We are trying to determine the aggregation number of SDS in micelles for surfactant solution with high concentration.

We use the following methodic: to SDS solution of certain concentration we add probe ([pyrene]=10^-6 M) and quencher (0 < [hexadecyl pyridinium bromide] < 0,000028 M). Then we take spectra and calculate the ratio between I’3 (without quencher) / I3 (with quencher). As a matter of fact, the greater the concentration of the quencher, the lower the intensity. Then from the dependence  ln (I’3/I3) – [quencher] we calculate the aggregation number. Excitation wavelength 335 nm. Cary Eclipse spectrofluorometer from Agilent is used. And there is a problem. If the surfactant concentration not much higher than CMC (approximately 70 mM, which is approximately 10 CMC), methodic is working, we obtain the values ​​of the aggregation numbers comparable to the literature data. As soon as we take more concentrated solutions, for instance 250 mM, it turns out nonsense. The intensity with a quencher becomes greater than the intensity without a quencher, so, the ratio of intensities is less than one, and the logarithm is negative ... We tried to increase the exposure time of the solutions, tried to vary the concentration of the quencher. The result is the same. Can someone tell what are we doing wrong? Share, please. We are very interested in details of the method applying to our systems (surfactant/organic monomer). Thank you in advance.