J Fluoresc (2008) 18:349–355
DOI 10.1007/s10895-007-0274-1
ORIGINAL PAPER
Spectrofluorimetric Determination
of Oxamniquine in Dosage Forms and Spiked
Human Plasma through Derivatization
with 1-dimethylaminonaphthalene-5-sulphonyl chloride
N. El-Enany & F. Belal & M. Rizk
Received: 5 September 2007 / Accepted: 16 October 2007 / Published online: 5 December 2007
# Springer Science + Business Media, LLC 2007
Abstract A sensitive, simple and selective spectrofluorimetric method was developed for the determination of
oxamniquine (OXM) in pharmaceutical formulations and
biological fluids. The method is based on the reaction
between the drug and 1-dimethylaminonaphthalene-5sulphonyl chloride (dansyl chloride) in presence of
0.5 M sodium carbonate (pH 10) to yield a highly
fluorescent derivative that is measured at 445 nm after
excitation at 335 nm. The different experimental parameters affecting the development and stability of the
reaction product were carefully studied and optimized.
The fluorescence concentration plot was rectilinear over
the range of 0.02–0.2 μg ml−1 with a lower detection
limit (LOD) of 0.007 μg ml−1 and limit of quantitation
(LOQ) of 0.02 μg ml−1. The proposed method was
successfully applied to the analysis of commercial capsules.
The results obtained were in good agreement with those
obtained using the official spectrophotometric method.
Furthermore, the method was applied for the determination
of oxamniquine in spiked human plasma, the mean %
recovery (n=4) is 97.77±1.19. A proposal of the reaction
pathway was presented.
N. El-Enany (*) : F. Belal
Department of Analytical Chemistry, Faculty of Pharmacy,
University of Mansoura,
35516 Mansoura, Egypt
e-mail: nelenany1@yahoo.com
M. Rizk
Department of Analytical Chemistry, Faculty of Pharmacy,
University of Helwan,
Cairo, Egypt
Keywords Oxamniquine . 1-dimethylaminonaphalene5-sulphonyl chloride . Dosage forms . Spiked human plasma
Introduction
Oxamniquine (OXM), 1,2,3,4-tetrahydro-2[(isopropylamino methyl]-7-nitro-6-quyinoline methanol is an antischistosomal agent that is indicated for the treatment of
schistosoma mansoni (intestinal schistosomiasis) infection
(Fig. 1). It has been shown to inhibit DNA, RNA and
protein synthesis in schistosomes. The oral bioavailability
of oxamniquine is good and effective plasma levels are
achieved in 1–1.5 h [1].
Oxamniquine is the subject of a monograph in the USP
(XXIII) [2] whereby a spectrophotometric method is recommended for its determination, whether in its pure form or in
capsules. Several methods have been published for the
determination of OXM, either per se or in pharmaceutical
preparations and biological fluids. These methods include:
spectrophotometry [3–5], non-aqueous titration [6], gas
chromatography [7], HPLC [8–13], capillary electrophoresis
[11], polarography [14], flow injection analysis [15], cyclic
voltammetry [16] and fluorimetry [17].
All these methods are either insufficiently sensitive or
tedious and require highly sophisticated and dedicated
instrumentation [8–13]. This led us to study the reaction
of oxamniquine with dansyl chloride to develop simple and
sensitive spectrofluorimetric method for its determination in
pharmaceutical preparations and biological fluids. Dansyl
chloride is a useful derivatizing agent for primary amines,
secondary amines, imidazoles and phenols, etc.. Several
pharmaceutical compounds have been determined through
this approach [18–24].
350
J Fluoresc (2008) 18:349–355
H
O2N
N
CH2
NH
H
C
(CH3)2
solutions were stable for seven days when kept in the
refrigerator.
General procedure
HOH2C
Fig. 1 Structural formula of oxamniquine
The reported spectrofluorimetric method for oxamniquine
[17] is tedious and time consuming. It involves the use of
2-cyanoacetamide, a hazard reagent.
Experimental
Apparatus
The spectrofluorimetric measurements were recorded using
ARF-1501 Shimadzu Spectrofluorometer, equipped with
Xenon arc lamp.
Aliquots of OXM standard solution were transferred into a
series of 10 ml volumetric flasks. 0.7±0.1 ml of 0.001%
of dansyl chloride reagent was added, followed by 0.4 ml
of acetone and mixed well. The reaction mixture was left
for 30 min, and then completed to the mark with IBMK.
the reaction mixture was allowed to stand for 10 min. The
fluorescence intensity of the reaction product was measured at 445 nm after excitation at 335 nm. Blank
experiment was carried out simultaneously. The corrected
fluorescence intensity was plotted vs the final drug
concentration (μg ml−1) to get the calibration graph.
Alternatively, the corresponding regression equation was
derived.
Applications
Materials and reagents
Procedure for commercial capsules
All reagents and solvents were of analytical reagent grade
The content of ten capsules were emptied, and mixed well.
A weighed quantity of the powder equivalent to 5.0 mg
OXM was transferred into a small conical flask, and
extracted with 2×10 ml of methanol. The extract was
filtered into 25 ml volumetric flask. The conical flask was
washed with several milliliters of methanol. The washing
was passed into the same volumetric flask, and the
combined extract was evaporated to dryness on a boiling
water bath. The residue was dissolved and diluted to
volume with a mixture of 5 ml of acetone and 20 ml of
0.5 M of sodium carbonate solution. Aliquots covering the
working concentration range (cited in Table 1) was
–
–
–
–
–
–
–
–
Oxamniquine pure sample was kindly provided by
Pfizer (Sandwich, UK).
Capsules containing 250 mg of Oxamniquine each
(Vansil capsules) were obtained from commercial
sources in the local market.
1-Dimethyl aminonaphthalene-5-sulphonyl chloride
(dansyl chloride), purchased from Sigma (St. Louis,
USA). A stock solution containing 0.1% of dansyl
chloride was freshly prepared in acetone and was
further diluted with the same solvent to obtain 0.001%
solution.
Sodium carbonate (BDH, UK) 0.5 M aqueous solution
(pH 10).
Sodium hydroxide (BDH, UK) 1 M aqueous solution.
Isobutylmethyl ketone (IBMK) (Merck, Darmstadt,
Germany).
Plasma was kindly provided by Mansoura University
Hospital, and kept frozen until assay after gentle
thawing.
Methanol and diethyl ether (Merck, Darmstadt,
Germany).
Standard solutions
A stock solution was prepared by dissolving 20.0 mg of
OXM in 20 ml of acetone and 80 ml of 0.5 M sodium
carbonate solution. This solution was further diluted with
the same solvent mixture as appropriate. The standard
Table 1 Performance data of the proposed method
Parameter
Proposed method
Concentration range (μg ml−1)
Minimum detection limit, LOD (μg ml−1)
Limit of Quantification, LOQ(μg ml−1)
Correlation coefficient (r)
Slope
Intercept
Sy/x
Sa
Sb
% Error
0.02–0.2
0.007
0.02
0.9999
3,473.114
0.574
1.273
7.733
8.965
0.28
Sy/x = standard deviation of the residuals
Sa = standard deviation of the intercept of regression line
Sb = standard deviation of the slope of regression line
% Error = RSD%/√ n
J Fluoresc (2008) 18:349–355
transferred into 10 ml volumetric flasks. The “General
procedure” was then applied. The nominal content of the
capsules was determined either from the calibration curve
or using the corresponding regression equation.
Procedure for spiked human plasma
A stock solution containing 20 μg ml−1 of OXM was
prepared. Control samples of plasma was spiked with
different quantities of OXM to give a final drug concentration cited in Table 5. One molar NaOH (0.8 ml) was added
to 1.0 ml of the spiked plasma and shaken genteelly. The
solution was vortexed with 3×5 ml of diethylether for
2 min, then centrifuged at 2,500 rpm for 5 min. The
resulting supernatant was evaporated to dryness under
nitrogen at ambient temperature. The residue was dissolved
and diluted to volume with a mixture of 5 ml of acetone and
20 ml of 0.5 M of sodium carbonate solution. Aliquots
covering the working concentration range was transferred
into 10 ml volumetric flasks. The recommended procedures
were then applied. The nominal content of the drug was
determined using the corresponding regression equation.
Results and discussion
Dansyl chloride was first introduced for the determination
of some primary, secondary amines, imidazoles and
phenols [18–20].
In recent reports. DNS was further used as a fluorogenic
reagent for the determination of some pharmaceutical
compounds [21–24].
In the present study, OXM was found to react with
Dansyl chloride at pH 10.0 forming a highly yellow
fluorescent derivative with l maximum emission at
445 nm after excitation at 335 nm (Fig. 2).
351
Optimization of experimental parameters
The spectrofluorimetric properties of the colored product as
well as the different experimental parameters affecting the
development of the reaction product and its stability were
carefully studied and optimized. Such factors were changed
individually while the others were kept constant. The
factors include pH, concentration of the reagent, type of
buffer, temperature, reaction time and dilution time.
Effect of pH
The influence of pH on the fluorescence intensity of the
reaction product was studied. Maximum fluorescence intensity was obtained upon using mixture of acetone and 0.5 M
sodium carbonate solution. The pH of the reaction mixture
was found to be 10.0. pH 10 was found to be the optimum pH
for dansylation because labeling of most amino acids,
amines, imidazoles and phenols has been found to be
optimal at pH 9.5–10.5 [25]. The rate of dansylation process
was found to increase with increasing the pH value this is
due to an increase in the rate of hydrolysis of dansyl
chloride into dansyl hydroxide [25]. The latter shows strong
fluorescence and hence interferes seriously in the determination. However, under the proposed chosen conditions and
wavelengths used, there was no interference arising from
any dansyl hydroxide formed, as indicated by the low
fluorescence intensity of the reagent.
Effect of concentration of dansyl chloride
The influence of the concentration of dansyl chloride was
studied using different volumes of 0.001% of the reagent
solution. It was found that, the reaction of dansyl chloride
with OXM started upon using 0.1 ml of the reagent in the
presence of sodium carbonate (pH 10.0). Increasing the
volume of the reagent, produces a proportional increase in
the fluorescence intensity of the reaction product up to
0.6 ml and remains constant up to 0.8 ml. Therefore, 0.7±
0.1 ml of 0.001% of dansyl chloride solution was chosen as
the optimal volume of the reagent (Fig. 3).
Effect of temperature
Increasing the reaction temperature higher than the room
temperature would result in a subsequent decrease in the
fluorescence intensity of the reaction product.
Effect of reaction time
Fig. 2 Fluorescence spectra of A and B excitation and emission
spectra of blank. Fluorescence spectra of A′ and B′ excitation and
emission spectra of oxamniquine (0.2 μg ml−1) with dansyl chloride at
pH 10.0
Different time intervals were tested to ascertain the time
after which the solution attains its highest fluorescence
intensity. It was found that after 30 min, the reaction
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J Fluoresc (2008) 18:349–355
Corrected fluorescence
intensity
1000
that dilution with IBMK after 10 min, the reaction product
reaches its highest fluorescence intensity (Fig. 5).
750
Analytical performance
500
Validation of the proposed methods The validity of the
method was tested regarding; linearity, specificity, accuracy,
repeatability and precision according to ICH Q2B recommendations [26].
250
0
0.00
0.25
0.50
0.75
1.00
volume of 0.001% dansyl chloride
(mL)
Linearity
Fig. 3 Effect of volume of dansyl chloride (0.001%) on the
fluorescence intensity of the reaction product of oxamniquine
(0.2 μg m−1) at pH 10.0
By using the above procedure, linear regression equation was
obtained. The regression plots showed that there was a linear
dependence of the fluorescence intensity on the concentration
of the drug over the ranges cited in Table 1. Linear regression
analysis of the data gave the following equation:
product reaches the highest fluorescence intensity (Fig. 4)
and remains stable at room temperature for 20 min.
F ¼ 0:574 þ 3; 473:114C
Effect of diluting solvent
Different solvents were tried to dilute the reaction mixture
through out the study. It was observed that isobutyl methyl
ketone gave the highest fluorescence intensity. Dilution
with 0.5 M sodium carbonate solution, water, acetone–
water produced almost very week fluorescence and did not
reduce the blank fluorescence intensity. While upon using
isobutyl methyl ketone, the fluorescence intensity attained
its highest value, this was attributed to the low fluorescence
value of the reagent.
Effect of dilution time
Dilution times were tested to ascertain the time after which
the solution attains its highest fluorescence. It was found
where F is the fluorescence intensity, C is the concentration
of the drug in μg ml−1 and r is the correlation coefficient.
The limit of quantification (LOQ) was determined by
establishing the lowest concentration that can be measured
according to ICH Q2B [26]. The results are shown in
Table 1. The limits of detection (LOD) were determined by
establishing the minimum level at which the analyte can be
reliably detected, and the results are also abridged in Table 1.
LOQ and LOD were calculated according to the
following equation [26]:
LOQ ¼ 10σ=S
LOD ¼ 3:3σ=S
Where σ: is the standard deviation of the intercept of
regression line. S: is the slope of the calibration curve.
The proposed methods were evaluated for the accuracy
as percent relative error (% Er) and the precision as percent
relative standard deviation (% RSD) (Tables 1 and 2).
1000
1000
Corrected fluorescence
intensity
Corrected fluorescence
intensity
ðr ¼ 0:9999Þ
750
500
250
0
750
500
250
0
0
10
20
30
40
50
Reaction time (min.)
Fig. 4 Effect of reaction time of on the fluorescence intensity of the
reaction product of oxamniquine (0.2 μg ml−1) with dansyl chloride
0
5
10
15
20
25
Dilution time (min.)
Fig. 5 Effect of dilution time on the fluorescence intensity of the
reaction product of oxamniquine (0.2 μg ml−1) with dansyl chloride
J Fluoresc (2008) 18:349–355
353
Table 2 Application of the proposed and official methods to the
determination of Oxamniquine in pure form
Table 4 Application of the proposed methods to the determination of
oxamniquine in capsules
Parameters
Spectrofluorimetric
method
Official method
[2]
Preparations
No. of experiments
Mean found (%)
± SD
% RSD
Variance
Student’s t value
Variance ratio F test
6
100.13
0.68
0.68
0.462
0.081 (2.31)
1.65 (5.41)
3
100.09
0.87
0.87
0.76
% Recovery
Proposed method
Figures between parentheses are the tabulated t and F values
respectively, at p=0.05 [27]
Vansil capsules (250 mg
oxamniquine/capsule)
Mean found (%)± SD
t value
F value
98.25
101.00
99.38
99.80
99.30
99.55 ± 0.99
1.67
1.66
Official method [2]
100.56 ± 0.77
The tabulated values of t and F are (2.37) and (6.59) respectively, at
p=0.05 [27]
Accuracy
Precision
To test the validity of the proposed method it was applied to
the determination of authentic sample of OXM over the
working concentration range. The results obtained were in
good agreement with those obtained using official method.
Using Student’s t test and variance ratio F test, [27]
revealed no significant difference between the performance
of the two methods regarding the accuracy and precision,
respectively (Table 2).
The validity of the methods was proved by statistical
evaluation of the regression lines, using the standard
deviation of the residuals (Sy/x), the standard deviation of
the intercept (Sa) and standard deviation of the slope (Sb).
The results are abridged in Table 1. The small values of the
figures point out to the low scattering of the points around
the calibration line and high precision.
a. Repeatability
The repeatability was performed by applying the
proposed methods for the determination of two concentrations of OXM in pure form on three successive times,
and the results are listed in Table 3.
b. Intermediate precision
It was performed through repeated analysis of OXM in
pure form, using the concentrations showed in Table 3 for a
period of three successive days. The results are summarized
in Table 3.
Table 3 Validation of the proposed method for the determination of
oxamniquine in pure form
Sample
concentration
% Recovery
(repeatability)
% Recovery intermediate
precision
0.08 μg ml−1
99.64
100.72
101.44
100.60
0.91
0.91
0.53
99.74
100.44
101.29
100.49
0.78
0.78
0.45
101.08
99.28
100.89
100.42
0.99
0.99
0.57
101.05
100.53
98.95
100.18
1.09
1.09
0.63
X′
± SD
%RSD
% Error
0.2 μg ml−1
X′
± SD
%RSD
% Error
Robustness of the method
The robustness of the method adopted is demonstrated by the
constancy of the fluorescence intensity with the deliberated
Table 5 Application of the proposed methods to the determination of
oxamniquine in spiked human plasma
Sample
Amount added
(μg ml−1)
Amount found
(μg ml−1)
% Recovery
1-a-Plasma (interday precision)
0.02
0.04
0.10
0.20
0.01957
0.03856
0.09754
0.19856
0.20
0.20
0.20
0.20
0.20
0.20
0.1914
0.1969
0.1948
0.1955
0.1979
0.1945
97.85
96.40
97.54
99.28
97.77
1.19
95.70
98.45
97.40
97.75
98.95
97.25
97.58
1.13
Mean
± SD
1-b-Plasma (interday precision)
Mean
± SD
Each result is the average of three separate determinations
354
J Fluoresc (2008) 18:349–355
Log fluorescence
3.00
linearity, specificity, accuracy, repeatability and precision
according to ICH Q2B recommendations.
a
2.75
Specificity
2.50
The specificity of the method was investigated by observing any interference encountered from the common capsule
excepients, such as talc, lactose, starch, avisil, gelatine, and
magnesium stearate. These excepients did not interfere with
the proposed method.
2.25
2.00
-7.00 -6.75 -6.50 -6.25 -6.00 -5.75 -5.50 -5.25
Log [dansyl chloride]
3.0
The results of the proposed methods were statistically
compared with those obtained using the official method
[2]. Statistical analysis [27] of the results, using Student’s
t test and variance ratio F test revealed no significant
difference between the performance of the proposed and
reference methods regarding the accuracy and precision,
respectively (Table 4).
b
Log fluorescence
Accuracy
2.5
2.0
Analysis of biological fluid
1.5
-7.5
-7.0
-6.5
-6.0
-5.5
Log [oxamniquine]
Fig. 6 Limiting logarithmic plots for the molar ratio. a Log F vs. Log
[dansyl chloride]. b Log F vs. log [oxamniquine]
minor changes in the experimental parameters such as
change in the volume of dansyl chloride (0.001%), 0.7 ±
0.1 ml, the change in reaction time 35 ± 5 min and the
change in dilution time 15 ± 5 min. These minor changes
that may take place during the experimental operation didn’t
affect the fluorescence intensity of the reaction product.
Pharmaceutical applications
The proposed methods were then applied to the determination of OXM in its capsules. The methods were tested for
Scheme 1 Proposed reaction
pathway between dansyl
chloride and oxamniquine
The high sensitivity of the proposed method allowed the
determination of OXM in spiked human plasma. Oxamniquine
is readily absorbed following oral ingestion, and a peak
concentration in plasma occurs within about 3 h. The presence
of food significantly delays absorption and limits the concentration achieved in plasma during the first several hours after
administration. Urinary excretion is the major route of
elimination in man [28]. Oxamniquine is given orally in a
dose of 250 mg three times daily; this leads to a final blood
level concentration of about 5 μg ml−1 i.e. higher than the
upper limit of the working concentration range of the
proposed method. The high sensitivity of the proposed
method allowed the determination of OXM in spiked human
plasma. The results are shown in Table 5.
The extraction procedure described by Woolhouse and
Wood [7] was adopted here. The results are satisfactorily
accurate and precise.
R'
SO2Cl
SO2
N
R
R'
+ R
NH
+ HCl
N
H3C
N
CH3
H 3C
CH3
J Fluoresc (2008) 18:349–355
Precision The within-day precision was evaluated through
replicate analysis of Plasma samples spiked with different
concentrations of the drug. The percentage recoveries based on
the average of four separate determinations were 97.77 ± 1.19,
thus indicating the high precision of the method (Table 5).
The inter-day precision was also evaluated through replicate
analysis of plasma samples spiked with 0.2 μg ml−1 of drug on
four successive days. The percentage recoveries based on the
average of four separate determinations were 97.58 ± 1.13.
The results are shown in Table 5.
355
6.
7.
8.
9.
10.
11.
Mechanism of the reaction
12.
The stoichiometry of the reaction was studied adopting the
limiting logarithmic method [29]. The fluorescence intensity
of the reaction product was alternatively measured in the
presence of excess of either dansyl chloride or OXM. A plot
of log fluorescence versus log [dansyl chloride] and log
[OXM] gave straight lines, the values of the slopes are 0.901
and 0.984 respectively (Fig. 6). Hence, it is concluded that,
the molar reactivity of the reaction is 0.901/0.984, i.e. the
reaction proceeds in the ratio of 1:1. Based on the observed
molar reactivity of the reaction, and depending on the
presence of secondary amino group and by analogy to
similar reports dealing with the reaction of dansyl chloride
with compounds containing secondary amino group, the
reaction pathway proposed in Scheme 1 is presented.
Conclusion
The proposed method has the advantage of being simple,
sensitive and suitable for routine analysis in quality control
laboratory. Also, it is suitable for the determination of
oxamniquine in spiked human plasma with minimum
detection limit lower than the reported value. In addition,
it could be applied to the determination of OXM in its
pharmaceutical preparation.
References
1. Delgado JN, Remers WA (Eds) (1991) Wilson and Gisvold’s text book
of organic medicinal and pharmaceutical chemistry, 9th edn, p 184
2. The USP Pharmacopoeia XXIII (1995) NF 18, The US Pharmaceutical Convention, Rockville, p.1120.
3. Hassan SM, Belal F, Sharf-El-Din M, Sultan M (1988) Spectrophotometric determination of some pharmaceutically nitro compounds in their dosage forms. Analyst 113:1807–1809
4. Bebawy LI, El-Kelani K, Abdel Fattah L, Ahmad AK (1997) Study
of 7,7′,8,8′-tetracyanoquinodimethane charge transfer complexes
with some lone-pair-donating drugs. J Pharm Sci 86:1030–1033
5. Rizk M, Belal F, Ibrahim F, Ahmed SM, El-Enany NM (2000) A
simple kinetic spectrophotometric method for the determination
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
of oxamniquine in formulations and spiked biological fluids.
J Pharm Biomed Anal 23:503–513
Korolkovas A, Haraguchi T (1980) Rev. Farm. Bioquim Univ.
Sao Paulo, 16, 12. Thro. Chem. Abstr. vol 94, pp 7846e, 1981
Woolhouse NM, Wood PR (1977) Determination of oxamniquine
in serum. J Pharm Sci 66:429–430
Jun HW, Radwan MA (1985) Anal Lett 18:1345–1355
Pierri EG, Almeida AE, Gremiao MP (2001) Determination of
oxamniquine in capsules by HPLC. J Pharm Biomed Anal 26:675–679
Masimirembwa CM, Hasler JA, Johansson I (1995), Inhibitory
effects of antiparasitic drugs on cytochrome P450 2D6. Eur J Clin
Pharmacol 48:35–38
Abushoffa MA, Clark BJ (1995) Resolution of the enantiomers of
oxamniquine by capillary electrophoresis and high-performance
liquid chromatography with cyclodextrins and heparin as chiral
selectors. J Chromatogr 700:51–58
Noctor TA, Fell AF, Kaye B (1990), High-performance liquid
chromatographic resolution of oxamniquine enantiomers: application to in vitro metabolism studies. Chirality 2:269–274
Fell AF, Noctor TA, Mama JE, Clark BJ (1988) Computer-aided
optimisation of drug enantiomer separation in chiral highperformance liquid chromatography. J Chromatogr 434:377–384
Belal F, Aly FA (1995) Polarographic behavior and determination
of oxamniquine in dosage forms. Electroanalysis 7:483–487
Mohamed MY, El-Gendy AE, El-Bardicy MG, Tawakol MS,
Ahmed AKS (1996) Spectrosc Lett 29:299–319
Radi A, Belal F (1998) Reaction of electrogenerated oxamniquine
radical anion with glutathione. J Electroanal Chem 441:39–42
Rizk M, Belal F, Ibrahim F, Ahmed SM, El-Enany NM (1999)
Fluorimetric determination of oxamniquine in biological fluids. Il
Farmaco 54:47–50
Ayad MM (1984) Spectrofluorimetric microdetermination of
imidazoline derivatives using 1-dimethylaminonaphthaline-5sulphonylchloride. Analyst 109:431–1434
Putter J (1979) A fluorometric method for the determination of
praziquantel in blood–plasma and urine. Eur J Drug Metab
Pharmacokinet 4:143–148
Frei-Hausler M, Frei RW (1973) An investigation of fluorigenic
labelling of chlorophenols with dansyl chloride. J Chromatogr
84:214–220
Lucca A, Gentilini G, Lopez-Silva S, Soldarini A (2000) Simultaneous
determination of human plasma levels of four selective serotonin
reuptake inhibitors By HPLC. Ther Drug Monit 22:271–276
Dennis Gmur J, Charles Bredl R, Sharon J, Steele SC, Donald R,
Devanter V, Pasqua AN (2003) Determination of polymyxin E1 in rat
plasma by high-performance liquid chromatography. J Chromatogr
B 789:365–372
Houdier S, Perrier S, Defrancq E, Legrand M (2000) A new
fluorescent probe for sensitive detection of carbonyl compounds:
sensitivity improvement and application to environmental water
samples. Anal Chim Acta 412:221–233
Bagdonaite K, Viklund G, Skog K, Kovic M (2006) Analysis
of 3 Amino-propionamide: apotential precursor of acrylamide.
J Biochem Biophys Methods 69:215–221
Seiler N (1970) Methods Biochem Anal 18:259
Guidance for industry bioanalytical method validation. US
Department of Health and Human Services, Food and Drug
Administration, Center for Drug Evaluation and Research,
Rockville, MD, May. 2001. http://www.fda.gov/eder/guidance/
4252fnl.pdf (accessed September 1, 2004)
Miller JN, Miller JC (2005) Statistics and chemometrics for
analytical chemistry, 5th edn. Prentice Hall, England, p 256
Iqbal A, Tauqir A (1991) Analytical profile of drug substances. In:
Florey K (ed) vol 20. Academic, New York, p 623
Rose J (1964) Advanced physico-chemical experiments. Pitman,
London