4.5.2.2.   Methanol, Ethanol and Propanol by the SPR Setup

For the multicomponent analysis of ternary alcohol mixtures, 2 data sets were recorded [193] using the SPR setup with a 300 nm Makrolon layer (more details in [194]). The calibration data set is a 6-level equidistant full factorial design whereby the relative saturation pressures of methanol, ethanol and 1-propanol were varied between 0 and 0.035. 18 concentration combinations were measured two more times for an estimation of the experimental signal inaccuracies. The validation data set is a 5-level equidistant full factorial design with relative saturation pressures between 0.0035 and 0.0315. Additional 15 measurements were performed with the pure analytes at the five concentration levels. 9 measurements were identified as outliers according to [192] whereby 7 measurements of the calibration data set and 2 measurements of the validation data set were removed. During all measurements the polycarbonate was exposed to the analyte mixtures for 600 seconds and afterwards to dry synthetic air during 4760 seconds with 28 time points recorded during exposure to analyte and 22 time points recorded during exposure to air resulting in 50 input variables in total. The sensor responses are shown in figure 16 for different concentrations of the single analytes. All measurements were performed in random order within the two data sets. The validation data set was recorded one month after the calibration data set and the signals of this data set were averaged using two measurements.

figure 16:  Signals of the SPR device during exposure to analyte and then to synthetic air for different concentrations of methanol ethanol and 1-propanol.