Chemistry Reference
In-Depth Information
9.7 LaNe-eYNON DeterMINatION OF reDUCING SUGarS
TheLane-Eynonmethoddeterminesonlythereducingsugars(monosaccharides,lactose,and
maltose), whereas nonreducing sugars, e.g., saccharose, need to be inverted so that they can be
determined.Thisisavolumetricdeterminationofsugarsinasolutionandisbasedonthefactthat,
whenbasiccoppersolutionsareheatedwithreducingsugarsolutions,copperisreducedtocopper
oxide,givingaredcolor.Accordingtothismethod,thevolumeofthesugarsolutionisdetermined
toreduceorneutralize10-or25-mlfeligianliquidusingmethyleneblueasanindicator.Basedon
theusedmillilitersofsugarsolutionwiththecoeficientsofsugarsfromspeciictables,thesugar
concentrationiscalculatedaccordingtoEquation9.3:
Sugar concentration (%) =
Σ*
100
A
,
(9.3)
where
A
refers to sugars in milligrams per 100 ml solution, andΣ refers to a coeficient from
tables.
9.7.1 Determination of reducing and total Sugars Using the Schoorl-
regenbogen Method in raw Materials and Final products
9.7.1.1 Principle
TheSchoorl-Regenbogenmethodisbasedonthetitrationoftheremainingquantityofcopper
arisingfromboilingofthesugarsolutionwithFeligianliquid.Itisanindirectmethodwithagreat
reproducibilityandtheadvantageofbeingcarriedoutunderthesameconditionsforsugars,includ-
ingpentosesandreducingdisaccharides.
Thismethodrequiresthefollowingequipmentforreagents:
•
Flask,400ml
•
High-speedmixer
•
Erlenmeyerlask,250ml
•
Bunsenburner
•
Waterbathat100°C
Thefollowingreagentsarealsoneeded:
•
CarrezIsolution:36.0gof(K
4
[Fe(CN)
6
]
.
3H
2
O)perliter
•
CarrezIIsolution:72.0gofzincsulphate(ZnSO
4
.
7H
2
O)perliter
•
NaOHsolution,0.1N
Asamplepretreatmentisdescribedasfollows:
•
A5.0-gwell-groundsampleisweighedina400-mllask.
•
Deionizedwater,175g,isadded.
•
Mixingiscarriedoutfor70-80sinahigh-speedmixertodissolvethesolublesolids.
•
Then,thefollowingsolutionsareaddedunderstirring:
•
5-mlCarrezI
•
5-mlCarrezII
•
10-mlNaOH0.1N
•
Stirringiscontinuedforanother30s.
•
Filtrationwithapapertowelfollows.Approximately70mlofiltrateisenoughforthedeterminations.
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