A Critical Study on the Potential of Solid-Phase Fluorescence Spectroscopy (SPFS) in Quantitative Analysis: Effect of Solid Diluent and Sampling Method on Signal Quality.

Abstract

Solid-phase fluorescence spectroscopy (SPFS) is a very useful non-destructive technique for directly analyzing samples in solid form without the use of solvents. However, due to the so-called inner-filter effect, it is sometimes necessary to dilute solid samples using non-fluorescent solids as diluents. This study aimed to explore the potential of SPFS in the quantitative analysis of fluorescent species based on: (1) the type of solid diluent; and (2) the sampling method used in the SPFS analysis. Four different solids were used as solid diluents in the preparation of standard mixtures having different concentrations of rhodamine b and fluorescein as model compounds. Standard mixtures of model compounds were sampled by two different methods called: (1) the powder-cell method; and (2) the adhesive tape method. LOQ and calibration sensitivity calculated from the calibration graphs were used to assess the measurement performance. The usability of SPFS in real-sample analyses was also evaluated in detail. Among the solid diluents studied, the best results were obtained with sodium carbonate. The powder-cell method yielded a significant advantage over the adhesive tape method. The lowest LOQs for rhodamine b and fluorescein were obtained by sodium carbonate and the powder-cell method as 0.06 and 0.11 mg/kg, respectively. The results of real-sample analyses were verified using conventional liquid-phase fluorescence spectroscopy (LPFS). Solid-diluent type and sampling method were found to affect the performance of the SPFS technique. A combination of sodium carbonate and the powder-cell method gave the best results. According to the t-test, no difference was observed between the means obtained by SPFS and LPFS techniques in real-sample analyses. In SPFS, toxic organic solvents and difficult sample preparation steps are not required. This makes the method advantageous over conventional fluorescence analyses performed in the liquid phase.