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by the dehydration of sugars by concentrated sulfuric acid. The test is
quick, but only provides qualitative information. Often, the color pro-
duced is obscured by charring (Foulger, 1931). At low contamination
levels, the method becomes unreliable. For quantitative estimation of
sugars,thephenol(orthymol)-sulfuricmethodisthemostfrequentlyused.
The sugarsgivean orange-yellow color whentreatedwith phenol(orthy-
mol) and concentrated sulfuric acid (Dubois et al., 1979). The method is
simple, rapid, and sensitive, and gives reproducible results. The color pro-
duced is permanent, and it is unnecessary to pay special attention to the
control of theconditions. Thus, tests using phenol and sulfuric acid are still
the most widely used analytical methods, even though these are labor
intensive andnot online. There have been attempts to automate these tests
with varied success (Reid and Dunsmore, 1991).
ii. Conductivity
Among the online monitoring methods, conductivity is used most
widely because it is affordable to implement. However, it is interesting
to note that, in the case of sugar process condensate, conductivity is in
fact strongly correlated with ammonia concentration (Figure 11.2).

Figure 11.2 Sugar mill process condensate conductivity versus ammonia concentration
based on analyses of several samples.