Polarimetric Detection Research Articles

First Results from the Submillimeter Polarimeter for Antarctic Remote Observations: Evidence of Large-Scale Toroidal Magnetic Fields in the Galactic Center

We have observed the linear polarization of 450 µm continuum emission from the Galactic center, using a new polarimetric detector system that is operated on a 2 m telescope at the South Pole. The resulting polarization map extends � 170 pc along the Galactic plane and � 30 pc in Galactic latitude, and thus covers a significant fraction of the central molecular zone. Our map shows that this region is permeated by large-scale toroidal magnetic fields. We consider our results together with radio observations that show evidence for poloidal fields in the Galactic center, and with Faraday rotation observations. We compare all of these observations with the predictions of a magnetodynamic model for the Galactic center that was proposed in order to explain the Galactic Center Radio Lobe as a magnetically driven gas outflow. We conclude that the observations are basically consistent with the model.

DETERMINATION OF CHIRAL DIAMINES BY LC-DAD AND LC WITH POLARIMETRIC DETECTION

ABSTRACT The chromatographic method for the separation of racemic aminoacetonitriles and diamines, the intermediates in the synthesis of N 1-alkyl-1-arylethylenediamines derivatives, possessing biological activity, was elaborated on. The results of pharmacological testing were acquired so far only for racemic mixtures, so that a method, which would allow the control of purity, is required. The DNBPG chiral stationary phase (R-3,5-Dinitrobenzoyl-phenylglycine) was used for the enantioseparation of derivatives of aminoacetonitriles and diamines. Using a polarimetric detector the optical rotation of the separated enantiomers was determined. he effect of various substituents on the retention and enantioselectivity was investigated. The potential possibility of using a DAD detector in characterisation of the separated enantiomers and checking their purity was also investigated.

Polarimetric adaptive detection in non-Gaussian noise

In this paper we address polarimetric adaptive detection of targets embedded in compound-Gaussian clutter with unknown covariance matrix. To this end we assume that a set of secondary data, free of signal components and with the same covariance structure of the cell under test, is available. We resort to a design procedure based upon the generalized likelihood ratio test (GLRT): first we derive the GLRT assuming that the textures are known, then we plug into the derived test suitable estimates of these parameters. Remarkably, the newly proposed detector has the constant false alarm rate (CFAR) property with respect to the texture statistical characterization. Moreover, even though it does not ensure the CFAR property with respect to the clutter covariance matrix, a sensitivity analysis shows that the probability of false alarm is only slightly affected by variations in the clutter correlation properties. Finally, the performance assessment, conducted via Monte Carlo simulations, confirms the capability of the receiver to operate in real radar scenarios.

Polarimetric adaptive detection of range-distributed targets

We address the problem of polarimetric adaptive detection of range-spread targets in Gaussian noise with unknown covariance matrix. At the design stage, we model the target echo from each polarimetric channel as a deterministic signal known up to a scaling factor (possibly varying from cell to cell), which accounts for the polarimetric scattering properties of the target. We first show the failure of the generalized likelihood ratio test (GLRT) procedure to deal with this kind of problem, and thus, we propose a fully adaptive detector based on the method of sieves. We also derive the analytical expression for the probability of false alarm and show that the newly introduced receiver can be made bounded constant false alarm rate (CFAR). Finally, we present simulation results highlighting the performance gain that can be achieved by resorting to polarization diversity in conjunction with high resolution.

Liquid chromatographic determination of alcohols in food and beverages with indirect polarimetric detection using a beta-cyclodextrin mobile phase.

An indirect polarimetric detection method for the determination of alcohols has been proposed in liquid chromatography (LC). Optically active mobile-phase additives, such as beta-cyclodextrin (beta-CD), could be used to visualize optically inactive alcohols in reversed-phase LC. The visualization of alcohols is based on a perturbation of the partition of beta-CD caused by the alcohols. The detection limits of the present system at a signal-to-noise ratio of 3 were 0.031, 0.019, 0.018, 0.013, 0.011, 0.008 and 0.008% (v/v) for ethanol, 2-propanol, 1-propanol, 2-methyl-2-propanol, 2-butanol, 2-methyl-1-propanol and 1-butanol, respectively. The method was successfully applied to the determination of ethanol present in food and beverage samples.

Asymmetric anionic polymerization of n -diphenyl-methylitaconimide with chiral ligand-organometal complex

Asymmetric anionic polymerizations of achiral N-diphenylmethylitaconimide (DPII) were performed with chiral ligand — organometal complexes in toluene. The obtained poly(DPII)s exhibited molecular weights of 1.5 × 103 to 6.3 × 103 and specific rotation between +7.5 to −18.4° (THF). The chirality of polymer was significantly affected by the organometals and chiral ligands. The poly(DPII) obtained with (4S)-2,2′-(1-ethylpropylidene)bis(4-benzyl-4,5-dihydrooxazole) (Bnbox) / n-butyllithium (n-BuLi) exhibited the highest specific rotation (−18.4°). The optical activities of the poly(DPII)s were attributed to configurational chirality of the main chain more than conformational chirality, judged from NMR, circular dichroism (CD) and GPC analyses using UV and polarimetric detectors.

Ground-based full-sky imaging polarimetry of rapidly changing skies and its use for polarimetric cloud detection.

For elimination of the shortcomings of imaging polarimeters that take the necessary three pictures sequentially through linear-polarization filters, a three-lens, three-camera, full-sky imaging polarimeter was designed that takes the required pictures simultaneously. With this polarimeter, celestial polarization patterns can be measured even if rapid temporal changes occur in the sky: under cloudy sky conditions, or immediately after sunrise or prior to sunset. One of the possible applications of our polarimeter is the ground-based detection of clouds. With use of the additional information of the degree and the angle of polarization patterns of cloudy skies measured in the red (650 nm), green (550 nm), and blue (450 nm) spectral ranges, improved algorithms of radiometric cloud detection can be offered. We present a combined radiometric and polarimetric algorithm that performs the detection of clouds more efficiently and reliably as compared with an exclusively radiometric cloud-detection algorithm. The advantages and the limits of three-lens, three-camera, full-sky imaging polarimeters as well as the possibilities of improving our polarimetric cloud detection method are discussed briefly.

Contribution of chiral HPLC in tandem with polarimetric detection in the determination of absolute configuration by chemical interconversion method: Example in 1-(thi)oxothiazolinyl-3-(thi)oxothiazolinyl toluene atropisomer series.

We report the determination of the absolute configuration of eight stereoisomers in the series of chiral 1-(thi)oxothiazolinyl-3-(thi)oxothiazolinyl toluene atropisomers 1-3, from the known absolute configuration of one stereoisomer, determined by X-ray crystallography. The method uses the affiliation between signs of rotation of polarised light during chemical transformations which preserve the absolute configuration and also during rotation around a single pivot bond producing a compound of known configuration. The use of chiral HPLC in tandem with a chirality detector gives a decisive advantage since such correlation can be performed on a mixture of a very limited quantity of compounds, without tedious purification steps. The method shown as an example in this article, which uses chiral HPLC with chirality detection, may prove useful in many other cases where the determination of the absolute configuration is necessary and where a chemical interconversion method can be used on a microscale.

Quantitative analysis of incomplete HPLC resolution of enantiomers. Fit of polarimetric detection for D- and L-phenylalanine to a gaussian function.

This report compares laser-based polarimetric and UV data for quantitating incompletely resolved enantiomers by HPLC. Using L- and D-phenylalanine as a working model, response data is shown across the entire detection region while emphasizing the regions at or near 100% L, 100% D and 50:50 L:D at resolutions between 0.4 and 1.4. In general, the poorer the resolution, the greater the improvement in detectability with the polarimeter when compared to UV detection. This is due to the inherent bipolar nature of the polarimetric signal, which creates a well-defined crossing point for integration of an enantiomeric pair. In our previous work, we described the improvement in measurement precision when applying a bipolar gaussian peak model to the raw chromatographic peak data. This study will measure the model's effect on improving accuracy. This study should be applicable to other chiroptical detection strategies that produce a bipolar signal for enantiomers, such as circular dichroism and circularly polarized luminescence.

Real-time assessment of enantiomeric purity via a polarimetric/absorption detector response function.

The development of methodology appropriate for the rapid and precise assessment of enantiomeric purity is a critical need in the life sciences with impact in a number of areas including biomedical research, biotechnology, and pharmaceutical science. Real-time assessment of enantiomeric purity is critical to decisions related to possible product purity and/or the need for, and the type of additional processing. Recently, we have shown that laser-based polarimetric detection, in combination with ultraviolet detection, can be used to assess enantiomeric purity in real-time as an adjunct to the separation process. A mass-independent response function is obtained from the ratio of the normalized polarimetric signal relative to the normalized UV signal. This response ratio will be shown to be equivalent to the enantiomeric excess and independent of concentration and chromatographic resolution. The methodology will be evaluated as a function of injected mass, enantiomeric excess, chromatographic resolution, and peak asymmetry.

A polarimetric adaptive matched filter

In this paper, we address polarimetric adaptive detection of targets embedded in Gaussian noise with unknown covariance matrix. To this end we assume that a set of secondary data, free of signal components and with the same covariance matrix of the cell under test, is available. We resort to a two-step design procedure based upon the generalized likelihood ratio test (GLRT). It is shown that the newly proposed detector has the constant false alarm rate property with respect to the covariance matrix of the noise. More remarkably, it has the same performance, but a lower complexity, than the corresponding plain GLRT.

Polarization patterns of the summer sky and its neutral points measured by full–sky imaging polarimetry in Finnish Lapland north of the Arctic Circle

Using 180° field–of–view (full–sky) imaging polarimetry, the patterns of the degree and angle of polarization of the entire summer sky were measured on 25 June 1999 at a location north of the Arctic Circle in Finnish Lapland as a function of the angular solar zenith distance. A detailed description of the used full–sky imaging polarimeter and its calibration is given. A series of the degree and angle of polarization pattern of the full sky is presented in the form of high–resolution circular maps measured in the blue (450 nm) spectral range as a function of the solar zenith distance. Graphs of the spectral dependence of the degree and angle of polarization of skylight at 90° from the Sun along the antisolar meridian are shown. The celestial regions of negative polarization and the consequence of the existence of this anomalous polarization, the neutral points, are visualized. The measured values of the angular zenith distance of the Arago and Babinet neutral points are presented as a function of the zenith distance of the Sun for the red (650 nm), green (550 nm) and blue (450 nm) ranges of the spectrum. The major aim of this work is to give a clear and comprehensive picture, with the help of full–sky imaging polarimetry, of what is going on in the entire polarized skydome. We demonstrate how variable the degree of polarization of skylight and the position of the neutral points can be within 24 h on a sunny, almost cloudless, visually clear day.

Recent advances in chiral detection for high performance liquid chromatography

The unique response characteristics of optical activity detectors make them an important adjunct to high performance liquid chromatography (HPLC) for the analysis of biologically active molecules. The recent commercial introduction of turn-key, circular dichroism (CD) and polarimetric detection systems compatible with the sensitivity and volume requirements of HPLC will allow these detection approaches to be applied to measurement problems in a number of areas including biomedical research and diagnosis, biotechnology, as well as pharmaceutical science. The CD and polarimetric detectors respond directly to the intrinsic optical activity of the analyte, and both the magnitude and sign of the response can be used for quantitative and qualitative determinations. The information available from these detectors is difficult or impossible to obtain by other methods. In this article, the instrumental basis for both the CD and laser-based polarimetric detectors will be reviewed. Several applications will be described in which the unique response characteristics of these detection systems, either alone or in tandem with other detectors, can be used to identify chiral materials, and determine enantiomeric excess. It will be shown that this methodology is effective either without enantiomeric separation, or under conditions of low enantio-selective resolution. With this technology, a real-time assessment of enantiomeric excess can be obtained as a means to optimize and guide enantio-selective separation processes.

Adaptive polarimetric target detection with coherent radar. II. Detection against non-Gaussian background

The derivation of a completely adaptive polarimetric coherent scheme to detect a radar target against a Gaussian background is presented. A previously proposed Generalized Likelihood Ratio Test (GLRT) polarimetric detector is extended to the case of a general number of channels; this exploits the polarimetric characteristics of the received radar echoes to improve the detection performance. Together with the fully adaptive scheme, a model-based detector is derived that has a lower estimation loss. A complete theoretical expression is derived for the detection performance of both proposed polarimetric detectors. They are shown to have Constant False Alarm Rate (CFAR) when operating against Gaussian clutter, but to be sensitive to deviations from the Gaussian statistic. The application to recorded radar data demonstrates the performance improvement achievable in practice.

Adaptive polarimetric target detection with coherent radar. I. Detection against Gaussian background

Adaptive polarimetric target detection with coherent radar. I. Detection against Gaussian background

D-β-Hydroxybutyrate Reaction Kinetics Studied in Nanoliter Volumes Using a Capillary Polarimeter

A laser-based capillary polarimetric detector (CPD) has been configured to allow for the analysis of optically active molecules at physiological temperatures and within a 40 nL sample volume. In the CPD, interference fringes contained within a 360° fan of scattered light result from the interaction between a polarized laser beam and a 240 μm i.d. capillary tube. Here it is shown that these fringes change in a reproducible manner with solute optical activity, facilitating a 3σ detection limit of 1.7 × 10−3 M d-β-hydroxybutyrate corresponding to 68 × 10−12 mole (7 × 10−9 gram) of solute. Further, with the use of this improved and novel polarimeter, the noninvasive study of enzyme reaction kinetics for d-β-hydroxybutyrate (50 mg/dL) and hydroxybutyrate dehydrogenase (100 μL of 50 units/L) has been evaluated for the first time in the absence of NAD. The rate constant for this reaction was found to follow first-order kinetics and determined to be 2.2 × 10−2 s−1. The prospect of directly studying the influence of enzyme cofactors on reaction kinetics is at hand, and the observations presented suggest that the application of monitoring insulin therapy for patients experiencing ketoacidosis is a tractable problem for the CPD.

Asymmetric Anionic Oligomerization of N-Substituted Citraconimide with the Chiral Ligand-Organometal Complex

Asymmetric anionic homopolymerizations of achiral N-substituted citraconimide (RCI, N-substituent: R=n-propyl(n-PrCI), n-butyl(n-BuCI), cyclohexyl(CHCI), phenyl(PhCI), benzyl(BzCI), 1-naphthyl (NCI), 4-(ethoxycarbonyl)phenyl(ECPCI), and α-methylbenzyl (MBzCI)) were performed with the chiral ligand-organometal complex in toluene or tetrahydrofuran(THF). The obtained oligo(RCI)s had very low molecular weights and relatively narrow polydispersity. The oligomers showed specific rotation ([α]43525+79.2° to −40.3°). Asymmetric induction took place on the polymer main chain and was confirmed by circular dichroism(CD) and GPC analysis using UV and polarimetric detectors.

Asymmetric Anionic Polymerization of Chiral (R)-(+)-N-α-Methylbenzylmaleimide with Chiral Ligand/Organometal Complex

Asymmetric anionic polymerizations of chiral (R)-(+)-N-α-methylbenzylmaleimide (MBZMI) were performed with (-)-sparteine (Sp) or (S, S)-(1-ethylpropylidene)bis(4-benzyl-2-oxazoline) (Bnbox)/organometal complexes in toluene or tetrahydrofuran (THF). All polymers obtained were optically active. Specific optical rotations ([α]43525) of the polymers initiated by Et2Zn/Sp and Et2Zn/Bnbox were −113.5° to −195.7° and +56.0° to +170.2°, respectively. Number-average molecular weights (M̅n) of the polymers were from 7.2×103 to 2.9×104. Chirality of the polymers was attributed not only to chirality of optically active MBZMI units but also to stereogenic centers (S, S) and (R, R), in the main chain induced by the polymerization, judging from the results of circular dichroism (CD), 1H and 13C NMR spectra, and GPC curves obtained with polarimetric and UV detectors. Anionic polymerizability of MBZMI using organometal with and without chiral ligand. and chiroptical properties of the polymers are discussed.

APPLICATIONS OF A SENSITIVE LASER POLARIMETRIC HPLC DETECTOR: CONFIRMATION OF ENANTIOMERIC EXCESS FOR DANOFLOXACIN AND ANALYSIS OF A NOVEL MACROLIDE

A commercially available laser-based polarimetric detector (Chiral Detector) was used to confirm the enantiomeric excess of danofloxacin and to analyze a novel macrolide. The detector is based on the work of Yeung et al.[1] and uses a low noise laser diode which emits 675 nm radiation. Selectivity is obtained not through chromatographic resolution but through the sign and magnitude of detector response. An area ratio of the detector signals (Chiral/UV) was used to calculate Danofloxacin's optical purity. By calculating the ratio of the two detector signals an accurate measure of optical purity or enantiomeric excess can be calculated relative to standard responses without concern for potency, optical rotation of impurities, exact sample concentration or injection precision. The molecule is ideal for this type of determination since it absorbs UV radiation strongly, has a large optical rotation and the HPLC method resolves potential process impurities, synthetic byproducts and degradation products. The signal ratio was found to be linear with respect to % optical purity from 100% to 0% and is expected to be accurate to within 2%. Samples of danofloxacin mesylate were optically pure to within the 2% limit of the methodology. A novel experimental macrolide was analyzed using a reversed phase HPLC system interfaced to both a UV detector and a laser-based polarimetric detector. Specific rotation of the novel macrolide was determined to be −23° in mobile phase using a bench top polarimeter. While polarimetric response for the experimental macrolide was shown to be reasonably linear from 0.1mg/mL to 1.5mg/mL, sensitivity was poor relative to UV detection at 210nm. The limit of quantitation was ∼5000 ng for the laser-based polarimetric detector which was 50 times less sensitive than the UV detector.

Polarimetric detection of the photon excitation of surface plasmons

A polarimetric method for the detection of surface plasmons, excited by linearly polarised light, was proposed and tested. It was established that this method is not only more sensitive to variations in the parameters of the waveguiding structure but also makes it possible to increase by one — two orders of magnitude the precision of determination of the excitation efficiency and of the phase velocity of the plasmons, compared with the amplitude method for plasmon detection. The possibility of applying the method in sensor devices, in polarimetry, and in the microscopy of conducting surfaces is discussed.