Capillary-scale polarimetry for flowing streams

Abstract

A micro-polarimeter with a 40 nL probe volume was configured so that it is compatible with capillary-scale flowing stream analysis. The optical configuration consists of two polarizing optics, a capillary, a laser source and a photodetector which is very simple to configure with low cost components. This unique polarimeter is based upon the interaction of a linearly polarized laser beam and a capillary tube, in this case one with an inner diameter of 250 microns. Side illumination of the tube results in a 360 degrees fan of scattered light, which contains a set of interference fringes that change in response to optically active solutes. Solutes that exhibit optical activity are quantifiable and are detected by analyzing the polarization state of the backscattered light. The ability of the instrument to make extremely sensitive optical activity measurements in flowing streams is shown by the determination of (R)-mandelic acid, with a detection limit of 66 x 10(-6) M (507 x 10(-12) g), and the non-optically active control, glycerol. Additionally, the detector was configured to minimize refractive index perturbations.

Microscale methodology for structure elucidation of natural products

“…[xli] Detection of optical rotation, α, by laser optical methods and flow techniques is adaptable to HPLC for on- the-fly characterization of chiral molecules. [xlii],[xliii]. Circular dichroism (CD) is observed when circularly polarized light (CPL) passes through a solution of a chiral, optically active compound whose molecular structure contains a chromophore.…”

A Fourier analysis approach for capillary polarimetry

“…2), or by introducing an optically active solute into the capillary. In this way, CPD can be used to quantify optically active solutes [2][3][4][5] or to determine optical rotary power of an unknown solute [5,6]. It is noteworthy that it has been previously shown that the polarimetry signal is contained within the high-frequency component of the CPD fringe pattern and the spatial frequency of this pattern does not change with concentration of nonoptically active solutes [2,5,6] (e.g., it is relatively insensitive to refractive index changes).…”

“…3B) of the fringe was obtained by using Matrox Inspector image processing software. Then two pixels from the line profile, each corresponding to the maximum and minimum intensity values of an adjacent peak and trough, were used to calculate depth of modulation (DOM) [2,3,5,6] (Fig. 3B):…”

“…Although DOM calculations facilitated nanoliter polarimetry at picogram sensitivity [2,3,5,6], this method has several drawbacks. First, DOM calculations are off-line measurements and very time-consuming since the fringe has to be manually obtained using the LBA and transferred to the computer.…”

“…It has been often used in pharmaceutical industry for purity control of certain biological substances, in chemical industry for polymer identification and characterization and can also be employed in the research environment for kinetic investigations, enzymatic cleavage studies, and identification of unknowns [1]. 1 It has been recently shown that polarimetry can be performed at high sensitivities and in nanoliter detection volumes [2][3][4][5]. This capillary polarimeteric detector (CPD) is based on the micro-interferometric backscatter configuration shown in Fig.…”