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Asian Journal of Chemistry Vol. 20, No. 8 (2008), 6310-6324 Vibrational Spectra and Qualitative Analysis of
Albendazole and Mebendazole
S. GUNASEKARAN and D. UTHRA* Department of Physics, D.G. Vaishnav College Chennai-600 106, India In this work, vibrational spectral analysis of two broad- spectrum anthelmintic drugs albendazole and mebendazole,that fall under the category of the WHO's model list of essentialdrugs for the eradication of helminthiasis, has been carriedout by employing FTIR, FT-Raman and UV-Visible spectroscopictechniques. The change in the quality of the drugs under variousstorage conditions has been studied by spectral techniques.
The results are indicative of the fact that it is essential to storethe drugs under the prescribed ones to maintain their qualityand the alteration in quality can be assessed by spectroscopyas a tool.
Key Words: Albendazole, Mebendazole, Storage, Quality,
FTIR, FT-Raman, UV-Visible.
Human beings have always been in need of solutions to address illness, injury and various health related issues. A drug may be defined as a substanceused in the prevention, diagnosis, treatment or cure of disease in man orother animals1. Pharmaceutical products differ considerably in their compo-sition, so naturally, they are subject to different forms of chemical degra-dation and in addition, there may be several simultaneous decompositionreactions occurring in a product. Some of the physical factors that influencechemical degradation are temperature, moisture, strong sunlight and ionizingradiation2. By taking care of the storage condition of the drug products,these degradations could be avoided to large extent. Numerous references inthe pharmaceutical literature3-5 refer to the instability of many drug productswhen exposed to strong sunlight. The photochemical degradation of a sensi-tive material can be reduced by protecting the drugs from light by storingin light-resistant containers are used. In the preparation of solid dosage †Postgraduate and Research Department of Physics, Pachaiyappa's College, Chennai- 600 030, India. E-mail: [email protected] Vol. 20, No. 8 (2008) Vibrational & Qualitative Analysis of Albendazole & Mebendazole 6311 from drugs whose chemical stability is affected by moisture, care is taken toensure an environment of controlled humidity in every stage like manufacturing,packaging and storage6. While increase in storage temperature than the labelledones can lead to certain types of degradation, a decrease too can cause harmto the drug quality7. As access to medicines must be accompanied by qualityassurance, there must be controls and checks to ensure that the medicinesultimately reaching the patients are of good quality, safe and effective8.
Deworming helps meet the Millennium Development Goals of the WHO. The control of worm-induced disease is a highly effective investmentin terms of health, education, poverty reduction and development which notonly takes the mankind onwards, but also upwards9. Periodic chemotherapywith single dose anthelmintic drugs for helminth control in developingcountries are in the mainstay in the public health related issues. In light ofthe increasing drug resistance of nematodes of livestock to anthelminticproducts, assessment and monitoring of efficacy of anthelmintic drugs inareas where they are commonly used has gained importance. Moreover,the WHO has urged for the creation of a global network for monitoringanthelmintic drug efficacy and drug resistance as a needed response to thisemerging threat. The choice of the most cost-effective drugs for use inhelminth control is guided principally by considerations of quality, efficacy,safety and cost10. The study of efficacy of these drugs in biological systems,their chemotherapeutic activity needs the knowledge of biological discip-lines and is a concern of pathologists and medical practitioners. Alterna-tively, with an eye of a spectroscopist, the current work is a study on thebehaviour of albendazole and mebendazole by tracing their vibrationalspectra for ensuring the presence of the basic functional groups and anal-yzing the change in their behaviour when stored at different conditions,thereby checking the quality of the drugs. In this paper, an attempt is madeto use infrared and UV-Visible spectroscopic techniques as a tool to indicatethe deterioration when albendazole and mebendazole are not stored as recom-mended.
High grade pure samples of albendazole and mebendazole were procured from reputed pharmaceutical firms in Chennai, India and used for spectralrecording as such. The FTIR spectra of the drugs were recorded with ABBBomem Series spectrophotometer over the region 4000-400 cm-1 by KBrpellet technique at Dr. CEEAL Analytical Lab, Chennai, India. The FT-Ramanspectra were recorded using 1064 nm line of Nd:YAG laser operating at200 mW on Bruker FRA106 spectrophotometer in the region 50-3500 cm-1with the spectral width of 4.29 cm-1 at SAIF, IIT, Chennai. The Indian 6312 Gunasekaran et al. Asian J. Chem. Pharmacopoeia recommends that albendazole and mebendazole should bestored in tightly closed, light-resistant containers11. To study the change inthe quality, the pure drugs were (i) stored in well-sealed light resistantcontainer, (ii) exposed to sunlight and (iii) at ice point and FTIR spectrumof each was recorded. All the spectra were recorded at the room temperature.
The UV-Visible spectral measurements were carried out using Shimadzu-160A spectrophotometer at Dr. CEEAL Analytical Lab, Chennai.
For the purpose, the linearity range in which the drugs obey Beer-Lambert'slaw has been figured out by analyzing the sample at various concentrations.
Accurately weighed 100 mg of each of the drug, albendazole and mebenda-zole are taken in separate 100 mL standard flasks to which 10 mL formicacid was added. The solutions are made up to the mark by adding 0.1 MHCl and sonicated to ensure thorough mixing of the contents. Each ofthese drug solutions are transferred into separate test tubes and furtherdiluted to obtain drug concentrations of 2, 4, 6 … 20 µg mL-1. The absorptionvalues for various concentrations of the drugs which fall within this linearityrange are used to plot the linearity curves. The absorbance values at 291and 262 nm of albendazole are noted and the absorbance peak at 284 nm ofmebendazole spectra are used to study the linearity behaviour. In order tosupport the qualitative analysis done by the FTIR method, UV-Visible spectro-scopic approach has been adopted to study the variation in the light absorptionproperties of the drugs stored in various conditions.
RESULTS AND DISCUSSION
The drugs, albendazole (Fig. 1) and mebendazole (Fig. 2) belong to benzimldazole group of drugs. Albendazole has the IUPAC name methyl[(5-propyl sulfanyl-3H-benzo-imidazol-2-yl)amino]formate, while the IndianPharmacopoeia mentions it as methyl 5-propylthio-1H-benzimidazol-2-yl-carbamate. The vibrational spectrum of a compound is the superpositionof vibrational bands of the various functional groups present in it. By obser-ving the nature, position, shape and relative intensity of the vibrationalbands and comparing them with that of structurally and chemically relatedcompounds, a satisfactory frequency assignment of these functional groupspresent has been done. The corresponding vibrational spectral assignmentsare summa-rized in Tables 1 and 2.
Fig. 1. Structure of albendazole Fig. 2. Structure of mebendazole Vol. 20, No. 8 (2008) Vibrational & Qualitative Analysis of Albendazole & Mebendazole 6313 VIBRATIONAL SPECTRA AND FREQUENCY ASSIGNMENT FOR ALBENDAZOLE Frequency (cm-1) Vibrational band assignment Aromatic C-H stretching Aromatic C-H stretching Aromatic C-H stretching Aromatic C-H stretching CH /CH C-H stretching CH /CH C-H stretching CH /CH C-H stretching CH /CH C-H stretching CH /CH C-H stretching CH /CH C-H stretching Aromatic ring stretching Aromatic CLC / CLN stretching Aromatic CLN stretching Amide II band /C-N stretching Aromatic CLC /CLN stretching Aromatic CLC /CLN stretching C-O/C-S stretching C-H in-plane deformation C-H in-plane deformation C-H in-plane deformation C-H out-of-plane deformation C-H out-of-plane deformation C-H out-of-plane deformation N-H out-of-plane deformation N-H out-of-plane deformation N-H out-of-plane deformation C-C out-of-plane deformation 6314 Gunasekaran et al. Asian J. Chem. VIBRATIONAL SPECTRA AND FREQUENCY ASSIGNMENT FOR MEBENDAZOLE Frequency (cm-1) Vibrational band assignment Aromatic C-H stretching Aromatic C-H stretching Aromatic C-H stretching Aromatic C-H stretching Aromatic C-H stretching Benzoyl C=O stretching Aromatic ring stretching Aromatic ring stretching Aromatic CLC /CLN stretching Aromatic CLC /CLN stretching Amide II Band /CLN ring stretching Aromatic ring stretching C-H in-plane deformation C-H in-plane deformation C-H in-plane deformation C-H out-of-plane deformation C-H out-of-plane deformation N-H out-of-plane deformation N-H out-of-plane deformation C-C in-plane deformation C-C out-of-plane deformation Vol. 20, No. 8 (2008) Vibrational & Qualitative Analysis of Albendazole & Mebendazole 6315 Urethane bands: Primary urethanes have a number of absorptions in
the region 3450-3200 cm-1 due to the N-H stretching vibration. Secondaryurethanes absorb near 3300 cm-1 if hydrogen-bonding occurs and at 3450-3390 cm-1 if it is absent12. Albendazole and mebendazole both being,N-aryl secondary urethanes exhibit a medium intensity peak at 3328 and3368 cm-1, respectively in their FTIR spectrum, that is attributed to N-Hstretching. The assignment has been verified by the presence of these vibra-tions in the FT-Raman spectrum of these compounds.
Urethanes, also called as carbamates exhibit carbonyl frequency at somewhat higher frequency than amides and lower than esters. This banddue to the carbonyl stretching vibration, termed as amide I band of urethanesoccurs in the region 1740-1680 cm-1. In CHCl3 solution, most primary carba-mates absorb at 1728-1722 cm-1 secondary carbamates at 1722-1705 cm-1and tertiary at 1691-1683 cm-1. In solid state, they are much the same,except that some primary carbamates give very broad bands which mayabsorb as low as 1690 cm-1. N-aryl urethanes in solid phase exhibit thisband in the region 1735-1705 cm-1, while strong hydrogen bonding mayresult in band as low as 1690 cm-1. In view of these, the sharp band presentat 1712 and 1731 cm-1 in the FTIR spectrum of albendazole and meben-dazole is assigned to the amide I vibration of the carbamate group present.
The FTRaman spectrum of the two drugs show this vibration at 1717 and1730 cm-1, respectively.
Associated secondary urethanes absorb strongly at 1540-1530 cm-1 due to CNH group vibration, similar to that of secondary amides and in dilutesolution this band is found at 1530-1510 cm-1 is termed as amide II bandinvolves both N-H deformation and predominantly absorbs strongly near1550 cm-1. The in-plane N-H bending frequency and the resonance stiffenedC-N bond stretching frequency fall close together and therefore interact.
This band very characteristic for monosubstituted amides which occurs inurethanes too, can be traced as the medium strong bands present at 1524cm-1 in FTIR and at 1535 cm-1 in the FT-Raman spectrum, respectively ofalbendazole. Similar peaks at 1530 and 1542 cm-1 of the vibrational spectraof mebendazole can be attributed to the CNH group which reflects thecorrectness of this assignment.
Urethanes also exhibit amide III band just like amides, but in the region 1260-1220 cm-1 in solid and is usually stronger than the C=O band. In thisline, the very strong band present at 1260 cm-1 in the FTIR spectrum ofmebendazole and at 1268 cm-1 of other three spectra is due to the combinationof N-H deformation and C-N stretching vibration motion.
Amide IV band that arises due to coupling between C-N and C-O stretching vibrations occur in the region 1265-1200 cm-1 in urethanes. Thestrong band present at 1223 cm-1 in FTIR spectrum is allotted as amide IV 6316 Gunasekaran et al. Asian J. Chem. band in albendazole. While the same can be traced at 1227 cm-1 in its FTRaman spectrum of albendazole and as a strong peak in the FTIR spectrumof mebendazole. The amide IV band for mebendazole is located at 1231cm-1 in its FT-Raman spectrum.
The band present at 1095 and 1089 cm-1 in the FTIR spectrum of the two drugs can be assigned to the C-O stretching of urethane group. In caseof albendazole, this peak is overlapped by the band due to aryl-S linkageresulting in a higher intensity peak compared to that of mebendazole. Thevariation in the intensity of this peak due to the presence of aryl-S linkageis even more pronounced in the FT-Raman spectrum of the compounds.
The out of plane deformation of the N-H group of urethane has resulted inweak to medium intensity peaks in 700-625 cm-1 region as expected.
Propyl-thio group vibrations: In general, the assignment of the band
due to the C-S stretching vibration in different compounds is difficult sinceit is of variable intensity and may be found over the wide region 1035-245cm-1. Both aliphatic and aromatic sulphides have a weak-to-medium banddue to the C-S stretching vibration in the region 710-570 cm-1, primarysulphides absorbing at the higher frequency end of the range and tertiarysulphides at the lower end. While C-S stretching frequency of CH3-S occursin the range 710-685 cm-1, R-CH2-S moeity results in this vibration in therange 660-630 cm-1, as the increase in the length of the alkyl group attachedto the sulphur atom decreases the C-S stretching frequency. Moreover, thisvibration does not give rise to strong bands in the infrared spectrum whichmakes this linkage difficult to detect in some cases, while it is a better bandin Raman spectrum usually13. With propyl group attached to the sulphuratom, a lowering in the stretching frequency of C-S band is expected. Afurther decrease is expected due to the double bond conjugation of thearomatic group attached to this link. Hence C-S stretching vibrational bandhas been traced at 570 cm-1 in the vibrational spectra of albendazole, whileno peak is found in this region in case of mebendazole indicating the absenceof such a linkage or bond of such nature.
A band near 1090 cm-1 is usually characteristic for the aryl-S linkage.
It is thought to be an aromatic vibration having some C-S stretching character.
The presence of this vibration can be immediately noted in albendazole,which happens to be also a region of C-O stretching vibration. In case ofmebendazole, the absence of C-S group can be verified from the variationin the intensity of the said band in both the molecules. The asymmetric andsymmetric stretching vibration of the CH2 group attached to the sulphuratom give rise to medium intensity bands in the region 2950-2920 and2880-2845 cm-1, respectively. In the characterization of certain mercapto-benzothiole compounds, Yadav et al.14 have identified the CH2-S methylenevibrational band at 2960 cm-1. The peak at 2927 and 2867 cm-1 of the FTIR Vol. 20, No. 8 (2008) Vibrational & Qualitative Analysis of Albendazole & Mebendazole 6317 and FT-Raman spectrum of albendazole is a sufficient proof for the presenceof this group in albendazole and not in mebendazole. Infrared absorptionbands characteristic of alkylthio groups have been discussed by Menefeeet al.15 who suggest that the bands near 1305 and 1420 cm-1 are attributedto methylene twisting and wagging vibrations in P-S-Et compounds.
Benzoyl group vibrations: Conjugation with a CLC bond results in
delocalization of the π electrons of both the unsaturated groups. This reducesthe double bond character of the C=O bond causing a decrease in forceconstant of this band which tends to decrease the carbonyl stretching frequ-ency. The position of the C=O stretching and is determined by the followingfactors (i) the physical state, (ii) electronic and mass effects of neighbouringsubstituents, (iii)conjugation, (iv) intermolecular and intramolecular hydrogenbonding and (v) ring strain. Consideration of these factors leads to a consi-derable amount of information about the environment of the C=O group16.
Among the title compounds, mebendazole shows a strong peak at 1644cm-1 in FTIR spectrum and at 1647 cm-1 in FT Raman spectrum due to theketone group vibration. A weak overtone of this vibration can be seen near3300 cm-1 in both the spectra of this compound.
Benzimidazole group vibrations: Several derivatives of benzimidazoles
are known to posses diverse types of biological activities. The characteristicstretching bands at about 3290-2460 cm-1 originating from imidazoles' N-Hgroup were observed in the infrared spectra of all the compounds synthe-sized17,18. Very broad absorption bands near 3000 cm-1 have been identifiedas due to N-H stretching vibration of benzimidazole group by Dubey et al.19.
In solid phase, five members heteroatomic compounds with two or morenitrogen atoms in the ring have a broad absorption at 2800-2600 cm-1 dueto NH .N bond. The FTIR band at 3328 and 3368 cm-1 in the spectrum ofalbendazole and mebendazole respectively has been already allotted to theN-H stretching vibration of the carbamate group. The same bands arere-allotted to the same mode of vibration here for the benzimidazole groupN-H moeity.
The C=N stretching of this group is expected at 1560-1520 cm-1 region.
Imidazoles have several bands of variable intensity in range 1660-1450cm-1 due to CLN and CLC stretching vibrations. Report16 shows thesevibrations to occur in the region 1615-1500 cm-1 and the current work alsoshows vibrations in the same region. In case of mebendazole, the CLCvibrational band occurs as a doublet, which indicates the presence of carbonylgroup in attached to the benzene zing. When C=O, C=C, C=N or NO2 isdirectly conjugated to the benzene ring, a doublet is observed at 1625-1575 cm-1. Substituent resulting in conjugation, such as C=C and C=O,increase the intensity of this doublet. The ring CLC and CLN stretchingvibrations occur19 in the region 1615-1575 cm-1. Mohan et al.20 have identified 6318 Gunasekaran et al. Asian J. Chem. the stretching frequency of CLN bond in benzimidazole at 1617 cm-1.
Chidambarathanu et al.21 have observed the ring carbon-carbon stretchingat 1574, 1498 and 1468 cm-1 in a poly-substituted pyrazole compound.
Vibrational bands present at 1535, 1567, 1579 and 1581 cm-1 are assignedto this aromatic CLC stretching in diazepam, a nitrogen containing hetero-cyclic compound, while the band present at 1605 cm-1 has been attributedto CLN stretching vibration22. Referring to the above assignments, the bandspresent in this region have been assigned to the ring stretching vibrations.
Aromatic C-H stretching vibrations: The C-H stretching vibrations
of aromatic and heteroaromatic structures of strong to medium intensityoccur in the region 3100-3000 cm-1 which is the characteristic region forready identification of this structure. These bands have been identified inthe 3095-3055 cm-1 region in some pyridine type benzimidazoles. TheRaman bands at 3078, 2989, 3102 and 3151 cm-1 of albendazole and theweak IR bands at 2980, 3104 and 3142 cm-1 are attributed to this vibration.
In case of mebendazole, a number of weak bands are present in 3069-2945cm-1 in both FTIR and FT-Raman spectrum. A band with upto five peaksmay be observed in this region. As might be expected, monosubstitutedbenzenes usually exhibit more peaks than di- or tri-substituted benzenes.
This reason may be attributed to the presence of more bands in this regionin case of mebendazole due to the presence of the benzoyl group in it, butnot in albendazole.
Other deformation vibrations: A number of CH in-plane deformation
bands, upto six occur in the region 1290-1000 cm-1 the bands usually beingsharp but of weak to medium intensity. However, these bands are not normallyof importance for interpretation purposes much. On the other hand, the frequ-encies of the C-H out-of-plane deformation vibrations give an importantmeans for determining the type of the aromatic substitution. These bandsare determined mainly by the number of adjacent hydrogen atoms on thering. Mono-substituted benzenes have a strong band in the region 770-735cm-1 with an additional band observed at 745-690 cm-1 in the spectra. Acoupling between adjacent hydrogen atoms is also observed for naphthalene,phenanthrenes, in pyridines and quinolines where the nitrogen atom beingtreated as a substituted carbon atom of a benzene ring and in other aromaticcompounds. Overtones and combination bands due to the C-H out-of-planedeformation vibrations occur in the region 1200-1600 cm-1. The absorptionpatterns observed are characteristic of different benzene ring substitutions.
In most hydrocarbons, CH2 deformation occurs near 1465 cm-1.
Unsaturation next to the CH2 lowers its deformation to about 1440 cm-1.
Sulphur, phosphorus, silicon, chlorine, bromine and iodine all lower thedeformation frequency of the CH2 group to 1450-1405 cm-1. The methylgroups give rise to two vibration bands, the asymmetric deformation band 6320 Gunasekaran et al. Asian J. Chem. INTERNAL STANDARD EVALUATION FOR ALBENDAZOLE Internal standard of specific modes of vibration at 3328 cm-1 3328/ 2957/ 1712/ 1633/ 1589/ 1460/ 1268/ 1194/ Labelled condition 1.0000 1.2397 1.1227 2.8296 2.3988 1.5569 2.7603 1.8488 Exposed to sunlight 1.0000 1.2311 1.1296 3.1464 2.5722 1.5881 3.0984 1.9281 At ice point 1.0000 1.2732 1.1311 3.5474 2.8455 1.6613 3.4912 2.0346 Internal standard of specific modes of vibration at 2957 cm-1 3328/ 2957/ 1712/ 1633/ 1589/ 1460/ 1268/ 1194/ Labelled condition 0.8066 1.0000 0.9056 2.2824 1.9349 1.2559 2.2265 1.4913 Exposed to sunlight 0.8123 1.0000 0.9175 2.5557 2.0893 1.2899 2.5167 1.5661 At ice point 0.7854 1.0000 0.8884 2.7861 2.2349 1.3048 2.7420 1.5980 Internal standard of specific modes of vibration at 1712 cm-1 3328/ 2957/ 1712/ 1633/ 1589/ 1460/ 1268/ 1194/ Labelled condition 0.8907 1.1043 1.0000 2.5204 2.1367 1.3868 2.4587 1.6468 Exposed to sunlight 0.8853 1.0899 1.0000 2.7854 2.2770 1.4059 2.7429 1.7069 At ice point 0.8841 1.1257 1.0000 3.1363 2.5157 1.4688 3.0866 1.7988 Internal standard of specific modes of vibration at 1633 cm-1 3328/ 2957/ 1712/ 1633/ 1589/ 1460/ 1268/ 1194/ Labelled condition 0.3534 0.4381 0.3968 1.0000 0.8477 0.5502 0.9755 0.6534 Exposed to sunlight 0.3178 0.3913 0.3590 1.0000 0.8175 0.5047 0.9847 0.6128 At ice point 0.2819 0.3589 0.3188 1.0000 0.8021 0.4683 0.9842 0.5735 Internal standard of specific modes of vibration at 1589 cm-1 3328/ 2957/ 1712/ 1633/ 1589/ 1460/ 1268/ 1194/ Labelled condition 0.4169 0.5168 0.4680 1.1796 1.0000 0.6491 1.1507 0.7707 Exposed to sunlight 0.3888 0.4786 0.4392 1.2233 1.0000 0.6174 1.2046 0.7496 At ice point 0.3514 0.4475 0.3975 1.2467 1.0000 0.5838 1.2269 0.7150 Internal standard of specific modes of vibration at 1460 cm-1 3328/ 2957/ 1712/ 1633/ 1589/ 1460/ 1268/ 1194/ Labelled condition 0.6423 0.7963 0.7211 1.8174 1.5407 1.0000 1.7729 1.1874 Exposed to sunlight 0.6297 0.7752 0.7113 1.9812 1.6196 1.0000 1.9510 1.2141 At ice point 0.6019 0.7664 0.6808 2.1353 1.7128 1.0000 2.1015 1.2247 Internal standard of specific modes of vibration at 1268c m-1 3328/ 2957/ 1712/ 1633/ 1589/ 1460/ 1268/ 1194/ Labelled condition 0.3623 0.4491 0.4067 1.0251 0.8690 0.5640 1.0000 0.6698 Exposed to sunlight 0.3227 0.3973 0.3646 1.0155 0.8302 0.5126 1.0000 0.6223 At ice point 0.2864 0.3647 0.3240 1.0161 0.8150 0.4759 1.0000 0.5828 Internal standard of specific modes of vibration at 1194 cm-1 3328/ 2957/ 1712/ 1633/ 1589/ 1460/ 1268/ 1194/ Labelled condition 0.5409 0.6706 0.6073 1.5305 1.2975 0.8422 1.4930 1.0000 Exposed to sunlight 0.5186 0.6385 0.5859 1.6319 1.3340 0.8237 1.6070 1.0000 At ice point 0.4915 0.6258 0.5559 1.7436 1.3986 0.8165 1.7159 1.0000 Vol. 20, No. 8 (2008) Vibrational & Qualitative Analysis of Albendazole & Mebendazole 6321 INTERNAL STANDARD EVALUATION FOR MEBENDAZOLE Internal standard of specific modes of vibration at 3368 cm-1 3368/ 2947/ 1731/ 1639/ 1593/ 1456/ 1259/ 1227/ Labelled condition 1.0000 0.5094 1.2017 1.2952 1.2697 0.9731 1.2975 1.1730 Exposed to sunlight 1.0000 0.4604 1.3973 1.8184 1.7114 0.9824 2.2556 1.3838 At ice point 1.0000 0.4807 1.3075 1.8636 1.7013 0.9508 2.0290 1.3353 Internal standard of specific modes of vibration at 2947 cm-1 3368/ 2947/ 1731/ 1639/ 1593/ 1456/ 1259/ 1227/ Labelled condition 1.9631 1.0000 2.3591 2.5427 2.4926 1.9104 2.5471 2.3028 Exposed to sunlight 2.1721 1.0000 3.0351 3.9497 3.7173 2.1337 4.8994 3.0057 At ice point 2.0803 1.0000 2.7200 3.8767 3.5392 1.9779 4.2208 2.7777 Internal standard of specific modes of vibration at 1731 cm-1 3368/ 2947/ 1731/ 1639/ 1593/ 1456/ 1259/ 1227/ Labelled condition 0.8321 0.4239 1.0000 1.0778 1.0566 0.8098 1.0797 0.9761 Exposed to sunlight 0.7157 0.3295 1.0000 1.3014 1.2248 0.7030 1.6143 0.9903 At ice point 0.7648 0.3676 1.0000 1.4252 1.3012 0.7271 1.5518 1.0212 Internal standard of specific modes of vibration at 1639cm-1 3368/ 2947/ 1731/ 1639/ 1593/ 1456/ 1259/ 1227/ Labelled condition 0.7721 0.3933 0.9278 1.0000 0.9803 0.7513 1.0017 0.9057 Exposed to sunlight 0.5499 0.2532 0.7684 1.0000 0.9412 0.5402 1.2404 0.7610 At ice point 0.5366 0.2579 0.7016 1.0000 0.9129 0.5102 1.0888 0.7165 Internal standard of specific modes of vibration at 1593 cm-1 3368/ 2947/ 1731/ 1639/ 1593/ 1456/ 1259/ 1227/ Labelled condition 0.7876 0.4012 0.9465 1.0201 1.0000 0.7664 1.0219 0.9238 Exposed to sunlight 0.5843 0.2690 0.8165 1.0625 1.0000 0.5740 1.3180 0.8086 At ice point 0.5878 0.2825 0.7685 1.0954 1.0000 0.5588 1.1926 0.7848 Internal standard of specific modes of vibration at 1456 cm-1 3368/ 2947/ 1731/ 1639/ 1593/ 1456/ 1259/ 1227/ Labelled condition 1.0276 0.5235 1.2349 1.3310 1.3048 1.0000 1.3333 1.2054 Exposed to sunlight 1.0180 0.4687 1.4224 1.8511 1.7422 1.0000 2.2962 1.4087 At ice point 1.0518 0.5056 1.3752 1.9601 1.7894 1.0000 2.1340 1.4044 Internal standard of specific modes of vibration at 1259 cm-1 3368/ 2947/ 1731/ 1639/ 1593/ 1456/ 1259/ 1227/ Labelled condition 0.7707 0.3926 0.9262 0.9983 0.9786 0.7500 1.0000 0.9041 Exposed to sunlight 0.4433 0.2041 0.6195 0.8062 0.7587 0.4355 1.0000 0.6135 At ice point 0.4929 0.2369 0.6444 0.9185 0.8385 0.4686 1.0000 0.6581 Internal standard of specific modes of vibration at 1227cm-1 3368/ 2947/ 1731/ 1639/ 1593/ 1456/ 1259/ 1227/ Labelled condition 0.8525 0.4343 1.0245 1.1042 1.0824 0.8296 1.1061 1.0000 Exposed to sunlight 0.7226 0.3327 1.0098 1.3141 1.2367 0.7099 1.6300 1.0000 At ice point 0.7489 0.3600 0.9792 1.3956 1.2741 0.7120 1.5195 1.0000 6322 Gunasekaran et al. Asian J. Chem. correlation factor in all the three cases happens to be greater than 0.99indicating the excellent linear behaviour of the drugs in the chosen range.
Overlay of the UV-Visible spectra of albendazole and mebendazole of 10ppm, the mid-concentration level of linearity range level stored at the threeconditions projected in Figs. 5 and 6. As albendazole shows two absorptionpeaks, the change in the quality of the drugs has been ascertained by calcula-ting the Q-factor or the internal standard ratio by dividing the absorbancevalues of various peaks of the spectra of albendazole. These results projectedin Table-5 and diagrammatically represented in Fig. 7 are in support of theresults from vibrational spectral study on quality and indicate that the drugshave a change in their behaviour with a deviation from the prescribed storagecondition.
VARIATION OF ABSORBANCE OF ALBENDAZOLE AND MEBENDAZOLE AND THE INTERNAL STANDARD RATIO FOR DIFFERENT STORAGE CONDITIONS Concentration = 10 ppm Storage condition Labelled storage condition Exposed to sunlight Fig. 5. A comparative representation of UV-Visible spectra of albendazole FTIR, FT-Raman and UV-Visible spectroscopic techniques have been employed for the qualitative analysis of the anthelmintic drugs, albendazoleand mebendazole. A satisfactory vibrational assignment of the drugs done Vol. 20, No. 8 (2008) Vibrational & Qualitative Analysis of Albendazole & Mebendazole 6323 Fig. 6. A comparative representation of UV-Visible spectra of mebendazole Variation in absorbance of albendazole and mebendazole under differentstorage conditions with the FTIR and FT-Raman spectra recorded confirms the basic functionalgroups present in the compounds. The intensity ratio calculation amongspecific modes of vibration clearly shows that some vibrational bands arealtered due to sunlight exposure and storage at ice point. In both the drugs,deviations are observed clearly from the values of the labelled storage condi-tion which denotes change in the quality of drugs due to change in thestorage condition. The results insist that the drugs must be stored only inlabelled condition for maintaining their quality and spectroscopy serves asan aid to check the quality of drugs.
One of the authors, D. Uthra is thankful to the authorities of University Grants Commission for granting the Teacher Fellowship under FacultyImprovement Program.
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(Received: 5 January 2008; Accepted: 14 July 2008) AJC-6685

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