Accuracy of Polarimeter
P H A R M AC E U T I C A L application note
Checking the accuracy of
PERKIN-ELMER POLARIMETERS
H. Stenz, Bodenseewerk Perkin-Elmer GmbH
Abstract
Quartz standards, sucrose solutions and optically active pure liquids are discussed as potential polarimetry standards. It is suggested to preferably use quartz standards for checking the accuracy of Perkin-Elmer polarimeters. Quartz standards are absolutely stable, have a high accuracy and are easy to use.
For laboratories working in an environment which is governed by GLP or GMP principles, it is compulsory to regularly check the accuracy of the analytical instruments used. The methods to be employed for these checks inevitably depend on the type of instrument concerned. This paper reviews the methods and standards which are commonly used (or have been considered in the literature) to check the accuracy of Perkin-Elmer precision polarimeters (Model 341 and Model 241 families of instruments). Before entering into this discussion, it is helpful to briefly describe the operating principle underlying Perkin-Elmer polarimeters. PerkinElmer polarimeters employ an optical null principle with automatic analyzer adjustment. An optically active sample generates an electrical signal which in turn drives a motor linked to the analyzer of the instrument via a precision gear train. This signal rotates the analyzer by exactly the angle by which the sample has rotated the plane of polarization of the optical beam. During analyzer adjustment, an optical encoder connected to the analyzer drive system directly monitors the size of the angle by which the analyzer is being rotated. Thus, similar to the divided circle provided on classical visual polarimeters, the angle of
rotation is directly obtained by the primary measurement. That is, the primary measurement does not involve any auxiliary parameters (such as electrical voltages or currents) which would need to be calibrated into angles of rotation, as is the case with other
Checking the accuracy of
PERKIN-ELMER POLARIMETERS
H. Stenz, Bodenseewerk Perkin-Elmer GmbH
Abstract
Quartz standards, sucrose solutions and optically active pure liquids are discussed as potential polarimetry standards. It is suggested to preferably use quartz standards for checking the accuracy of Perkin-Elmer polarimeters. Quartz standards are absolutely stable, have a high accuracy and are easy to use.
For laboratories working in an environment which is governed by GLP or GMP principles, it is compulsory to regularly check the accuracy of the analytical instruments used. The methods to be employed for these checks inevitably depend on the type of instrument concerned. This paper reviews the methods and standards which are commonly used (or have been considered in the literature) to check the accuracy of Perkin-Elmer precision polarimeters (Model 341 and Model 241 families of instruments). Before entering into this discussion, it is helpful to briefly describe the operating principle underlying Perkin-Elmer polarimeters. PerkinElmer polarimeters employ an optical null principle with automatic analyzer adjustment. An optically active sample generates an electrical signal which in turn drives a motor linked to the analyzer of the instrument via a precision gear train. This signal rotates the analyzer by exactly the angle by which the sample has rotated the plane of polarization of the optical beam. During analyzer adjustment, an optical encoder connected to the analyzer drive system directly monitors the size of the angle by which the analyzer is being rotated. Thus, similar to the divided circle provided on classical visual polarimeters, the angle of
rotation is directly obtained by the primary measurement. That is, the primary measurement does not involve any auxiliary parameters (such as electrical voltages or currents) which would need to be calibrated into angles of rotation, as is the case with other