Polarimetric Detection in Liquid Chromatography: An Approach to Correct Refractive Index Artefacts

Chiral and Achiral Enantiomeric Separation of (±)-Alprenolol

The chiral separation of enantiomers is crucial for pharmacovigilance within drug discovery. Although a large number of prescribed medications are marketed as pure enantiomers, this is not always the case and many are in fact racemic mixtures. Drug scandals, such as that of Thalidomide in 1961, provide a clear example of the social and economic repercussions that can be caused by negligence of these chiral compounds. Two high performance liquid chromatography (HPLC) methods are presented to determine, separate and quantitate a commonly prescribed chiral beta blocker, (-)-Alprenolol. The first method utilises a chiral column to physically separate the two enantiomers of Alprenolol in 25 minutes, before quantitating with two detectors. Fluorimetry gave the better limit of detection of 0.16-0.41ng and a correlation coefficient of 0.999. The second method used an achiral column coupled with polarimetry to quantitate (-)-Alprenolol without the need for physical separation in 10 minutes. The limit of detection achieved was 27-37μg and demonstrated a correlation coefficient of -0.999.

Self-referenced, microdegree, optical rotation polarimeter for biomedical applications: an analysis

We comprehensively analyze the performance of a type of optical rotation (OR) polarimeter, which has been designed from the outset to fit the special requirements of two major applications: general chiral detection during the separation of optical isomers by high-pressure liquid chromatography systems in the pharmaceutical industry, and monitoring of glucose in the interstitial fluid of diabetics by a fully implanted long-term optical sensor. Both very demanding applications call for an OR polarimeter that can be miniaturized while maintaining high resolution and accuracy in the microdegree range in the face of considerable noise from various sources. These two characteristics—miniature size and immunity to noise—set this polarimeter apart from the traditional OR polarimeters currently in use, which are both bulky and very susceptible to noise. The following detailed analysis demonstrates the advantages of this polarimeter and its potential as an analytic and diagnostic tool.

Compact, high-resolution, self-referenced, optical activity polarimeter for high-pressure liquid chromatography systems

Optical rotation (OR) polarimeters measure only the OR of a linearly polarized wave vector caused by the optical activity of the measured material. Such polarimeters are used to detect optically active materials and measure their concentration. Here we describe a novel type of high-resolution OR polarimeter. The new polarimeter is a compact device, based on a combination of two novel mechanisms: a referencing mechanism and an optical signal-gain mechanism. The patented referencing mechanism allows accurate measurements of small ORs in the presence of considerable polarization noise. The current limit of detection of the polarimeter is ∼20 micro-degrees, which we believe can be lowered further. The polarimeter is intended to serve as an add-on detector for existing high-pressure liquid chromatography (HPLC) systems in the pharmaceutical industry. The need for such a polarimeter, its optical setup, analysis of its performance, and experimental results are hereby given and discussed.

HPLC enantioseparation of alkaloid malacitanine using fluorimetric/polarimetric detection

This work reports two methods developed for the separation and determination of the enantiomers of the new alkaloid malacitanine (MLC) and the determination of the enantiomeric purity in mixtures. First, the isomers were separated using a Chirex 3020 (250 mm × 4.6 mm, 5 μm) chiral column with a mobile phase of cyclohexane-1,2-dichloroethane-ethanol-trifluoroacetic acid (64:30:6:0.6, v/v/v/v) at a flow rate of 1 mL/min and fluorimetric detection. Obtained retention times were 12.4 and 15.9 min (+ and -) with a resolution Rs of 1.13. Relative standard deviations (RSDs) were 2.5 and 2.4% at the 0.5-μg level (four determinations). Second, a nonenantioselective procedure for the determination of enantiomeric purity of MLC using a Lichrospher ® Si-60 (250 mm × 5 mm, 5 μm) normal phase with a mobile phase of 100% ethanol at a flow rate of 0.9 mL/min coupled to two detectors in series, fluorimetric and polarimetric. RSD of 3.3% was obtained. Calculated enantiomeric purity by chiral chromatography gave 48.6% (-)-MLC in the near racemic product. Using polarimetric signal of the nonseparated enantiomers and comparing the slopes of the calibration curves (enantiomers) from the racemic product gave 47.8% (-)-MLC content. A study of accuracy of (-)-MLC gave recoveries from 98.3 to 100.7%.