Internal multiple-scattering hole-enhanced Raman spectroscopy: improved backscattering Fourier transform Raman sampling in pharmaceutical tablets utilizing cylindrical-conical holes

The benefits of Raman signal enhancement and improved measurement precision are demonstrated using 180° backscattering Fourier transform Raman (FT-Raman) spectroscopy from drilled cylindrical-conical holes within pharmaceutical tablet cores. Multiple scattering of the incident laser light within the holes results in an increased Raman signal due to the larger Raman sampling volume. This is important for overcoming typical sub-sampling issues encountered when employing FT-Raman backscattering of heterogeneous pharmaceutical tablets. Hole depth and diameter were found to be important experimental parameters and were optimized to yield the greatest signal enhancement. The FT-Raman spectra collected using backscattering from cylindrical-conical holes is compared to typical 180° backscattering from flat surfaces using tablet cores of Excedrin? and Vivarin?. Raman chemical images are used to establish a representative sampling area. We observe a three- to five-fold increase in the Raman intensity and a two-fold improvement in the measurement precision when sampling from cylindrical-conical holes rather than classic backscattering from flat tablet cores. Self-absorption effects on analyte band ratios are negligible in the fingerprint region but are more significant at the higher near-infrared (NIR) absorbances found in the C-H/O-H/-N-H stretching region. The sampling technique will facilitate developing quantitative FT-Raman methods for application to pharmaceutical tablets using the fingerprint spectral region.     

Monitoring of the manufacturing process for ambroxol hydrochloride tablet using NIR-chemometric methods: compression effect on content uniformity model and relevant process parameters testing

This study aimed at using near-infrared (NIR) spectroscopy to monitor compaction pressure for simultaneously determining the tensile strength and content uniformity, as well as moisture and mean particle size of ambroxol hydrochloride tablets. The content uniformity, compression force and tensile strength of the laboratory samples were obtained by pressing a mixture of active principle and excipient components into tablets. To reduce the spectral baseline shift of the laboratory samples, the compaction pressure applied to the mixture was assessed by a variable pressure test. Production samples were added to the test and subjected to principal component analysis. The expanded partial least-squares (PLS) calibration model used to quantify the active content was more accurate than the model constructed from laboratory samples using the production tablets included in the calibration set. The model showed good predictability, with correlation coefficient (R) 0.9977. The validation and reliability of the content model were evaluated to determine trueness and reliability for the measurement of individual production tablets and the laboratory tablets with drug content ranging from 24 to 36?mg. The PLS calibration models for compression force and tensile strength were constructed using the same spectral set assuming both were highly related. These models yielded high R values (0.9955 and 0.9910). The R values of the moisture and mean particle size were 0.9994 and 0.9919, respectively. This study demonstrated that NIR spectroscopy combined with chemometric techniques can be successfully used to quantitatively monitor the tablet manufacturing process in the pharmaceutical industry.     

Time-resolved NIR spectroscopy for quantitative analysis of intact pharmaceutical tablets

Near-infrared (NIR) spectroscopy is a useful technique for quantitative measurements of intact tablets, but it suffers from limitations due to the fact that changes in the physical properties of a sample strongly affect the recorded spectrum. In this work, time-resolved transmission NIR spectroscopy was utilized to conduct quantitative measurements of intact tablets. The technique enables separation of the absorption properties of the sample from the scattering properties and can therefore handle changes of the physical parameters of the samples in a better way than conventional NIR transmission spectroscopy. The experiments were conducted using a pulsed Ti:sapphire laser coupled into a nonlinear photonic crystal fiber as light source. The light transmitted through the sample was measured by a time-resolving streak camera. A comparison of the results from the time-resolved technique with the results from conventional transmission NIR spectroscopy was made using tablets containing different concentrations of iron oxide and manufactured with different thicknesses. A PLS model made with data from the time-resolved technique predicted samples 5 times better than a PLS model made data from the conventional NIR transmission technique. Furthermore, an improvement to predict samples with physical properties outside those included in the calibration set was demonstrated.     

New methodology to obtain a calibration model for noninvasive near-infrared blood glucose monitoring

This paper reports new methodology to obtain a calibration model for noninvasive blood glucose monitoring using diffuse reflectance near-infrared (NIR) spectroscopy. Conventional studies of noninvasive blood glucose monitoring with NIR spectroscopy use a calibration model developed by in vivo experimental data sets. In order to create a calibration model, we have used a numerical simulation of light propagation in skin tissue to obtain simulated NIR diffuse reflectance spectra. The numerical simulation method enables us to design parameters affecting the prediction of blood glucose levels and their variation ranges for a data set to create a calibration model using multivariate analysis without any in vivo experiments in advance. By designing the parameters and their variation ranges appropriately, we can prevent a calibration model from chance temporal correlations that are often observed in conventional studies using NIR spectroscopy. The calibration model (regression coefficient vector) obtained by the numerical simulation has a characteristic positive peak at the wavelength around 1600 nm. This characteristic feature of the regression coefficient vector is very similar to those obtained by our previous in vitro and in vivo experimental studies. This positive peak at around 1600 nm also corresponds to the characteristic absorption band of glucose. The present study has reinforced that the characteristic absorbance of glucose at around 1600 nm is useful to predict the blood glucose level by diffuse reflectance NIR spectroscopy. We have validated this new calibration methodology using in vivo experiments. As a result, we obtained a coefficient of determination, r2, of 0.87 and a standard error of prediction (SEP) of 12.3 mg/dL between the predicted blood glucose levels and the reference blood glucose levels for all the experiments we have conducted. These results of in vivo experiments indicate that if the parameters and their vibration ranges are appropriately taken into account in a numerical simulation, the new calibration methodology provides us with a very good calibration model that can predict blood glucose levels with small errors without conducting any experiments in advance to create a calibration model for each individual patient. This new calibration methodology using numerical simulation has promising potential for NIR spectroscopy, especially for noninvasive blood glucose monitoring.     

Transmission fourier transform Raman spectroscopy of pharmaceutical tablet cores

Transmission Fourier transform (FT) Raman spectroscopy of pharmaceutical tablet cores is demonstrated using traditional, unmodified commercial instrumentation. The benefits of improved precision over backscattering Raman spectroscopy due to increased sample volume are demonstrated. Self-absorption effects on analyte band ratios and sample probe volume are apparent, however. A survey of near-infrared (NIR) absorption spectra in the FT-Raman spectral range (approximately 0 to 3500 wavenumber shift from 1064 nm, or 1064 to 1700 nm) of molecules with a wide range of NIR-active functional groups shows that although absorption at the laser wavelength (1064 nm) is relatively small, some regions of the Raman spectrum coincide with NIR absorbances of 0.5 per cm or greater. Fortunately, the pharmaceutically important regions of the Raman shift spectrum from 0 to 600 cm(-1) and from 1400 to 1900 cm(-1) exhibit low self-absorption for most organic materials. A statistical analysis of transmission FT-Raman noise in spectra collected from different regions of a pharmaceutical tablet provides insight into both spectral distortion and reduced sampling volume caused by self-absorption.     

Determination of carbamazepine polymorphic contents in double-layered tablets using transmittance- and reflectance-near-infrared spectroscopy involving chemometrics

Background: Since polymorphs exhibit differences in chemical and physicochemical stability, characteristics, and dissolution rate of the bulk powder, they may significantly affect on the bioavailability of pharmaceutical compounds. Aim: The purpose of the present study is to establish a method for determining the carbamazepine (CBZ) polymorphic content of a double-layered tablet containing various ratios of forms I and III by using transmittance- and reflectance-near-infrared (TNIR and RNIR) spectroscopy involving chemometrics. Methods: Both TNIR and RNIR instruments were used to analyze both top (form I) and wire (form III) sides of the compacts, respectively. NIR spectra were analyzed to predict polymorphic content by a principal component regression analysis. NIR data of the tablets were divided into two wavelength ranges: between 860 and 1680 nm (FW), and 1245 and 1285 nm (NW). Results: The calibration models for polymorphic content based on TNIR had a linear relationship, but those based on RNIR did not. The accuracy of the calibration models suggested that the double-sided data set is more robust than the single-sided data set. Since the spectra of FW involved various information, the calibration models showed a linear correlation, but it is difficult to understand their model. In contrast, those of NW provided limited information on polymorphic forms making it very easy to understand the model. Conclusion: Limiting the wavelength of the spectra is useful to help understand the calibration-complicated model.     

Comparison of the determination of a low-concentration active ingredient in pharmaceutical tablets by backscatter and transmission Raman spectrometry

A total of 383 tablets of a pharmaceutical product were analyzed by backscatter and transmission Raman spectrometry to determine the concentration of an active pharmaceutical ingredient (API), chlorpheniramine maleate, at the 2% m/m (4 mg) level. As the exact composition of the tablets was unknown, external calibration samples were prepared from chlorpheniramine maleate and microcrystalline cellulose (Avicel) of different particle size. The API peak at 1594 cm(-1) in the second derivative Raman spectra was used to generate linear calibration models. The API concentration predicted using backscatter Raman measurements was relatively insensitive to the particle size of Avicel. With transmission, however, particle size effects were greater and accurate prediction of the API content was only possible when the photon propagation properties of the calibration and sample tablets were matched. Good agreement was obtained with HPLC analysis when matched calibration tablets were used for both modes. When the calibration and sample tablets are not chemically matched, spectral normalization based on calculation of relative intensities cannot be used to reduce the effects of differences in physical properties. The main conclusion is that although better for whole tablet analysis, transmission Raman is more sensitive to differences in the photon propagation properties of the calibration and sample tablets.     

Rapid, noninvasive quantitative determination of acyclovir in pharmaceutical solid dosage forms through their poly(vinyl chloride) blister package by solid-state Fourier transform Raman spectroscopy

Fourier transform (FT) Raman spectroscopy based on band intensity or band area measurements was used for the quantitative determination of acyclovir in pharmaceutical solid dosage forms through their poly(vinyl chloride) blister package. Univariate calibration using the bands observed at 1690, 1630, 1574, 1482, 1181, 578, and 508 cm(-1) was found to be sufficient for the analysis. Calibration curves were linear, the correlation coefficients being 0.997-0.9993 and 0.996-0.9991 for band intensity and band area measurements, respectively. Results obtained compare well, as indicated by the t-test, with those obtained by the current United States Pharmacopoeia (USP 24) and National Formulary (NF 19) method. Precision ranged from 0.7-4.5 and 0.4-4.0% RSD (n = 3) for band intensity and band area measurements, respectively. The developed nondestructive FT-Raman method is rapid, simple, and can be used for the on-line, real-time monitoring of acyclovir formulation production lines.     

Development and validation of NIR-chemometric methods for chemical and pharmaceutical characterization of meloxicam tablets

Context: Near-Infrared (NIR) spectroscopy is an important component of a Process Analytical Technology (PAT) toolbox and is a key technology for enabling the rapid analysis of pharmaceutical tablets.

Objective: The aim of this research work was to develop and validate NIR-chemometric methods not only for the determination of active pharmaceutical ingredients content but also pharmaceutical properties (crushing strength, disintegration time) of meloxicam tablets.

Materials and methods: The development of the method for active content assay was performed on samples corresponding to 80%, 90%, 100%, 110% and 120% of meloxicam content and the development of the methods for pharmaceutical characterization was performed on samples prepared at seven different compression forces (ranging from 7 to 45?kN) using NIR transmission spectra of intact tablets and PLS as a regression method.

Results: The results show that the developed methods have good trueness, precision and accuracy and are appropriate for direct active content assay in tablets (ranging from 12 to 18 mg/tablet) and also for predicting crushing strength and disintegration time of intact meloxicam tablets.

Discussion: The comparative data show that the proposed methods are in good agreement with the reference methods currently used for the characterization of meloxicam tablets (HPLC-UV methods for the assay and European Pharmacopeia methods for determining the crushing strength and disintegration time).

Conclusion: The results show the possibility to predict both chemical properties (active content) and physical/pharmaceutical properties (crushing strength and disintegration time) directly, without any sample preparation, from the same NIR transmission spectrum of meloxicam tablets.     

Determination of the polymorphic forms of bicifadine hydrochloride by differential scanning calorimetry-thermogravimetric analysis, X-ray powder diffraction, attenuated total reflectance-infrared spectroscopy, and attenuated total reflectance-near-infrared spectroscopy

The pharmaceutical compound bicifadine hydrochloride, which has been found to crystallize in two polymorphic forms, has been characterized by thermal analysis, X-ray powder diffraction (XRPD), infrared (IR) spectroscopy, and near-infrared (NIR) spectroscopy. A series of 22 sample mixtures of polymorph 1 and polymorph 2 were prepared and calibration models for the quantitation of these binary mixtures have been developed for each of the XRPD, attenuated total reflectance (ATR)-IR, and ATR-NIR analytical techniques. The quantitative results were obtained using a partial least squares (PLS) algorithm, which predicted the concentration of polymorph 1 from the XRPD spectra with a root mean standard error of prediction (RMSEP) of 4.4%, from the IR spectra with a RMSEP of 3.8%, and from the NIR spectra with a RMSEP of 1.4%. The studies indicate that when analyses are carried out on equivalent sets of spectra, NIR spectroscopy offers significant advantages in quantitative accuracy as a tool for the determination of polymorphs in the solid state and is also more convenient to use than both the ATR-IR and XRPD methods. Density functional theory (DFT) B3LYP calculations and IR spectral simulation have been used to determine the nature of the vibrational modes that are the most sensitive in the analysis.     

Applications of terahertz spectroscopy to pharmaceutical sciences

The application of terahertz pulsed spectroscopy within the US Food and Drug Administration's (FDA's) recent process analytical technology (PAT) initiative is considered. As a case study the potency levels in paracetamol (4-acetamidophenol) and aspirin (acetylsalicylic acid) test tablets have been recovered from the terahertz absorption spectra using a multivariate partial-least-squares (PLS) calibration model. Root-mean-square errors of cross-validation (RMSECVs) of 2.85% and 3.90% were obtained for paracetamol and aspirin, respectively. Information about other excipients can also be obtained; for example, using the strong lactose absorption lines in the tablets, RMSECVs of 3.65% and 4.30% could be recovered from the paracetamol and aspirin samples, respectively. As active ingredients may also change their solid-state form during formulation processing or storage and as this can adversely affect the final dosage performance, monitoring of pharmaceutical ingredients is essential for a 'right-first-time' philosophy within the industry. Terahertz pulse spectroscopy is a high-throughput technique with many areas of potential exploitation in the pharmaceutical industry; these issues are discussed in this paper.     

Near-infrared spectroscopic analysis of the breaking force of extended-release matrix tablets prepared by roller-compaction: influence of plasticizer levels and sintering temperature

The aim of this study was to investigate the feasibility of near-infrared (NIR) spectroscopy for the determination of the influence of sintering temperature and plasticizer levels on the breaking force of extended-release matrix tablets prepared via roller-compaction. Six formulations using theophylline as a model drug, Eudragit® RL PO or Eudragit® RS PO as a matrix former and three levels of TEC (triethyl citrate) as a plasticizer were prepared. The powder blend was roller compacted using a fixed roll-gap of 1.5?mm, feed screw speed to roller speed ratio of 5:1 and roll pressure of 4?MPa. The granules, after removing fines, were compacted into tablets on a Stokes B2 rotary tablet press at a compression force of 7?kN. The tablets were thermally treated at different temperatures (Room Temperature, 50, 75 and 100?°C) for 5?h. These tablets were scanned in reflectance mode in the wavelength range of 400–2500?nm and were evaluated for breaking force. Tablet breaking force significantly increased with increasing plasticizer levels and with increases in the sintering temperature. An increase in tablet hardness produced an upward shift (increase in absorbance) in the NIR spectra. The principle component analysis (PCA) of the spectra was able to distinguish samples with different plasticizer levels and sintering temperatures. In addition, a 9-factor partial least squares (PLS) regression model for tablets containing Eudragit® RL PO had an r² of 0.9797, a standard error of calibration of 0.6255 and a standard error of cross validation (SECV) of 0.7594. Similar analysis of tablets containing Eudragit® RS PO showed an r² of 0.9831, a standard error of calibration of 0.9711 and an SECV of 1.192.     

Advanced calibration strategy for in situ quantitative monitoring of phase transition processes in suspensions using FT-Raman spectroscopy

There is an increasing interest in using Raman spectroscopy to identify polymorphic forms and monitor phase changes in pharmaceutical products for quality control. Compared with other analytical techniques for the identification of polymorphs such as X-ray powder diffractometry and infrared spectroscopy, FT-Raman spectroscopy has the advantages of enabling fast, in situ, and nondestructive measurements of complex systems such as suspension samples. However, for suspension samples, Raman intensities depend on the analyte concentrations as well as the particle size, overall solid content, and homogeneity of the solid phase in the mixtures, which makes quantitative Raman analysis rather difficult. In this contribution, an advanced model has been derived to explicitly account for the confounding effects of a sample's physical properties on Raman intensities. On the basis of this model, a unique calibration strategy called multiplicative effects correction (MEC) was proposed to separate the Raman contributions due to changes in analyte concentration from those caused by the multiplicative confounding effects of the sample's physical properties. MEC has been applied to predict the anhydrate concentrations from in situ FT-Raman measurements made during the crystallization and phase transition processes of citric acid in water. The experimental results show that MEC can effectively correct for the confounding effects of the particle size and overall solid content of the solid phase on Raman intensities and, therefore, provide much more accurate in situ quantitative predictions of anhydrate concentration during crystallization and phase transition processes than traditional PLS calibration methods.     

Effects of lubricant-mixing time on prolongation of dissolution time and its prediction by measuring near infrared spectra from tablets

The relationship between lubricant-mixing time and dissolution time was investigated, and we established a calibration model to predict dissolution time by near infrared (NIR) spectroscopy and the rationale of the prediction. The bulk powder consisted of theophylline, lactose, and potato starch were pre-mixed. After magnesium stearate (Mg-St) was added, the material was mixed for up to 180?min. The mixed powders were compressed to tablets and dissolution tests were performed. From each dissolution curve, 50% dissolution time (T50) was calculated. The NIR spectra of each tablet's upper surface was measured and a chemometric analysis was conducted. With the extension of mixing time, T50 was prolonged. The Mg-St widely covered the surface of each particle of the bulk powder after material mixing. This coating effect may decrease the wettability of the particles and cause the prolongation of dissolution time. The T50 was predicted by NIR spectroscopy with chemometrics and a calibration model was established. The regression vector showed typical peaks derived from -CH group of Mg-St, and it is suggested that those peaks, which were caused by the thin layer extension of Mg-St particles over the particle surfaces of other materials, contributed to the prediction of T50 prolongation. These studies show the usefulness of NIR measurements to control the effect of a lubricant in the process of raw powder material mixing.     

Effects of lubricant-mixing time on prolongation of dissolution time and its prediction by measuring near infrared spectra from tablets

The relationship between lubricant-mixing time and dissolution time was investigated, and we established a calibration model to predict dissolution time by near infrared (NIR) spectroscopy and the rationale of the prediction. The bulk powder consisted of theophylline, lactose, and potato starch were pre-mixed. After magnesium stearate (Mg-St) was added, the material was mixed for up to 180?min. The mixed powders were compressed to tablets and dissolution tests were performed. From each dissolution curve, 50% dissolution time (T50) was calculated. The NIR spectra of each tablet’s upper surface was measured and a chemometric analysis was conducted. With the extension of mixing time, T50 was prolonged. The Mg-St widely covered the surface of each particle of the bulk powder after material mixing. This coating effect may decrease the wettability of the particles and cause the prolongation of dissolution time. The T50 was predicted by NIR spectroscopy with chemometrics and a calibration model was established. The regression vector showed typical peaks derived from ?CH group of Mg-St, and it is suggested that those peaks, which were caused by the thin layer extension of Mg-St particles over the particle surfaces of other materials, contributed to the prediction of T50 prolongation. These studies show the usefulness of NIR measurements to control the effect of a lubricant in the process of raw powder material mixing.     

Development and validation of a near-infrared method for the quantitation of caffeine in intact single tablets

A near-infrared spectroscopic method was developed and validated for determining the caffeine concentration of single and intact tablets in a Finnish pharmaceutical product containing 58.82% (m/m) caffeine.The spectral region of interest contained a total of 474 data points. The second derivative of Savitsky-Golay, a standard normal variate, and mean centering were used as spectral preprocessing options. The feasibility study showed nonuniformity of caffeine repartition within each tablet. Thus, spectra were recorded from both faces of the tablets, and the analysis result for a single tablet was reported as the average of both face determinations. Precision of the method was validated because the relative standard deviations from repeatability and intermediate precision tests were below 0.75% (m/m). Accuracy validation proved that the NIR results were not significantly different (P = 0.09, n = 12) from the results obtained with the reference HPLC method. The limit of quantification for caffeine was 13.7% (m/m) in the tablets. The method was found to be unaffected by NIR source replacement, but the repeatability of the results was affected if the sample holder was not placed in the correct position in the light beam. Routine NIR analysis of caffeine in tablet form was found to be more flexible and much faster than that performed with the HPLC method.     

The use of near-infrared spectroscopy for the quantitation of a drug in hot-melt extruded films

The objective of the study was to demonstrate the utility of near-infrared spectroscopy (NIRS) for quantitative analysis of a model drug in hot-melt extruded film formulations. Polyethylene oxide (PEO) films with clotrimazole (CT) as a model drug were prepared by hot-melt extrusion (HME) incorporating drug concentrations ranging from 0-20% and analyzed using a Fourier transform near-infrared (FT-NIR) spectrophotometer in the reflectance mode. High performance liquid chromatography (HPLC) was the reference method used for this study. The NIR calibration model derived for CT was composed of 21 frequency ranges that were correlated to the values quantified using the HPLC reference method. The NIR method developed resulted in an assayed CT amount in the film matrix to be within 3.5% of the quantity determined by the reference method. These studies clearly demonstrate that NIRS is a powerful method for the quantitation of active drug substances contained in films produced by HME and warrants further investigation.     

Optimization of informative spectral variables for the quantification of EGCG in green tea using Fourier transform near-infrared (FT-NIR) spectroscopy and multivariate calibration

Epigallocatechin-3-gallate (EGCG) is credited with the majority of the health benefits associated with green tea consumption. It has a high economic and medicinal value. The feasibility of using different variable selection approaches in Fourier transform near-infrared (FT-NIR) spectroscopy for a rapid and conclusive quantitative determination of EGCG in green tea was investigated. Graphically oriented multivariate calibration modeling procedures such as interval partial least squares (iPLS), synergy interval partial least squares (siPLS), and genetic algorithm optimization combined with siPLS (siPLS-GA) were applied to select the most efficient spectral variables that provided the lowest prediction error. The performance of the final model was evaluated according to the root mean square error of prediction (RMSEP) and coefficient of determination (R(2)) for the prediction set. Experimental results showed that the siPLS-GA model obtained the best results in comparison to other models. The optimal models were achieved with R(2)(p) = 0.97 and RMSEP = 0.32. The model can be obtained with only 36 variables retained and it provides a robust model with good estimation accuracy. This demonstrates the potential of NIR spectroscopy with multivariate calibration methods to quickly detect the bioactive component in green tea.     

Characterization of the sources of variation affecting near-infrared spectroscopy using chemometric methods

A rapid assessment of product quality can often be made using a combination of near-infrared spectroscopy (NIR) and multivariate calibration. The robustness of such a method is determined by the sensitivity of the multivariate calibration model to variations in the spectral data. An approach is described that uses a combination of experimental design methodology and principal component analysis to identify the main sources of variation in the spectra and to estimate their influence on the quantitative predictions. This is accomplished by comparing variations in a set of measured, replicate spectra to spectra with simulated variations. The approach was applied to the hydroxyl number determination of polyols by NIR spectroscopy and partial least-squares calibration. The results indicated that the most significant sources of variation were due to a variable cell path length and a variable curved background. Correction for these errors resulted in a 58% reduction in the standard deviation of the hydroxyl number predictions, indicating that a substantial improvement in the method precision is possible.     

Determination of the crystallinity of cephalexin in pharmaceutical formulations by chemometrical near-infrared spectroscopy

Background: Near-infrared (NIR) spectroscopy has gained wide acceptance in the pharmaceutical industry as a rapid and non destructive method for drug identification and the determination of the drug content of preparations. Aim: The crystallinity of cephalexin (CEX) in microcrystalline cellulose (MCC) was determined using a nondestructive NIR reflectance spectroscopic technique. The molecular interaction of a ground amorphous solid of CEX was investigated by the method. Method: Six kinds of standard material with various degrees of crystallinity were prepared by the physical mixing of crystalline, amorphous CEX, and MCC. X-ray powder diffraction profiles and NIR spectra were recorded for standard samples. A chemometric analysis of the NIR spectral data sets was conducted using principal component regression (PCR). Results: The correlation between the actual crystallinity of CEX and that predicted using the conventional X-ray diffraction method showed a straight line with a slope of 1.000, an intercept of ?2.071 × 10^?5 and a correlation coefficient of determination (R²) of 0.974. The NIR spectrum of amorphous CEX showed significantly different peaks at 1176 and 1206 nm because of the CH₃ group from those of CEX. PCR was performed on various kinds of pretransformed NIR spectral data sets of standard samples of CEX. To minimize the SE of cross-validation (SECV), the spectral data sets were subjected to the leave-one-out method. The second derivative treatment in the range of 1176–1206 nm yielded the lowest SECV values. Based on a two-component model, a plot of the calibration data between the actual crystallinity of CEX and that predicted by the NIR method was obtained. The plot showed a straight line (Y = 0.995X + 0.117 and R² = 0.994; n = 18). The mean bias for the NIR and X-ray powder diffraction methods was calculated to be 1.52% and 2.26%, and mean accuracy was 3.06% and 7.14%, respectively. Conclusion: NIR spectral changes of crystalline CEX during grinding suggested that the intermolecular hydrogen bonds between the amino and carboxyl groups are destroyed and the binding of methyl groups is heightened by the resonance effect of carboxyl groups, and the crystals are transformed into amorphous CEX.