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Lateral Diffusion of 1,1'-dioctadecyl-3,3,3'3'-tetramethylindocarbocyanine Perchlorate at the Interfaces of C18 and Chromatographic Solvents

Lateral Diffusion of 1,1'-dioctadecyl-3,3,3'3'-tetramethylindocarbocyanine Perchlorate at the Interfaces of C18 and Chromatographic Solvents

DJ Swinton, MJ Wirth

Anal Chem. 2000 Aug 15;72(16):3725-30.

PMID: 10959955

Abstract:

The influence of mobile phase on the lateral diffusion of an amphiphilic dye was studied for four chromatographic interfaces using fluorescence correlation spectroscopy. The fluorescent dye was DiI (1,1'-dioctadecyl-3,3,3'3'-tetramethylindocarbocyanine perchlorate); the stationary phase was a covalently bonded monolayer of dimethyloctadecylsiloxane on fused silica; and the four mobile phases were acetonitrile, methanol, tetrahydrofuran, and water. Time-resolved measurements at varying focal positions of the microscope confirmed negligible fluorescence from solution. Single-molecule spectroscopy showed that exchange between mobile and immobile adsorbates was negligible. The lateral diffusion of DiI was the fastest for tetrahydrofuran, D = 5.3 x 10(-5) cm2/s, and slowest for water, D = 2.5 x 10(-6) cm2/s. Methanol and acetonitrile gave intermediate rates of diffusion, D = 3.4 x 10(-6) and 4.8 x 10(-6), respectively. There was no correlation of the lateral diffusion coefficient with solvent viscosity, a weak correlation with interfacial tension, and a strong correlation with 13C NMR line shapes for the terminal methyl group of the hydrocarbon chain. The increased wetting of the C18 interphase in the order water < methanol < acetonitrile < tetrahydrofuran agreed with data for the miscibility of these solvents with n-hexadecane. It is concluded that the wetting of the hydrocarbon interphase by the mobile phase enhances the lateral diffusion of the amphiphile.

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
AP41085998	1,1′-Dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate		41085-99-8	Price

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