Fig. 5. DA analysis of unknown concentration samples for (a) SCN– and (b) AsO4 3– using calibration curves generated by standard concentrations noted on the figure. Smooth curves were plotted through calibration standards, and unknown responses were mapped onto the nearest points on the curves. Only sensors with increasing magnitudes of ΔRGB versus concentration were used (four out of eight for both anions; see main text for list). Centroids of four trials performed on separate occasions were plotted (black squares), and calibration curves were plotted using a best-fit curve. Unknown concentrations (white triangles representing centroid of four trials) were compared with interpolation using shortest orthogonal line to the curves. (a) UB (300 μM) was interpolated successfully but not UA (30 μM). (b) For arsenate, UC was successfully interpolated at 800 μM but not UA (5 μM) nor UB (20 μM), indicating a detection limit above these concentrations.
