D. Baunsgaard et al., Evaluation of the quality of solid sugar samples by fluorescence spectroscopy and chemometrics, APPL SPECTR, 54(3), 2000, pp. 438-444
It has been shown that fluorescence spectroscopy of sugar in aqueous soluti
on carries important quality and process information related to beet sugar
factories, which is accessible by multivariate analyses, A method for measu
ring crystalline sugar directly on-line in the process should be advantageo
us. In this paper we compare the solution measurement technique with two me
thods of fluorescence measurement on solid sugar. Surprisingly, it was poss
ible to measure fluorescence through the sugar crystals by using the same t
ransmission techniques with 90 degrees detection as with the sugar solution
s. This method was compared with a 45 degrees front-surface reflection meth
od. Sugar samples from six different sugar factories were examined. The spe
ctral responses were reasonable, but they were influenced by the heterogeno
us sample composition and the sample geometry. It was possible with the two
methods to separate sugar samples according to factory with the use of pri
ncipal component analysis (PCA). Seasonal time trends were found in weekly
samples front the same factory. Partial least-squares regression (PLS) was
used to predict quality parameters, where color (range: 6-41), ash (range:
0.003-0.018), and alpha-amino-N (range: 0.28-5.07) could be modeled with er
rors of 2.3-2.6, 0.0015-0.0016, and 0.40-0.42, respectively. Model errors f
or similar solution data have been determined to 2.4, 0.0012, and 0.266, re
spectively.