Timing is everything: a simple chemical method to determine the bioavailable surface concentration of insecticide for insecticide-treated net evaluation

CAM dosages correlated strongly with MKDT (r = - 0.91, p = 0.0006), inter-sample variation below 2%, and comparable RT estimates. CAM surface extracts also correlated well with MKDT. WIs derived by chemical methods were longer than these determined by standard WHO method. Comparison of acetone and soap-washed nets indicate that part of the surface available pyrethroid has little biological activity, likely due to recrystallization on the yarn surface, confirmed by electron microscopy. Combining MKDT and SWAM after soap-wash could improve predictions of ITN performance. BAM can be used to measure loss of bio-active AI from the yarn surface following protocols currently recommended by WHO.