Thin Layer Chromatography Coupled with Surface-Enhanced Raman Scattering as a Facile Method for On-Site Quantitative Monitoring of Chemical Reactions

Abstract

By coupling surface-enhanced Raman spectroscopy (SERS) with thin layer chromatography (TLC), a facile and powerful method was developed for on-site monitoring the process of chemical reactions. Samples were preseparated on a TLC plate following a common TLC procedure, and then determined by SERS after fabricating a large-area, uniform SERS substrate on the TLC plate by spraying gold nanoparticles (AuNPs). Reproducible and strong SERS signals were obtained with substrates prepared by spraying 42-nm AuNPs at a density of 5.54 × 10 10 N/cm 2 on the TLC plate. The capacity of this TLC-SERS method was evaluated by monitoring a typical Suzuki coupling reaction of phenylboronic acid and 2-bromopyridine as a model. Results showed that this proposed method is able to identify reaction product that is invisible to the naked eye, and distinguish the reactant 2-bromopyridine and product 2-phenylpyridine, which showed almost the same retention factors (R f ). Under the optimized conditions, the peak area of the characteristic Raman band (755 cm −1 ) of the product 2-phenylpyridine showed a good linear correlation with concentration in the range of 2−200 mg/L (R 2 = 0.9741), the estimated detection limit (1 mg/L 2-phenylpyridine) is much lower than the concentration of the chemicals in the common organic synthesis reaction system, and the product yield determined by the proposed TLC-SERS method agreed very well with that by UPLC-MS/MS. In addition, a new byproduct in the reaction system was found and identified through continuous Raman detection from the point of sample to the solvent front. This facile TLC-SERS method is quick, easy to handle, low-cost, sensitive, and can be exploited in on-site monitoring the processes of chemical reactions, as well as environmental and biological processes.

Biogenic aldehyde determination by reactive paper spray ionization mass spectrometry

“…Trace organic analysis [1][2][3] is commonly performed by combining a chromatographic method [4] with mass spectrometry (MS) [5]. Ambient ionization [6][7][8][9][10][11][12][13][14] is a relatively recent approach to MS analysis which avoids chromatography and is characterized by the absence of any requirement for sample preparation.…”

Rapid on-site detection of ephedrine and its analogues used as adulterants in slimming dietary supplements by TLC-SERS

“…The combination of TLC and SERS would be propitious for on-site detection due to its simplicity, rapidity, and sensitivity. For example, it has been used for detection of tobacco-related biomarkers in urine samples [22], identification of alkaloids from the seed extract of Syian rue (Peganum harmala) [23], distinguishing from structural analogues [24], and monitoring of chemical reactions [25].…”

Review of SERS Substrates for Chemical Sensing

“…However the SERS spectra are distictly different. SERS has also been coupled with thin layer chromatography (TLC) [46,136,137,138]. Two approaches have been taken.…”

“…One approach does the chromatographic separation on a TLC plate first [136,137]. After development and drying of the plate, either the Ag/Au NPs are applied directly on the spots [13] or the entire plate is sprayed with Ag/Au NPs [137]. The other approach used inkjet-printed paper SERS substrates [138].…”