An evaluation of the air stream Faraday cage in the electrostatic charge measurement of interactive drug systems

Abstract

An air stream Faraday cage was used to measure the electrostatic charge generated when adhered particles were detached from an interactive unit interface. Theoretical and practical considerations in the design of the apparatus were discussed. Average charge to mass ratios in the range 1.7–7.6 μC·g −1 and their polarities were determined for a number of drug materials in relation to a polymer-coated carrier. Spurious charging due to the surrounding electrical field, air streaming and carrier-carrier or carrier-cage interaction was less than 1% of the total charge measured and was not a significant consideration under the charge-measuring conditions used in this study. The electrostatic charge produced on drug particle detachment was not altered by further drug-carrier or drug-cage interaction in the interactive systems studies. However, when highly triboelectrified interactive systems were used, drug-cage interaction occurred negating some of the electrostatic charge and providing average charge to mass ratios which were not representative of all of the particles in the interactive system. Incremental air flow charge measurements allowed the determination of the interactive systems' charge distribution.