American Journal of Anal yt ical Chemistry, 2011, 2, 919-928
doi:10.4236/ajac.2011.28106 Published Online December 2011 (
Copyright © 2011 SciRes. AJAC
Chemical Fingerprinting of Counterfeits of Viagra and
Cialis Tablets and Analogues via Electrospray Ionization
Mass Spectrometry
Rafael S. Ortiz1,2, Kristiane de Cássia Mariotti2, Wanderson Romão3,4*, Marcos N. Eberlin3,
Renata P. Limberger2, Paulo Mayorga2
1Rio Grande do Sul Technical and Scientifical Division, Brazilian Federal Police,
Porto Alegre, Brazil
2Departme n t of Pharmacy , Federal University of Rio Grande do Sul, Porto Alegre, Brazil
3ThoMSon Mass Spectrome try Laboratory, Institute of Chemistry, University of Campinas -
UNICAMP, Campinas, Brazil
4Department of Chemistry, Federal University of Espírito Santo, Vitória, Brazil.
Received October 18, 2011; revised November 25, 2011; accepted December 13, 2011
Direct infusion electrospray ionization mass spectrometry (ESI-MS) is shown to provide an efficient tech- nique
for the investigation of polar composition of forensic tablets for male erectile dysfunction. ESI-MS fingerprinting
of 41 commercial sildenafil samples (Viagra®, Cialis®, Lazar®, Libiden®, Maxfil®, Plenovit®, Potent 75®, Rigix®,
V-50®, Vimax®, Pramil 75® and Pramil®) and 56 counterfeit samples (Viagra and Cialis) were obtained. The
spectra for the authentic Viagra® tablets showed abundant ions exclusively corresponding to the sildenafil (SLD)
molecule: [SLD + H]+ of m/z 475; [SLD + Na]+ of m/z 497; and [2SLD + H]+ of m/z 949. The spectra for com-
mercial sildenafil samples also showed predominat SLD ions. Tablets of authentic Cialis® showed mainly ions of
m/z 343, 365 and 707 from the lactose molecule (the excipient); as well as a minor ion of m/z 390 corresponding
to the active ingredient tadalafil (TAD) in its protonated form [TAD + H]+. For counterfeit Cialis samples, how-
ever, normally TAD ions of much high abundances was observed, together with ions corresponding to sildenafil
analogues such as those of m/z 489 (homosildenafil) and 505 (hydroxyhomosildenafil). Principal component
analysis was applied to ESI-MS fingerprint data, placing samples according to their contents of active ingredients
hence authentic and counterfeit samples are easily recognized.
Keywords: ESI-MS, Fingerprinting, Counterfeiting, Viagra®, Cialis®
1. Introduction
Sildenafil (SLD) and tadalafil (TAD) are selective
inhibitors of phosphodiesterase type-5 (PDE-5) [1]
acting therefore as efficient drugs to treat male erectile
dysfunction. The two most common commercial formu-
lations containing these active pharmacological ingre-
dients (API) are Viagra® (sildenafil citrate, Pfizer) and
Cialis® (tadalafil, Eli Lilly)1 and the analysis of their
tablets is currently a common practice for many forensic
laboratories. Besides the criminal aspect, the illegal trade
of these drugs can cause serious health problems due to
uncontrolled amounts, low quality and diverse com-
positions. The counterfeiting of inhibitors of PDE-5 has
become an important and dangerous problem for phar-
maceutical market. Therefore, rapid and secure analytical
tools able to control the quality of pharmaceutical for-
mulations are highly desirable.
The identification of SLD or TAD in pure form or in
pharmaceutical formulationsincluding counterfeits
have been performed by different analytical techniques
such as Raman spectroscopy, nuclear magnetic resonance
spectroscopy, Fourier transform infrared spectroscopy,
liquid chromatography, mass spectrometry using elec-
trospray ionization or fast-atom bombardment, and X-ray
diffractometry [2-8].
Direct infusion electrospray ionization mass spec-
1The symbol ® will be used only in reference to the original medicines.
trometry (ESI-MS) has been shown to provide a fast and
robust technique for quality control of complex chemical
mixtures such as those of alcoholic [9] and non alcoholic
[10] beverages, biodiesel [11], coffees [12], perfumes
[13], vegetable oils [14], propolis [15] and drugs of
abuse [16]. The use of direct infusion ESI-MS in the
chemical characterization of forensic samples of PDE-5
inhibitors seems therefore advantageous, since it would
eliminate the need for isolation and prior chromato-
graphic separation, minimizing the time of analysis and
interferences. Chemometrics methods applied to ESI-MS
data [17,18] could also improve selectivity for secure
counterfeit screening.
In this study, ESI-MS in the positive ion mode was
shown to provide fast (less than a minute) and secure
technique of the forensic analysis of samples of PDE-5
inhibitors. To test this ability, forty one commercial
samples (Viagra®, Cialis®, Lazar®, Libiden®, Maxfil®,
Plenovit®, Potent 75®, Rigix®, V-50®, Vimax®, Pramil
75® and Pramil®) and fifty seven counterfeit samples
(Viagra and Cialis) were analyzed, and the data subjected
to principal component analysis, PCA.
2. Materials and Methods
HPLC-grade methanol and formic acid solutions were
purchased from Sigma-Aldrich and used with no further
purification. Eight authentic samples of Viagra® and
Cialis® containing 50 mg of SLD (4) and 20 mg of TAD
(4), respectively, were supplied by Pfizer Ltda and Eli
Lilly do Brasil Ltda laboratories. The thirty three tablets
of different trademarks of foreign origin and fifty six
counterfeit samples (Table 1) were provided by the Bra-
zilian Federal Police forensic laboratory (Rio Grande do
Sul, Brazil).
2.1. ESI-MS
An API 2000 Q-Trap LC-MS/MS mass spectrometer
from MDS Sciex/Applied Biosystems (Foster City, CA,
USA) coupled to a Alliance 2695 Separations Module
LC (Waters, Milford Massachusetts, USA) was used.
Data acquisition and processing were performed using
the Analyst software from Applied Biosystems (Foster
City, CA, USA). General conditions were as follows:
source temperature of 100˚C, capillary voltage of 3.0 kV
and cone voltage of 40 V. The sample preparation con-
sists in dissolution of a small fractionabout 10 mgof
the core of each tablet in a solution containing 40 mL of
methanol and 40 μL of concentrated formic acid aqueous
solution. ESI-MS was performed with the automatic in-
jection of each sample in the module chromatography
(LC) programmed to elute all the soluble components in
a single peak. Mass spectra were acquired and accumu-
lated over 60 s on the range of m/z 50 to 1000. Structural
analysis of some diagnostic ions was performed by
ESI-MS/MS using collision energies varying from 15 to
45 eV. The collision gas pressure (argon) was optimized
to produce extensive fragmentation of the ions under
2.2. Chemometric Treatment
Multivariate analysis by PCA was performed by running
the software STATISTICA, version 7 (StatSoft®). The
ESI-MS data were compiled to generate a final matrix of
Table 1. Details of seizure samples investigated.
Samples Number of
samples seized
Number of
samples analyzed
of seizure Samples Number of
samples analyzed
Viagra® - 4 - Lazar® 3
132 10 I Potent 75® 2
8 1 II Vimax® 3
3 1 III Maxfil® 3
Counterfeit Viagra
9 7 IV Rigix® 2
Cialis® - 4 - Plenovit® 6
6 1 V Pramil® 8
7 1 VI Pramil® 75 2
40 16 VII V-50® 3
40 10 VIII Libiden® 1
Counterfeit Cialis
40 9 IX
Copyright © 2011 SciRes. AJAC
Copyright © 2011 SciRes. AJAC
97 cases (samples) and 99 variables (m/z values with their
respective relative intensities). Only ions with a relative
abundance higher than 10% were considered for the final
matrix data. These data were previously mean-centered
and auto scaled to variance 1, ensuring an equal contri-
bution of all variables.
3. Results and Discussion
3.1. ESI(+)-MS Fingerprinting
A set of 23 Viagra samples classified as authentic (4) or
counterfeit (19) termed as I, II, III and IV (Table 1),
were analyzed by ESI(+)-MS. Figure 1(a) shows typical
ESI(+)-MS obtained for authentic Viagra® tablets. The
main ions correspond to the SLD molecule detected in
different forms such as [SLD + H]+ of m/z 475; [SLD +
Na]+ of m/z 497; [2SLD + H]+ of m/z 949, and fragment
ions of m/z 377, 311, 283 and 99 [19,20]. Therefore,
ESI(+)-MS provides, for the methanolic extract, a typical
fingerprint data showing mainly SLD ions from the ac-
tive pharmaceutical ingredient present in standard Via-
gra® samples.
To confirm SLD detection, ESI(+)-MS/MS was per-
formed for the ions of m/z 475 and 949 (Figures
2(a)-(b)). The collision-induced dissociation (CID) of
[SLD + H]+ of m/z 475 (Figure 2(a)) agrees well with its
structure and connectivity, and reported spectra [8]. The
ion of m/z 949 [2SLD + H]+ formed, as expected, [SLD +
H]+ of m/z 475 as the main fragment (Figure 2(b)).
Figures 1(b)-(e) show ESI(+)-MS spectra for coun-
terfeit Viagra samples (seizures I-IV, Table 1). SDL ions
also predominate but for seizures I and II (Figures
1(b)-(c)), the ESI(+)-MS detects an ion of m/z 489 cor-
responding probably to the protonated molecule of an
immediate analogue of SLD. The ESI(+)-MS/MS data
for this ion (Figure 2(c)) display fragments similar or the
same as those produced by [SDL + H]+: those of m/z 58,
70, 84, 99, 254, 283, 297, 313 and 325. This molecule
can be attributed to homosildenafil (HSD), being distin-
guished from another possible isomer, vardenafil, by the
absence of an abundant ion of m/z 151 [21]. The pres-
ence of analogue species of SLD can result from inten-
tional addition or from inadequate purification.
Figure 1(e) shows the presence of low abundant but
unique ions of m/z of 221, 237, 355, 429 and 445. For
sample III, however, a very similar ESI(+)-MS data as
that observed for authentic Viagra® samples (Figure 1(d))
was acquired.
Authentic and counterfeit Cialis samples were also
analyzed by ESI(+)-MS (Figures 3(a)-(f)). The spectrum
for the authentic Cialis® sample (Figure 3(a)) shows a
low abundant but diagnostic [TAD + H]+ ion of m/z of
390. More abundant ions were attributed to the lactose
excipient , that is: [lactose + H]+ of m/z 343; [lactose +
Na]+ of m/z 365; and [2lactose + Na]+ of m/z 707 [25,26].
Cialis tablet are known to contain 20 mg of TAD and
245 mg of lactose.
The structures of the ions of m/z 365, 390 and 779
were investigated by ESI-MS/MS (Figures 4(a)-(b)).
[TAD + H]+ of m/z 390 dissociated as expected from
reported data (Figure 4(a)) [21] whereas the proton-
bonded dimer [2TAD + H]+ of m/z 779 dissociates
mainly to [TAD + H]+ of m/z 390 (Figure 4(b)). For
[lactose + H]+ of m/z 365 (Figure 4(c)) also dissociated
as expected from reported data [17,22] whereas
[2Lactose + Na]+ forms [lactose + Na]+ of m/z 365.
The counterfeit Cialis samples displayed very con-
trasting and variable spectra (Figures 3(b)-(f)). Seizure
V displayed much more abundant TAD ions which indi-
cate the (potentially harmful) use of higher amounts of
the active ingredient. For seizures VI, VIII and IX, how-
ever, instead of TAD ions, abundant SLD ions were de-
tected. For seizure VII, both TAD and SDL ions were
detected. An ion of quite low abundance (m/z 505) was
also observed in Figure 3(b) corresponding to another
analogue of SLD, namely hydroxyhomosildenafil (OH-
HSD) [23], as confirmed by ESI(+)-MS/MS (Figure
2(d)) [21]. The HSD and OH-HSD analogues display
higher pharmacological activity than SLD [24].
For commercial samplesknown to be manufactured
in neighboring countries as Paraguay and Uruguaytwo
most typical EASI(+)-MS data were obtained: samples
commercialized under the trademarks Lazar®, Potent 75®,
Vimax®, Maxfil®, Rigix®, Plenovit® and Pramil® (Figure
5(a)) show only SLD ions whereas samples of Pramil
75®, V-50® and Libiden® (Figure 5(b)) showed also the
presence of lactose ions. These drugs are not approved
by the National Health Surveillance Agency (ANVISA)
to be sold in Brazil, but the ESI(+)-MS data show similar
compositions as those of the commercial samples (Fig-
ure 1(a)).
3.2. Chemometry
ESI(+)-MS data were subjected to chemometric treat-
ment via PCA, Figures 6-7. PCA was used to statistic-
cally evaluate the performance of ESI-MS fingerprints in
classifying of sildenafil citrate and tadalafil samples for
quality control purposes. Figures 6 shows PC1 x PC2 x
PC3 scores plots, where the 3 first PCs account for 91%
of total variance. Three groups are observed: authentic
Viagra®, counterfeit Viagra, commercial and some
counterfeit Cialis samples containing the SLD molecule
form group I; counterfeit Cialis samples containing the
TAD molecule form group II; and authentic Cialis® sam-
ples form group III. The ion of m/z 707, 475, 412, 390, s
Figure 1. ESI(+)-MS of representative (a) authentic Viagra® and counterfeit Viagra samples: (b) I, (c) II, (d) III and (e) IV.
Copyright © 2011 SciRes. AJAC
Figure 2. ESI(+)-MS/MS for some diagnostic ions: (a) [SLD + H]+ of m/z 475; (b) [2SLD + H]+ of m/z 949; (c) [Homosil-
denafil + H]+ of m/z 489; and (d) [Hydroxyhomosildenafil + H]+ of m/z 505.
Copyright © 2011 SciRes. AJAC
Copyright © 2011 SciRes. AJAC
Figure 3. ESI(+)-MS for authentic and counterfeit Cialis® samples.
Copyright © 2011 SciRes. AJAC
Figure 4. ESI(+)-MS/MS for some diagnostic ions: (a) [TAD + H]+ of m/z 390; (b) [2TAD + H]+ of m/z 779; (c) [Lactose + Na]+
of m/z 365; and (d) [2Lactose + Na]+ of m/z 707.
Figure 5. ESI(+)-MS spectra of commercial products as (a) Pramil®, Lazar®, Maxfil®, Plenovit®, Potent 75®, Rigix®, Vimax®;
and (b) Pramil 75®, V-50® and Libiden®.
Copyright © 2011 SciRes. AJAC
Copyright © 2011 SciRes. AJAC
365, 268, 262, and 58 have a greatest influence for the
3PCs loadings.
feit Viagra samples) and group IB (commercial SLD
Authentic Viagra® and counterfeit Viagra samples
were both grouped together (group I) in Figure 6 There-
fore, a new PCA analysis was performed treating only
the samples from group 1 (Figure 7). Note that this pro-
cedure provides now two subgroups: group IA (counter-
4. Conclusions
Direct infusion ESI(+)-MS of methanolic extrats of tab-
lets provides a relatively simple and fast screening tool
control the quality and to characterize via chemical pro-
files sildenafil and tadalafil tablets for forensic investiga-
tions. This technique requires little sample preparation,
minimizing interferences. Principal component analysis
(PCA) applied to ESI-MS fingerprint data helps to clas-
sify the samples in a more unbiased mode.
5. Acknowledgements
The authors thank the Brazilian Federal Police for pro-
viding the sildenafil citrate and tadalafil samples. This
research has also been generously funded by: FAPESP,
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