Coulometric titration of thiols with chlorine in solution containing different electrolytes has been performed. Optimum determination conditions have been found. The developed method was applied to the determinaton of mesna (0.2510 µmol), L-cysteine (0.252 µmol), mercaptosuccinic acid (0.52.5 µmol), 3-mercaptopropionic acid (0.428.3 µmol), cysteamine hydrochloride (0.53 µmol), carbimazole (0.252 µmol), thiopental (0.11 µmol), thioglycolic acid (0.8710 µmol), D-penicillamine (0.1255 µmol), L-glutathione (0.510 µmol) and mesna in pharmaceutical preparations (Mistabron and AntiUron). Determination error was below 1%. Przeprowadzono miareczkowanie kulometryczne tioli z u¿yciem chloru jako titranta w rodowisku ró¿nych elektrolitów. Opracowano optymalne warunki oznaczenia. Za pomoc¹ opracowanej metody oznaczono mesnê (0.2510 µmol), L-cysteinê (0.252 µmol), kwas merkaptobursztynowy (0.52.5 µmol), kwas 3-mercaptopropionowy (0.428.3 µmol), chlorowodorek cysteaminy (0.53 µmol), karbimazol (0.252 µmol), tiopental (0.11 µmol), kwas tioglikolowy (0.8710 µmol), D-penicyloaminê (0.1255 µmol), L-glutation (0.510 µmol) oraz mesnê w preparatach farmaceutycznych Mistabron i AntiUron. Opracowana metoda umo¿liwia oznaczanie tioli z b³êdem poni¿ej 1%

Monika Skowron

Witold Ciesielski

CiteSeerX

Chem. Anal. (Warsaw), 49, 619 (2004)
*  Corresponding author. E-mail: zaiciesielski@hotmail.com; Fax: +48-42-678-39-85.
Key words: coulometric titration, thiols, mesna, electrogenerated chlorine
Coulometric Titration of Thiols
with Electrogenerated Chlorine
by Witold Ciesielski* and Monika Skowron
Department of Instrumental Analysis, University of £ód,
ul. Pomorska 163, 90-236 £ód, Poland
Coulometric titration of thiols with chlorine in solution containing different electrolytes has
been performed. Optimum determination conditions have been found. The developed method
was applied to the determinaton of mesna (0.2510 µmol), L-cysteine (0.252 µmol),
mercaptosuccinic acid (0.52.5 µmol), 3-mercaptopropionic acid (0.428.3 µmol), cyste-
amine hydrochloride (0.53 µmol), carbimazole (0.252 µmol), thiopental (0.11 µmol),
thioglycolic acid (0.8710 µmol), D-penicillamine (0.1255 µmol), L-glutathione
(0.510 µmol) and mesna in pharmaceutical preparations (Mistabron and AntiUron). De-
termination error was below 1%.
Przeprowadzono miareczkowanie kulometryczne tioli z u¿yciem chloru jako titranta w rodo-
wisku ró¿nych elektrolitów. Opracowano optymalne warunki oznaczenia. Za pomoc¹ opra-
cowanej metody oznaczono mesnê (0.2510 µmol), L-cysteinê (0.252 µmol), kwas
merkaptobursztynowy (0.52.5 µmol), kwas 3-mercaptopropionowy (0.428.3 µmol),
chlorowodorek cysteaminy (0.53 µmol), karbimazol (0.252 µmol), tiopental (0.11 µmol),
kwas tioglikolowy (0.8710 µmol), D-penicyloaminê (0.1255 µmol), L-glutation (0.510
µmol) oraz mesnê w preparatach farmaceutycznych Mistabron i AntiUron. Opracowana
metoda umo¿liwia oznaczanie tioli z b³êdem poni¿ej 1%.
620 W. Ciesielski and M. Skowron
The coulometric titration method with anodically generated chlorine has been
known for about 50 years [1]. It has been successively applied to the determination of
many organic compounds, such as thiols (e.g. N-acetyl-L-cysteine [2], 6-mercaptopu-
rine [3], 6-thioguanine [4], captopril [5]), disulfides (e.g. 2,2-dithiodiglycolic acid,
L-cystine, cystamine dihydrochloride [6a]) and thiophosphorous compounds
(e.g. methamidophos, iso-malation, fenitrothion) [6b]. In this paper we present coulo-
metric titration of cysteamine hydrochloride, thioglycolic acid, 3-mercaptopropionic
acid, mercapto-succinic acid, L-cysteine, D-penicillamine, L-glutathione, mesna,
carbimazole and thiopental performed with anodically generated chlorine as titrant
and applying biamperometric end-point detection.
Thiols studied in this paper are commonly used in many different fields of tech-
nology, cosmetology and medicine.
Thioglycolic acid was titrated coulometrically with electrogenerated iodine using
potentiometric [7,8] and biamperometric [9] end-point detection. Electrogenerated
manganese(III) [10] and hypobromite ions [11] were also used as titrants. L-cysteine
was titrated with anodically generated bromine and iodine, applying biampero-met-
ric [12] and potentiometric [12,13] end-point detection. Anodically generated silver(I)
ions and biamperometric end-point detection were also applied for the determination
of L-cysteine [14]. D-penicillamine was titrated with mercury(II) ions generated from
an amalgamated gold anode [15]. Mercaptosuccinic acid was titrated with electrogene-
rated manganese(III) ions, as well as with cerium(IV) ions generated from cerium(III)
nitrate [16]. End-point was detected biamperometrically [10], potentiometrically [17]
and bipotentiometrically [18]. L-glutathione was determined using generated silver(I)
ions and biamperometric end-point detection [19]. Carbimazole was titrated coulome-
trically with electrogenerated iodine in alkaline medium using biamperometric end-
point detection [20]. Carbimazole was also determined coulometrically involving iodi-
ne-azide reaction [21]. Thiopental was titrated coulometrically using electrogenerated
bromine [22] or mercury(II) [23] as titrant. Determination was carried out in two steps.
In the first one the sample was reduced at the constant potential. After that the analyte
was titrated with generated mercury(II).
According to our current knowledge, there are no literature reports on the coulo-
metric determination of 3-mercaptopropionic acid, cysteamine hydrochloride and
mesna.
EXPERIMENTAL
Apparatus
Measurements were performed using a universal coulometric analyser, model OH404, Radelkis, Hun-
gary. An electrolysis cell with two platinum electrodes each with the area of 5 cm2, working in the generating
621Coulometric titration of thiols
circuit, and the double electroede OH9381 working in biamperometric indicator circuit were used. Catho-
dic and anodic compartments of the electrolytic cell were separated with a sintered glass G4 disc.
Reagents and solutions
Doubly distilled water was used throughout. Sulfuric acid, sodium chloride and acetonitrile were pur-
chased from POCH, Gliwice.
The following compounds were used: cysteamine hydrochloride (98%, Aldrich) thioglycolic acid (98%,
Sigma), 3-mercaptopropionic acid (99%, Aldrich), L-cysteine (98%, Roanal), D-penicillamine (99%, Sigma),
mercaptosuccinic acid (97%, Aldrich), L-glutathione (98%, Sigma), mesna (98%, Aldrich), carbimazole
(97%, Lancaster), thiopental (United Pharmaceutical Works, Prague), Mistabron 600 mg (PLIVA, Kraków),
AntiUron 200 mg (Polfa, Kraków).
Analyte solutions of the concentration of 5 × 10-3 mol L-1 were prepared freshly before use by dissol-
ving weighed amounts of the reagents in the solvent.
Aqueous solution containing hydrochloric acid or sulfuric acid, and sodium chloride at different con-
centrations (Tab. 1) served as the supporting electrolyte solution.
Table 1. Determination results of thiols in the solutions of various supporting electrolytes
Supporting electrolyte  
mol L-1 Compound 
HCl H2SO4 NaCl 
z* 
RSD 
% 
1   5.76 0.24 
 0.25 0.2 5.63 0.28 
 0.5 0.1 5.53 0.23 
 0.5 0.2 5.97 0.22 
Mesna 
 0.5 0.4 5.55 0.20 
1   5.98 0.13 
 0.25 0.2 6.10 0.16 
 0.5 0.1 6.34 0.12 
 0.5 0.2 6.40 0.10 
Carbimazole 
 0.5 0.4 6.50 0.20 
1   5.00 0.12 
 0.25 0.2 5.05 0.20 
 0.5 0.1 4.94 0.18 
 0.5 0.2 4.95 0.11 
Thiopental 
 0.5 0.4 4.94 0.16 
(Continuation on the next page)
622 W. Ciesielski and M. Skowron
Procedure
Sample solution containing the analytes was introduced into the supporting electrolyte solution (25 mL)
and placed in the anodic compartment of the electrolytic cell. 150-mV potential was applied to the indicator
system. After switching the mechanical stirrer on, a constant current was passed through the solution. The
current in the generating circuit was adjusted between 1 and 10 mA, according to the amount of the analyte.
Titration time was maintained at the level of several minutes. When the current in the indicator circuit
achieved 0.04 µA, titration was completed and the charge Q was measured. The excess of chlorine that
appeared in the solution after the reaction was finished allowed one to detect the end-point. In the same way
the sample was titrated in the absence of the analyte (blank experiment), and the charge of 710 mC (Q
o
)
was measured.
The content [µmol] of the analyte in the sample was estimated according to the Faradays law:
3
10
zF
Q
n ´=
Ä
where:
∆Q = Q  Q
o
 [mC]; Q
o
 charge corresponding to the blank titration; z  number of electrons transferred
(5 for thiopental, 6 for other compounds), F  Faraday constant (96 485 C mol-1).
Determination of mesna in drugs
The contents of ten drug phials were quantitatively introduced into 100 mL which was fixed up with
water. The mixture was diluted 10-fold and 100 µL of the resulting solution was introduced into 25 mL of
the supporting electrolyte solution, in the anodic part of electrolytic cell. The sample was titrated similarly as
pure analyte. The content of mesna in each dosage form was calculated using Faradays laws.
RESULTS AND DISCUSSIONS
Efficiency of chlorine generation and reaction rate between chlorine and the ana-
lytes depends on the concentration of hydrogen and chloride ions in the solution.
Both should be optimised experimentally [24] in order to provide accurate and reprodu-
Table 1. (Continuation)
* Number of electrons transferred.
1   5.87 0.12 
 0.25 0.2 6.07 0.10 
 0.5 0.1 6.00 0.09 
 0.5 0.2 5.99 0.09 
3-Mercaptopropionic acid 
 0.5 0.4 5.98 0.11 
 
623Coulometric titration of thiols
cible results, constant number of transferred electrons, and low RSD. Thus, various
concentrations of hydrochloride or sulfuric acid and sodium chloride were applied.
The number of electrons transferred in the presence of various supporting electrolytes
was calculated. Some of the results are given in Table 1.
The biamperometric end-point detection provided correct and reproducible re-
sults of the determination of thiols in the concentration ranges given in Table 2. How-
ever, the error increased above 1% when larger or smaller amounts of the analytes
than those presented in Table 2 were determined. The literature data concerning the
determination error and RSD of the coulometric titration with chlorine and visual
end-point detection were less satisfactory  these factors amounted to several percent
[2,4].
Table 2. Determination results of thiols; n = 6
Compound 
(supporting electrolyte) 
Taken 
µmol 
Found 
µmol 
RSD 
% 
0.2500 0.2515 0.31 
2.500 2.483 0.05 
Mesna 
(0.5 mol L-1 H2SO4  
0.2 mol L-1 NaCl) 
10.000 9.960 0.04 
0.1250 0.1243 0.18 
0.5000 0.5014 0.08 
L-cysteine 
(0.5 mol L-1 H2SO4 
0.2 mol L-1 NaCl) 
2.500 2.497 0.01 
0.5000 0.5022 0.07 
1.000 1.005 0.04 
Mercaptosuccinic acid 
(0.5 mol L-1 H2SO4 
0.2 mol L-1 NaCl) 
2.500 2.499 0.02 
0.4160 0.4188 0.05 
1.108 1.108 0.03 
3-Mercaptopropionic acid 
(0.5 mol L-1 H2SO4 
0.1 mol L-1 NaCl) 
8.310 8.273 0.01 
0.5000 0.4988 0.15 
1.000 0.9988 0.06 
Cysteamine hydrochloride 
(0.5 mol L-1 H2SO4 
0.1 mol L-1 NaCl) 
3.000 2.984 0.01 
0.2500 0.2488 0.23 
1.000 1.001 0.04 
Carbimazole 
(1 mol L-1 HCl) 
2.002 2.012 0.03 
(Continuation on the next page)
624 W. Ciesielski and M. Skowron
0.1001 0.0996 0.64 
0.5007 0.5001 0.12 
Thiopental 
(1 mol L-1 HCl) 
1.0014 1.0094 0.07 
0.8670 0.8622 0.04 
2.890 2.891 0.02 
Thioglycolic acid 
(1 mol L-1 HCl) 
10.11 10.13 0.01 
0.1250 0.1252 0.28 
1.000 1.008 0.07 
D-penicillamine 
(1 mol L-1 HCl) 
5.000 5.036 0.01 
0.5000 0.5025 0.25 
2.500 2.514 0.09 
L-glutathione 
(0.5 mol L-1 HCl) 
5.000 5.002 0.05 
 
Table 2. (Continuation)
The reaction mechanism between most of the analytes and chlorine is given be-
low:
RSH + 3Cl2 + 3H2O RSO3H + 6HCl
where:
(1)
CH
2
CH
NH
C NHCH2COOH
C CH
2
CH
2
(NH
2
)COOH
O
O
Na+
R =  -CH2CH2NH2  HCl                                        for cysteamine hydrochloride
       -CH2COOH                                                  for thioglycolic acid
       -CH2CH2COOH                                             for 3-mercaptopropionic acid
       -CH2CH(NH2)COOH                                    for L-cysteine
       -C(CH3)2CH(NH2)COOH                              for D-penicillamine
       -CH(COOH) CH2COOH                               for mercaptosuccinic acid 
.
      
for L-glutathione
-C2H4SO3                                                                                for mesna
-
625Coulometric titration of thiols
N
C
N SH
CH
3
N
C
N
COOC
2
H
5
S
CH
3
N
C
N
H
S
CH
3
H+
+ H2O + C2H5OH + CO2
(2)
Carbimazole exists only in the thione form, but it was proved that in an acidic
medium it undergoes hydrolysis and decarboxylation [25], according to the equation:
1-methylimidazole-2-thiol is formed as the product, which reacts directly with
chlorine (equation 1).
Thiopental reacts with chlorine according to the following reaction scheme:
N
NH
O
O
H7C3(H3C)HC
H5C2
SH
N
NH
O
O
CH(CH3)C3H7
C2H5
SO2N
NH
O
O
H7C3(H3C)HC
H5C2
SO2
+ 5Cl2 + 4H2O
+ 10HCl
2
(3)
The presented method of coulometric determination of thiols is characterised by
 short analysis time, high precision and accuracy, and simplicity (does not involve
complex chemical reactions). The method requires the use of only commonly avail-
able reagents, and can be partly automated. As an absolute method it requires no
standard solutions. It was applied to the determination of mesna in Mistabron and
Anti-Uron drugs. The results of these determinations are given in Table 3.
626 W. Ciesielski and M. Skowron
Coulometric titration with chlorine can be applied to the determination of thiols,
which react rapidly with chlorine. However, for those reacting slowly (e.g. 2-thiobarbi-
turic acid, 3-mercapto-1,2,4-triazole, 2-mercapto-4(3H)quinazolinone, 2-mercaptoben-
zothiazole, 2-mercaptobenzimidazole, 2,5-dimercapto-1,3,4-thiadiazole) no conditions
were found to determine them using coulometric titration.
REFERENCES
1. Farrington P.S. and Swift E.H., Anal. Chem., 22, 889 (1950).
2. Nikoliè K.I., Vesaleviè K.R. and Javanoviè T., Pharmazie, 42, 134 (1987).
3. Nikoliè K.I. and Vesaleviè K.R., J. Pharm. Belg., 46, 455 (1988).
4. Nikoliè K.I., Vesaleviè K.R. and Zimowa N., Il. Farmaco, 46, 409 (1991).
5. Nikoliè K.I., Vesaleviè K.R., Acta. Polon. Pharm., 48, 5 (1991).
6a. Ciesielski W. and Skowron M., Chem. Anal. (Warsaw), in press.
6b. Ciesielski W., Skowron M., Ba³czewski P. and Szadowiak A., Talanta, 60, 725 (2003).
7. Pastor T.J., Vajgand V.J. and Antonijevic V.V., Mikrochim. Acta, 3, 203 (1983).
8. Pastor T.J. and Antonijevic V.V., Anal. Chim. Acta, 196, 229 (1987).
9. Ruettinger H.H. and Spohn U., Anal. Chim. Acta, 202, 75 (1987).
10. Pastor T.J., Vajgand V.J. and Antonijevic V.V., Glas. Hem. Drus. Beograd, 44, 651 (1979);
Chem. Abstr., 92:226164t (1980).
11. Palma R.J., Gupta H.K.L. and Boltz D.F., Anal. Lett., 4, 277 (1971).
12. Kreshkov A.P. and Oganeshyan L.B., Zh. Anal. Khim., 26, 614 (1971).
13. Kreshkov A.P. and Oganeshyan L.B., Zh. Anal. Khim., 28, 2260 (1973).
14. Ladenson J.H. and Purdy W.C., Anal. Chim. Acta, 64, 259 (1973).
15. Forsman U., Anal. Chim. Acta, 93, 153 (1977).
16. Pastor T.J., Vajgand V., Civic Ivan, Magy. Kem. Foly, 88, 519 (1982); Chem. Abstr., 98:46241f
(1983).
17. Pastor T.J. and Civic I., Mikrochim. Acta, 1, 435 (1984).
18. Pastor T.J. and Antonijevic V.V., Mikrochim. Acta, 1, 313 (1990).
19. Ladenson J.H. and Purdy W.C., Anal. Chim. Acta, 64, 259 (1973).
20. Ciesielski W. and Krenc A.; Anal. Lett., 33, 1545 (2000)
21. Ciesielski W., Zakrzewski R. and Skowron M., Chem. Anal., 46, 873 (2001).
22. Kalinowski K. and Piotrowska A., Acta Polon. Pharm., 26, 107 (1959).
23. Mairesse-Ducarmois C.A., J. Pharm. Belg., 28, 3000 (1973).
24. Lingane J.J., Electroanalytical Chemistry, Interscience Publ., New York 1958, (in Polish).
25. El-Bardicy M.G., El-Saharty Y.S. and Tawakkal M.S., Talanta, 40, 577 (1993).
Received October 2003
Accepted July 2004
Table 3. Determination results of mesna in drugs; n = 6
Drug 
Declared Content 
mg 
Found 
mg 
RSD 
% 
Mistabron 600 602 0.07 
Anti-Uron 200 201 0.04 
 


Coulometric Titration of Thiols with Electrogenerated Chlorine

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Coulometric Titration of Thiols with Electrogenerated Chlorine

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