Microcoulometry has been widely used to measure halides in hydrocarbons. While microcoulometric analysis is well-established, some types of hydrocarbons (i.e., crude oils, heavy fuel oils, hydraulic fluids, and others) require special attention due to their physical and chemical properties. In the past, slow combustion with higher temperatures (1000°C or greater) was recommended; however, sluggish response due to refractory components, the presence of heavy metals, or the rapid aging of the quartz combustion tube under such conditions has made data interpretation difficult at times.
Analysis of heavy hydrocarbons was improved by changing the combustion tube design and adding cupric oxide wire to the combustion outlet zone. With this scheme, it is not necessary to use high furnace outlet temperatures. Combustion efficiency and system response improve, while the effects of deposits and corrosion are greatly reduced. Crude and #6 fuel oils, phosphate ester fluid, and base lube oil additives were tested under these conditions, yielding better recovery and improved precision for some by a factor of three or greater.
A post-combustion scrubber developed for solvent analysis was evaluated for refractory hydrocarbon analysis. It had little effect on the detection limit, but could be used to remove deposits.