INDIRECT TENSAMMETRIC METHOD FOR THE DETERMINATION OF NONIONIC SURFACTANTS .3. PROPERTIES OF THE ANALYTICAL SIGNAL OF MIXTURES OF NONIONIC SURFACTANTS

Seven binary and three multi-component mixtures of non-ionic surfactants and a mixture of ethylene glycol and PEG 400 were investigated using tensammetry with ''normal'' recording and one binary mixture by using ''reverse'' recording. Within the initial section of the Gamma-shaped calibration graph, the investigated mixtures show no or small deviations from the plot for the standard (Triton X-100) and most of the mixtures show good additivity. In the case of two mixtures showing deviation from additivity the results deviated less from the plot for the standard than would be expected presuming additivity. Within the range 0.1-1.0 mg l(-1) the mixtures can be determined using a Triton X-100 calibration graph without serious error. The shape of the calibration graph as a whole depends strongly on the average number of oxyethylene subunits of a mixture, but depends only slightly on the molecular weight distribution of the mixture. Therefore, the behaviour of polydisperse surfactants can be simulated by a mixture of two different polydisperse surfactants.