656 M. Dubernet
Two determinations are made at 560 nm in the presence of para-rosaniline (or basic
fuschine) and segmentation of the stream is with nitrogen to avoid oxidation of
sulphur dioxide into sulphuric acid.
SO 2 +rosaniline−→colourless complex+formaldehyde−→coloured complex.
The method is applicable over the concentration range 0–200mg/L.
Characteristics of the Method
Inter-laboratory reproducibility free sulphur dioxide: 7mg/L
Inter-laboratory reproducibilitytotal sulphur dioxide: 27mg/L12.2.2.8 Determination of Free and Total Sulphur Dioxide in Wines
and Musts by Distillation
Principle
An alternative to the above method is alsolargely applied. Dialysis is replaced by a
distillation step using a micro distillation column. In the case of total sulphur diox-
ide, alkaline hydrolysis is replaced by strong acidification and a higher distillation
temperature.
Characteristics of the Method
Inter-laboratory reproducibility free sulphur dioxide: 7mg/L
Inter-laboratory reproducibilitytotal sulphur dioxide: 27mg/L12.3 Sequential Analysers
12.3.1 Principle and Organisation of a Sequential Analyser
These are often multi-parameter analysers and enable several determinations to be
carried out on the same sample; furthermore, the number of determinations can be
programmed for each individual sample.An aliquot of the sample is placed in a
transparent measurement cuvette; following addition of the reagents, a colorimetric
measurement is then carried out directlyon the cuvette. The analysis rate varies
from 50 to 1000 determinations per hour, and the principal applications are carried
out either by chemical or enzymatic analysis. The volumes of reagent required for
sequential analysis are small by comparison with FIA which substantially reduces
the cost per analysis, particularly for enzymatic determinations.