L-Cysteine purchased from Sigma-Aldrich was used as a model sample of biomass. Standard Ca(OH)2 was obtained from Sigma-Aldrich. Durian pulp was purchased from local market in form of frozen durian.

Figure 4.1 shows the schematic diagram of a combination system of hydrother­mal reaction and mass spectrometry developed by our group for direct detection of heteroatomic compounds generated during hydrothermal reactions.

The system has been reported in our previous paper (Alif et al. 2011). A stainless steel tube from the Swagelok (V= 10 cm3, ID = 1.3 cm, L = 14.4 cm) was used as a
reactor cell (a) for hydrothermal reaction. Approximately 0.2 g of L-cysteine or 0.5 g for durian was placed into the reactor with 6 ml of deionized H2O. Air in the reactor was purged with nitrogen gas to give an inert atmosphere. The reactor was put into the GC oven (Shimadzu GC-8A) (b) programmed at different temperatures (250, 300, 350, and 380°C). The reactor was kept at each temperature until a con­stant pressure was reached. The pressure inside the reactor was monitored simulta­neously by the pressure sensor (c). After the reaction is completed at a certain time, the gas produced at the desired temperature and pressure was stored in the tube between the two valves (d and e) (V= 1.6 ml, ID = 0.2 cm, L = 10 cm). By opening the second valve (e), the products were introduced from a capillary column (f) into a quadrupole mass spectrometer (Anelva AQA-360) through the sampling (g) and skimmer (h) cones. A scan mode or selective ion monitoring (SIM) mode was used. A gaseous sample uptake was conducted for 2 min at all temperatures.

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