An improved back-flush-to-vent gas chromatographic method for determination of trace permanent gases and carbon dioxide in ultra-high purity ammonia

• Low-ppb GC-PDHID quantification of H2, O2, N2, CH4, CO, and CO2 in UHP ammonia.
• Back-flush flow system with auxiliary NaHSO4 trap prior to the analytical column.
• NaHSO4 trap for traces of ammonia does not affect the impurity content of the sample.
• Low-maintenance high-capacity configuration preventing deterioration of GC system.
• The GC-PDHID/TCD system has been applied at the production line of UHP ammonia.

A novel method for rapid, quantitative determination of trace permanent gases and carbon dioxide in ultra-high purity ammonia by dual-channel two-dimensional GC-PDHID is presented. An improved matrix back-flush-to-vent approach combining back-flush column switching technique with auxiliary NaHSO4 ammonia trap is described. The NaHSO4 trap prevents traces of ammonia from entering the analytical column and is shown not to affect the impurity content of the sample. The approach allows shortening the analysis time and increasing the amount of measurements without extensive maintenance of the GC-system. The performance of the configuration has been evaluated utilizing ammonia- and helium-based calibration standards. The method has been applied for the analysis of 99.9999+% ammonia purified by high-pressure distillation at the production site.