Capillary electrophoresis (CE) with capacitively coupled contactless conductivity detection (C4D) was used for determination of sodium and potassium concentrations in diet and non-diet soft drinks. Higher sodium concentrations were found in the diet samples due to the utilization of sodium salts of cyclamate and saccharine as sweeteners. The CE-C 4D method can be used by food industries and health regulatory agencies for monitoring sodium and potassium content, not only in soft drink but in many others food products.3435156Macgregor, G.A., (2001) Am. J. Kidney Dis., 37, pp. S34He, F.J., MacGregor, G.A., (2001) Br. Med. J., 323, p. 497Toseto, A., (2005), Master's Dissertation, Universidade Estadual de Ponta Grossa, BrazilTavares, M.F.M., (1996) Quim. Nova, 19, p. 173Jorgenson, J.W., Lukacs, K.D., (1981) Anal. Chem., 53, p. 1298Da Silva, J.A.F., Lago, C.L., (1998) Anal. Chem., 70, p. 4339Silva, J.A.F.D., Guzman, N., Lago, C.L., (2002) J. Chromatogr. a, 942, p. 249Munhõz, R.A.A., Richter, E.M., Jesus, D.P., Lago, C.L., Angnes, L., (2004) J. Braz. Chem. Soc., 15, p. 523Richter, E.M., Munhõz, R.A.A., Jesus, D.P., Lago, C.L., Angnes, L., (2005) J. Braz. Chem. Soc., 16, p. 1134Carvalho, A.Z., Da Silva, J.A.F., Lago, C.L., (2003) Electrophoresis, 24, p. 2138Gong, X.Y., Hauser, P.C., (2006) Electrophoresis, 27, p. 468Samcova, E., Tuma, P., (2006) Electrophoresis, 18, p. 15

Da Silva J.A.F.

De Jesus D.P.

Guimaraes I.C.

Repositorio da Producao Cientifica e Intelectual da Unicamp

www.scielo.br/eq
Volume 34, número 3, 2009
51
Comparison of Potassium and Sodium Content in Diet and 
Non-Diet Soft Drinks by Using Capillary Electrophoresis with 
Capacitively Coupled Contactless Conductivity Detection
Ivanilce Cristina Guimarães, José Alberto Fracassi da Silva, and Dosil Pereira de Jesus*
Institute of Chemistry, University of Campinas – UNICAMP, 13083-970, Campinas, SP, Brazil.
Instituto Nacional de Ciência e Tecnologia em Bioanalítica, Campinas, SP, Brazil.
*Corresponding Author: Prof. Dr. Dosil Pereira de Jesus - Grupo de Eletroforese e Microssistemas de Análise 
Instituto de Química, Universidade Estadual de Campinas - P.O. Box 6154, 13083-970 Campinas, SP, Brazil 
Fax: +55 (19) 3521-3023 - E-mail: dosil@iqm.unicamp.br 
Abstract: Capillary electrophoresis (CE) with capacitively coupled contactless conductivity 
detection (C4D) was used for determination of sodium and potassium concentrations in diet and 
non-diet soft drinks. Higher sodium concentrations were found in the diet samples due to the 
utilization of sodium salts of cyclamate and saccharine as sweeteners. The CE-C4D method can 
be used by food industries and health regulatory agencies for monitoring sodium and potassium 
content, not only in soft drink but in many others food products.
Keywords: capillary electrophoresis, capacitively coupled contactless conductivity detection, soft drinks, 
sodium, potassium
 Introduction
Sodium and potassium concentrations in 
foods are important nutritional information es-
pecially for people suffering from arterial hyper-
tension since high sodium intake leads to blood 
pressure increase, stroke, heart attack, and others 
diseases [1]. On the other hand, potassium is also 
involved in the control of many human physiolo-
gical processes, such as arterial pressure and uri-
nary calcium excretion [2]. Therefore monitoring 
potassium and sodium content in foods is always 
required by industries and health regulatory agen-
cies.
Diet soft drinks consumption has drama-
tically increased since the last decade, not only 
among people that suffer from diabetes, but par-
ticularly by those that follow low calories diet in 
order to control or loose weight. The low calo-
ries in diet soft drinks are attained by adding of 
a combination of artificial sweeteners (cyclamate, 
saccharine, acesulfame, and aspartame) instead of 
carbohydrates, such as glucose and sucrose [3]. 
However some of these sweeteners are usually 
added as sodium salts (cyclamate and sacchari-
ne) what makes diet soft drinks richer in sodium 
than ordinary soft drinks. On the other hand, diet 
soft drinks sweetened with acesulfame generally 
present a higher concentration of potassium than 
the non-diet version, since acesulfame potassium 
salts are usually used. Aspartame addition does 
not contribute to increase neither potassium nor 
sodium concentration since this peptide is added 
as a non-salt-type.
Potassium and sodium concentrations are 
usually determined by atomic absorption or emis-
sion techniques. Nevertheless, CE can be an ad-
vantageous alternative method for this application 
because it is a powerful separation technique, 
mainly for ionic compounds [4-5]. CE is able to 
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Ecl. Quím., São Paulo, 34(3): 51 - 56, 200952
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separate analytes in a short time with good reso-
lution and small sample consumption (nL). The 
coupling of CE and C4D is more suitable for small 
ions detection than the usually indirect UV-vis de-
tection method. Although utilization of C4D [6-7] 
is relatively recent it has been applied for deter-
mination of several cations, anions [8-9], sugars 
[10], amines [11] and biomolecules [12] in diffe-
rent kinds of samples. Here we use the CE-C4D 
for comparing potassium and sodium concentra-
tions in diet and normal soft drink.
Experimental
Reagents and Solutions
Analytical grade lactic acid (Lac), L-his-
tidine (His), KCl, NaCl, and LiCl were used as 
received (Fluka, Bucks, Switzerland). Deionized 
water (Nanopure UV system-Barnstead, Dubu-
que, IA, USA) was used for solutions preparation. 
A 20 mmol L-1 His/Lac buffer at pH 5.0 was used 
as background electrolyte (BGE). Stock solutions 
(100 mmol L-1) of the K+, Na+, and Li+ were pre-
pared by dissolving the solids in deionized water. 
Standard solutions were prepared by dilution of 
the stock solutions as required.
Sample Preparation
Three different commercial, non-diet and 
diet, soft drinks were acquired at local market. 
Two of the samples were guarana-flavoured soft 
drinks (samples A and B) and another one was 
a cola soft drink (sample C). The samples were 
degassed with ultrasonic bath during 10 min and 
diluted with deionized water as required. Lithium 
was introduced (100 µmol/L in the samples) as in-
ternal standard. 
CE Separation
A commercial Waters CE system with adap-
ted C4D was used for the analysis. The control and 
data acquisition was carried out with a computer 
interfaced to the equipment. A 50 cm long bare 
fused-silica capillary with internal diameter of 75 
µm was used. The effective separation length was 
40 cm, i.e. detector was placed at 10 cm from the 
capillary end. The detector was operated at 560 
kHz and 2 V peak amplitude. The separation vol-
tage was 25 kV.
Results and Discussion
Figure 1 shows electropherograms for se-
paration of K+, Na+ and Li+ (internal standard) in 
a standard solution and samples of non-diet and 
diet soft drinks. As we can see separations with 
good peak resolution were attained in less than 2.5 
min.
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fused-non-fused-Figure 1
1.4 1.6 1.8 2.0 2.2
0.4
0.6
0.8
1.0
1.2
*
*
*
32
A
1
B
C
Si
gn
al
 / 
V
Time / min
Figure 1. Electropherograms: (A) Standard solution containing 100 µmol L-1 of (1) potassium, (2) sodium, 
and (3) lithium (internal standard); (B) non-diet and (C) diet soft drinks diluted 10-fold with deionized water. 
Running buffer: 20 mmol L-1 His/ Lac. Separation voltage 25 kV; gravity injection at 100 mm for 30 s; fused-
silica capillary with 75 µm inner diameter and 50 cm long (40 cm effective); (*) not identified peaks.
Table 1 shows the main analytical characteristics of the CE method.
Table 1. Analytical characteristics of the CE method
Analytes LOD
a
(mg L-1)
LODa
(mol L-1)
LOQb
(mg L-1)
LOQb
(mol L-1)
Sensitivity
(V min mol-1 L) R
2c
K+ 0.13 3.26 x 10-6 0.43 1.08 x 10-5 0.25 0.996
Na+ 0.13 5.57 x 10-6 0.43 1.86 x 10-5 0.19 0.993
a Limit of Detection for SNR = 3; b Limit of Quantification for SNR = 10; c Regression coefficient (concentration 
range: 20 to 100 µmol L-1)
Table 2. Concentrations of K+ and Na+ in the evaluated soft drinks
Samples K+ (mg L-1) Na+ (mg L-1)
A 24 ± 4 61 ± 5
A* 15.1 ± 0.8 181 ± 24
B 22 ± 2 68 ± 2
B* 9 ± 1 124 ± 17
C 25 ± 3 43 ± 6
C* 67 ± 3 193 ± 6
* diet version of the soft drinks
Table 3. Sweeteners present in the evaluated diet soft drinks.
Sweeteners Samples that contain* Added as potassium salt Added as sodium salt
Saccharine A, B no yes
Cyclamate A, B, C no yes
Acesulfame C yes no
Aspartame B, C no no
* Only in diet version
a Limit of Detection for SNR = 3; b Limit of Quantification for SNR = 10; c Regression coefficient 
(concentration range: 20 to 100 µ ol L-1)
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Table 2 shows the results for potassium and sodium determination in the soft drink samples.
Table 2. Concentrations of K+ and Na+ in the evaluated soft drinks
Table 1. Analytical characteristics of the CE method
Analytes LOD
a
(mg L-1)
LODa
(mol L-1)
LOQb
(mg L-1)
LOQb
(mol L-1)
Sensitivity
(V min mol-1 L) R
2c
K+ 0.13 3.26 x 10-6 0.43 1.08 x 10-5 0.25 0.996
Na+ 0.13 5.57 x 10-6 0.43 1.86 x 10-5 0.19 0.993
a Limit of Detection for SNR = 3; b Limit of Quantification for SNR = 10; c Regression coefficient (concentration 
range: 20 to 100 µmol L-1)
Table 2. Concentrations of K+ and Na+ in the evaluated soft drinks
Samples K+ (mg L-1) Na+ (mg L-1)
A 24 ± 4 61 ± 5
A* 15.1 ± 0.8 181 ± 24
B 22 ± 2 68 ± 2
B* 9 ± 1 124 ± 17
C 25 ± 3 43 ± 6
C* 67 ± 3 193 ± 6
* diet version of the soft drinks
Table 3. Sweeteners present in the evaluated diet soft drinks.
Sweeteners Samples that contain* Added as potassium salt Added as sodium salt
Saccharine A, B no yes
Cyclamate A, B, C no yes
Acesulfame C yes no
Aspartame B, C no no
* Only in diet version
* diet version of the soft drinks
le . eete ers rese t i  t e e al ated diet soft drinks.
Table 1. Analytical characteristics of the CE method
Analytes LOD
a
(mg L-1)
LODa
(mol L-1)
LOQb
(mg L-1)
LOQb
(mol L-1)
Sensitivity
(V min mol-1 L) R
2c
K+ 0.13 3.26 x 10-6 0.43 1.08 x 10-5 0.25 0.996
Na+ 0.13 5.57 x 10-6 0.43 1.86 x 10-5 0.19 0.993
a Limit of Detection for SNR = 3; b Limit of Quantification for SNR = 10; c Regression coefficient (concentration 
range: 20 to 100 µmol L-1)
Table 2. Concentrations of K+ and Na+ in the evaluated soft drinks
Samples K+ (mg L-1) Na+ (mg L-1)
A 24 ± 4 61 ± 5
A* 15.1 ± 0.8 181 ± 24
B 22 ± 2 68 ± 2
B* 9 ± 1 124 ± 17
C 25 ± 3 43 ± 6
C* 67 ± 3 193 ± 6
* diet version of the soft drinks
Table 3. Sweeteners present in the evaluated diet soft drinks.
Sweeteners Samples that contain* Added as potassium salt Added as sodium salt
Saccharine A, B no yes
Cyclamate A, B, C no yes
Acesulfame C yes no
Aspartame B, C no no
* Only in diet version Only in diet version
Sodium benzoate, added as conservative, is 
the main sodium source in non-diet soft drinks. In 
diet soft drinks sweeteners (cyclamate and saccha-
rine) are added in a sodium-salt-type. For all diet 
soft drinks studied here higher sodium concentra-
tions were found compared to non-diet version. 
Therefore, people that need to control sodium 
intake has to moderate the consumption of diet 
soft drink, especially those containing cyclamate 
and saccharine. Although aspartame addition does 
not provide increase in the sodium concentration 
the diet version of the samples B and C also show 
higher sodium content than the non-diet version. 
This can also be explained by the presence of 
sodium cyclamate and saccharine salts in these 
samples. Diet soft drinks generally contain a com-
bination of two or more sweeteners in order to im-
prove taste and the sweetening power [3]. 
For all samples potassium concentrations 
were found to be lower than the respective sodium 
ones. The diet version of sample C presents the hi-
ghest potassium content (see also figure 2), which 
is larger than sodium concentration in the non-diet 
version. This can be understood by considering 
the manufacturer information that acesulfame is 
added (see table 3) as potassium salt in the diet 
version of sample C.
Ecl. Quím., São Paulo, 34(3): 51 - 56, 2009 55
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1.4 1.6 1.8 2.0 2.2
0.2
0.4
0.6
0.8
* *
*
3
2
1
B
A
Si
gn
al
 / 
V
Time / min
Figure 2. Electropherograms for (A) diet and (B) respective non-diet version of soft drinks diluted 25-fold 
with deionized water. Running buffer: 20 mmol L-1 His/Lac. Separation voltage 25 kV; gravity injection at 
100 mm for 30 s; fused-silica capillary with 75 µm inner diameter and 50 cm long (40 cm effective); Peaks: 
(1) potassium, (2) sodium, (3) lithium that was used as internal standard (100 µmol L-1), and (*) not identi-
fied peaks.
Conclusions
Sodium and potassium content in foods 
have gained a huge importance because depen-
ding on the level intake these nutrients can be har-
mful or beneficent to the human health. CE-C4D 
method used in this work is shown to be a rapid 
and low sample consumption (nL) analytical tech-
nique for potassium and sodium determination in 
soft drinks. Results obtained for soft drinks consu-
med in the Brazilian market show that diet version 
of soft drinks usually contain higher sodium con-
centration than non-diet version. That information 
is certainly helpful for people that need to control 
sodium intake. Hence, the CE-C4D technique can 
benefit food industries and health regulatory agen-
cies in monitoring concentrations of potassium, 
sodium, and other cations not only in soft drinks, 
but also in many others food products. 
Acknowledgments
This work was supported by the Funda-
ção de Amparo à Pesquisa do Estado de São 
Paulo (FAFESP), Fundação de Apoio ao Ensino, 
à Pesquisa e à Extensão da Unicamp (FAEPEX-
Unicamp), and Conselho Nacional de Desenvolvi-
mento Científico e Tecnológico (CNPq).
Ecl. Quím., São Paulo, 34(3): 51 - 56, 200956
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Article
References
[1] G. A. MacGregor, Am. J. Kidney Dis. 37 (2001) S34.
[2] F. J. He, G. A. MacGregor, Br. Med. J. 323 (2001) 497.
[3] A. Toseto, Master’s Dissertation, Universidade Estadual 
de Ponta Grossa, Brazil, 2005.
[4] M. F. M. Tavares, Quim. Nova 19 (1996) 173.
[5] J. W. Jorgenson, K. D. Lukacs, Anal. Chem. 53 (1981) 
1298.
[6] J. A Fracassi da Silva, C. L. Lago, Anal. Chem. 70 (1998) 
4339.
[7] J. A. Fracassi da Silva, N. Guzman, C. L. Lago, J. Chro-
matogr. A 942 (2002) 249.
[8] R. A. A. Munhõz, E. M. Richter, D. P. Jesus, C. L. Lago, 
L. Angnes, J. Braz. Chem. Soc. 15 (2004) 523.
[9] E. M. Richter, R. A. A. Munhõz, D. P. Jesus, C. L. Lago, 
Angnes L., J. Braz. Chem. Soc. 16 (2005) 1134.
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[11] X. Y. Gong, P. C. Hauser, Electrophoresis 27 (2006) 
468.
[12] E. Samcova, P. Tuma, Electrophoresis 18 (2006) 152.


Comparison Of Potassium And Sodium Content In Diet And Non-diet Soft Drinks By Using Capillary Electrophoresis With Capacitively Coupled Contactless Conductivity Detection

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Comparison Of Potassium And Sodium Content In Diet And Non-diet Soft Drinks By Using Capillary Electrophoresis With Capacitively Coupled Contactless Conductivity Detection

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