Polarimeter detector

LC provides good reproducibility and high-quality results the cost is reasonable for routine applications and it is fairly easy to operate the equipment. UV-visible detectors are most commonly used for routine impurity determinations by LC. Other detectors that are useful for the identification of impurities or for specialized purposes are refractive index, fluorescence, electrothermal detectors, polarimeters, Fourier transform infrared spectrometers, and mass spectrometers. 

Figure 2.10 Chromatograms of ( + )-trans-stilbene oxide. Conditions column, Chiralpak OP( + ), 25 cm x 4.6 mm i.d. eluent, methanol column temperature, ambient flow rate, 1 ml min -detector A, polarimeter B, refractive index.

The strategy in the design of any optical polarimeter is the use of the appropriate optical elements comprising the PSG and PSA to retrieve the desired information from the sample. Symbolically, this can be understood by considering the following expression for the intensity measured at the detector,... 

Figure 8.10 Polarimeter design for the measurement of circular dichroism. The intensity measured at the detector is...

Meinard, C. Bruneau, P. Perronett, J. High-Performance hquid chromatograph coupled with two detectors a UV spectrometer and a polarimeter. J. Chromatogr. 1985, 349, 109-116. 

As an example, Fig. 6.20 gives the experimental breakthrough curve for a racemic mixture of EMD53986 using Chiralpack AD (dp = 20 gm, Daicel) as adsorbent and ethanol as eluent. Here a two-detector set-up of polarimeter and UV-detector was used, permitting the solute-specific detection of both components (Mannschreck, 1992, Jupke, 2004 and Epping, 2005). 

Breakthrough curves (lines in Fig. 6.20) are calculated from the detector signals (symbols). The rotation angle detected by the polarimeter is zero if both enantiomers are present (t > 800 s) while the UV signal is additive and has the highest value there. 

A racemic Troger s base mixture was separated on an ICLC 16-10 plant (Pro-chrom) (Mihlbachler et al., 2001 and 2002 and Jupke, 2004). The measurement system consisted of polarimeter and UV detectors that had to be implemented in different parts of the product streams because the equipment does not have a recycle stream. All columns showed good homogeneity. Model validation was performed... 

Figure 17.18 Internal Concentration Profiles of the Troger s base enantiomers measured with (a) a polarimeter and (b) a UV detector. Concentrations of each enantiomer. Solid line experimental data at port 6. Dotted line experimental data at port 5, ) Calculated profiles using the 3-layer isotherm model. K. Mihlbachler, A. Seidel-Morgenstem, G. Guiochon, AIChE J., 50 (2004) 611 (Figs. 8 and 9). Reproduced by permission of the American Institute of Chemical Engineers. 1997 AIChE. All rights reserved.

A polarimeter may be used as a detector if the conditions allow (high concentration... 

Practical schemes for constructing polarimeters up to 1970 can be found in [11]. All detectors of optical radiation react to a change of intensity of luminous flux, but do not react to a state of its polarization. Therefore all methods for determining polarization are grounded in the transformation of the Stokes vector a scalar value. A polarization modulator installed prior to the detector is used for this purpose. The simplest modulator is used for the analysis of linearly polarized radiation. It may be a Polaroid, prism, grating... 

A Nicolet Magna 550 Fourier Transform Infrared Spectrometer (FTIR) and a Bruker MW 250 MHz proton NMR were used to verify the chemical structure of all monomers and polymers. Optical activity of the compounds was measured at 25 on a Perkin-Elmer Polarimeter in chloroform. A Waters Gel Permeation Chromatograph with 440 UV absorption detector and R401 differential refructometer was used to determine the molecular weights of the polymers tetrahydrofuran was used as the mobile phase at 1.0 mL/min, and the Waters polystyrene gel columns were calibrated with monodisperse polystyrene standards. Polarizing optical microscopy was used to identify liquid crystalline phases using a Leitz optical microscope with a CCD camera attachment... 

Rhodium microanalyses were performed by Service Central de Microanalyses du CNRS. Optical rotations were measured on a Perkin-Elmer 141 automatic polarimeter. NMR spectra were performed using a Perkin-Elmer R 32 90 MHz spectrometer and GLC analyses with a Carlo-Erba Fractovap GI chromatograph equipped with a flame ionization detector. 

It turned out that the localization of the concentration fronts based on measured chromatograms is difficult even when two independent sensors are available per outlet stream and in the recycle (UV detectors and polarimeters) due to backmixing effects, and that stabilizing the front positions does not suffice to guarantee the product purities due to plant-model mismatch such that an additional control layer for purity control is needed (Hanisch, 2002). In the case of nonlinear isotherms, dynamic neural network models were used in a nonlinear MPG scheme (Wang et al, 2003). 

---