In order to develop a confident sampling technique, we designed and constructed a 6-port manifold MFC sampling system for collecting gaseous pollutants in air. Using this instrumentation, we tested the performance criteria of MFC system in terms of: (1) flow rate; (2) MFC-to-MFC variability; (3) tube-to-tube variability; and (4) time. It was interesting to find that the later two factors did not show any significant variations, while the former two show substantially large variations. However, as most of those variabilities are consistent enough to form systematic patterns, we were able to explain the occurrence patterns of all those MFC biases in terms of those four major variables. The overall results of our experiment suggest that one needs to use correction factor for each MFC unit under a given flow rate to maintain optimal accuracy and precision for sampling of those pollutants.