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 lo w-pressure permeation device, and solid sodium nitrite allows the cont inuous production of highly pure nitrous acid (purity > 99.5%) and thu s the generation of standard atmosphere in a very wide range of nitrou s acid mixing ratio (5-20000 ppb). The system is of easy construction and exhibits a very high reproducibility and excellent long-term outpu t stability. These features allow us to obtain any desired value of ni trous acid mass flow rate by simply tuning the temperature and flow ra te values. As a consequence of the high purity of the generated compou nd, it was possible to obtain a clear absorption spectrum of nitrous a cid without performing any correction for NO2 interference.