Hd. Isengard et Jm. Farber, 'Hidden parameters' of infrared drying for determining low water contents in instant powders, TALANTA, 50(2), 1999, pp. 239-246
Drying techniques are very frequently used and in many cases official metho
ds for moisture determination. These methods, however, do not yield the wat
er content as a result but a mass loss which is caused not only by the evap
oration of water but by all substances volatile under the drying conditions
, be they original components of the product or be they produced by decompo
sition reactions during the drying process. This mass loss varies therefore
with the parameters applied like time, temperature, form of energy transfe
r, atmospheric pressure or surrounding humidity. To shorten determination t
imes of many hours in common air ovens with convective heating, techniques
with more efficient heating principles have been developed. One of these is
infrared drying. With such methods, however, the danger of product decompo
sition and, consequently, of wrong results rises, particularly when the wat
er content is low. It could be shown, however, that analyses are possible,
even for beverage instant powders with very low water contents. Moreover, p
arameter sets could be found to match the infrared results exactly with the
true water content determined by Karl Fischer titration. Another essential
finding was that not only the parameters for the drying programme itself l
ike time, temperature and end-point criterion are important, but also, and
this to a surprisingly great extent, the number of consecutive measurements
and the duration of the intervals between analyses. This effect again depe
nds extremely on the type of apparatus. (C) 1999 Elsevier Science B.V. All
rights reserved.