Critical micelle concentration (CMC) is the main chemical physical parameter to be determined on pure surfactants for their characterization in terms of surface activity and self-assembled aggregation. CMC values can be calculated using different techniques (e.g. tensiometry, conductivity, fluorescence spectroscopy), able to follow the variation of a physical property over surfactant concentrations. Different mathematical approaches have been applied for the determination of CMC values from the raw experimental data. Most of them are independent from the operator, despite not all the fitting procedures employed so far can be applied for all techniques. In this experimental work, the second derivative of the experimental data has been proposed as a unique approach to determine CMC values from different techniques (tensiometry, conductimetry, densimetry, spectrofluorimetry and high-resolution ultrasound spectroscopy). To this end, CMC values of five different surfactants, specifically, three anionic (sodium dodecyl sulfate, sodium deoxycolate and N-lauroyl sarcosinate) and two non-ionic as polyethylene glycol ester surfactants (Polyethylenglicol (8) monostearate and Polyethylenglicol (8) monolaurate) have been determined by this approach. The “second derivate” approach provides a reliable determination of the CMC values among all the techniques investigated, which were comparable to those calculated from the other operator-free routinely methods employed such as segmental linear regression or Boltzmann regression. This study also highlighted the strengths and shortcomings of each technique over the others providing an overview on the CMC values of commonly used anionic and non-ionic surfactants in the pharmaceutical field, determined by employing different experimental approaches.

Poly(glycolic acid), poly(lactic acid) and poly(lactic-co-glycolic acid) were approved by the United States Food and Drug Administration (FDA) in the 1970s as materials for the manufacturing of bioresorbable surgical sutures, but soon became the reference materials for the preparation of sustained release formulations, especially injectable microparticles. Since the 1986 approval of Decapeptyl^® SR, the first product based on PLGA microspheres, more than 15 such products have been approved for clinical use.