H-POINT STANDARD ADDITIONS METHOD FOR RESOLUTION OF BINARY-MIXTURES WITH SIMULTANEOUS ADDITION OF BOTH ANALYTES

The basis of the H-point standard additions method, HPSAM, with simult aneous addition of both analytes is proposed for the resolution of bin ary mixtures. It is a modification of the previously described H-point standard additions method that permits the resolution of both species from a unique calibration set by making the simultaneous addition of the two analytes. The method uses as analytical signals the absorbance s at pairs of wavelengths where each species shows the same absorbance . The required data to apply the method are the absorbance values at t he previously selected wavelengths for the sample alone and spiked wit h both species at known concentrations. Linear relations between absor bance values and added concentration of analyte are found, and the int ersection of the lines at the previously selected wavelengths permits to obtain the analyte concentration in the sample. Wavelength pairs ca n be selected to obtain the most precise results. The effect of the re lation of the concentrations of the two species in the standard and in the sample has been studied. Some mixtures of phenol and o-cresol, sp ecies highly overlapped (absorption maxima: for phenol at 234.6 and 28 7.0 Mn; for o-cresol at 236.6 and 288.4 nm) and with similar absorptiv ities have been tested. If the matrix effect is known to be absent, th e method can be employed with absortivity coefficients of the pure com pounds.