EVALUATION OF A HIGH-PURITY AND HIGH-STABILITY CONTINUOUS GENERATION SYSTEM FOR NITROUS-ACID

A flow-type system for the generation of nitrous acid in the mass flow rate range of 3.5-400 nmol/min is described. The system based on the reaction between gaseous hydrochloric acid, generated by means of a low-pressure permeation device, and solid sodium nitrite allows the continuous production of highly pure nitrous acid (purity > 99.5%) and thus the generation of standard atmosphere in a very wide range of nitrous acid mixing ratio (5-20000 ppb). The system is of easy construction and exhibits a very high reproducibility and excellent long-term output stability. These features allow us to obtain any desired value of nitrous acid mass flow rate by simply tuning the temperature and flow rate values. As a consequence of the high purity of the generated compound, it was possible to obtain a clear absorption spectrum of nitrous acid without performing any correction for NO2 interference.