P001 - Polarimetry and Polarimeters - a simple explanation
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Bellingham + Stanley Longfield Road, Tunbridge Wells, Kent, TN2 3EY, UK Tel +44 (0) 1892 500400 Fax +44 (0) 1892 543115 TECHNICAL BULLETIN - P001 Title: Polarimetry & Polarimeters – a simple explanation Polarimeters are optical instruments for measuring the rotation or ‘twisting’ of light. Industrial and academic laboratories use polarimeters for a variety of purposes ranging from simple quality control to fundamental research into complex chemical structures. Bellingham + Stanley has been designing and manufacturing high quality polarimeters for 100 years. Principle of polarimetry Polarised light is light that has passed through a ‘polariser’, which forces the randomised electromagnetic waveforms into one plane. When this plane-polarised light then passes through an optically active substance (e.g. solution of an optically active chemical) the PLANE of polarisation is rotated by an amount which is characteristic of the test substance. Polarimeters detect the position of the PLANE and compare it to its original position, the difference being the rotation, normally expressed in angular degrees (°A). Every effort has been made to ensure the accuracy of the contents of this Bulletin. However, Bellingham + Stanley assumes no responsibility for errors contained herein or their consequences.

Bellingham + Stanley Longfield Road, Tunbridge Wells, Kent, TN2 3EY, UK Tel +44 (0) 1892 500400 Fax +44 (0) 1892 543115 A sample tube containing the test liquid (solution) is placed between two polarising elements (polaroid strip or a calcite crystal). The first element, the polariser, polarises the light before it passes into the sample. The second element, the analyser, can be rotated to counteract any rotation by the sample and hence locates the resultant angular position of the light plane and hence the amount of rotation caused by the sample. In the sugar industry, the rotation is...

Bellingham + Stanley Longfield Road, Tunbridge Wells, Kent, TN2 3EY, UK Tel +44 (0) 1892 500400 Fax +44 (0) 1892 543115 Calculation of Specific Rotation (optically active liquids/solutions) is the corrected optical rotation is the specific rotation at t C in the polarised light of wavelength . is the length of the polarimeter tube in metres is the relative density of the liquid or solution at 20 C is the concentration of the solute expressed in grams per mL of solution is the concentration of the solute expressed in gram per gram solution Wavelength The sodium wavelength of 589 nm is by far...

Bellingham + Stanley Longfield Road, Tunbridge Wells, Kent, TN2 3EY, UK Tel +44 (0) 1892 500400 Fax +44 (0) 1892 543115 The instrument cannot decide itself how many times the plane has passed the 180° reference position along the sample path length. It is up to the user to either know the range (angular segment) in which the result will fall approximately or to be prepared to experiment to establish the absolute rotation. It is for this reason that, with automatic digital polarimeters such as the B+S ADP 220, the user must select the measuring angular range, knowing (approximately) where...