The use of Near Infrared Polarimetry to determine the polarization of raw sugar

The optical rotation of raw sugar analyzed using Celite filtration and a NIR polarimeter at 880 nm was compared with conventional clarification using basic lead acetate and determination at 589 nm. Satisfactory sample preparation for the NIR polarimeter was accomplished by filtration of the sample solution through a glass fibre paper with Celite 505 as filter aid. The polarization of standard sugar was 0.06 °Z lower in the NIR polarimeter than in the conventional polarimeter. It is thought that the use of Biinnagel’s formulae for determining the sugar value of a standardizing quartz plate at 880 nm may be in error by this amount. Optical rotation of Australian raw sugar filtered with Celite and read on the NIR polarimeter was lower than with lead clarification and read on a conventional polarimeter. The difference increased as the optical rotation decreased, being 0.13 °Z for VHP, 0.18 °Z for brand 1 and 0.29 °Z for brand JA raw sugar. A lower difference of 0.03-0.08 °Z was found for overseas raw sugars. These samples had dextran concentration up to 0.16% and this impurity has an optical rotation about three times that of sucrose. A substantial proportion of dextran is removed by lead clarification but not by Celite filtration. The difference between results obtained with lead clarification and Celite filtration was not caused by reducing sugars or colour.