Study on Adsorption Behavior of Nitrogen Compounds on Porous Polymer Beads for Air Sampling

Abstract

Adsorption behavior of N-containing compounds on porous polymer beads was studied in terms of the breakthrough curve with a dynamic adsorption technique.
A sample gas stream for each compound in a constant concentration was prepared with a permeation tube by diluting with a dry air. The collection tube was a glass tube (i. d. 6mm) packed with about 0.6 g of adsorbents, such as TENAX-GC, Porapak T, Chromosorb T, Chromosorb 103 and alkalized Porasil A.
From S-shaped breakthrough curve, the breakthrough volumes (V_b) for the nitrogen compounds on the adsorbents were calculated by multiplying a sampling rate to the breakthrough time. The temperature dependence curve for all of compounds studied exhibits a linear relationship between log V_b and 1/T but a saturation for amines in a region of low temperatures.
The adsorbed amount in the collection tube measured with FID-GC after enrichment and thermal injection increased with sample volume but reached the constant value around the equilibrium point. The magnitude of the maximum amount adsorbed (maximum loading capacity) varied with a gas concentration.
Adsorption isotherms were constructed from the maximum loading capacity as a function of gas concentration for TMA, acetonitrile and acrylonitrile on TENAX-GC, Chromosorb 103 and alkalized Porasil A.
From the results obtained, alkalized Porasil A turned out to be suitable for the adsorbent for air sampling and to make a sampling of at least 20 l for amines and nitriles at ppb levels.