America n Journal of Analy tic al Chemistry, 2011, 2, 383-391
doi:10.4236/ajac.2011. 23047 Published Online July 2011 (http://www.scirp.org/journal/ajac)
383
Analytical Determination of Benzophenone-3 in Sunscreen
Preparations Using Boron-D oped Diamond Electrodes
Michelli Thomaz Laranjeira1, Fabio de Lima1, Silvio Cesar de Oliveira1, Valdir Souza Ferreira1,
Robson Tadeu Soares de Oliveira*2
1Departamento de Química, Universidade Federal de Mato Grosso do Sul, Campo Grande, Brazil
2Instituto de Ciências Biológicas e Naturais-ICBN, Universidade Federal do Triângulo Mineiro, Uberaba, Brazil
Received October 17, 2010; revised November 17, 2010; accepted May 1, 2011
Abstrac
A new electroanalytical procedure was developed for the determination of Benzophenone-3 (BENZO) in
commercial sunscreen as the active ingredient. The procedure is based on the use of electrochemical methods
as cyclic and square-wave voltammetry, with boron-doped diamond (BDD) electrodes. The reduction of
BENZO in Britton-Robinson buffer (0.1 mol·L–1) using this type of electrode gives rise to one irreversible
peak in –1.30 V (versus Ag/AgCl) in presence of cationic surfactant cetyltrimethylammonium bromide
(CTABr). The proposed electrochemical method was successfully applied to the analysis of commercially
available pharmaceu tical pr epar at ions.
Keywords: Boron-Doped Diamond, Benzophenone-3 BENZO and Square-Wave Voltammetry
1. Introduction
Benzophenone-3 (BENZO) (Figure 1) is the organic
compound widely used in sunscreen agent that absorbs
and dissipates ultraviolet radiation or in a variety of cos
metic products [1]. BENZO also has been used as ultra
violet stabilizer in p lastic surface coatings for food pack-
aging to prevent polymer or food photodegradation [2]
and is approved by the U.S. Food and Drug Adminstra-
tion as an indirect food additive.
The focus of pharmaceuticals and ingredients in per-
sonal care products, including organic sunscreen agents,
as environmental pollutants is increasing because these
compounds may enter the aquatic environment not pri-
marily as a result of manufacturing practices, but from
Figure 1 . Chemical structure of ben zophenone-3.
their steady and widespread use in human and veterinary
dai ly a ctivities [3]. Furt her more, little is kno wn about the
potential hazards associated with recurring human or
ecologic exposures to these synthetic substances, many
of which are bioactive. BENZO, one of these substances,
has been detected in surface waters [4], drinking water,
and wastewater [5]. The development of methods capa-
ble of directly quantifying BENZO in commercial phar-
maceutical preparations also becomes important in qual-
ity control of sunscreens.
The most often techniques observed in the literature
for the determination sunscreen composition are high-
performance liquid chromatography (HPLC) [6,7] and
gas chromatography (GC) coupled with various detection
methods such as ultraviolet (UV) [8] and mass spectro-
metry [9]. However, electrochemical techniques are use-
ful alternative methods widely used in pharmaceutical
applications. They are usually easy and rapid to perform
and are less expensive than chromatographic methods. In
addition, the sensitivity of electrochemical methods is
often greater t han that of spectrophotometric procedures.
A few studies have reported the use of electroanalyti-
cal methods to determine BENZO and related com-
pounds. Vidal, et al. [10] applied chemically surface-
modified carbon nanoparticles for the extraction and
electrochemical deter mina tion of phenolic impurities
such as BENZO (2-hydroxy-4-methoxybenzophenone).

M. T. LARANJEIRA ET AL. 384
The hydrophilic carbon nanoparticles were readily sus-
pended and separated by centrifugation prior to deposi-
tion onto suitable electrode surfaces and voltammetric
analysis. Voltammetric peaks provide concentration in-
formation over a 10 - 100 μM range and an estimated
limit of detection of ca. 10 μM (or 2.3 ppm) for BENZO.
Alternatively, analyte -free carbon nanoparticles immobi-
lized at a graphite or glassy carbon electrode surface and
directly immersed in analyte solution bind BENZO with
an estimated Langmuir binding constants of
6000K≈
mo l ·L−1 at pH 9.5 and it also give characteristic voltam-
metric cathodic response for BE NZO with a linear range
of ca. 1 - 120 μM. The estimated limit of detection is im-
proved to ca. 5 μM (or 1.2 ppm) for BE NZO.
Razak, et a l. [10] rep orted the use of differential pulse
polarographic method for detection and trace determina-
tion of benzophenone (the main impurity) in phenytoin
powder. The method depends upon the polarographic
activity of benzophenone in Britto n-Robinson buffer pH
5.6. The limit of detection was found to be 2.5 × 10−6
μg·mL−1. Phenytoin has been analysed polarographically
after oxidation with alkaline permanganate to give ben-
zophenone; the limit of detection was found to be 6 ×
10−6 μg·mL−1. In a study performed by Cardoso, et al.
[12], was proposed a methodology based on electro-
chemical reduction for the simultaneous determinatio n of
three sunscreen agents, namely 4-methylbenzylidene
camphor (MBC), BENZO and 2-ethylhexyl-4-methox y -
cinnamate (EHMC) by differential-pulse polarography
(DP P). The hi ghest p eak cur rents and op timal separation
of reduction peaks were obtained by using a supporting
electrolyte consisted of Britton-Robinson buffer-me t h a -
nol (8:2) solutio n at pH 4.0 a nd cationic surfactant 3.0 ×
10−4 mol ·L−1 cetyltrimethylammonium bromide
(CTABr). The methodology was validated using four
commercial sunscreen preparations as a sample and the
results sh- owed high recovery rates. The efficiency of
the proposed methodology was demonstrated by com-
paring the results obtained by DPP with those obtained
by the highperformance liquid chromatography (HPLC)
method.
The procedures in electroanalysis strongly depend on
working-electrode materials, increasing the interest in the
development of new electrode materials. Carbon materi-
als such as pyrolytic graphite, glassy carbon, and bo-
ron-doped diamond (BDD) have been widely used for
electrochemical applications [13-17]. It is well establi sh-
ed that BDD electrodes have several advantages com-
pared with other carbon surfaces. BDD electrodes have
been extensively studied in recent years, both for their
fundamental electrochemical properties [18-21] and its
various applications [22,23].
The o utstanding electrochemical features of this mate-
rial, including a wide potential window in aqueo us solu-
tions [24,25], very low background current [26], weak
adsorption for most types of organic molecules [27], high
stability of response [28,29], and good electroactivity
toward certain organic species all of which deactivate the
surface of other conventional electrodes [30,31]—make
this new material p ro mising fo r electr oanal ytical app lica -
tions [32-37], electrosynthesis [38,39], and electroche-
mical combustion [40-43], as well as for use as a sup-
porting material in electrocatalysis [44-46]. Recent stu-
dies reported in the literature have shown that several
inorganic, organic and biomolecules can be satisfactorily
determined with the use of BDD electrodes [32,47-49].
The combination of square-wave voltammetry (SWV)
and BDD electrodes has proved to be an interesting and
desirable alternative for the analytical determination of
some organic molecules [49,50]. So, in view of the lack
of a simple and direct electroanalytical method for the
determinatio n of BENZO, the purpose of this investiga-
tion is the development of an electrochemical method
capable of directly quantifying BENZO in commercial
pharmaceutical preparations available in sunscreen form,
using cyclic voltammetry and SWV with BDD as the
working electrode.
2. Experimental
The stock solution of BENZO (Merck 99%) was pre-
pared by direct weighing in order to obtain a solution 1.0
× 10−3 mol ·L −1 dissolved in methanol, followed by a di-
lution to a concentration of 1.0 × 10−4 mol ·L −1. The ca-
tionic cetyltrimethylammonium bromide (CTABr)
(Acros, New Jersey, USA) surfactant was prepared to a
concentration of 1% (m/V). The supporting electrolyte
was pre- pared by dissolution of boric acid followed by
dilution with acetic acid and phosphoric acid (all from
Merck, Darmstadt, Germany) to a concentration of 0.04
mo l · L −1. The solutions had their pH adjusted by sodium
hydroxide solution (Merck, Darmstadt, Germany). All
reagents were of analytical grade. The deionized water
was puri- fied with a Milli-Q plus system (Millipore,
Bedford, MA, USA). The samples were prepared by di-
rect weighing in a 15 mL beaker, followed by solubiliza-
tion in 10 mL of methanol with sonication for 5 min.
This solution was quantitatively transferred to a 25 mL
volume tric flask and methanol was added to the mark.
The use of methanol in the supporting electrolyte was
necessary due to the low solubility of the sunscreen
agents in aqueous me dium.
The BDD electrodes were prepared in the Centre
Suisse d’Electronique et de Microtechnique SA (CSEM),
Neuchâtel, Switzerland, using the hot filament chemical
vapor deposition (HF-CVD) technique with filament

M. T. LARANJEIRA ET AL. 385
temperatures in the range of 2440˚C - 2560˚C and a ga-
seous mixture containing methane, H2, and trimethylbo-
ron, with a final boron content of the order of 800 ppm.
The electrochemical experiments were carried out in a
single-body Pyrex glass cell provided with three elec-
trodes and degassing facilities for N 2 bub b li ng. The B D D
electrode was glued onto a copper plate using a silver
paste as previously reported in the literature [49,50]. T he
copper plate and the BDD edges were later isolated with
Araldite® resin, leaving an exposed area of 0.025 cm2.
The reference electrode used was Ag/AgCl, where the
all potentials are referred to this electrode. The auxiliary
electrode was a 2.0 cm2·Pt foil. The electrochemical ex-
periments were also performed using a Model 283 EG&
G PARC electrochemical instrument controlled by a per-
sonal micro computer through the EG&G Princeton Ap-
plied Research model 270 Research Electrochemistry
Software. All solutions were deoxygenated by bubbling
N2 for 10 min prior to measurements and the solutions
were blanketed with the ga s d uri n g mea s urements .
Analytical curves were obtained by means of spiking
the supporting electrolyte. The measurements were per-
formed without pre-treatment of the solutions, but pH
was appropriately adjusted to the desired value.
3. Resul t s and Discussion
3.1. Electrochemical Behavior
A cathodic polarization was necessary for conditioning
the BDD surface prior to electroanalytical determina-
tions. Such pre-treatment improves the voltammetric
response of BDD surfaces, resulting in very low quanti-
fication limits and high data reproducibility [20]. Sala-
zar-Banda, et al. [21] observed that after cathodic
pre-treatments BDD electrodes exhibit dynamic electro-
chemical behav- ior—i.e., a progressive decrease in the
electron transfer rate for the Fe(CN)64–/3– redox couple as
a function of time. This behavior has to be associated
with a loss of superficial hydrogen due to oxidation by
oxygen from the air. These results stress the need for
performing ca- thodic pre-treatment just before the elec-
trochemical ex- periments are conducted, in order to en-
sure reliable and reproducible results. In the literature
there are several papers that used BDD electrode cathod-
ically pretreated for electroanalytical applications
[45,46,49-51]. Thus, before each analysis the BDD elec-
trodes were pre-treated at + 3.2 V, in order to oxidize
possible adsorbed species on the electrode surface, and
after at –2.8 V (vs. Ag/AgCl), 30 s each, in HClO4 solu-
tion (0.1 mol·L–1).
In this investigation, cyclic (CV) and square wave
voltammetry (SWV) were utilized as electroanalytical
tools for BENZO determination in aqueous solutions
using sunscreen such as amount (commercial pharma-
ceutical preparations). Initially the cyclic voltammetric
experiments were conducted using a standard solution of
BENZO (2.0 × 10–4 mo l ·L–1) in Britton-Robinson buffer
solution (pH 6). The voltammetric profile of currents
shown in Figure 2 reveals a peak related to reduction of
BENZO on the BDD electrode in presence of cationic
surfactant cetyltrimethylammonium bromide (1.0%
m/V).
It can be observed (Figure 2) the presence of a well-
defined irreversible peak in the presence of surfactant
(CTABr) cationic BENZO reduction in BDD, as well a
Figure 2. Cyclic voltammogram obtained in media of B-R
buffer solution (pH 6) on a BBD electrode (solid line) and
for be nz op he n on e-3 (2.0 × 10–4 mol·L–1) in presence (d ashe d
line) and absence (doted line) of CTABr (1.0% m/v) on a
BDD electrode at 0 .1 V·s–1.
Figure 3. Dependence of the current peak of benzo phe-
none-3 (1.0 × 10–4 mol·L–1) on the CTABr concentration in

M. T. LARANJEIRA ET AL. 386
Britton-Robinson buffer solution (pH 6), Scan rate 0.1 V·s–1.
shift in peak potential for considerably less negative val-
ue and thus away from discharge potential of electro-
lyte. The influence of concentration on CTABr BENZO
reduction in BDD was inve stigated (Figure 3). However,
the BENZO reduction response on BDD was studied in
presence of CTABr in range of 1.30 × 10–5 until 1.43 ×
10–4 mol·L–1 using as electrolyte B-R buffer solution
(pH6). The best results with respect to enhancement a nd
shape of the peak current were obtained with 4.0 × 10–5
mo l ·L–1 of CTABr.
Meanwhile, the influence of pH of supporting electro-
Figure 4. Influence of pH on peak current and pea k poten-
tials for cyclic voltammetry on a BDD electrode for benzo-
phenone-3 (1.0 × 10–4 mol·L–1) in Britton-Robinson buffer
solutions (0.1 mol·L–1). [CTABr] = 4.0 × 10–5 mol·L–1 and
Scan r ate, 0.1 V·s–1.
Figure 5. Dependence of the current peak on frequency at
20 mV as amplitude value for experiments carried out un-
der the following conditions: [CTABr] = 4.0 × 10–5 mol·L–1,
benzophenone-3 (1.0 × 10–4 mol·L–1) in Britton-Robinson
buffer solution (pH 6) and
s
E
= 2 mV .
lyte on the reduction of BENZO in the presence of
CTABr was studied in the pH range of 2 - 10 by using
CV. These experiments showed that the analytical signal
obtained had a significant increase between pH 2 and 6
(Figure 4) and that to higher pH values the peak current
decreases slightly up to pH 10. Quantitatively, data on
the response of peak current showed the best values with
neutral solutions. This finding led to the choice of Brit-
ton-Robinson buffer at pH 6 and CTABr (4.0 × 10–5
mo l ·L–1) as electrol yte for the analytical determinatio ns.
It is also observed that with increasing pH of electro-
lyte, there is a shift of peak potential to more negative
values, indicating that a chemical reaction (proton trans-
fer reaction) precedes the process that occurs at the elec-
trode surface [52].
3.2. Optimization of SWV Parameters
Several experimental parameters related to the square-
wave potential scan, such as frequency (
f
) and ampli-
tude (
sw
E
), were studied and optimized to provide
maximal current peak (
p
I
) and repeatability. Thus, the
amplitude and frequency of SWV for the standard solu-
tion of BENZO (1 × 10–4 mol ·L–1) in B -R buffer solution
pH 6 with CTABr were analyzed. SWV amplitude was
evaluated using 100 Hz as frequency value and 2 mV as
scan increment. The maximum current peak at amplitude
was obtained in approximately 20 mV. Likewise, Figure
5 reveals that the frequency exhibits linear behavior
when
p
I
does not exceed 90 Hz, whereas for values
higher than 120 Hz no contribution can be observed in
the electroanalytical response. Linear behavior of fre-
quency as a function of Ip is characteristic of an electro-
chemical irreversible process [53,54]. The solid lines
presented in Figure 5 show the deviations of the l inearity
between
p
I
vs frequency.
3.3. Analytical Application
The electroanalytical determination of BENZO was per-
formed using the maximal values of peak current as a
function of amplitude and the frequency values. In this
case, these conditions are interrelated and optimal peak
current oxidatio n of BEN ZO was ob tained on BDD e lec-
trodes using 90 Hz and 20 mV vs Ag/AgCl as SWV fre-
quency and amplitude, respectively.
With these optimized voltammetric parameters, an
electroanalytical methodology were developed for de-
termination of BENZO in pharmaceutical preparations.
The square-wave voltammograms of the standard solu-
tions as a function of BENZO concentration in aqueous
solution pH 6 (B-R buffer) in presence of CTABr are

M. T. LARANJEIRA ET AL. 387
shown in Figure 6(a). The calibration plot yielded a
straight line (
0.998r=
,
3n=
) for BENZO (Figure
6(b)). Linear regression analysis of current (µA) versus
concentration (mol·L–1) profiles showed a reasonable
linearity from 1.5 × 10–5 to 1.95 ×10–4 mo l·L–1 on the
BDD electrode, as shown in the inset of Figure 6.
The dete rmination (LD) a nd quantifica tion (LQ) li mits
for BENZO were obtained in aqueous solutions (B-R
buffer, pH 6) using the procedure recommended by IU-
PAC [55-57]. Thus, the standard deviation of the mean
value of currents (
B
S
) measured at the BENZO reduc-
tion potential for 10 voltammograms of the blank solu-
tion in different samples was used in conjunction with
the slope of the straight l ine (
b
) of t he anal ytical c urves
(Figure 6(b)) and Equation 1 and 2:
3
B
S
LD b =
(1)
10
B
S
LQ b =
(2)
The detection and quantification limits were obtained
for five determinations of BENZO in pure water using
BDD electrodes and SWV as the analytic technique. The
results of the linear regression of the analytic curve and
detection and quantification limits are presente d i n Table
1. The SWV method was applied to determine the
BENZO content in commercial sunscreen. Determination
of BENZO content in the preparation was performed by
using the standard addition method. Each sample of
cosmetic was treated as described in experimental sec-
tion.
Figure 6 . (a) Square-w ave v olta mmet ry res pons es of a B DD
electrode for different benzophenone-3 concentrations in
Britton-Robinson buffer solution (pH 6); (b) Linear de-
pendence of the peak current on benzophenone-3 concen-
tration. [CTABr] = 4.0 × 10–5 mol·L–1,
f
= 90 Hz,
a
=
20 mV,
s
E
= 2 mV.
Table 1 . Re sult of the l in ear regressio n of the a nal yti c curve
and detection and qua ntification limits obtai ned for benzo-
phenone-3 in medium of B-R buff er pH 6.
Sample
Intercept
(µA)
Slope
(mA/mol·L-1) Sb (µA)
DL (× 10–7
mol·L-1)
QL (× 10–7
mol·L-1)
Benzo-
phenone 1.20 ± 0.45
1.48 × 102 ±
18.5 0.007 1.37 ± 0.12
4.54 ± 0.4
All measurements were performed in triplicate. The
recovery efficiencies (
%R
) for the s yste ms unde r invest-
tigation were calculated using Equation 3, where the
“found” value refers to the concentration obtained by
extrapolation o f the ana lyti cal cur ve in the c or resp ond ing
standard solution of BENZO.
[ ]
[ ]
Benzophenone-3 found
%100 Benzophenone-3 added R=
(3)
The pharmaceutical preparations analyzed were sun-
screen containing BENZO (5% w/w). In Figure 7 it can
be observed that the voltammetric behavior of the
BENZO present in the pharmaceutical preparation is
similar to that obtained with a standard solution (Figure
6(a)).
No influence of others agents content in sunscreen
such as octyl metoxycinammate, propyleneglycol or 4-
methylbenzilid ine camphor on the vo ltammetric response
was thus observed in the interest potential range. The
recoveries of known amounts of BENZO contained in
pharmaceutical preparations (Table 2) ranged from
97.2% to 98.1%.
Figure 7. Square-wave voltammograms profiles of benzo-
phenone-3 contained in a commercial pharmaceutical pre-
paration in Britton-Robinson buffer solution (pH 6).
[CTABr] = 4.0 × 10–5 mol·L–1,
f
= 90 Hz,
a
= 20 mV,

M. T. LARANJEIRA ET AL. 388
s
E
= 2 mV .
Table 2 . Rec overies of benzop henone-3 samples in commer-
cial cosmetic preparations (nominal conc. 5.0% w/w) using
square wave voltammetry experiments carried out using
the following conditions:
f
= 90 Hz,
a
= 20 mV and
s
E
= 2 mV (
n
= 3).
Sunblock
Lotion
Added (mol·L–1
benzophenone-3)
Found (mol·L–1
benzophenone-3) Recovery (%)
R.S.D (%)
A 1.00 × 10–5 9.81 × 10–6 98.1 0.8
B 1.00 × 10–5 9.72 × 10–6 97.2 1.1
C 1.0 × 10–5 9.78 × 10–6 97.5 0.9
4. Conclusions
In this investigation, BENZO was found to provide a
reductive peak when cyclic and square-wave voltam-
metry experiments where conducted using BDD elec-
trodes. Based on these experiments, an electroanalytical
method for the determination of BENZO in water and
commercial sunscreen was developed. The electro-
chemical responses of pharmaceutical preparations were
identical to those of standard BENZO and no influence
of others agents content in sunscreen on the voltammet-
ric responses was observed. BENZO recoveries values
ranged from 97.2% to 98.1% demonstrate the elevated
efficiency of the methodology. Consequently, given it’s
easily of use, high sensitivity, and brevity, the method
proposed can be successfully used to determine trace
amounts of BENZO in several commercial products.
5. Acknowledgements
The authors thank the Brazilian Research Funding Insti-
tutions CNPq, Capes, Fundect and Fapemig for financial
support.
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