Fluorescent kinetics combined with fourth-order calibration for the determination of diclofenac sodium in environmental water.

A method that combines five-way fluorescence kinetics with fourth-order calibration for interference-free quantification of diclofenac sodium in river water was proposed and tested. Traditional fluorescence methods may not be suitable for such measurements since the fluorescence properties of the analyte are highly dependent on both pH and irradiation time in situ. In the method considered here, a five-way emission-excitation-time-pH data array was obtained from the samples by introducing the pH level and irradiation time as two extra modes. Then the data array was resolved by three fourth-order calibration algorithms: alternating fitting weighted residue quinquelinear decomposition (AFWRQQLD), five-way parallel factor analysis (five-PARAFAC), and alternating quinquelinear decomposition (AQQLD). The average recoveries and detection limits calculated for diclofenac sodium in a set of analyte-spiked river water samples using AFWRQQLD, five-PARAFAC, and AQQLD were 97.2 ± 3.2% and 1.9 ng mL-1 , 96.8 ± 3.0% and 4.0 ng mL-1 , and 92.6 ± 2.7% and 2.5 ng mL-1 , respectively. A study of other figures of merit, statistical analysis, an elliptical joint confidence region test, and a t-test were additionally carried out to validate the analytical performance of the proposed method in detail. The results demonstrated that this new method required only two steps (fluorescence measurement and algorithm analysis) to determine the analyte concentration. It could therefore provide the basis for developing novel reliable and sensitive approaches for the accurate detection of pharmaceutical pollutants with unstable fluorescence properties in real complex matrices such as environmental water samples. Graphical Abstract ᅟ.