed before pyrolysis in a cold zone, and it also ensures optimum pressure condition within the pyrolysis chamber, thus guaranteeing an efficient transport to the GC injection system [12]. 

Pyrolysis can also be used in flow-based determinations with electrothermal atomic absorption spectrometry, as demonstrated in the determination of nickel in environmental and biological reference materials using a sequential injection system with renewable beads [313]. After analyte sorption, the beads were directed towards the furnace of the spectrometer and stopped there pyrolysis was accomplished as usual in order to release the analyte and destroy the beads. This innovation has often been exploited in the lab-on-valve system, but spectrophotometric applications have not been proposed to date. 

Once the sample has been pyrolyzed, volatile fragments are swept from the heated pyrolysis/injection port by carrier gas into the GC or GC/MS system. In Py-MS, it is likewise desired to transfer pyrolysis products to the ionization source of the MS without appreciable degradation, condensation loss, or recombination. Designs of Curie-point Py-MS systems have incorporated glass reaction tubes, expansion chambers, heated walls, and positioning of the pyrolysis reactor directly in front of the ion source."... 

In the noncatalytic HTO systems, sample volumes of 5—10 pL are injected in the pyrolysis tubes using an autosampler. Seawater samples can be previously treated with HQ (3 mol L ) in order to remove the dissolved inorganic carbon that causes formation of residues in the injection system. Ultrapure oxygen is used as carrier gas, as oxidant agent in the furnace, and as ozone generator. Pyrolysis is carried out at 1000°C-1100°C, and the detection system is based on the chemiluminescence of NO2 [40,80,148,149,156]. 

Creation of a dual-inlet (pyrolysis and auto-sampler) system, sufficiently flexible to use both kinds of injection system,... 

Figure 12.8 Mia ocolumn size exclusion chromatogram of a styrene-aaylonitrile copolymer sample fractions ti ansfeired to the pyrolysis system are indicated 1-6. Conditions fused-silica column (50 cm X 250 p.m i.d.) packed with Zorbax PSM-1000 (7p.m 4f) eluent, THF flow rate, 2.0 p.L/min detector, Jasco Uvidec V at 220 nm injection size, 20 nL. Reprinted from Analytical Chemistry, 61, H. J. Cortes et al, Multidimensional chromatography using on-line microcolumn liquid chromatography and pyrolysis gas chromatography for polymer characterization , pp. 961 -965, copyright 1989, with peimission from the American Chemical Society.

SEC in combination with multidimensional liquid chromatography (LC-LC) may be used to carry out polymer/additive analysis. In this approach, the sample is dissolved before injection into the SEC system for prefractionation of the polymer fractions. High-MW components are separated from the additives. The additive fraction is collected, concentrated by evaporation, and injected to a multidimensional RPLC system consisting of two columns of different selectivity. The first column is used for sample prefractionation and cleanup, after which the additive fraction is transferred to the analytical column for the final separation. The total method (SEC, LC-LC) has been used for the analysis of the main phenolic compounds in complex pyrolysis oils with minimal sample preparation [974]. The identification is reliable because three analytical steps (SEC, RPLC and RPLC) with different selectivities are employed. The complexity of pyrolysis oils makes their analysis a demanding task, and careful sample preparation is typically required. 

Attachment of the Pyrolysis System. The attachment of a pyrolyzer to a GC system should be made so that minimum dead volume remains in the system. Dead volume can be tested for by injection of methane into the GC column a tailing methane peak indicates the existence of dead volume. Such voids drastically reduce resolution and may also trap polar or more volatile fragments. The system should also be tested for contamination from previous runs by firing the pyrolyzer without sample. Generally, such a blank run should be made from time to time to ensure the absence of memory effects. A typical configuration of the so-called on-line approach is presented in Fig. 4.7.4. 

The sample is secured inside the tube or boat which is carefully slid into the heating coil. The probe can be connected either directly to a horizontal GC injection port or first into the heated interface of the Pyroprobe system (see Fig. 4.7.4) that is connected with the GC injection port. The interface temperature is set typically between 200 and 250 °C. After sample insertion but before triggering the pyrolysis, a period of 5 to 10 s is required to eliminate oxygen from the system. 

A schematic diagram of the entrained flow reactor is shown in Figure 1. At the top of the reactor, a screw feeder and semi-venturi system is used to entrain the ground coal particles in the cold primary gas stream. The coal is then injected into the reactor where it is entrained in, and heated by, the preheated secondary gas. The pyrolyzing coal particles fall in a thin stream through the reactor and are collected by a movable water-cooled collector probe. The time which the particles spend in the reactor is controlled by moving the collector probe up and down the reactor axis. The pyrolysis reactions are rapidly quenched in the collector probe, and the particles are separated from the gas stream by a cyclone in the collection system. 

In this separation, a 10-mL sample (large volume) containing a solution in tert-butyl methyl ether (tBME) of the pyrolysate of 1 mg cellulose obtained at 600° C was injected (off-line pyrolysis). The PTV injector was programmed at 20° C initial temperature for 2 min. and ramped with 10° C/min at 250° C and kept at this temperature for 1 min. Then the injector was further heated at 300° C. The split vent purge time was 2.5 min. The oven temperature for the first dimension separation was kept at 35° C for 2.5 min. then heated with 30° C/min. at 55° C and further heated with 3° C/min. to 240° C. The detector used in the first dimension was an MS system, which allowed the identification of a series of compounds from this chromatogram. The peak identification is given in Table 5.2.2. 

Fig. 3.6. Automatic system for injection of sample into pyrolyser, pyrolysis and GC separation of pyrolysis products. For identification of components, see te. t. From ref. 69.

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