Application of fluorescence spectroscopy combined with interval partial least squares to the determination of enantiomeric composition of tryptophan

• It is shown spectral region selection is important in the fluorescence spectroscopy analysis.
• Interval partial least squares was applied to fluorescence spectroscopy analysis.
• iPLS was used to select spectral region and build the calibration model.
• Using iPLS instead of PLS can build more accurate calibration model.
• The enantiomeric composition of Trp was determined at the total concentration of 2.50 μmol·L− 1.

The application of interval partial least squares (iPLS) method to the fluorescence spectroscopy analysis was investigated. The practicability of spectral region selection in the fluorescence spectroscopy analysis was studied. A method which combines fluorescence spectroscopy and iPLS was proposed for determining the enantiomeric composition of tryptophan (Trp). Fluorescence spectroscopy was used to measure the diastereomeric interaction between the enantiomers of Trp and bovine serum albumin, which plays the role of chiral selector. iPLS was used to select the spectral region and build the calibration model between the fluorescence spectral data and enantiomeric composition of Trp. The spectral region from 300 nm to 356 nm was selected and used to build the calibration model. Leave-one-out cross validation and external test validation were used to validate the obtained models. By selecting the spectral region, iPLS provided better prediction performance, in comparison to the full-spectrum PLS model. The root mean square relative error (RMSRE) of leave-one-out validation has decreased from 10.24 to 7.17, and the RMSRE of external test validation has decreased from 8.59 to 7.06. In addition, four local-spectrum PLS models were developed in order to make a comparison to the iPLS model. The result demonstrates the iPLS model is superior to the four local-spectrum PLS models. The result of this work demonstrates the proposed method is practicable for determining the enantiomeric composition of Trp at trace level. When there is 2.50 μmol·L− 1 Trp in the samples, the enantiomeric composition can be accurately determined. Moreover, the result demonstrates the selection of spectral region has significant influence on the fluorescence spectroscopy analysis and iPLS is a practicable method for spectral region selection.