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Application of Fourier Transform Infrared Spectrophotometry inPharmaceutical Drugs AnalysisAndrei A. Bunaciua; Hassan Y. Aboul-Eneinbc; Serban Fleschind

a CROMATEC_PLUS SRL, Analytical Research Department, Bucharest, Romania b Pharmaceutical andMedicinal Chemistry Department, Pharmaceutical and Drug Industries Research Division, Dokki,Cairo, Egypt c Department of Pharmaceutical Chemistry, College of Pharmacy, King Saud University,Riyadh, Saudi Arabia d Department of Organic Chemistry, Faculty of Chemistry, University ofBucharest, Panduri, Bucharest, Romania

Accepted uncorrected manuscript posted online: 09 February 2010

Online publication date: 09 February 2010

To cite this Article Bunaciu, Andrei A. , Aboul-Enein, Hassan Y. and Fleschin, Serban(2010) 'Application of FourierTransform Infrared Spectrophotometry in Pharmaceutical Drugs Analysis', Applied Spectroscopy Reviews, 45: 3, 206 —219, doi: 10.1080/00387011003601044, First posted on: 09 February 2010 (iFirst)To link to this Article: DOI: 10.1080/00387011003601044URL: http://dx.doi.org/10.1080/00387011003601044

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Applied Spectroscopy Reviews, 45:206–219, 2010Copyright © Taylor & Francis Group, LLCISSN: 0570-4928 print / 1520-569X onlineDOI: 10.1080/00387011003601044

Application of Fourier Transform InfraredSpectrophotometry in Pharmaceutical

Drugs Analysis

ANDREI A. BUNACIU,1 HASSAN Y. ABOUL-ENEIN,2,3

AND SERBAN FLESCHIN4

1CROMATEC PLUS SRL, Analytical Research Department, Bucharest,Romania2Pharmaceutical and Medicinal Chemistry Department, Pharmaceuticaland Drug Industries Research Division, Dokki, Cairo, Egypt3Department of Pharmaceutical Chemistry, College of Pharmacy,King Saud University, Riyadh, Saudi Arabia4Department of Organic Chemistry, Faculty of Chemistry, Universityof Bucharest, Panduri, Bucharest, Romania

Abstract: This review provides some background to infrared spectroscopy includingFourier transform infrared spectroscopy. It is not meant to be complete or exhaus-tive but to provide the reader with sufficient background for selected applications inpharmaceutical analysis. Fourier transform infrared spectroscopy (FTIR) is a fast andnondestructive analytical method. Associated with chemometrics, it can become a pow-erful tool for the pharmaceutical industry. Indeed, it is suitable for analysis of solid,liquid, and biotechnological pharmaceutical forms. This review focuses on pharma-ceutical FTIR applications used for qualitative and quantitative analysis. Moreover,it can be implemented during pharmaceutical development, in production for processmonitoring, and in quality control laboratories.

Keywords: FTIR analysis, drug analysis, quality control

INTRODUCTION

Infrared (IR) spectroscopy is one of the most important analytical techniques available toscientists. One of the great advantages of IR spectroscopy is that any sample in virtuallyany state may be studied. As a consequence of improved instrumentation, a variety of newsensitive techniques have now been developed in order to examine formerly intractable ordifficult samples (1, 2).

The infrared region starts immediately after the visible region at 700 nm. The classicalinfrared region extends from 2,500 to 50,000 nm. This spectral region encompasses three

Address correspondence to Professor Hassan Y. Aboul-Enein, Pharmaceutical and MedicinalChemistry Department, Pharmaceutical and Drug Industries Research Division, Dokki, Cairo 12311,Egypt. E-mail: [email protected]

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FTIR in Pharmaceutical Drugs Analysis 207

subdivisions: the far-infrared (FIR: 400–10 cm−1 or 26–1,000 µm), mid-infrared (MIR:4,000–400 cm−1 or 2.6–26 µm), and near-infrared (NIR: 13,000–4,000 cm−1 or 0.76–2.6 µm), named in relation to the visible region. Infrared spectroscopists often usewavenumbers to describe the infrared spectral region. The energies of infrared radiationrange from 48 kJ mol−1 at 2,500 nm to 2.4 kJ mol−1 at 50,000 nm. These low energiesare not sufficient to cause electron transitions but they are sufficient to cause vibrationalchanges within molecules.

Two units are used in vibrational spectroscopy: cm−1 (wavenumbers) or nm. Thechoice of one of the units depends either on the type of spectrometer (dispersive vs. Fouriertransform [FT]) or to avoid too large numbers in the NIR range where nm is more oftenused. The relationship between the two units is given by Eq. (1):

[cm−1] = 1

[nm] × 10−7(1)

The basic principle of IR spectroscopy is the measurement of the amount of IR radia-tion, which is absorbed (or emitted) by a sample as a function of the wavelength (3). TheIR measurement can be carried out in the modality of transmission or reflectance. The firstone is the most popular. Infrared spectroscopy is often called vibrational spectroscopy.

An IR spectrum is obtained by passing infrared radiation through a sample and de-termining what fraction of the incident radiation is absorbed at a particular frequency.Therefore, IR spectroscopy is based on the absorption of electromagnetic radiation by amolecular system. IR spectra provide images of vibrations of the atoms of a compound.

IR spectroscopy has a high potential for the elucidation of molecular structures. TheIR spectrum of a poly-atomic molecule is based on molecular vibrations, each specificallydependent on atomic masses, bond strengths, and intra- and intermolecular interactions. Asa consequence, the entire IR spectra of an organic compound provide a unique fingerprint,which can be readily distinguished from the IR absorption pattern of other compoundsincluding isomers. In other words, when reference spectra are available, most compoundscan be unambiguously identified on the basis of their IR spectra.

The vast majority of molecules exhibit infrared bands in the mid-infrared regionbetween 400 and 4,000 cm−1. The position and intensity of a vibrational band are charac-teristic of the underlying molecular motion and consequently of the atoms participating inthe chemical bond, their conformation, and their immediate environment. Thus, a certainsubmolecular group produces bands in a characteristic spectral region. These characteristicbands form the empirical basis for the interpretation of vibrational spectra. The reader inter-ested in details of the basic principles of vibrational spectroscopy and the interpretation ofvibrational spectra is referred to relevant books (4–7). Moreover, characteristic absorptionbands can be used for compound-specific detection.

Finally, IR spectroscopy obeys a law, similar to that described by Beer-Lambert’s law,and can thus be used for quantitative purposes. The major advantage of IR over otherspectroscopic techniques is that practically all compounds show absorption (emission)and can thus be analyzed both qualitatively and quantitatively. Besides, IR spectroscopyis nondestructive and allows in situ and remote measurements of almost any sample,irrespective of the physical state and without elaborate sample preparation (8, 9).

The introduction of Fourier transform infrared (FTIR) instrumentation generated atrue revolution in IR spectrometry; due to the great advantages it provides (10–14). FTIRspectrometry is a fast analytical technique that provides very interesting qualitative andquantitative information from solid, liquid, and gaseous samples. At this point it is important


208 A. A. Bunaciu et al.

to point out that the use of IR for quantitative purposes has grown dramatically in recentyears. FTIR was originally a spectroscopic technique to identify the functional groupsof chemical constituents but has been widely used and applied in recent years for theidentification, quality control, and manufacturing process supervision of pharmaceuticaldrugs.

The objective of this article is to review new developments in applications of FTIRspectroscopy in pharmaceutical or drug analysis, covering the period between 2005 and2009. Prior to a review on this subject, it is useful to give a short introduction to theconcept of the FTIR technique and to briefly explain the principles of attenuated totalreflection (ATR) as well as diffuse reflectance infrared spectroscopy (DRIFTS) methods. Inthe major section quantitative and qualitative determination of active principle ingredient(API) content in different dosage forms will be presented in alphabetic order of the API.

FOURIER TRANSFORM INFRARED TECHNIQUE

FTIR spectrometers have almost entirely replaced dispersive instruments because of theirimproved performance in nearly all respects. The application of this technique has improvedthe acquisition of IR spectra dramatically. The heart of the optical hardware in such FTspectrometers is the interferometer. The classic two-beam Michelson interferometer isshown schematically in Figure 1 and consists of two mutually perpendicular plane mirrors:a fixed mirror and a movable one. A semi-reflecting mirror, the beam splitter, bisects theplanes of these two mirrors. A beam emitted by a source is split in two by the beam splitter.The reflected part of the beam travels to the fixed mirror, is reflected there, and hits thebeam splitter again. The same happens to the transmitted radiation. Because the two splitbeams are spatially coherent, they interfere on recombination. The beam, modulated by themovement of the mirror, leaves the interferometer and is finally focused on the detector asshown in Figure 2. The signal actually registered by the detector, the interferogram, is thus

Figure 1. Schematic of a Michelson interferometer.



Figure 2. Schematic of an FTIR spectrometer.

the radiation intensity of the combined beams as a function of the position of the movablemirror.

The mathematics of the conversion of an interferogram into a spectrum is the Fouriertransformation. Based on fully developed software, a computer performs this transforma-tion. The essential steps for obtaining an FTIR spectrum are to produce an interferogramwith and without a sample in the beam and then to transform these interferograms intospectra of the source with sample absorption and the source without sample absorption.The ratio of the former to the latter is the IR transmission spectrum of the sample. In thecase of FTIR spectroscopy, the sample is usually placed between the interferometer andthe detector.

In transmission measurement, the source illuminates the sample and the detector isplaced behind the sample (Figure 3) to acquire the fraction of light transmitted through thesample. Transmission analysis requires the sample to be partly transparent. In most cases, inthe MIR range, samples must be diluted in nonabsorbing matrix; otherwise, no light mightbe transmitted to the detector. Liquid can be prepared as a dilute solution in a cell. Solidsamples are dispersed usually in a potassium bromide (KBr) disk or mull. Moreover, thepowder particle size must be smaller than the radiation wavelength to avoid the Christiansenscattering effect, which appears as band distortion in the spectra (4). Transmission has beenextensively used to analyze thin samples such as films (15) or tissues (16). It is not possiblewith thick samples such as tablets.

D e t e c t o rSampleS o u r c e

Figure 3. Schematic representation of transmission measurements.



Figure 4. Schematic representation of ATR crystal.

In reflection measurement, the detector is placed on the same side of the sample as thesource to record the signal reflected by the sample. The sample is presumed infinitely thickand incapable of transmission. The two types of reflection measurement commonly usedin CI analysis of pharmaceutical forms are attenuated total reflection (ATR) and diffusereflection (DRIFTS).

In attenuated total reflection, the sample is placed in optical contact against a specialcrystal, termed the ATR crystal, which is composed of a material with a high index ofrefraction (e.g., usually made of zinc selenide [ZnSe], diamond, silicon [Si], or germanium[Ge]). The IR beam from the spectrometer is focused onto the beveled edge of the ATRelement by a set of mirrors, reflected through the crystal, and then directed to the detector byanother set of mirrors. The use of ATR in spectroscopy is based upon the fact that althoughcompleted internal reflection occurs at the sample–crystal interface, radiation does in factpenetrate a short distance into the sample (see Figure 4).

The penetration depth, dp, is given (17) by Eq. (2):

dp = λi

2πn1(sin2 θ − n2

21

)1/2 (2)

where λ is the wavelength; n1 and n2 are the refractive indices of the ATR crystal andthe sample, respectively; and θ is the angle of incidence. Obviously, the penetration depthof the beam depends on the wavelength. Furthermore, Eq. (1) shows that total reflectionoccurs when the angle of incidence is larger than the critical angle θ = sin−1(n2/n1).

Samples examined by FTIR-ATR generally require minimal or no sample prepara-tion, but an intimate optical contact between the sample and the ATR crystal is crucial.Unfortunately, the crystal will degrade with surface scratching and cracking.

Figure 5. Schematic representation of DRIFTS measurements.



In diffuse reflection, DRIFTS, incoming radiation interacts with the sample and isscattered by interaction with the particles. A fraction of this light is reflected by the sampleand recorded by the detector (Figure 5). In the MIR range, DRIFTS requires the sampleto be diluted between 10 and 100 times to avoid saturation and band distortion (18).For this reason, MIR-DRIFTS is rarely used for imaging; its use has not been reportedin the literature. On the other hand, because samples need no dilution at all in the NIRrange (the bands are weak), NIR-DRIFTS is widely used for the image analysis of thick,nontransparent samples in various noninvasive applications such as pharmaceutics (19, 20);e.g., tablets.

SELECTED PHARMACEUTICAL APPLICATIONS

The literature studied shows a great number of papers dedicated to pharmaceutical druganalysis using FTIR. Most of the papers are related to qualitative assay of an activecompound, but there are also many papers dedicated to quantitative methods, even thoughpharmacopoeia had introduced (omologated) FTIR spectroscopy for such determinations.

Ampicilline and nitrofurantoin, in both anhydrous and hydrate forms, were character-ized by powder DRIFTS, X-ray diffractometry (XRD), and thermogravimetric and differen-tial thermal analyses (TG/DTA) (21). Of all the analytical tools applied, only DRIFTS wasable to indicate the formation of hydrogen bonds between the molecules of the anhydrousdrug substance and crystalline water uptaken from atmospheric moisture as evidenced bythe significant absorption at 3,500–3,700 cm−1 corresponding to crystal water. Significantdifferences were observed in the DRIFTS patterns between the anhydrous and hydrateforms of ampicilline. The FTIR spectral patterns of the anhydrous and hydrate forms ofnitrofurantoin also exhibited significant differences.

A Fourier transform infrared spectrometric method was developed for the rapid anddirect measurement of acetylsalicylic acid (ASA) in different pharmaceutical products(22). Conventional KBr spectra were compared for the best determination of the activesubstance in drug preparations. Beer-Lambert’s law and two chemometric approaches,partial least squares (PLS) and principal components regression (PCR+) methods, wereused in data processing. The authors studied the possibility of using the Beer-Lambert lawfor the quantitative determination of ASA in pharmaceutical products at 1,605.49 cm−1.The results are very similar, and the authors suggest the use of the PCR+ method becauseof the smaller value of relative standard devaiaition (RSD; <3.0%).

FTIR spectrometry was used for the rapid, direct measurement of ascorbic acid (vitaminC) and biotin (vitamin H) in different pharmaceutical products. Conventional KBr spectrawere compared for the best determination of active substances in drug preparations. TheBeer-Lambert law and chemometric approaches were applied in data processing (23).Vitamin C is an essential nutrient for a large number of higher primate species (24),representing 20% of all mammalian species, and a small number of other species such as theguinea pig and a few species of birds and fish. Vitamin H or B7 is a water-soluble B-complexvitamin composed of a ureido (tetrahydroimidizalone) ring fused with a tetrahydrothiophenering.

A Fourier transform infrared spectrometric method was developed for the rapid, di-rect measurement of bucillamine (25). Bucillamine, N-(2-mercapto-2-methylpropionyl)-l-cysteine, is a novel disease-modifying antirheumatic drug. Conventional KBr-spectra andDRIFTS spectra were compared for best determination of active substance in drug prepara-tions. A good similarity between the spectra in the fingerprint region (1,500–750 cm−1) was



obtained using the two methods proposed by Bunaciu et al. (25) (DRIFTS and KBr-disk).Two chemometric approaches, PLS and PCR+ methods, were used in data processing.Similar results were obtained with both chemometric methods, but the authors suggest theuse of the PCR+ method because of the smaller value of RSD (<2.0%).

Carbamazepine is a poorly soluble drug, with known bioavailability problems relatedto its polymorphism, and a form (C-monoclinic or form IV) less soluble than the pharma-ceutically acceptable (P-monoclinic or form III) can be formed under various conditionsduring drug formulation. Therefore, quantitative analysis of form IV in form III is im-portant to the drug formulators. A fast and simple nondestructive method was developedfor quantification of form IV in form III, by using DRIFTS spectral data subjected to thestandard normal variate transformation (row centering and scaling) and to the lazy learningalgorithm (26). Diffuse reflectance FTIR spectroscopy coupled with modern multivariatecalibration methods, namely, artificial neural networks (ANNs) in two versions (ANN-raw and ANN-pca), support vector machines (SVMs), lazy learning (LL), and partial leastsquares (PLS) regression, in this study for the quantification of carbamazepine crystal formsin ternary powder mixtures (I, III, and IV) (27). Two spectral regions (675–1,180 and 3,400–3,600 cm−1) were selected and the data were partitioned into training and test subsets apply-ing the Kennard-Stone design. It was found that all the selected algorithms perform betterthan the PLS regression (root mean squared error of prediction [RMSEP]) from 3.0 to8.2%).

An FTIR spectrometric method was developed for the rapid, direct measurement ofchromium (tris) picolinate [Cr(pic)3] in different pharmaceutical products. ConventionalKBr spectra were compared for best determination of active substance in drug preparations.Beer-Lambert’s law and two chemometric approaches, PLS and PCR+ methods, wereused in data processing (28). The data interval was expanded and parts of the spectrawere eliminated to reduce the size of the data matrix required by the calibration modeling.The first range used was between 4,000 and 400 cm−1 and the second range was 2,000–400 cm−1. In both cases no blanks were first selected, but after calibration was performed,the computer itself selects ranges of blanks due to the thresholds. The results are verysimilar, and the authors suggest the use of the method that demands a blank with theprincipal excipient because of the smaller value of RSD (about 2.0%).

A spectrometric method was developed for the rapid, direct measurement of coenzymeQ10 (CoQ10) in different pharmaceutical products. Conventional KBr spectra were com-pared for the best determination of active substance in drug preparations. Beer-Lambert’slaw and the two chemometric approaches, PLS and PCR+ methods, were used in dataprocessing (29). The results obtained using chemometric approaches are much higher thanthe expected values, taking into account that the determination was made possible usingBeer-Lambert’s law.

A study in the development of a quantification method to detect the amount of amor-phous cyclosporine (cyclosporine A) using FTIR was performed (30). The mixing ofdifferent percentages of crystalline cyclosporine with amorphous cyclosporine was usedto obtain a set of standards, composed of cyclosporine samples characterized by dif-ferent percentages of amorphous cyclosporine. Calibration models were generated byPLS method over the wavelength ranges of 450–1,125 cm−1 and 1,515–3,200 cm−1,with the exclusion of the spectral regions from 1,125 to 1,515 cm−1 and from 3,200 to4,000 cm−1, to which a blank function has been applied. The regions where crystallineand amorphous cyclosporine spectra are essentially similar, and consequently are not in-dicative of significative differences between the two forms, were subjected to the blankfunction.



Diclofenac sodium (DS) is a nonsteroidal antiinflammatory drug widely used in painfuland inflammatory diseases. In standard conditions, by exposure to relative humidity even be-low 60% at 25◦C, the anhydrous form DS gives rise to a hydrate species DSH, a tetrahydrateform different from that obtained by crystallization from water and previously described.Data from FTIR spectroscopy, XRD, and thermal analysis were used for the identificationand the characterization of DSH. DS and DSH were easily differentiated by their FTIRspectra, X-ray patterns, and thermal behavior (31). The methods of preparation of thetrihydrate form (named DSH3) were described and its physicochemical properties wereinvestigated (32). Data from FTIR spectroscopy, XRD, and thermal analysis were used foridentification and characterization of DSH3 in comparison with the anhydrous form (DS,the commercial form) and the hydrate form DSH (obtained by exposure of DS to relativehumidity even below 60%). FTIR spectroscopy was a useful tool to distinguish the newform from DS and DSH: DSH3 exhibited significant differences in the observed vibrationaltransitions in the 3,600–2,000 cm−1 range of frequencies.

An FTIR spectrometric method was developed for the rapid, direct measurement of de-hydroepiandrosterone (DHEA) in drugs (33). Conventional KBr spectra and KBr + 2.0 mgMCC (microcrystalline cellulose) spectra were compared for best determination of theactive substance in drug preparations. Two chemometric approaches, PLS and PCR+methods, were used in data processing. The best results were obtained with PCR+ method.It is of interest to mention that there are no significant changes between the two spectrain the fingerprint region (under 2,000 cm−1). The peaks in the DHEA-MCC spectra are alittle more evident than in the DHEA-KBr one. The authors suggest the use of the PCR+method because the peak to peak error value must be a maximum of five times greater thanthe RMS error value. Plus the concentration values of DHEA/tablet are a little higher inDHEA-MCC than in DHEA-KBr because of possible interfering signals in spectra.

Diffuse reflectance infrared Fourier transform spectroscopy coupled with PLS dataanalysis has been used to determine the minor component in a mixture of structurally similarsolid-state compounds. There are a number of situations when there is a need to determinethe concentrations of components in solid-state mixtures without dissolving the sample,in this case mixtures of ephedrine and pseudoephedrine (34). These spectral data wereconverted to −log(R/R0) and Kubelka–Munk units, assembled into data files, and subjectedto PLS analysis. The differences in the IR spectra of ephedrine and pseudoephedrine are dueto differences in the intermolecular interactions between the molecules in the solid-stateforms; hence, they have properties similar to that of polymorphs. There is, for example, adifference in the frequency of the O-H stretching vibration in the two forms.

A novel analytical procedure has been developed for quantitative determination oflevodopa and carbidopa in aqueous binary solutions acidified by HCl and without anyother sample pretreatment. The method is based partially on least squares treatment ofdata obtained by ATR-FTIR spectrometry in 1,211–1,315 cm−1 and 1,488–1,550 cm−1

spectral regions. The simple, rapid, and accurate proposed method was applied to determinelevodopa and carbidopa in Levodopa-C R© tablets (Alborz Daruou Pharmaceutical Company,Tehran, Iran) (35).

A new method is presented for quantitative determination of naltrexone in aqueoussolutions based up on the wavelength selection in mid-FTIR spectra using PLS technique.The main aim is to find wavelengths that produce significant improvements in PLS predic-tion. PLS wavelength selection treatment is performed on the data obtained by ATR-FTIRspectrometry in 830–1,800 cm−1 wavenumber range (36).

A simple, rapid, and convenient analytical method without sample handling proceduresis proposed for the determination of niflumic acid in a pharmaceutical gel with ATR/FTIR



(37). A PLS calibration model for the prediction of niflumic acid contents was developedusing 81 and 27 spectra of standard gels as training and validation sets, respectively.The used spectral range of niflumic acid for the establishment of this model was 2,300–1,100 cm−1. All spectra were obtained in the transmittance mode, then normalized and firstderivative transformed.

A quantitative IR and Raman spectroscopic approach for determination of phenacetin(Phen) and salophen (Salo) in binary solid mixtures with caffeine:phenacetin/caffeine (sys-tem 1) and salophen/caffeine (system 2) is presented (38). Absorbance ratios of 746 or721 cm−1 peaks (characteristic for each of determined compounds in the Systems 1 and2) to 1,509 and 1.616 cm−1 (attributed to Phen and Salo, respectively) were used. The IRspectroscopy gives confidence of 98.9% (system 1) and 98.3% (system 2), whereas theRaman spectroscopic data are with slightly higher confidence of 99.1% for both systems.The IR measurements gave a standard deviation of 0.013 and 0.013 at p = 0.0513 and0.0507 for both systems.

An analytical reflectometric method that has an objective not only of industrial qualitycontrol but detecting possible falsifications and/or adulterations of propranolol in pharma-ceutical formulations was proposed (39). The method is based on the diffuse reflectancemeasurements of the colored product (III) of the spot test reaction between propranololhydrochloride (I) and 2,6-dichloroquinone-4-chloroimide (II) using filter paper as solidsupport. The methodology involving the combination spot test–diffuse reflectance spec-troscopy offers advantages, such as simplicity and extremely low consumption of reagents.

A PLS procedure in combination with infrared spectroscopy has been developed forsimultaneous determination of sulphamethoxazole (SMZ) and trimethoprim (TMP) in rawmaterial powder mixtures used for manufacturing commercial pharmaceutical products(39). Spectral data were recorded between 650 and 4,000 cm−1 with a 4 cm−1 resolutionby FTIR spectroscopy coupled with an ATR accessory (40).

FTIR spectroscopy can be interesting in stability studying of cosmetic or pharmaceu-tical oil-in-water (O/W) emulsions. During the aging process, modifications of chemicalfunctions are measured by FTIR (using spectrometric indices); such modifications includeda decrease of unsaturation index, an increase of carbonyl index, and a broadening of thecarbonyl band (41).

The amounts of drug and excipient were predicted from ATR-FTIR spectra using twomultiway modeling techniques, parallel factor analysis (PARAFAC) and multilinear partialleast squares (N-PLS) (42). Data matrices consisted of dissolved and undissolved parallelsamples having different drug content and spectra, which were collected at axially cut sur-faces of the flat-faced matrix tablets. Spectra were recorded comprehensively at differentpoints on the axially cut surface of the tablet. Chemical images of compacted pharma-ceutical tablets were obtained in situ using a miniature compaction cell and a diamondATR accessory (43). Combining this in situ ATR approach with FTIR imaging yieldedchemical images based on the spatial distribution of the absorbance of the spectral bandsfor corresponding excipients in the tablets. Model excipients and drug used in these exper-iments were avicel, hydroxypropylmethylcellulose (HPMC), lactose, magnesium stearate,and paracetamol. Water-soluble polymers are often used in tablet compaction for theirdesirable compaction and dissolution properties (44). ATR-FTIR spectroscopic imaginghas been used to analyze in situ the spatial distribution of different components in tabletswith different compositions. Caffeine tablets made of three different polymer matrices,microcrystalline cellulose, HPMC, and lactose, were investigated.

Counterfeit drugs are becoming a serious problem because they can damage health bysupplying inappropriate substances or products devoid of API. FTIR is a useful weapon in



rapid counterfeit detection. The counterfeiting of pharmaceuticals has been detected sinceabout 1990 and, recently, the problem has escalated. Many more cases are being discoverednot only in the developing world but, increasingly, in developed countries.

The World Health Organization (WHO) has defined counterfeit drugs as those that are

deliberately mislabeled with respect to identity and/or source. Counterfeitingcan apply to both branded and generic products with counterfeit products in-cluding drugs with the correct ingredients or with the wrong ingredients; with-out active ingredients, with insufficient active ingredient or with fake packaging.(45)

Some papers related to counterfeit detection using FTIR spectrometry will be brieflydiscussed as most of the investigations reported were performed using NIR spectrometry.

A scientific and systemic method for differentiation and quality estimation of a well-known Chinese traditional medicine, Cordyceps, has not been established (46). But FTIRand two-dimensional correlation infrared spectroscopy (2D-IR) are employed to proposea method for its analysis. The different fingerprints display different chemical constitutessuch as fatty acids, nucleotides, sterols, mannitol and polysaccharides. It has presentedthat IR spectra of real Cordyceps of different origins and counterfeits have their ownmacroscopic fingerprints, with discriminated shapes, positions, and intensities. Throughthe three steps, different Cordyceps and their counterfeits can be discriminated effectivelyand their qualities distinctly displayed.

In support of the efforts to combat the illegal sale and distribution of counterfeitantimalarial drugs, a new analytical approach for the characterization and fast screeningof fake and genuine artesunate tablets (47) using a combination of Raman spectroscopy,spatially offset Raman spectroscopy (SORS), and ATR-FTIR imaging. Vibrational spec-troscopy provided chemically specific information on the composition of the tablets; thecomplementary nature of Raman scattering and FTIR imaging allowed the characterizationof both the overall and surface composition of the tablets. The advantages provided bya combination of SORS and ATR-FTIR imaging in this context confirm its potential forinclusion in the analytical protocol for forensic investigation of counterfeit medicines.

The quality of pharmaceutical products such as ginseng is important for ensuringconsumer safety and efficacy (48, 49). Ginseng is an expensive herb, and adulteration withother cheaper products may occur. Quality assurance of ginseng is needed because manyof its commercial products now come in various formulations such as capsules, powder,softgels, and tea (48). The herbal materials of Asian ginseng (the root of Panax ginseng),American ginseng (the root of Panax quinquefolius), and Notoginseng (the root of Panaxnotoginseng) were differentiated by conventional Fourier transform infrared spectroscopy(1D-FTIR) and two-dimensional (2D) correlation FTIR applying a thermal perturbation(49). However, variation in peak intensity was observed at about 1,640, 1,416, 1,372, and1,048 cm−1 in the FTIR spectra among these species for their ease differentiation.

During the last 5–10 years, the molecular solid state has gained recognition by thepharmaceutical industry for its role in drug manufacturing, stability, and activity. In addition,definition of the crystalline phase has become as important as molecular composition inpatent protection. Numerous methods have been used to measure the solid-state compositionof pharmaceuticals; these include X-ray diffraction, optical microscopy, thermal analysis,dissolution testing, particle size analysis, NMR, and IR and Raman spectroscopy. Changesin polymorphic form and purity often influence physical properties and pharmaceuticalperformance of a product (50, 51).



Crystalline product should exist in optimal polymorphic form. Robust and reliablemethods for polymorph characterization are of great importance. Several authors (52–57)studied polymorphic forms.

Two polymorphic and a pseudopolymorphic crystal form of the local anestheticdrug hydroxyprocaine hydrochloride are characterized by spectroscopy (FTIR, FT-Raman,SSNMR spectroscopy), thermal analysis (hot stage microscopy, differential scanningcalorimetry, and thermogravimetry), powder X-ray diffractometry, and water vapor sorptionanalysis (52).

The quality assurance of the sulfathiazole product during the whole development andmanufacturing cycle of pharmaceuticals through increased level of process understandingis the main aspect to be considered within process analytical technology (PAT). multivariatestatistical process control (MSPC), soft independent modeling of class analogy (SIMCA),and PLS together with orthogonal signal correction (OSC) techniques were utilized tocharacterize the polymorphic composition of bulk samples from DRIFT data (53). Sul-fathiazole crystallization from five different mixtures of water and 1-propanol using fourdifferent constant cooling rates was studied (54). ATR-FTIR was applied for in situ con-centration measurement to be able to evaluate concentration level effects to outcome ofproduct. Estimations of polymorphic composition were carried out by correlating calcu-lated X-ray powder diffraction (XRPD) diffractograms from Cambridge CrystallographicData Center (CCDC) to the XRPD measurements from samples.

Five polymorphic forms of tranilast were characterized by thermal, diffractometric,and spectroscopic techniques. From a pharmaceutical development perspective, it is shownthat although the anhydrous forms of tranilast have similar thermal properties, they canbe reliably distinguished by spectroscopic methods (55). Because FTIR can be performedmore rapidly and for less cost than most other techniques, an IR method was used duringprocess development and manufacturing of tranilast to check for phase purity in Form I(the desired form). The presence of Form II was detectable at ca. 5% levels by observationof a band at 843 cm−1. Form III could be detected at similar levels by use of a signal at1,378 cm−1.

Nevirapine is a lipophilic drug of low aqueous solubility used in AIDS treatment.Three different crystal forms of this non-nucleoside reverse transcriptase inhibitor wereobtained after recrystallization procedures (56). Two new pseudopolymorphs have beencharacterized, too: nevirapine hemihydrate and nevirapine hemiethyl acetate. Polymorphsand pseudopolymorphs of a drug may exhibit different chemical and physical properties,which can affect dissolution, besides manufacturing, stability, and bioavailability. For thisreason, an investigation on the behavior of the two nevirapine pseudopolymorphs throughthe dissolution test has been described.

Identification of the crystal phase of an active pharmaceutical ingredient in a phar-maceutical tablet is of outmost importance because different polymorphs exhibit differentphysicochemical properties. Furthermore, some of the crystal phases are protected bypatents. Identification of risperidone polymorph A in film coated commercial tablets wasattempted using IR spectroscopy, Raman spectroscopy, and XRPD (57). The stability ofthis polymorph through time and during the manufacturing process was also examined.

CONCLUSION

The recent analytical methods in quality control of API were reviewed. It is obvious thatFTIR spectrometry is capable of the analytical quantification of pharmaceutical products.



With the commercial software involving chemometric approaches, the methods proposedare simple, precise, and not time consuming compared to other methods that are avaialblein literature. Quantification can be done in about 10–15 min, including sample preparationand spectral acquisition.

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