but also as quickly as practicable so as not to allow for evaporation of sterilant peroxide which could provide a false negative the most preferred approach for collecting the residual sterilant is for the test piece simply to be immersed in the collector solution ideally it is not removed from the collector solution for the remainder of the test alternatively however the test piece can be rinsed with a collector solution and the total rinse volume collected the collector solution is preferably used in a predetermined amount so that the concentration of the sterilant collected can be determined the step of measuring the amount of residual sterilant in the collector solution can be by direct or indirect means the choice of direct or indirect measurement will depend upon the nature of the sterilant for example direct measurement may be applicable for a sterilant that is uv active having an aromatic ring or forming a charge transfer complex for instance directly subjecting the collector solution or a treated collector solution to uv spectroscopy the use of a calibration curve will enable the concentration of the residual sterilant in the collector solution to be determined because the volume of collector solution is known the total amount of sterilant can thus.