In Situ Arsenic Speciation using Surface-enhanced Raman Spectroscopy and the Coffee Ring Effect

Authors

Valery LiamtsauFollow

Document Type

Dissertation

Degree

Doctor of Philosophy (PhD)

Major/Program

Chemistry

First Advisor's Name

Yong Cai

First Advisor's Committee Title

committee chair

Second Advisor's Name

Barry P. Rosen

Second Advisor's Committee Title

committee member

Third Advisor's Name

Yaroslava Miksovska

Third Advisor's Committee Title

committee member

Fourth Advisor's Name

Anthony McGoron

Fourth Advisor's Committee Title

committee member

Fifth Advisor's Name

Bruce McCord

Fifth Advisor's Committee Title

committee member

Keywords

Raman spectroscopy, : Coffee ring effect, Arsenic speciation

Date of Defense

6-8-2021

Abstract

The coffee ring effect (CRE) phenomenon is originated from the nonuniform solvent evaporation of a sessile droplet deposited onto the flat substrate. Once the evaporation starts, the droplet suspended particles move outwards by the radial flow and concentrate in the edge region of the evaporating droplet, resulting in the formation of the so-called CRE stains. In this work we have expanded the applications of the CRE from separation of particles and macromolecules to small molecules, in particular, coupled to surface-enhanced Raman spectroscopy (SERS). Herein, we have developed a theoretical framework to describe the CRE-driven separation process of small molecules, using SERS analysis of dimethylarsinic acid (DMA^V), dimethylmonothioarsinic acid (DMMTA^V), and dimethyldithioarsinic acid (DMDTA^V) on gold nanofilm (AuNF) as an example. By combining the CRE theory for the radial flow and the Extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory for mass transfer between solution and AuNF surface, we adapted the conventional chromatographic theory to derive a modified van Deemter equation for the CRE-driven separation. By using this model, we predicted the travel distances of arsenicals based on the different affinity of analytes to AuNF and evaluated the possibility of separation of unknown analytes by CRE-based SERS, demonstrating the successful adaptation of classic chromatographic theory to CRE-driven nanochromatography.

Furthermore, we have extrapolated the application of the developed method for the speciation of the peptide-like arsenic-based anticancer drug Darinaparsin (DAR) and its major breakdown product dimethylarsino-cysteine (DMAC). Despite the overlap of DAR and DMAC’s Raman spectra in the final CRE deposit, we were able to identify each compound due to their unique SERS fingerprint. Overall, the developed method was able not only to separate and identify the S-conjugated arsenicals, but at the same time to preserve the DAR and DMAC’s As^III oxidations state and the fragile As – S moiety, thus providing an alternative speciation method for unstable thioarsenicals. The key advantage of the application of this method for peptides separation is the separation coupled with the mild detection providing the rich structural information of each metabolite.

Identifier

FIDC010228

Previously Published In

Anal. Chem. 2019, 91, 13, 8280–8288

Analytica Chimica Acta, Volume 1106, 15 April 2020, Pages 88-95

Recommended Citation

Liamtsau, Valery, "In Situ Arsenic Speciation using Surface-enhanced Raman Spectroscopy and the Coffee Ring Effect" (2021). FIU Electronic Theses and Dissertations. 4711.
https://digitalcommons.fiu.edu/etd/4711