1988 Volume 37 Issue 2 Pages T22-T26
Although the differential thermal conductivity method is widely used for the determination of carbon, hydrogen and nitrogen in organic compounds, some troubles have happened with the apparatus in routine analysis. For example, leaks were occurred by deterioration of the O-ring at the combustion plug, by pinholes in the combustion tube, by contamination of the plunger of the solenoid valve, or by cracks in the end of the absorption trap. These leaks had an influence on helium blank values, blank values, zero signals and sensitivity factors. When the deteriorated O-ring was used at the fitting plug of the combustion tube, the filling time fluctuated and the blank values and the sensitivity factors of carbon, hydrogen and nitrogen varied widely. It was necessary to change the O-ring every 500 runs. The pinhole in the combustion tube increased the three blank values and the sensitivity factor of nitrogen, and decreased the sensitivity factors of carbon and hydrogen. The leak at the solenoid valve D decreased sensitivity factors and lowered the precision. Since the contamination of the plunger packings caused the carrier gas to leak, it was necessary to wash the plunger with deionized water. The leak at the water absorption trap increased the variation range of zero signals and made the blank values to drift irregularly. The unusual values were helpful to know the position of leak. The apparatus was adjusted according to signals of the unusual values.
