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1622114 Ab 098 4 En 1 Essay

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Application Bulletin 98/4 e

Determination of ascorbic acid (vitamin C) and its compounds Branch
pharmaceutical industry; food, stimulants,
flavours; biochemistry, biology;


Bi-voltammetric determination
with iodine

Titrator with MET mode


10 mL burette

Ascorbic acid; titration; bi-voltametric titration; photometric titration; polarography; vitamin C; ISO 6557/2; branch 1;
branch 3; branch 4; branch 7; branch 8; 6.0309.100;


Double Pt-sheet electrode


In addition to the natural occurrence, ascorbic acid (vitamin C) is added to food and beverages as an antioxidant. It can
also be found in various pharmaceutical products.
Ascorbic acid, as well as its salts and esters, can be
determined by titration or by means of polarography. The
determination is based on the oxidation of ascorbic acid to
dehydroascorbic acid.




- 2 H+ - 2 e




Volumetric iodine solution, c(I2) = 0.01 mol/L

Glyoxal, w(C2H2O2) = 40%

Sodium hydroxide solution, c(NaOH) = 1 mol/L

Sulfuric acid, w(H2SO4) = 25%

Disodium thiosulfate pentahydrate, Na2S2O3 5 H2O

Acetic acid, c(CH3COOH) = 2 mol/L



For the titrimetric determination bi-voltametric or photometric equivalence point indication can be used. The bi-voltametric indication is independent of inherent coloration of the


c(I2) = 0.01 mol/L

Glyoxal solution

w(C2H2O2) = 40%
200 mL w(C2H2O2) = 40% is
adjusted with c(NaOH) = 1 mol/L
to pH = 7.0.
The solution has to be stored in a
dark bottle in a refrigerator.

The polarographic method is the most selective of the
described methods, since other reducing or oxidizing
substances do not interfere.
Disodium thiosulfate

Disodium thiosulfate pentahydrate
is dried at 120 °C for 2 h and
cooled down in a desiccator for at
least 1 h.

Sample preparation

Drinks, fruits and vegetable juices can be analyzed

Page 1 of 9

Application Bulletin 98/4 e
Determination of ascorbic acid (vitamin C) and its compounds

For tablets and other vitamin preparations, a diluted
solution in degased dist. water is prepared. Thereof an
aliquot is used for the titrimetric determination.
Foods, stimulants and animal feeds are extracted using
the appropriate procedures.


VEP1 × 2 × cI2 × MA


Approximately 50 mg Na2S2O3 · 5 H2O is weighed into a
titration beaker with an accuracy of 0.1 mg, 5 mL
c(CH3COOH) = 2 mol/L is added and the solution is diluted
to approximately 80 mL with deionized water. The solution is then titrated with c(I2) = 0.01 mol/L until after the first
equivalence point.
50 mL sample (containing 0.05…0.5 mg ascorbic acid) is
pipetted into a titration beaker, 2 mL glyoxal solution is
added and the mixture is stirred briefly and allowed to stand for 5 min. After the addition of 5 mL sulfuric acid w(H2SO4) = 25% it is titrated with c(I2) = 0.01 mol/L until after the
equivalence point.

cI2 :
MA :


MET Ipol

Vol. increment

0.1 mL

Signal drift

50 mV/min

Max. waiting time

26 s


1 μA

EP criterion

30 mV

EP recognition


Mass concentration of ascorbic acid (AA) in
Titrant consumption until the first equivalence
point in mL

cI2 :

Concentration of titrant in mol/L


Correction factor («titer») without unit...

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-0.011 -0.05 -09 -1 -10.0 -19 -3 -4 -5.00 -7 -81 -90 /0.999 0 0.01 0.04 0.05 0.06 0.1 0.10 0.2 0.20 0.25 0.41 0.5 0.6 098 1 1.00 10 10.0 100 1000 120 127 13.61 15 15.0 150 1622114 174 176.13 179 18 1971 1973 1983 1988 2 200 2000 200n 243.506 248.18 25 253 26 271 274 28 3 30 300 32 329 3h2o 4 4.6 40 400n 42 5 5.00 50 50.0 500 520 6 6.0309.100 6.0343.000 6.0728.020 6.1115.000 6.1226.030 6.1245.010 6.1246.120 60 600n 6131 64 6557/2 7 7.0 703.1 760 763 8 8.2 80 800n 9 98/4 aa ab accuraci acet acid ad addit adjust ae ag/agcl akademiai aliquot allow alon also amin amplitud anal analysi analyt analyz anhydr anim antioxid apart applic appropri approxim ascorb ascorbinometr ascorbinsäur assay astm author automat base baselin beaker bestimmungsmethoden beverag bi bi-voltametr bi-voltammetr biochemistri biolog blank blanksampl blanktit blood bottl branch briefli brown budapest buffer bujak bulletin burett c c2h2o2 c2h2o4 c6h8o6 calcul calibr cannot capabl capillari carbon carri cas center ch3cooh ch3coona chem chemistri chloramin chloramine-t chlorid ci2 cm color comment compet compound concentr condit consumpt contain content convers cool copper correct cosmet criterion curv d d1193 daili dark day dega degas dehydroascorb deioniz deriv describ desicc dessen determin dichlorophenol dichlorophenol-indophenol dichlorophenolindophenol differenti dihydr dilut dioxid direct disodium dissolv dist disturb dme doubl dp dpip dri drift drink drop e e.g eder eder-trifunov electrod electrolyt en end ensur ep equilibr equival erdey ester everi exampl extract f factor fe feed fig fill filtrat first flask flavour follow food found fresenius fresh fruit für g g.pongracz g/l g/mol general given glass glyoxal grade greatest h h2c2o4 h2o h2so4 headquart ho hot hydrodynam hydrogen hydroxid i2 iii increment independ indic indophenol industri inher instead instrument interfer intern iodide/iodate iodin iodometr ion ipol iron iso j juic kcl keep keyword kiado kniewald kozar l l-ascorb larg larger lead least lebensmittelbuch light linear long m ma maa made mark mass max mean measur mercuri met method method1560.1 metrohm mg mg/l microchem min mixtur ml mode mol/l molar ms multi multi-mod mv mv/min na2s2o3 nahco3 name naoh natur neue nitrat nitrogen nm o occurr oh one oper optrod orang organ oxal oxid oxidiz oxygen page paramet part paus peak pentahydr perform ph pharmaceut photometr pipet point pol polarogram polarograph polarographi potenti potentiometrisch precipit prepar present pro procedur process product pt pt-sheet pulp puls quantifi quantiti rate re reagent recognit recommend record reduc refer refriger remain remov replic resist rod routin salt sampl sauerkraut schweizerisch select sensit separ sheet signal silver sinc so2 sodium solut speed stand standard start step stimul stir stirrer stoichiometr store stuff subsequ substanc sulfit sulfur summari support svehla sweep tablet therefor thereof thiosulf time tin titer titrant titrat titrimetr togeth toler transfer trifunov trihydr two type u ultrapur und unit use v v/s va valu various veget vep1 verbindungen vessel vex vitamin vol voltametr voltammetr voltammetri volum volumetr vs vstd w wait water week weigh well without z β βaa βdpip βstd μa