Microchip isotachophoresis coupled to surface-enhanced Raman spectroscopy for pharmaceutical analysis.

A novel online coupling of microchip isotachophoresis (μITP) with surface-enhanced Raman spectroscopy (SERS) for the analysis of complex samples is presented. Polymeric microchip with coupled channels was used for μITP-SERS analysis of four structurally similar Raman active synthetic dyes (brilliant black BN, carmoisine, ponceau 4R, and sunset yellow FCF) in pharmaceuticals. The μITP separation and simultaneous pre-concentration of the analytes were performed in the first channel of the microchip at pH 6.0 with the aid of non-Raman active discrete spacers (acetate, butyrate, glutarate, pantothenate, and valerate). Silver nanoparticles used for Raman enhancement were present in the second channel, and individual SERS spectra of the dyes were acquired by a mini Raman spectrometer operating at 532 nm. The analytical enhancement factors for silver nanoparticles were 1-5 × 10. The microchip with coupled channels enabled independent μITP separation and SERS detection, and eliminated any adverse impact of nanoparticles on the separation. The developed approach allowed reliable online SERS identification and detection of dyes with limits of detection ranging from 12 to 62 nM. Synthetic dyes were successfully separated, identified, and quantified in pharmaceutical preparations within 7 min without the need for complex or time-consuming sample pretreatment. The results were in good agreement with those obtained by an independent analytical method reported for studied dyes. Graphical abstract.