Development and validation_of_a_normal-p

Journal of Chromatography A, 1216 (2009) 7102–7107
Contents lists available at ScienceDirect
Journal of Chromatography A
journal homepage: www.elsevier.com/locate/chroma
Development and validation of a normal-phase high-performance thin layer
chromatographic method for the analysis of sulfamethoxazole
and trimethoprim in co-trimoxazole tablets
D.H. Shewiyoa,b,c, E. Kaaleb L.T., ,Muungo P.G.Rishab
, B. Dejaegherc , J. Smeyers–Verbekec
,
Y. Vander Heydenc,∗
a
Directorate of Laboratory Services, Tanzania Food and Drugs Authority, P.O. Box 77150, Dar es Salaam, Tanzania
b
School of Pharmacy, Muhimbili University of Health and Allied Sciences, P.O. Box 65526, Dar es Salaam, Tanzania
c
Analytical Chemistry and Pharmaceutical Technology, Pharmaceutical Institute, Vrije Universiteit Brussel (VUB), Laarbeeklaan 103, 1090 Brussels, Belgium
a r t i c l e i n f o
Article history:
Received 7 July 2009
Received in revised form 25 August 2009
Accepted 28 August 2009
Available online 1 September 2009
Keywords:
Method development
Method validation
Normal-phase HPTLC
Sulfamethoxazole (SMX)
Trimethoprim (TMP)
Co-trimoxazole tablets
a b s t r a c t
Pneumocystis carinii pneumonia (PCP) is often the ultimate mortal cause for immunocompromised indi-
viduals, such as HIV/AIDS patients. Currently, the most effective medicine for treatment and prophylaxis
is co-trimoxazole, a synergistic combination of sulfamethoxazole (SMX) and trimethoprim (TMP). In
order to ensure a continued availability of high quality co-trimoxazole tablets within resource-limited
countries, Medicines Regulatory Authorities must perform quality control of these products. However,
most pharmacopoeial methods are based on high-performance liquid chromatographic (HPLC) methods.
Because of the lack of equipment, the Tanzania Food and Drugs Authority (TFDA) laboratory decided to
develop and validate an alternative method of analysis based on the TLC technique with densitometric
detection, for the routine quality control of co-trimoxazole tablets. SMX and TMP were separated on glass-
backed silica gel 60 F254 plates in a high-performance thin layer chromatograph (HPTLC). The mobile phase
was comprised of toluene, ethylacetate and methanol (50:28.5:21.5, v:v:v). Detection wavelength was
254 nm. The Rf values were 0.30 and 0.61 for TMP and SMX, respectively. This method was validated for
linearity, precision, trueness, speciﬁcity and robustness. Cochran’s criterion test indicated homoscedas-
ticity of variances for the calibration data. The F-tests for lack-of-ﬁt indicated that straight lines were
adequate to describe the relationship between spot areas and concentrations for each compound. The
percentage relative standard deviations for repeatability and time-different precisions were 0.98 and
1.32, and 0.83 and 1.64 for SMX and TMP, respectively. Percentage recovery values were 99.00% ± 1.83
and 99.66% ± 1.21 for SMX and TMP, respectively. The method was found to be robust and was then
successfully applied to analyze co-trimoxazole tablet samples.
© 2009 Elsevier B.V. All rights reserved.
1. Introduction
One of the most common opportunistic infections in HIV/AIDS
patients is pneumocystis carinii pneumonia (PCP) caused by
Pneumocystis jirovecii, which mostly attacks the lungs. It is
often the ultimate mortal cause for immunocompromised
individuals. Currently, the most effective treatment is co-
trimoxazole, a synergistic combination of sulfamethoxazole and
trimethoprim in a ratio of 5:1 [1–3]. Chemically SMX is 4-
amino-N-(5-methyl-3-isoxazolyl) benzene sulfonamide and TMP
5-(3,4,5-trimethoxybenzyl) pyrimidine-2,4-diamine (Fig. 1). Co-
trimoxazole is lifesaving, simple and provides inexpensive
intervention against PCP.
∗ Corresponding author. Tel.: +32 2 477 47 34; fax: +32 2 477 47 35.
E-mail address: yvanvdh@vub.ac.be (Y. Vander Heyden).
In an effort to facilitate adoption of co-trimoxazole prophylaxis
against PCP in resource-limited countries, the World Health Organi-
zation (WHO) has developed guidelines providing global technical
and operational recommendations for the use of co-trimoxazole
prophylaxis in HIV-exposed children, children living with HIV, and
adolescents and adults living with HIV in the context of scaling
up HIV care [2]. It is therefore imperative for resource-limited
countries to ensure that high quality co-trimoxazole products are
continuously available in their markets for effective implementa-
tion of these recommendations.
The Tanzania Food and Drugs Authority (TFDA), a regulatory
body under the Ministry of Health and Social Welfare, is imple-
menting a two tier quality assurance program where, at the ports
of entry, inspectors are trained and provided with a Minilab® kit
for screening selected medicines in tier one [4]. The Minilab® kit
is a non-laboratory-based Thin Layer Chromatography (TLC) test-
ing kit. It can be used as a stand-alone testing site in remote areas
0021-9673/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.chroma.2009.08.076
b b
c

D.H. Shewiyo et al. / J. Chromatogr. A 1216 (2009) 7102–7107 7103
Fig. 1. Chemical structures of (a) sulfamethoxazole and (b) trimethoprim.
with minimal facilities. The tier two site is the central TFDA labo-
ratory which performs full pharmacopoeial monograph testing to
determine compliance to legal standards for samples which failed
the screening tests [4]. The analytical method currently used for
the analysis of co-trimoxazole in this laboratory is the HPLC one
described in the United States Pharmacopoeia (USP) [5]. However,
the lack of equipment and the long analysis time significantly affect
timely release of laboratory results for regulatory action. Therefore,
there was a need for an alternative method.
Most of the methods reported in the literature to analyze co-
trimoxazole in pharmaceutical dosage forms, as well as in biological
fluids, use HPLC [6–13] or spectrophotometry [14,15]. The draw-
backs of HPLC for the TFDA laboratory have been mentioned. A
spectrophotometric method also was not favored since the aim was
to maintain and strengthen the use of the TLC technique. To our
knowledge, the only method revealed in the literature using high-
performance thin layer chromatography (HPTLC)—densitometry
for the analysis of co-trimoxazole is reported by Dhasan et al. [16],
where the effect of cystone on the availability of SMX and TMP in
rabbits was studied. The drugs were assayed from rabbit’s plasma
and the TLC plate was scanned at two wavelengths, i.e. 265 and
350 nm for SMX and TMP, respectively. To apply the method for the
analysis of SMX and TMP in dosage form formulations this method
requires modifications in sample pretreatment, as well as the use
of only one single wavelength to reduce analysis time.
In this study, a method for the routine analysis of SMX and
TMP in co-trimoxazole tablets, which is precise, true, robust, and
quick, is developed and validated. This method is based on HPTLC
with ultraviolet/visible (UV/vis) densitometry scanning at a single
wavelength. It strengthens tier two of the quality assurance pro-
gram at the main TFDA laboratory by utilizing the same organic
solvents as with the Minilab® kit. It also sustains the benefits of
TLC, where up to 20 samples simultaneously can be analyzed on
one plate. This results in a fast analysis with less cost per run and
limited mobile phase consumption. Repeated scanning can be done
by changing the scanning conditions [17,18]. The method was val-
idated for linearity, precision, trueness, specificity and robustness,
as recommended [19,20].
2. Experimental and methodology
2.1. Materials, chemicals and equipment
Ethylacetate was procured from Applichem (Darmstadt, Ger-
many), methanol from Merck (Darmstadt) and toluene from BDH
(Poole, England). All were of analytical grade.
SMX and TMP reference standards were obtained from the
WHO Collaborating Centre for Chemical Reference Substances
(Stockholm, Sweden). The tablet formulation matrix without active
ingredient was a gift from Shelys Pharmaceuticals (Dar es Salaam,
Tanzania). The matrix contained microcrystalline cellulose, sodium
starch glycolate, magnesium stearate and purified starch. Co-
trimoxazole tablets from different manufacturers were bought
from retail pharmacies in Dar es Salaam, Tanzania.
HPTLC glass plates pre-coated with silica gel 60 F254
(10 cm × 20 cm) were from Merck. Densitometry was carried out
with a Camag TLC Scanner 3 (Muttenz, Switzerland) fitted with
winCATS 1.4.0 planar chromatography manager software. Samples
were applied on the HPTLC plates using the spray-on technique of
Camag Linomat V under nitrogen gas flow, and plates were devel-
oped in a Camag 20 cm × 20 cm twin trough chamber.
2.2. Method development and validation
2.2.1. Method development
HPTLC plates were pre-washed with methanol using the ascend-
ing technique and dried in an oven at 105 ◦C for 5 min. Standard
and sample volumes of 2 ␮L were applied on the HPTLC plates as
6 mm bands. Application positions were at least 15 mm from the
sides and 10 mm from the bottom of the plates. Reference stan-
dards, sample and spiked tablet matrix solutions were made using
methanol as solvent. Mobile phase components were freshly mixed
and the development chamber was left to saturate with mobile
phase vapour for 15 min before each run. Development of the plate
was carried out by the ascending technique to a migration distance
of 6 cm. Then the plates were dried on a hot plate which is supplied
with the Minilab® kit.
Densitometric scanning was done in absorbance/reflectance
mode at 254 nm using a deuterium lamp. The slit dimensions were
set at 5 mm × 0.45 mm, the scanning speed at 20 mm/s, and the
data resolution at 100 ␮m/step. The laboratory room was under air
conditioning and always maintained at 22 ± 2 ◦C temperature and
55 ± 5% relative humidity.
The separation of the spots was based on the TLC screening
test for co-trimoxazole tablets, described in the GPHF Minilab® kit
[21], in which the mobile phase was composed of ethyl acetate and
methanol (75:15, v:v). The result of this procedure was a tailing
TMP spot, and an SMX spot showing incomplete resolution from the
solvent front. Therefore, several combinations of the mobile phase
components were tested. Further addition of a third organic com-
ponent, toluene, to the mobile phase was tested at varying ratios,
with the objective of achieving a reproducible optimal separation
between the spots (Rs ≥ 1) and migration of spots within Rf values
between 0.2 and 0.8 [22].
2.2.2. Method validation
Prior to the method validation process, instrument precision
was evaluated in terms of sample application, positioning of TLC
scanner stage and scanning of the same spot, as described in [22].
A reference standard solution with 74 and 98 mg/L SMX and TMP,
respectively, prepared in methanol was used for these tests. For
the test on sample application, a 100 ␮L syringe was filled with
standard solution, and fixed on the sample application machine,
Linomat V. 2 ␮L of the solution was repeatedly applied on the plate
to make seven bands. The plate was developed and scanned. For the
test on positioning the scanner stage, the plate developed during
the sample application evaluation, was used. The scanning of the
same spot was repeated seven times while the scanner stage was
repositioned each time. For the test on scanning the same spot, the
scanning of a given spot was repeated seven times. For all tests, the
percentages relative standard deviations (%RSD) of the spot areas
for each test were calculated and compared to the stated limits [22].

7104 D.H. Shewiyo et al. / J. Chromatogr. A 1216 (2009) 7102–7107
2.2.3. Linearity of the calibration line
A stock standard solution containing 660.0 and 816.0 mg/L SMX
and TMP, respectively, was prepared and serially diluted to obtain
solutions with 26.4, 52.8, 79.2, 105.6 and 132.0 mg/L SMX and 32.64,
65.28, 97.92, 130.56 and 163.20 mg/L TMP. For each standard solu-
tion, three bands of 2 ␮L were applied on the HPTLC plate in a
distribution pattern with one on the left, middle and right side of
the plate, respectively. This procedure was repeated for three days.
Homoscedasticity of variances along the regression line was
verified using Cochran’s test [23,24]. Since the variances were con-
sidered homoscedastic (see Section 3) for both regression lines, the
slope and the intercept with their 95% confidence intervals were
calculated using ordinary least squares [24]. The correlation coef-
ficient r for both regression lines was also given.
The linearity was evaluated visually from the plotted calibration
data, and statistically by performing an F-test for lack-of-fit (LOF).
The LOF test examines whether the chosen model is appropriate,
i.e. in this study, whether the straight line adequately fits the data
[24].
2.2.4. Precision
The repeatability (within-day precision) and time-different
intermediate precision (between-days precision) were determined
simultaneously in one experimental set up. Solutions containing
60.0, 75.0, and 90.0 mg/L SMX and 75.0, 90.0, and 108.0 mg/L TMP
were prepared in tablet matrix using methanol as solvent. They rep-
resented 80%, 100% and 120% of the target concentrations of each
compound. Each day, they were analyzed in triplicate and this was
repeated for six consecutive days. Fresh calibration curves to esti-
mate the percentage recoveries were measured daily. The matrix
used is composed with the most commonly used excipients.
The repeatability (s2
r ), and the time-different intermediate pre-
cision (s2
I(t)
), at each concentration level were estimated from an
ANOVA table and Eq. (3) [23]
s2
I(t)
= s2
r + s2
between
(3)
where s2
between
represents the between-days variance.
2.2.5. Trueness
Tablet matrix portions were spiked with drug components at
80%, 100%, and 120% of the target sample concentrations, and
extracted with methanol with the method procedure to obtain
solutions with expected final concentrations of 60.3, 75.0, and
90.1 mg/L SMX and 72.2, 90.4, and 108.7 mg/L TMP. Three 2 ␮L vol-
umes of these solutions were applied on the plate, in a pattern
described in Section 2.2.3. Solutions were prepared in triplicate
and analyzed for three consecutive days. Fresh calibration curves
were measured daily to calculate the concentration of drug per
spot. Trueness for each spot, evaluated by means of the percentage
recovery, was calculated as;
% recovery =
Cobs
Cexp
× 100 (4)
where Cobs and Cexp are the observed and the expected concentra-
tions per spot, respectively.
The overall mean % recovery for each compound was calculated
as;
Mean % recovery =
Rtot
n
(5)
where Rtot is the sum of all % recoveries and n the number of obser-
vations.
2.2.6. Specificity
Solutions of tablet matrix without drug components, and tablet
matrix spiked with the drugs components at the same ratio as in
tablets formulations (5:1 SMX:TMP) were prepared in methanol.
About 200 mg of tablets matrix powder which is about twice the
amount of matrix in each tablet was dissolved in a 100-mL volumet-
ric flask using methanol. This solution of tablet matrix without drug
components was made at high excipient concentration to enable
detection of any excipients’ spots with similar Rf values as the drug
components. The two solutions were analyzed on the same plate
and the chromatograms recorded.
2.2.7. Robustness
Experimental design-based robustness testing was carried out
and evaluated as described in [25], using a Placket–Burman
(PB) design with eight experiments. Factors whose effects were
screened included (A) the developing distance of spots, (B) the
amount of methanol in the mobile phase, (C) the drying conditions
applied to the HPTLC plate after development, and (D) spot band
size (Table 1). These parameters were chosen from observations
made during method development and own experience. The limits
were set to represent typical errors encountered in the laboratory;
or were the only available options (for types of drying conditions).
Since four factors were examined, three dummy columns were
included in the 8-experiments PB design (Table 2). All factors were
studied at two levels. The effects of these factors on the responses
percentage recoveries of SMX and TMP, Rf values of SMX and TMP,
and resolution between SMX and TMP were estimated as follows;
Ex =
Y(+)
N/2
−
Y(−)
N/2
(6)
where Ex is the effect of factor x on the response Y, Y(+) and
Y(−) are the sums of the (corrected) responses where x is at (+)
and (−) levels, respectively, and N is the number of design experi-
ments.
A solution of tablet matrix spiked with SMX and TMP was mea-
sured at each design experiment. Spiking was performed at 100% of
the target sample concentrations, i.e. 75.0 mg/L SMX and 90.0 mg/L
Table 1
The four factors and their levels.
Factor Levels
(−) Nominal (0) (+)
(A) Developing distance of the spots
(cm)
5 6 7
(B) Amount of methanol in the mobile
phase
(toluene:ethylacetate:methanol)
(mL/L)
160 215 270
(C) Drying conditions applied on the
plate after development
Air Hot plate Hot plate
(D) Spot band size (mm) 5 6 7

Table 2
Plackett–Burman design to examine four factors (A–D) and three dummies (di) in 8-experiments.
Experiment Factors Responses
A d1 B d2 C d3 D % Recovery Rf value Resolution
SMX TMP SMX TMP TMP–SMX
1 +1 +1 +1 −1 +1 −1 −1 99.66 98.42 0.58 0.29 19.33
2 −1 +1 +1 +1 −1 +1 −1 98.50 98.71 0.57 0.29 18.67
3 −1 −1 +1 +1 +1 −1 +1 100.12 99.65 0.56 0.28 18.67
4 +1 −1 −1 +1 +1 +1 −1 100.87 98.11 0.68 0.27 27.33
5 −1 +1 −1 −1 +1 +1 +1 97.75 98.34 0.71 0.34 24.14
6 +1 −1 +1 −1 −1 +1 +1 99.40 100.32 0.64 0.33 20.12
7 +1 +1 −1 +1 −1 −1 +1 99.66 100.88 0.62 0.27 23.33
8 −1 −1 −1 −1 −1 −1 −1 100.00 101.72 0.55 0.36 12.67
Responses Effects of factors Critical effect
A d1 B d2 C d3 D ME␣ = 0.05
% Recovery SMX 0.81 −0.15 −0.21 0.53 1.21 −0.59 −0.73 1.63
% Recovery TMP −0.17 −0.49 −1.78 −0.56 −0.86 −0.36 1.30 2.25
Rf value SMX 0.033 0.058 −0.038 −0.038 0.012 0.013 0.072 0.101
Rf value TMP −0.028 −0.013 −0.018 −0.003 −0.013 0.052 0.008 0.038
Resolution (SMX–TMP) 3.99 2.67 −3.67 2.07 1.67 2.94 4.07 7.41
TMP. For each design experiment, standard solutions for calibration
curves were also measured to calculate the percentage recoveries.
Factor effects were evaluated using Dong’s algorithm, described
in [25]. The algorithm of Dong, calculates from an initial estimate of
error on an effect, s0 (Eq. (7)) a final estimation of a standard error,
s1 (Eq. (8))
s0 = 1.5 · median Ex (7)
s1 = m−1 E2
i
for all Ei ≤ 2.5s0 (8)
where Ei is an effect that in absolute value is smaller than or equal
to 2.5s0, and m the number of such effects. Then, a critical effect
called the margin of error, ME, is calculated as follows,
ME = t(1−˛/2·df ) · si (9)
where df = m and ˛ = 0.05. Factor values that are in absolute value
larger than or equal to ME are considered significant.
2.2.8. Analysis of co-trimoxazole tablet formulation samples
The developed method was used to determine the amounts of
SMX and TMP in three marketed co-trimoxazole tablet formula-
tions samples. The label claims in all samples were 400 mg SMX
and 80 mg TMP.
For each formulation, ten tablets were accurately weighed and
ground to fine powder. SMX and TMP were determined in differ-
ent solutions. Amounts of powder equivalent to 30 mg SMX and
36 mg TMP were accurately weighed into separate 100.0-mL volu-
metric flasks, where 70 mL of methanol was added. The two flasks
were sonicated for 10 min, diluted to volume with methanol and
mixed well. 5.0 mL of each solution was diluted into separate 20.0-
mL volumetric flask to obtain final solutions with approximately
75.0 mg/L for the SMX solution and 90.0 mg/L for the TMP solution,
respectively. A three-points calibration covering the upper, middle
and lower limit of the calibration range were used to estimate the
amount of drug in the sample formulations. The plates were devel-
oped and scanned using the densitometer to obtain the peak areas.
The analysis was performed in triplicate.
3. Results and discussions
3.1. Method development
Since the initially tested mobile phase [21], which was com-
posed of ethyl acetate and methanol (75:15, v:v) resulted in
a tailing TMP spot and an SMX spot showing incomplete sep-
aration from the solvent front, several other combinations of
the same mobile phase components were tested. Such combina-
tions included ethyl acetate: methanol (50:50, v:v), (25:75, v:v),
(90:10, v:v), (60:40, v:v) and (95:5, v:v). However, since these
binary mobile phases did not lead to the aimed result, i.e. well-
resolved spots (Rs ≥ 1) with Rf values between 0.2 and 0.8, ternary
mobile phases were evaluated. Toluene was introduced as a third
component into the mobile phase, and it was observed to slow
down the movement of SMX, separating it from the solvent front.
Tested ternary mobile phase compositions included the combi-
nations of toluene, ethyl acetate and methanol (60:25:15, v:v:v),
(50:30:20, v:v:v), and (45:30:15, v:v:v). Finally, a mobile phase with
a combination of toluene, ethylacetate and methanol (50:28.5:21.5,
v:v:v) gave compact, symmetrical, well-resolved spots with Rf
values of 0.30 and 0.61 for TMP and SMX, respectively. Rf val-
ues between 0.2 and 0.8, i.e. situations which are away from
the spotting position and the solvent front, have been reported
to have high Rf-value reproducibility and are hence considered
appropriate for quantification of compounds in HPTLC methods
[22]. The development was done for 6 cm on the plate and the
development time was 17 min. The development chamber was
saturated for about 20 min and after development, drying of the
plates was done using a hot plate. Simultaneous detection of
SMX and TMP was performed at 254 nm since both compounds
are well known to exhibit sufficient ultraviolet absorption at this
wavelength.
3.2. Instrument precision
The results for repeatability of sample application showed that
the %RSD were 0.85% and 0.93% for SMX and TMP, respectively.
These were within the stated limit, i.e. %RSD < 1.0% [22].
The results for position of the TLC scanner stage were %RSD
0.87% and 1.25% for SMX and TMP, respectively, complying with
the stated limit (%RSD < 3.0) [22]. For the test on the ability of the
instrument to scan the same spots repeatedly, it is stated that the %
RSD of the spot areas should not be more than 2.0%. The results were

7106 D.H. Shewiyo et al. / J. Chromatogr. A 1216 (2009) 7102–7107
0.81% and 1.02% for SMX and TMP, respectively, hence, complying
with the limit [22].
3.3. Linearity of the calibration line
Before performing regression, the homoscedasticity of the cal-
ibration standards was verified using a Cochran’s test. For SMX,
the test statistic, Ccalc, was found to be 0.261, and for TMP, it was
0.336. These calculated test-statistic values were smaller than the
critical value, Ctab(˛ = 0.05; k = 5, n = 9) = 0.439. Thus, the variances of the
calibration standards were considered to be homoscedastic. There-
fore, ordinary least squares were used to estimate the regression
lines.
The equations of the calibrations lines were AreaSMX = 8.66
CSMX(ng/spot) + 490.75 and AreaTMP = 5.40CTMP(ng/spot) + 66.34 for
SMX and TMP, respectively. For SMX, the values for the slope
and the intercept with their confidence limits at 95% level were
8.66 ± 0.16 and 490.75 ± 60.70, respectively. The values of these
parameters for TMP were 5.40 ± 0.06 and 66.34 ± 27.90, respec-
tively. The correlation coefficients, r, were 0.9997 and 0.9999 for
the SMX and the TMP calibration curves, respectively.
Visual observation of the calibration curves showed that the
lines were straight. The lack-of-fit test result for the SMX calibration
data was Fcalc = 0.360 and for TMP, it was Fcalc = 0.156. These val-
ues were smaller than the critical value, Ftab(˛=0.05; df1=3, df2=40) =
2.839. This means that straight lines were considered adequate to
describe the relationships between the spot areas and the concen-
trations (weight per spot) for each compound.
From the above it is observed that though the straight line model
is correct for the considered calibration ranges, the intercept of
the calibration lines is significantly different from zero. We also
observed this for the HPTLC analysis of other compounds. A pos-
sible explanation is that intrinsically this kind of methods shows
saturation on the spots and therefore produces curved calibrations.
However, at narrow range, as here is the case, linearity can fit the
calibration responses but resulting in an intercept deviating from
zero. Consequences of the above are that a one-point calibration
does not result in a proper estimation of a sample concentration
and that at least two standards in the observed linear range need
to be measured for calibration purposes.
3.4. Precision
The repeatability (within-days precision) expressed as percent-
age relative standard deviations (%RSD) for the SMX concentration
at the 80%, 100%, and 120% levels were 0.72, 0.85 and
1.38, respectively, and the time-different intermediate precision
(between-days precision) %RSD values were 1.40, 0.95 and 1.74,
respectively. The %RSD values for the TMP concentration at the
same concentration levels were 0.75, 0.97 and 0.77, respec-
tively, for repeatability, and 1.80, 1.57 and 1.54, respectively, for
time-different intermediate precision. The pooled repeatability
precisions were 0.98 and 0.83 for the SMX and the TMP concen-
trations, respectively, and the pooled time-different intermediate
precisions were 1.32 and 1.64, respectively.
All the values for the repeatability and the time-different inter-
mediate precisions were found to be comparable to HPLC methods
Fig. 2. Chromatogram of tablet matrix solution spiked with trimethoprim (1) and
sulfamethoxazole (2).
as those described in [6], where a micellar and a reversed-phase liq-
uid chromatography method for the determination of SMX and TMP
in commercial pharmaceutical products, are compared. In both
cases the percentage relative standard deviations are well below
2%. In conclusion, our %RSDs were considered acceptable.
3.5. Trueness
The recovery results obtained for SMX at the 80%, 100% and
120% concentration levels were 99.00% ± 1.64, 100.15% ± 2.12 and
100.27% ± 1.55, respectively. For TMP, they were 99.95% ± 1.11,
99.43% ± 1.47 and 99.61% ± 1.11, respectively. The ranges of the
% recovery values covering all concentration levels for each com-
pound were 96.56–102.93% for SMX and 97.46–101.95% for TMP.
The overall mean recoveries for SMX and TMP were 99.00% ± 1.83
and 99.66% ± 1.21, respectively. Thus, the method was considered
to have an acceptable recovery.
3.6. Specificity
The chromatogram of the solution of tablet matrix which was
not spiked with SMX and TMP did not show any spot, while the
chromatogram of the solution of tablet matrix spiked with SMX
and TMP showed clear, compact and well-separated peaks of SMX
and TMP (Fig. 2). Moreover, from Fig. 2, it was seen that no other
peaks eluted besides the two active compounds. The method was
therefore considered specific.
3.7. Robustness
The factor effects were calculated for each response (Eq. (6)),
and presented in Table 2. Using Eqs. (7–9), the margin of errors
or the critical effects were calculated for each response. All fac-
tor effects on a given response that are in absolute value larger
than or equal to the critical effect for the considered response are
considered significant.
Table 3
Results of analysis of marketed formulations.
Product name Manufacturer Batch No. Percentage amount found
SMX TMP
Shetrim®
Shelys Pharmaceuticals Ltd, Tanzania F020 98.6 ± 1.6 101.6 ± 2.1
Altran®
Alpa Laboratories Ltd, India TV-1783 97.2 ± 2.5 94.1 ± 3.7
Co-trimoxazole North China Pharmaceutical Ltd, China 0803125 100.0 ± 2.4 101.9 ± 3.1

All absolute factor effects on the responses % recovery of SMX
and of TMP, which represent the quantitative aspects of the
method, were found to be smaller than the corresponding critical
effects, i.e. ME˛ = 0.05 = 1.63 for SMX and 2.25 for TMP. Since no sig-
nificant factor effects were found for these quantitative responses,
the method was considered robust.
All absolute factor effects on the qualitative response Rf values
of SMX were smaller than the critical effect, ME˛ = 0.05 = 0.101. On
the other hand, on the response Rf values of TMP, one dummy, d3
was considered to have a significant effect, since its absolute value,
0.052, was larger than the critical effect, ME˛ = 0.05 = 0.038. Since it
concerns a dummy factor, it is considered non-significant by def-
inition and it is further ignored. Moreover, since one is working
at ˛ = 0.05, statistically one considers a non-significant effect as
significant in one case out of twenty, which probably is the case
here.
For the separation quality related response resolution between
the SMX and the TMP spots, the absolute factor effects were smaller
than the critical effect, ME˛ = 0.05 = 7.410. Thus, no significant effects
were indicated for the response resolution.
3.8. Results of analysis of co-trimoxazole tablets formulations
Analysis of real samples of marketed co-trimoxazole tablet
formulations was performed using this method. The percentage
amounts for SMX and TMP were calculated from the label claims, i.e.
400 mg SMX and 80 mg TMP. These are reported with their standard
deviations in Table 3. Percentage amounts of SMX in all formula-
tions were found to range between 97.2% and 100% and from 94.1%
to 101.9% for the TMP. They all complied with the prescribed limits
by the USP (90.0–110.0%), in which the assay is performed using
HPLC [5].
4. Conclusion
A quick, precise and true method in normal-phase HPTLC for
routine analysis of SMX and TMP in co-trimoxazole tablet formula-
tions has been developed and validated. It uses the chemicals and
solvents that are also applied in the Minilab® kit, hence strengthen-
ing the ongoing quality assurance program for medicines at TFDA.
Up to 20 samples can be analyzed on one plate in a short time, there-
fore saves time and cost per run. While it takes about 15–17 min
to develop one plate that may contain as many as 20 samples,
it takes about 8 min to run one injection on HPLC (about 2:40 h
for 20 samples). If we consider sample preparation until densit-
ometric evaluation for the above plate, it takes about 45 min to
1 h, whereas it takes more than 3 h for the HPLC method. In terms
of cost, the extra time acquired in HPTLC is used for analysis of
more samples. Again, while the HPLC method consumes about
250 mL of mobile phase for the above samples, HPTLC utilizes less
than 20 mL.
With this method, regulatory decisions are timely facilitated,
which helps to have a continuous availability of high quality co-
trimoxazole tablets in the Tanzanian market for the treatment and
prophylaxis of various infections, including Pneumocystis jirovecii
(PCP), in HIV/AIDS patients.
Acknowledgements
D.H. Shewiyo would like to express his sincere appreciations to
the Belgium Technical Cooperation (BTC) for financial support and
to Mr. P. Makaranga, a technician at TFDA laboratory for carrying
out most of the experiments. B. Dejaegher is a postdoctoral fellow
of the Fund for Scientific Research (FWO-Flanders).
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