The effect of an acid scavenger on the performance of rapid pregnancy tests

摘要

Two types of injection-molded ABS (acrylonitrile-butadiene-styrene) thermoplastics, one with MgO as the acid scavenger and one without the MgO, were used as the housings of the membrane strips for pregnancy tests and heat stressed at 37 °C for two months. Membrane strips in ABS containing MgO showed premature pink color around the end of test indicator. This pink color is normally an indication of the completion of the medical test and should be colorless prior to conducting the test. No color appearance was observed for membrane strips in ABS without MgO. X-ray photoelectron spectroscopy spectra revealed that the pink color appearance was caused by the diffusion of sulfuric acid - the key compound that prevents premature color formation in membrane strips. The diffused acids went into the ABS housing and the diffusion was enhanced by the presence of MgO acting as a strong sink for the diffused sulfuric acid. This study demonstrates the importance of understanding the delicate interaction between thermoplastics and medical devices.