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Chemical Structure of Nonoxynol-9. The nine in Nonoxynol-9 indicates the number of carbon atoms in the alkyl chain attached to the phenyl group para to the ethoxy groups side chain. It does not represent the number of ethoxy groups in the chain. As used in commerce, Nonoxynol-9 is a mixture of oligomers that all have the nine carbon alkyl group attached to the phenyl group, but the number of ethoxy groups is represented in the formula by a subscripted n after the parenthesis around the ethoxy groups. A mass spectrum of commercial Nonoxynol-9 that produces a series of protonated molecular ions will show a series of peaks with each peak spaced 44 amu from its adjacent peaks. The mass represented by each peak should equal the mass for that oligomer plus one if the peaks are protonated molecular ions, or the oligomer’s mass plus twentythree if the peaks are sodiated molecular ions.