Traces of oxygen in elementary and combined form in naphtha have become important in varrous petroleum-refining processes. Dissolved clcmcntal oxygen causes fouling in heat cxchangersl. 'Tracts of water impair the activity of rcformcr catalystsz. Sometimes tllc undesirable constituent is'carbon dioxrde, carbon monoxide, or some other oxygenated compound. Although specific methods for each type of oxygen compound arc available, thcrc has been no satisfactory method of drrcctly determining the total oxygen content of low-boiling petroleum distillates.
The direct dctennination of total oxygen in organic substances has been the subject of many recent papers s--11. Methods most widely used have been moclifications of the SCH~TZE methodo, in which the sample is pyrolyzed over carbon at about IIOO~. The oxygen is quantitatively converted to carbon monosidc and, after oxidation to carbon dioxide, is determined manomctricallya, volumetricallyb, gravrmetri-cally4*e*Q, or iodornctrically3* 11. However, these modifications arc not accurate below 0.1 o/O oxygen.
Nevertheless, the SCHOTZE method could be used for determining trace amounts of oxygen in light hydrocarbons if the problems of sensitivity and volatility were overcome. To obtain a measurable amount of carbon droxide, a large sample must be pyrolyzed. To prevent dangerous explosions, the pyrolysis rate must be carefully regulated. To minimize evaporation, during weighing and handling the sample must bc enclosed in a container having relatively small openings. Provision must be made to purge atmospheric oxygen from the system after the sample is placed inside the pyrolysis tube. Finally, the sample container must remam inert at the pyrolysis tcmpcrature.
Fulfillment of these strict requircmcnts was made possible by handlmg the sample in the magnetically controlled spiral shown in Fig. , rather than in a boat. Made of quartz, rt is open at both ends and has a small quartz hook at one end. Evaporation during weighing and purging is minimized by the small open ends. The spiral can be completely filled without entrapping any air.
The spiral is manipulated by a bar magnet completely enclosed in quartz, with a hook on one end to engage the hook on the spiral. Spiral and manipulator can be controlled as a unit from the outside of the pyrolysis tube by an external magnet. Rotating the external magnet about the pyrolysis tube in the region of the manipula-Anal. Chm. Ada.