Journal of Pharmaceutical and Biomedical Analysis 37 (2005) 569575

Comparative study of the continuous wavpplntiid ium

a UniveUniveScienc

d Nationa nces, M

Received 1 August 2004; received in revised form 9 November 2004; accepted 12 November 2004Available online 22 December 2004

Abstract

The simupresence ofpartial leastobtained bycoefficientsconcentratiowere testedpharmaceutianalytical m 2004 Pub

Keywords: C

1. Introdu

A mixtu(ASA) haspharmaceudrugs haveabove drugwere determtrofluorimetive spectroderivative m

CorresponE-mail ad

0731-7085/$doi:10.1016/jltaneous spectrophotometric determination of ascorbic acid (AA) and acetylsalicylic acid (ASA) in effervescent tablets in thethe overlapping spectra was accomplished by the continuous wavelet transform (CWT), derivative spectrophotometry (DS) andsquares (PLS) approaches without using any chemical pre-treatment. CWT and DS calibration equations for AA and ASA weremeasuring the CWT and DS amplitudes corresponding to zero-crossing points of spectra obtained by plotting continuous waveletand first-derivative absorbance values versus the wavelengths, respectively. The PLS calibration was constructed by using then set and its full absorbance data consisting of 850 points from 220 to 305 nm in the range of 210310 nm. These three methodsby analyzing the synthetic mixtures of the above drugs and they were applied to the real samples containing two commercialcal preparations of subjected drugs. A comparative study was carried out by using the experimental results obtained from threeethodologies and precise and accurate results were obtained.lished by Elsevier B.V.

ontinuous wavelet transform; Derivative spectrophotometry; Partial least squares; Ascorbic acid; Acetylsalicylic acid; Effervescent tablets

ction

re of ascorbic acid (AA) and acetylsalicylic acidworldwide use for pain and fever relief in the

tical preparations. The content of AA and ASAbeen analyzed simultaneously by LC [1,2]. Thes in combination with other active compoundsined by differential spectrophotometry [3], spec-

try [4], HPLC [5,6], potentiometry [7], deriva-photometry [8,9], voltametry [10], ratio-spectraethods [11].

ding author. Tel.: +90 312 215 4886; fax: +90 312 213 1081.dress: dinc@pharmacy.ankara.edu.tr (E. Dinc).

Although HPLC and other conventional spectrophotomet-ric methods have been extensively applied to the simultane-ous analysis of mixtures concerning biological, environmen-tal and pharmaceutical problems, they have some well-knowndisadvantages in the analytical applications. However, the ad-vent of the new mathematical methods, namely the wavelettransforms [1218] and the chemometric methods [1922]have fostered the development of the curve resolution of theoverlapping peaks in the spectra of multi-mixtures. In ana-lytical chemistry, the wavelet method has been used in com-bination of other calibration techniques such as partial leastsquares (PLS) [2325] and zero-crossing techniques [2628]for the quantitative determination of active compounds insamples.

see front matter 2004 Published by Elsevier B.V..jpba.2004.11.020and partial least squares methods aspectra for the simultaneous qua

ascorbic acid and acetylsalicylic acErdal Dinca,, Abdil Ozdemirb, D

a Department of Analytical Chemistry, Faculty of Pharmacy, Ankarb Department of Chemistry, Faculty of Arts and Sciences, Sakarya

c Department of Mathematics and Computer Sciences, Faculty of Arts andl Institute for Laser, Plasma and Radiation Physics, Institute of Space Scieelet transform, derivativeied to the overlappingtative resolution ofn effervescent tablets

itru Baleanuc,d

rsity, 06100 Tandogan, Ankara, Turkeyrsity, 54100 Serdivan, Sakarya, Turkeyes, Cankaya University, 06530 Ankara, Turkeyagurele-Bucharest, P.O. Box MG-23, R 76911, Romania

570 E. Dinc et al. / Journal of Pharmaceutical and Biomedical Analysis 37 (2005) 569575

In analytical chemistry, for a long period of time, deriva-tive spectrophotometry (DS) has been considered as a com-parative method for the quantitation of active compoundsin pharmaccontains vamixture sphigher orde

PLS andgreat succechemometrcontent andof these chcalibrationother shortfields of ap

For thesshould be pysis and ro

Continunew and p[2123] anCWT comone to thefamilies intion to obtwavelet famnal transfotwo or morsibility to c

The maiity of CWTpharmaceuplied to a rin the synthcal effervewas carriedtechniquestained resu

2. Experim

2.1. Appar

A Shimtometer pocomputer lDeskJet 60tra. All theature. Thelength rang

The dat(512 Mb RMathWorkformed byPLS calcul

culations and calibrations were performed by using MicrosoftExcel.

Pharm

o co

ideredtablets

0611t and Aayer Diningy usin

Stand

ock soound

e soluttock soixture20gsolutg twosolut

Efferv

entymortaratedd untly. Aftwith

sart, was dimeth

ERGINolutionthe 0.cted f

esults

e absure ar1031minatformura. The simoundsing Dutical

d for teutical samples. On the other hand this methodrious disadvantages including fair resolution of

ectra due to the diminished peak amplitude withr derivation procedure.other chemometric methods can be applied withss to complex pharmaceutical mixtures. Theseic methods need to use an abstract mathematicalit is not easy to apply and understand the theory

emometric techniques particularly PCR and PLStheory. Although they have abstract theories andcomings, they have been already applied to manyplied science as well as analytical chemistry.e reasons, we strongly believe that new methodsresented for the quality control, quantitative anal-utine analysis of the drugs in their samples.ous wavelet transform (CWT) method is a quiteromising method in the area of pharmaceuticald other signal processing area. The importance ofes from the signal transformation of the originalother form of signal giving opportunity of manycluding Haar, Daubechies and Mexican hat func-ain the best calibration signals. The selection of

ily is the most important step to get the best sig-rmation for a given mixture. It may happen thate families give satisfactory results, so there is pos-hoose one of them for the problem solution.n purpose of this study is to show the applicabil-to quantitate the amount of active ingredients in

tical samples. CWT as a graphical method was ap-apid simultaneous determination of AA and ASAetic mixtures and two commercial pharmaceuti-

scent tablet formulations. A detailed comparisonout by derivative spectrophotometry and PLS

and good agreements were found between the ob-lts.

ental

atus and software

adzu UV-160 double beam UVVis spectropho-ssessing a fixed slit width (2 nm) connected to aoaded with Shimadzu UVPC software and a HP0 printer were used to record the absorption spec-measurements were realized at ambient temper-

absorption spectra were recorded over the wave-e of 210310 nm against a blank (0.1 M HCl).a treatment was done in a Pentium 4 2.8 GHzAM) computer using MATLAB 7.0 software (Thes, Natick, MA, USA). CWT calculations were per-means of Wavelet toolbox in MATLAB 7.0 andations were done in PLS-Toolbox 3.0. The DS cal-

2.2.

Twcons

centno. Gtableby Bcontaied b

2.3.

Stcompof ththe s16 mof 0stocktaininstock

2.4.

Twin acalibstirrepleteteredminitionthreeSED(II) swithprote

3. R

Thmixtof 2deterticalspectfor thcompapplymace

testeaceutical preparation

mmercial effervescent tablet formulations werein this study, namely, SEDERGINE efferves-(produced by Laboratories UPSA, France, Batch) consisting of 200 mg AA and 330 mg ASA perSPIRIN Plus C effervescent tablets (produced

rug Industry, Istanbul-Turkey, Batch no. 3 E 173)240 mg AA and 400 mg ASA per tablet were stud-g CWT, DS and PLS methods.

ard solution

lutions of 50 mg/100 mL AA and ASA for eachwere prepared in 0.1 M HCl. A standard seriesions containing 420g/mL were obtained fromlutions for CWT and DS. A concentration set ofsolutions containing in the concentration range

/mL AA and ASA was freshly prepared from theions. A validation set of 10 mixture solutions con-compounds was also prepared by using the same

ions.

escent tablet analysis

effervescent tablets were weighted and powderedr. A tablet amount was transferred to a 100 mLflask and dissolved in 100 mL 0.1 M HCl andil effervescence tablet particles dissolved com-er dissolution process prepared solutions were fil-0.2m disposable membrane filter (Sartorious,= 0.20m) by using an injector. The final solu-luted to the working range for application of theods. An analogous procedure was applied to both

E (I) and ASPIRIN Plus C (II) tablets. (I) ands were diluted in the working concentration range

1 M HCl. All the solutions prepared freshly androm light.

and discussion

orption spectra of AA and ASA in the samee strongly overlapping in the wavelength range0 nm as it can be seen in Fig. 1. The direction of subjected compound in the pharmaceu-lation is not possible due to their overlappingerefore, a new approach, CWT was developedultaneous determination of the above-mentioned. The confirmation of CWT was carried out byS and PLS to the same binary mixtures and phar-samples. The different concentration ranges werehe preparation of calibrations for both drugs and

E. Dinc et al. / Journal of Pharmaceutical and Biomedical Analysis 37 (2005) 569575 571

Fig. 1. Absor(a) 4g/mL,

the workinan appropr

CWT mous determcommerciawithout anybased on aand PLS mmethods. Inand favoredof AA andCWT methus the succThe procedsections.

3.1. CWT

A wavelnal functiodifferent sc

a,b() =

Here aused to con

. CWTL, (b)

HCl.

ter conumbeions lation)our c

and AtransveletproceWT ss wav

crossid by mt 267.ed inht-lines were calculated as higher than 0.999 and also

Table 1Linear regress

CWT258.1267.5

DS244.0258.6ption spectra of AA ( ) and ASA () in the concentration of(b) 8g/mL, (c) 12g/mL, (d) 16g/mL and (e) 20g/mL.

g range between 4 and 20g/mL was selected asiate spectral window.ethod was utilized and applied for the simultane-ination of AA and ASA in the mixtures and twol pharmaceutical effervescent tablet formulations

separation or any other chemical process. CWTn integration procedure was compared with DSethods regarding the performance of these threethe last section, first DS and PLS as well knownmethods of analysis were applied to the mixtures

ASA with the aim of comparison of the developedod. We observed that these three methods giveessful results for the determination of two drugs.ures of these methods were given in the following

method

Fig. 24g/m0.1 M

rame

realfuncttrans

InAAwere

to wawere

and Cversu

zero-

taineand amarizstraiget transform involves the decomposition of a sig-n or vector into simpler, fixed building blocks atales and positions:

1 |a|(ba

), a = 0, a, bR (1)

denotes the scale parameter which is a variabletrol the scaling, b represents the translation pa-

other statisutilizationdrugs. In thequations fpendent vaASA in thTheir resulgiven in Ta

ion analysis and its statistical results by CWT and DS

Regression equation r

A=0.02611CASA 0.00411 0.9996A=0.04884CAA 0.00468 0.9998

A=0.02624CASA 0.00045 0.9999A=0.02514CAA 0.00071 0.9997spectra of AA and ASA in the concentration range of (a)8g/mL, (c) 12g/mL, (d) 16g/mL and (e) 20g/mL in

ntrolling the translation and R is the domain ofrs. A mother wavelet () generates the set ofa,b() by scaling (or dilatation) and shifting (or

.ase, the absorbance values of standard series ofSA in the concentration range of 420g/mLferred as absorbance data vectors from EXCELdomain. The transferred absorbance data vectorsssed by Mexican CWT at the scaling factor a= 50pectra were obtained by plotting Ca,b coefficientselengths as could be seen in Fig. 2. By usingng technique, CWT calibration equations were ob-easuring the CWT signals at 258.1 nm for ASA

5 nm for AA and their statistical results were sum-Table 1. The correlation coefficients of equationstical parameters are in acceptable range for theof calibration lines for the determination of bothe recovery studies, the obtained CWT calibrationor both drugs were tested by analyzing an inde-lidation set of 10 mixture solutions of AA ande working concentration region of 420g/mL.ts as mean and relative standard deviation wereble 4. The analytical values indicate the preci-

S.E. (m) S.E. (n) S.E. (r)

0.0004 0.0056 0.00530.0005 0.0071 0.0068

0.0002 0.0029 0.00270.0004 0.0047 0.0044

572 E. Dinc et al. / Journal of Pharmaceutical and Biomedical Analysis 37 (2005) 569575

sion and accuracy of the application of CWT method to thesamples.

CWT calibration graphs were also applied to real samplescontaining two commercial effervescent tablet formulations.The experimental results of this CWT application showedgood agreement with the label claim of both commercialdosage forms.

3.2. Derivative spectrophotometry

In this method, the calibration graphs of AA and ASAin the concentration range of 420g/mL were obtainedby measuring the dA/d values at 244.0 and 258.6 nm cor-responding to zero-crossing points, respectively. The zero-crossing points give the opportunity of determining AA andASA amount in their mixture without any priori separationstep. Table 1 shows the statistical parameters correspondingto the calibration graphs for both drugs in the chosen wave-lengths.

In the optimization of the experimental conditions of DS,the effect of and scaling factor was tested to find the bestderivative spectra. The values of= 4 nm and scaling factor10 in the first derivative of the absorption spectra were foundas considerable values for both drugs determination. Fig. 3shows theinterval anshown in F

The valitures considrugs. Thefound to band ASA, radding knothe recovermethod.

Fig. 3. First dof (a) 4g/mLin 0.1 M HCl.

Table 2The matrix of concentration set consisting of two drugs

No AA (g/mL) ASA (g/mL)1 4.0 16.52 8.0 16.53 12.0 16.54 16.0 16.55 20.0 16.56 0.0 12.07 10.0 4.08 10.0 8.09 10.0 12.0

10 10.0 16.0111213141516

3.3. PLS m

In our cin samplescalibration

nd ab= UQ

e W is+bA,conce

ndingin the

e PLStimal

sing 1arriedationhe RMndicatinimuuares)ther halope of PLS calibration using the first four factors werelated and shown in Table 3.the prediction step, the constructed PLS calibration wased to the synthetic mixtures (Table 4) and the abilityis calibration was checked by using the statistical pa-ters namely SEP, correlation coefficient, intercept and

according to the relation between added and found

3ical parameters of the concentration matrix in the PLS calibration steps

eter AA ASA

S 0.1296 0.07450.0900 0.06820.9999 0.99990.0030 0.00180.9997 0.9999first derivative spectra obtained with = 4 nmd scaling factor 10 from the absorption spectraig. 1.dation of DS was checked by using various mix-sting of AA and ASA in the working range of twomeans and their relative standard deviations weree 99.5 and 1.67% and 101.6 and 2.11% for AAespectively, in the synthetic mixtures prepared bywn amounts of AA and ASA. As seen in Table 4y results were found reliable for the ability of this

erivative spectra of AA and ASA in the concentration range, (b) 8g/mL, (c) 12g/mL, (d) 16g/mL and (e) 20g/mL

tion aand CwherC= a

Arespoturesin thof opby uwas c

validand tand iing mof sqthe oand scalcu

Inappliof thrame

slope

TableStatist

Param

PRESSECRNM10.0 20.012.0 0.010.0 17.018.0 12.020.0 20.0

4.0 4.0

ethod

ase, the simultaneous prediction of AA and ASAwas accomplished by PLS calibration. The PLSis done by the composition of both concentra-

sorbance matrix into latent variables, A= TPT +ET +F. The vector b is given as b=W (PTW)lQ,a weight matrix. By using the linear regressionthe constant a is given by a=Cmean ATmeanb.ntration set design of the concentration data cor-to the 16 samples containing the AAASA mix-range of 020g/mL was randomly organizedcalibration as shown in Table 2. The selectionfactor was done by cross-validation procedure

6 absorption spectra of samples. This procedureout by PLS Toolbox 3.0. According to the cross-

process, the different factor numbers were testedSECV values versus factor numbers were plotteded in Fig. 4. In our case, the first four factors hav-m values of PRESS (prediction residual error sumwere found appropriate for PLS calibration. Onnd PRESS, SEC, correlation coefficient, intercept

E. Dinc et al. / Journal of Pharmaceutical and Biomedical Analysis 37 (2005) 569575 573

Fig. 4. RMSECV graph of the calibration set in PLS calibration step.

concentration were studied for the constructed PLS calibra-tion. The Sfor ASA. T0.9997 forability of PASA amoutest was dothe predictrandomly s

The PLSin the samfirmed by dmixtures. Tthe workinof PLS. Asstandard d101.1 and

Fig. 5. Concentration residuals for the predicted concentration of AA andASA by using PLS.

thetic mixtures were prepared by adding known quantities ofnd ASe matestedard ednt tab

fervesstandaas 99.01.10

for A0 15 1rdingy wasx effed.

Table 4Recoveries of

No.

Add

AA

1 4.02 8.03 12.04 16.05 20.06 10.07 10.08 10.09 10.0

10 10.0

MeanR.S.D.R.S.D.: relativEP values were found as 0.130 for AA and 0.085he correlation coefficients are 0.9987 for AA andASA and these values indicate good predictiveLS calibration in the prediction of the AA andnts in the mixture solutions. In another analyticalne by plotting the concentration residuals againsted concentrations. We observed that the residualscattered around zero as shown in Fig. 5calibration is used for the estimation of two drugs

ples. The applicability of PLS method was con-etermining AA and ASA in the synthetic binaryhe various mixtures consisting of AA and ASA in

g range of two drugs were used for the validationit can be seen in Table 4, mean and their relative

eviations were found to be 99.9 and 1.70% and1.80 % for AA and ASA, respectively. The syn-

AA aTh

was tstandvesce

to eftheirlated(I), 1(II)102.1100.9Accocurac

matriserveAA and ASA in various synthetic mixtures by CWT, DS and PLS

CWT DS

ed (g/mL) Found (g/mL) Recovery (%) Found (g/mL)ASA AA ASA AA ASA AA ASA

16.5 3.89 16.49 97.3 100.0 3.94 16.4916.5 7.99 16.58 99.9 100.5 7.96 16.5216.5 11.81 16.63 98.5 100.8 11.93 16.4716.5 16.03 16.79 100.2 101.7 16.15 16.6716.5 20.12 16.94 100.6 102.7 20.17 16.844.0 9.81 4.03 98.1 100.8 9.81 4.108.0 10.12 8.37 101.2 104.6 10.14 8.18

12.0 9.97 12.36 99.7 103.0 9.71 12.2416.0 10.11 16.39 101.1 102.4 10.16 16.2320.0 9.94 20.00 99.4 100.0 9.75 21.45

99.6 101.71.30 1.49

e standard deviation.A.rix effect of excipients in the effervescent tabletsfor CWT, DS and PLS methods. For this reason,ition method was applied to commercial effer-lets. In application of standard addition method

cent tablets, the mean percentage recoveries andrd deviation for the CWT, DS and PLS were calcu-0 1.11% (I), 100.05 1.30% (II); 98.9 1.45% 1.81% (II); 99.5 1.62% (I), 98.05 1.95%

A and 100.8 0.98% (I), 98.50 2.05% (II);.75% (I), 97.50 2.52% (II); 98.80 1.52% (I),.09% (II) for ASA, respectively for five replicates.to the obtained results a good precision and ac-observed for three methods. Consequently, the

ct of the excipients in tablet analysis was not ob-PLS

Recovery (%) Found (g/mL) Recovery (%)AA ASA AA ASA AA ASA

98.5 99.9 3.93 16.47 98.2 99.899.5 100.1 8.02 16.47 100.2 99.899.4 99.8 11.89 16.45 99.1 99.7

100.9 101.0 16.10 16.58 100.6 100.5100.9 102.1 20.11 16.67 100.6 101.198.1 102.6 9.97 4.08 99.7 102.1

101.4 102.2 10.26 8.09 102.6 101.197.1 102.0 9.77 12.09 97.7 100.7

101.6 101.4 10.21 16.12 102.1 100.797.5 107.3 9.79 21.18 97.9 105.9

99.5 101.8 99.9 101.11.67 2.11 1.70 1.80

574 E. Dinc et al. / Journal of Pharmaceutical and Biomedical Analysis 37 (2005) 569575

Table 5Results of the commercial effervescent tablet preparations by investigated methods

Method CWT DS PLS

Parameter AA ASA AA ASA

I II I II I II I

Mean 197.7 236.7 344.8 395.9 199.4 238.5 340.5S.D. 1.52 2.22 4.88 3.87 1.88 0.88 8.4R.S.D. 0.77 0.94 1.41 0.98 0.94 0.37 2.4S.E. 0.88 1.28 2.81 2.24 1.09 0.51 4.8CL (P= 0.05) 1.77 2.58 5.67 4.51 2.19 1.02 9.8SEDERGINE VITAMIN EE C effervescent tablet: 200 mg AA and 330 mg ASA per tablet (I). AASA per tablet (II).

3.4. Analysis of effervescent tablets

The obtained results by applying CWT, DS and PLS meth-ods to two commercial effervescent tablet preparations wereshown in Table 5. A good coincidence was observed betweenthe experimental results and label claim of the commercialeffervescent preparation in this study. The numerical valuesof all statistical parameters calculated in Table 5 are accept-able determination limits in application of two methods tothe effervescent tablets.

To compare CWT, DS and PLS, one-way ANOVA test wasapplied to the obtained results for two commercial efferves-cent tablet formulations. The calculated F-values (P= 0.05,n1 = 4 and n2 = 12) were found lower than the tabulatedF-value and the ANOVA test results were not significant;the variances differ only randomly. The results of one-wayANOVA te

Table 6The ANOVAceutical efferv

Sum of squar

Degree of fre

Mean squares

Calculated F-

Tabulated F-v

three methsets of sub-

4. Conclu

The maito the simin their miprior chemoverlappin

Good rePLS methoAA and ASwas found

lthougtheirparingg peaked peaach.e belieique talyticod. Thts foruld beese th

se rouuticalst were shown in Table 6. We can accept by these

results by applying three methods to two commercial pharma-escent preparations

Drug Sample Source of variations

Betweengroups

Withingroups

Total

es AA I 11.17 31.50 42.67II 17.64 33.59 51.23

ASA I 47.48 403.04 450.52II 127.69 996.79 1124.48

edom AA I 2 12 14II

ASA III

AA I 5.59 2.62

Aysis,Comas bicreas

approW

technof anmethresulas co

ThprecimaceII 8.82 2.80ASA I 23.74 33.59

II 63.84 83.07

value AA I 2.13II 3.15

ASA I 0.71II 0.77

alue AA I 3.89II

ASA III

Reference

[1] V. Kmet[2] R. Thom

183018[3] H.N. Do[4] N. Ram

Capitan[5] A.M. Di

A 729 ([6] C. Akay

metab. DAA ASA

II I II I (II)395.1 197.5 239.4 342.0 389.4

4 14.95 1.42 1.64 2.40 3.258 3.78 0.72 0.69 0.70 0.847 8.63 0.82 0.95 1.39 1.882 17.40 1.65 1.91 2.79 3.79

SPIRIN Plus C effervescent tablet: 230 mg AA and 400 mg

ods that there is no difference between the threesamples.

sion

n purpose of this study was to apply CWT methodultaneous determination of AA and ASA drugsxtures and effervescent tablets without using anyical pre-treatment in the presence of the stronglyg spectra.sults were obtained by utilizing CWT, DS andds as a comparative study for the quantitation ofA and a good agreement with the literature results[25].h CWT and DS are based on the use of signal anal-theoretical aspects are different from each other.

to DS method, CWT gives us many advantagesintensity and more zero-crossing points. The in-k intensity provides a higher sensitivity for CWT

ve that the ability of CWT based on zero-crossingo drug analysis will gain importance in the fieldal chemistry as an alternative to the derivativeis approach gives us repeatable, rapid and reliablethe quantitation of active compounds in samples,seen in this study.ree methods were found suitable for simple andtine quality control analysis of the selected phar-samples.s

ec, J. Pharm. Biomed. Anal. 10 (1992) 10731076.is, E. Roets, J. Hoogmartens, J. Pharm. Sci. 73 (1984)

33.gan, A. Duran, Pharmazie 53 (1998) 781803.os Martos, A. Molina Diaza, A. Navalon, I.O. Paya, L.F.Vallvey, J. Pharm. Biomed. Anal. 23 (2000) 837844.Pietra, R. Gatti, V. Andrisano, V. Cavrini, J. Chromatogr.

1996) 355361., B. Gumusel, T. Degim, S. Tartlmus, S. Cerheloglu, Drugrug Interact. 15 (1999) 197205.

E. Dinc et al. / Journal of Pharmaceutical and Biomedical Analysis 37 (2005) 569575 575

[7] L.T. Kubota, J.C.B. Fernandes, L. Rover, G. Oliviera Neto, Talanta50 (1999) 661667.

[8] M.E. Abdel-Hamid, M.H. Baray, E.M. Hassan, M.A. Elsayed, Ana-lyst 110 (1985) 831835.

[9] M.I. Toral, N. Lara, P. Richter, A. Tassara, A.E. Tapia, C. Rodriguez,J. AOAC Int. 84 (2001) 3742.

[10] K. Mielech, J. Trace Micropr. Techniq. 21 (2003) 111121.[11] E. Dinc, Talanta 48 (1999) 11451157.[12] B.K. Alsberg, A.M. Woodward, D.B. Kell, Chemom. Intell. Lab.

Sys. 37 (1997) 215239.[13] A.K. Leung, F. Chau, J. Gao, Chemom. Intell. Lab. Sys. 43 (1998)

165184.[14] L. Shao, X. Lin, X. Shao, Appl. Spect. Rev. 37 (2002) 429450.[15] M. Cocchi, J.L. Hidalgo-de-Cisneros, I. Naranjo-Rodrguez, J.M.

Palacios-Santander, R. Seeber, A. Ulrici, Talanta 59 (2003) 735749.[16] X. Lu, H. Liu, J. Kang, Anal. Chim. Acta 484 (2003) 201

210.

[17] X.G. Ma, Z.X. Zhang, Anal. Chim. Acta 485 (2003) 233239.[18] B. Walczak, Wavelets in Chemistry, Elsevier Press, Amsterdam, The

Netherlands, 2000.[19] K. Kramer, Chemometric Techniques for Quantitative Analysis, Mar-

cel Dekker Inc., 1998.[20] P. Geladi, B.R. Kowalski, Anal. Chim. Acta 185 (1986) 117.[21] D.M. Haaland, G. Easterling, D.A. Vopicka, Appl. Spectrosc. 39

(1985) 7384.[22] K.D. Zissis, R.G. Brereton, S. Dunkerley, R.E.A. Escott, Ann. Chim.

Acta 384 (1999) 7181.[23] S. Ren, L. Gao, Talanta 50 (2000) 11631173.[24] G. Chen, P.B. Harrington, Anal. Chim. Acta 484 (2003) 7591.[25] M.M. Sena, J.C.B. Fernandes, L. Rover, R.J. Poppi, L.T. Kubota,

Ann. Chim. Acta 409 (2000) 159170.[26] E. Dinc, D. Baleanu, Talanta 59 (2003) 707717.[27] E. Dinc, D. Baleanu, Spectrosc. Lett. 36 (2003) 341355.[28] E. Dinc, D. Baleanu, J. Pharm. Biomed. Anal. 31 (2003) 969978.

Comparative study of the continuous wavelet transform, derivative and partial least squares methods applied to the overlapping spectra for the simultaneous quantitative resolution of ascorbic acid and acetylsalicylic acid in effervescent tabletsIntroductionExperimentalApparatus and softwarePharmaceutical preparationStandard solutionEffervescent tablet analysis

Results and discussionCWT methodDerivative spectrophotometryPLS methodAnalysis of effervescent tablets

ConclusionReferences