LAUSR

BACKGROUND 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. OBJECTIVE This study aimed to explore the potential of SPFS in the quantitative analysis of fluorescent species based on (i) the type of solid-diluent and (ii) the sampling method used in the SPFS analysis. METHOD 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 (i) powder-cell method and (ii) adhesive-tape method. Limit of quantitation, 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. RESULTS 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 quantitation limits for rhodamine b and fluorescein were obtained by sodium carbonate and powder-cell method as 0.06 mg/kg and 0.11 mg/kg, respectively. The results of real sample analyses were verified using the conventional liquid-phase fluorescence spectroscopy (LPFS). CONCLUSIONS 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. HIGHLIGHTS 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.