Simultaneous fluorometric determination of nalidixic acid and 7-hydroxymethylnalidixic acid by partial least squares calibration

The resolution of binary mixtures of nalidixic acid (NA) and 7-hydroxymethylnalidixic acid (OH-NA) has been accomplished by partial least squares (PLS) and principal component regression (PCR) multivariate calibration. The method of determination is based on the fluorescence emission of these compounds in the presence of gamma-cyclodextrin (gamma-CD). The formation of the inclusion compounds gives rise to an increase of the fluorescence emission compared to aqueous solution. The total luminescence information of the compounds has been used to optimize the spectral data set to perform the calibration. A comparison between the predictive ability of three multivariate calibration methods, PLS-1, PLS-2 and PCR, on three spectral data sets, excitation, emission and synchronous spectra has been performed. The PLS-1 method, applied to the emission spectra, has been selected as optimum. The proposed method has been applied to the simultaneous determination of NA and OH-NA in urine. Recovery values from urine samples containing (NA) and (OH-NA) range from 91 to 103% (mean 97%), and from 92 to 105% (mean 99%), respectively.