NIR POLARIMETRY/SAMPLE PREPARATION FOR SUCROSE MEASUREMENT AND ASSESSMENT OF AN AUTOMATED SYSTEM FOR TURBIDITY, COLOUR AND ASH DETERMINATION

摘要

Several new methods for measurement of sucrose in sugar processing streams are being introduced worldwide to replace the traditional lead clarification method in order to improve the quality and process control. Some problems that have prevented the wide acceptance of some of these methods are related to sample preparation. In this paper, NIR polarimetry has been selected for investigation. It is the most promising measurement system, because it is a rapid method and has a low environmental impact. Problems associated with NIR polarimetry such as sample preparation (i.e. turbidity and filterability) have been overcome by using a newly developed pressurised filtration device. The sample composition differs from the traditional lead clarification method since, in the new method with filtration and NIR polarimetry, non-sugars are not removed. The differences in results for the two methods are discussed. Measurement of turbidity and colour in industrial sugar solutions using different instruments suffers from lack of comparability due to the different behaviour of scattered light detection systems. A new ICUMSA method has recently been developed using formazin standards to allow comparable measurements for turbidity and colour determination with photometers or colorimeters. This method allows calibration of the instruments with NTU and ICUMSA colour units as well as validation and comparability of results. This paper introduces a new automatic system for the combined determination of conductometric ash, colour and turbidity in solution. The system successfully performs preparation of appropriately diluted samples (50 and 28 Brix), carries out membrane filtration, transports the samples to the instruments and analyses them with minimum participation by the operator. Performance shows stable and reliable results during the whole production season.