Application of diffuse reflectance near-infrared spectroscopy for determination of crystallinity

Studies were conducted to investigate the use of near-infrared spectroscopy (NIRS) for determining degree of crystallinity. Physical mixtures of amorphous/crystalline indomethacin and amorphous/crystalline sucrose were prepared over several composition ranges. Spectra were obtained on powder samples contained in glass vials using diffuse reflectance sampling. Parallel studies were conducted using X-ray powder diffraction (XRPD) and differential scanning calorimetry (DSC) for comparison. NIRS standard curves were constructed by plotting crystalline weight percent against the ratio of responses at two wavelengths or by partial least squares regression. NIRS standard curves demonstrated higher coefficients of determination and lower standard errors than either XRPD or DSC. Validation standards confirmed the accuracy of NIRS over XRPD. Method error analysis demonstrated comparable accuracy for NIRS and XRPD, with NIRS showing slightly better precision in repeated crystallinity determinations for a 50% crystalline sucrose sample. Interpretive analysis of the NIRS spectra was performed using neutron scattering and polarized Raman spectroscopy data obtained from the literature. Results indicated that the NIRS differences between crystalline and amorphous sucrose may be attributed to the disruption of regular vibrational modes when crystalline sucrose is rendered amorphous.     

Determination of indomethacin crystallinity in the presence of excipients using diffuse reflectance near-infrared spectroscopy.

Studies were conducted to investigate the use of near-infrared spectroscopy for determining the crystallinity of indomethacin in multi-component physical mixtures. Three calibration sets of amorphous/crystalline indomethacin physical mixtures were prepared over the composition range of 0-100% crystallinity. Each of the three calibration sets was diluted step-wise with increasing amounts of a single excipient (Avicel, alpha-lactose monohydrate, or sodium chloride). Near-infrared spectra were obtained after each round of dilutions using diffuse reflectance sampling on samples contained in glass vials. After a second derivative transformation, standard curves were constructed by plotting percent indomethacin crystallinity against the ratio of responses at two wavelengths. At dilution levels up to 75% Avicel or lactose, the calibration models demonstrated high coefficients of determination and low standard errors. Dilution with sodium chloride did not produce comparable results and it was necessary to use partial least-squares regression to achieve a similar level of error. These findings were confirmed with separate validation sets. An investigation of instrument error showed that the impact of instrument variability on quantification generally increased as a function of the dilution level.     

Determination of Indomethacin Crystallinity in the Presence of Excipients Using Diffuse Reflectance Near-Infrared Spectroscopy

Studies were conducted to investigate the use of near-infrared spectroscopy for determining the crystallinity of indomethacin in multi-component physical mixtures. Three calibration sets of amorphous/crystalline indomethacin physical mixtures were prepared over the composition range of 0–100% crystallinity. Each of the three calibration sets was diluted step-wise with increasing amounts of a single excipient (Avicel, α-lactose monohydrate, or sodium chloride). Near-infrared spectra were obtained after each round of dilutions using diffuse reflectance sampling on samples contained in glass vials. After a second derivative transformation, standard curves were constructed by plotting percent indomethacin crystallinity against the ratio of responses at two wavelengths. At dilution levels up to 75% Avicel or lactose, the calibration models demonstrated high coefficients of determination and low standard errors. Dilution with sodium chloride did not produce comparable results and it was necessary to use partial least-squares regression to achieve a similar level of error. These findings were confirmed with separate validation sets. An investigation of instrument error showed that the impact of instrument variability on quantification generally increased as a function of the dilution level.     

Assessment of Crystallinity in Processed Sucrose by Near‐Infrared Spectroscopy and Application to Lyophiles

The objective of this study was to investigate the capability of near‐infrared spectroscopy (NIRS) to determine crystallinity in processed sucrose using a common set of calibration standards derived from binary physical mixtures. NIRS was applied as a primary method using binary mixtures of amorphous and crystalline standards to predict crystallinity in sucrose that was either rendered partially amorphous by milling, partially recrystallized from the amorphous phase, or amorphous lyophiles annealed to induce recrystallization. Crystallinity prediction in the case of milled crystalline and recrystallized amorphous sucrose was feasible using the two‐state binary calibration mixtures applying a univariate model. NIRS results for milled sucrose were comparable to those obtained using X‐ray powder diffraction. The changes in crystallinity after milling and recrystallization showed expected trends. However, the same NIRS univariate calibration method could not be successfully applied for directly through the vial. To overcome this complication, NIRS was applied as a secondary method relative to water vapor sorption (WVS) where a set of processed samples were measured using both NIRS and WVS and a partial least‐squares model applied. The NIRS secondary method was successfully applied and provided a standard error of calibration of 2.11% and standard error of prediction of 3.76%. © 2014 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 103:2884–2895, 2014     

Comparative evaluation of the degree of indomethacin crystallinity by chemoinfometrical fourie-transformed near-infrared spectroscopy and conventional powder X-ray diffractiometry

A chemoinfometrical method for evaluating the degree of crystallinity based on fourie-transformed near-infrared (FT-NIR) spectroscopy was established and compared with the conventional powder X-ray diffraction method. Powder X-ray diffraction profiles and FT-NIR spectra were recorded for 11 kinds of standard materials with various degrees of crystallinity obtained by physically mixing crystalline and amorphous indomethacin (IMC). Chemoinfometric analysis was performed on the FT-NIR spectral data sets by multiple linear regression (MLR) (MLR-Set-Up Search program). The crystalline and amorphous forms showed significant NIR spectral peaks. MLR analysis was performed based on normalized NIR spectra sets for standard samples of known crystallinity. A calibration equation was determined to minimize the root mean square error of prediction. The predicted crystallinity values were reproducible and had a smaller standard deviation. The values of crystallinity predicted by X-ray powder diffractometry and FT-NIR spectrometry suggested a satisfactory correlation between the 2 techniques. The results indicated that FT-NIR spectroscopy provides for an accurate quantitative analysis of crystallinity compared with conventional X-ray diffractometry.     

Quantifying crystalline form composition in binary powder mixtures using near-infrared reflectance spectroscopy

The objectives of this study were to assess the utility of near-infrared reflectance spectroscopy (NIRS) in differentiating crystalline forms of pharmaceutical materials and determine the accuracy of this technique in quantifying crystalline forms of solids in binary mixtures. Various crystalline forms of sulfamethoxazole, sulfathiazole, lactose, and ampicillin, independently characterized with other methods, were analyzed qualitatively and quantitatively. The observed differences in near-infrared (NIR) spectra of crystalline form pairs were interpretable on the basis of the features of their crystalline and molecular structures and mid-infrared spectra. NIR spectra of binary physical mixtures of crystalline form pairs were obtained directly through glass vials over the wavelength range of 1100-2500 nm. The calibration lines were constructed using an inverted least-squares regression method. The ratio of the response of the second derivative of the reflectance spectra at two wavelengths was plotted versus crystal form composition. The correlation coefficients for plots of predicted versus theoretical composition were generally greater than 0.99 and standard errors were all low. Parallel studies comparing the NIRS method to a quantitative x-ray powder diffraction method using sulfamethoxazole and sulfathiazole confirmed the accuracy of the results. Additional NIRS studies were conducted in the 0-10% composition range with ampicillin and sulfamethoxazole. These results indicated that prediction down to the 1% level was possible. This study demonstrates that NIRS can be used as a quantitative physical characterization method, is comparable in accuracy to other techniques, and is capable of detecting low levels of one crystal form in the presence of another.     

Lactose modifications enhance its drug performance in the novel multiple dose Taifun DPI

Drug–carrier particle interactions greatly affect the detachment of drug from the carrier in inhalation powders. In this study, a novel multiple dose, reservoir-based Taifun^® was used as a dry powder inhaler, and the effects of carrier physical properties were evaluated on the pulmonary deposition of budesonide, along with physical stability of the inhalation powder. In this study, untreated commercial preparation of -lactose monohydrate, highly amorphous spray dried lactose, crystallized spray dried lactose, Flowlac-100^® and Flowlac-100^® mixed with crystalline micronized lactose were used as carriers. Dry powder formulations were prepared by the suspension method, where the budesonide–carrier ratio was 1:15.1 (w/w). Carriers and formulations were initially characterized, and again after 1 month’s storage at 40 °C/75% RH. The physical properties of the carriers strongly affected the pulmonary deposition of budesonide and the physical stability of the inhalation powder. Initially, amorphous contents of the carriers were 0–64%, but spontaneous crystallisation of the amorphous lactose occurred during storage and, thus all carriers were 100% crystalline after storage. When compared to an untreated -lactose monohydrate, the highly amorphous spray dried lactose and Flowlac-100^® did not improve aerosol performance of the inhalation powder. When crystalline spray dried lactose was used as a carrier, the highest RF% values were achieved, and RF % values did not alter during storage but the emitted budesonide dose was lower than the theoretical dose. When Flowlac-100^® mixed with crystalline micronized lactose was used as a carrier, the emitted budesonide dose was close to the theoretical dose, and high RF % values were achieved but these changed during storage.     

Studies on the crystallinity of a pharmaceutical development drug substance

The crystallinity and amorphous content of a micronized pharmaceutical development drug substance have been independently determined. An evaluation of different techniques for this purpose has been carried out, and it was found that solid-state nuclear magnetic resonance (ss NMR) and X-ray powder diffraction (XRPD) were suitable for the former and latter, respectively. The baseline intensities of X-ray powder diffractograms, associated with the amorphous component of the sample, have been used to detect levels of non-crystalline material greater than 5%w/w with an absolute accuracy of +/-3%. ss NMR has been employed to quantify crystalline defects at levels of greater than 3%w/w with an estimated uncertainty of +/-2%. It is proposed that such crystalline defects arise from molecular conformational differences that only have a small effect on crystal lattice parameters and, by implication, only have small effects on X-ray powder diffractograms. In both cases the techniques are shown to be highly reproducible and require minimal sample preparation. Excellent linearity is demonstrated for the determination of amorphous material using prepared standards. The present account describes the choice of analytical method, method validation and the results obtained for typical samples of drug substance. It is demonstrated that solid-state NMR should be used as a complementary technique with respect to XRPD for studying crystallinity.     

The development of DMA for the detection of amorphous content in pharmaceutical powdered materials

The aim of this short study was to develop a novel method of sample presentation that will allow currently available DMA apparatus designed for the testing of self-supporting materials to detect amorphous content in controlled mixtures of amorphous and crystalline powders. The preparation of amorphous lactose was carried out by spraying drying, using a Büchi mini spray drier. Controlled mixtures of amorphous and crystalline lactose were produced to give eight samples ranging between 2% and 75% (w/w) amorphous content. These powdered mixtures were loaded into the DMA using a novel powder-pocket device, which consisted of folded sheet of stainless steel. The pocket was clamped directly into the DMA using a single cantilever configuration, and subjected to oscillating displacement, forcing horizontal shearing of the powder between the two plates of the pocket. Typical experimental parameters were a dynamic displacement of 0.05 mm with a frequency of 1 Hz and a heating rate of 5 degrees C/min, from 25 degrees C to 250 degrees C. Over the glass transition region of amorphous lactose, the storage modulus decreased rapidly and a peak was observed in the tandelta signal, which are typical DMA responses for self-supporting glassy materials over their glass transition region. In both the storage modulus and tandelta signals, contributions from both plasticized and non-plasticized amorphous lactose were demonstrated. Such an observation was caused by the powder pocket restricting the loss of the 2.5% (w/w) water present in the spray-dried lactose within the time scale of the first heating cycle. The tandelta peak for the non-plasticized amorphous lactose showed Arrhenius behaviour as function of oscillation frequency. The relationship between the increase in the tandelta peak with increasing frequency allowed the determination of an activation energy that was comparable to the literature values for similar compounds. The height of the tandelta peak for the non-plasticized material was directly proportional to the amount of amorphous lactose present in the mixtures. The glass transition response was still detectable in mixtures containing as little as 2% (w/w) amorphous content, however the theoretical limit of detection was higher than that determined for the same mixtures using solution calorimetry. The results demonstrate that the novel powder pocket allows the use of conventional DMA instruments for the analysis of pharmaceutical powders, however the technique requires more development to further reduce its theoretical limit of detection.     

Comparison of high sensitivity micro differential scanning calorimetry with X-ray powder diffractometry and FTIR spectroscopy for the characterization of pharmaceutically relevant non-crystalline materials

In this study, high sensitivity micro differential scanning calorimetry (MDSC) in the scanning of dynamic mode was compared to X-ray powder diffractometry (XRPD) for quantifying amorphous nifedipine in mixtures crystalline nifedipine. This technique was also compared with FTIR for quantifying polymorph A of chloramphenicol palmitate (CAP) and poly DL-lactide-co-glycolide) (PLGA) in pharmaceutical formulations. The limit of determination (LOD) achieved by MDSC were 0.06% compared to 5% for XRPD quantification of amorphous nifedipine and 0.02% compared to 7% for IR quanitfication of polymorph A of CAP. As little as 0.165 mg PLGA could be measured in excipients mixtures. Desirable linearity and repeatability were established in all cases.     

Measurement of lactose crystallinity using Raman spectroscopy

Raman spectroscopy (RS) was used to determine the crystallinity of lactose (a commonly used carrier in dry powder inhaler (DPI) formulations). Samples of alpha-lactose monohydrate and amorphous lactose were prepared using ethanol precipitation and lyophilisation respectively. The anomeric forms were confirmed using DSC at a rate of 10 degrees C/min and heated to 250 degrees C. The Raman spectra of both alpha-lactose monohydrate and amorphous lactose were obtained. Distinguishable differences were seen between the two spectra including peak areas and intensities. Depolarisation ratios (rho) of each form were then determined to identify the crystallinity of the lactose carrier samples. At the prominent Raman bands 865 and 1082 cm-1, significant differences in rho values were observed for crystalline (0.80+/-0.07, 0.89+/-0.06 respectively) and amorphous samples (0.44+/-0.07, 0.51+/-0.10).     

托伐普坦固体分散体的制备及体外溶出特性考察

目的 采用固体分散技术提高难溶性药物托伐普坦的体外溶出度。方法 选用聚维酮K_29/32为载体材料,以溶剂蒸发法制备托伐普坦固体分散体。采用差示扫描量热法(DSC)、X-射线粉末衍射法(XRPD)对所得固体分散体进行鉴定, 并进行溶解度、体外溶出实验。结果 固体分散体的DSC 图谱及X-射线粉末衍射确定了托伐普坦以无定形态分散在载体中, 体外溶解实验表明其溶出较原料药、物理混合物均有明显提高。结论 将托伐普坦与PVP K_29/32制成固体分散体,其分散状态发生了改变,溶出性能明显提高。     

The Quantitative Analysis of Crystallinity Using FT-Raman Spectroscopy

Purpose. To establish if FT-Raman Spectroscopy can be used to quantitate the degree of crystallinity in a model compound. Methods. Mixtures containing different proportions of amorphous and crystalline indomethacin were prepared. Using the peak intensity ratio 1698 cm^–1 (crystalline) to 1680 cm^–1 (amorphous), a correlation curve was prepared. This correlation curve was validated by testing further samples of known composition. Partially crystalline indomethacin was prepared by milling crystalline indomethacin. Results. A linear correlation curve was obtained across the entire range of 0–100% crystallinity. Using this method, it was possible to detect down to either 1% amorphous or crystalline content. The largest errors were found to result from inhomogeneities in the mixing of the calibration and validation samples. The spectra of the mechanically processed samples were similar to the spectra of the calibration samples, and the degree of crystallinity could be estimated in these samples. Conclusions. FT-Raman Spectroscopy is a potentially useful method to complement existing techniques for the quantitative determination of crystallinity.     

Formation,Physical Stability,and Quantification of Process-Induced Disorder in Cryomilled Samples of a Model Polymorphic Drug

The formation and physical stability of amorphous sulfathiazole obtained from polymorphic forms I and III by cryomilling was investigated by X‐ray powder diffraction (XRPD) and near‐infrared (NIR) spectroscopy. Principal component analysis was applied to the NIR data to monitor the generation of crystalline disorder with milling time and to study subsequent recrystallization under different storage conditions. Complete conversion into the amorphous phase was observed for both forms after 45 (form I) and 150 min (form III) milling time. Upon storage under vacuum over silica gel for 14 days at 4°C, amorphous samples remained amorphous. However, under the same conditions at ambient temperature, recrystallization occurred. Amorphous samples obtained from form I had crystallized back to the original polymorph, whereas those prepared from form III had partially crystallized to mixtures of polymorphs. Amorphous samples stored at ambient temperature and humidity absorbed moisture, which facilitated crystallization to a mixture of polymorphs in both cases. Quantitative analyses of amorphous content in binary mixtures with forms I and III were carried out by XRPD and NIR spectroscopy combined with partial least squares regression. The calibration models had root mean square error of prediction values of <2.0% and were applied to quantify the extent of crystalline disorder during cryomilling.     

Quantifying amorphous content of lactose using parallel beam X-ray powder diffraction and whole pattern fitting.

The objective of this study was to demonstrate the applicability of parallel beam X-ray powder diffraction (XRPD) and a new method for whole pattern fitting to the quantification of the residual amount of amorphous content in a pharmaceutical solid using lactose as a model system. Lactose monohydrate, prepared by slurry conversion of anhydrous lactose, was mixed with different amounts of amorphous lactose produced by lyophilization. X-ray powder diffractograms of each mixture were recorded and analyzed by whole pattern fitting using Percentage Crystallinity Determination Software from Kratos Analytical Inc. The polycapillary X-ray optic, which provides a parallel beam of X-radiation, has advantages over Bragg-Brentano Optics with respect to sample height artifacts. Significant shifts in peak position with changes in sample height of lactose monohydrate were observed using Bragg-Brentano Optics while no change was detected for the polycapillary X-ray optic. A technique to normalize all diffractograms to have the same total integrated intensity was necessary to eliminate tube fluctuation effects. After normalization, the amorphous content of lactose in the range of 1-10% was reproducibly predicted (small standard deviation between samplings) using whole pattern fitting. The limit of detection was calculated to be 0.37% amorphous content. The results indicated that parallel beam XRPD and whole pattern fitting can provide accurate analysis of relatively small amounts of amorphous content in pharmaceuticals compared to typical XRPD analysis.     

Chemometric Methods for the Quantification of Crystalline Tacrolimus in Solid Dispersion by Powder X‐Ray Diffractrometry

The objective of this study was to develop powder X‐ray diffraction (XRPD) chemometric model for quantifying crystalline tacrolimus from solid dispersion (SD). Three SDs (amorphous tacrolimus component) with varying drug to excipient ratios (24.4%, 6.7%, and 4.3% drug) were prepared. Placebo SDs were mixed with crystalline tacrolimus to make their composition equivalent to three SD (crystalline tacrolimus component). These two components were mixed to cover 0%–100% of crystalline drug. Uniformity of the sample mixtures was confirmed by near‐infrared chemical imaging. XRPD showed three distinct peaks of crystalline drug at 8.5°, 10.3°, and 11.2° (2θ), which were nonoverlapping with the excipients. Principal component regressions (PCR) and partial least square (PLS) regression used in model development showed high R² (>0.99) for all the mixtures. Overall, the model showed low root mean square of standard error, standard error, and bias, which was smaller in PLS than PCR‐based model. Furthermore, the model performance was evaluated on the formulations with known percentage of crystalline drug. Model‐calculated crystalline drug percentage values were close to actual value. Therefore, these studies strongly suggest the application of chemometric‐XRPD models as a quality control tool to quantitatively predict the crystalline drug in the formulation. © 2014 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 103:2819–2828, 2014     

The use of isothermal microcalorimetry in the study of small degrees of amorphous content of a hydrophobic powder

The crystallinity of a hydrophobic drug (L-365,260) has been investigated by X-ray powder diffraction (XRPD), differential scanning calorimetry (DSC) and isothermal microcalorimetry. The crystallinity was assessed in the isothermal microcalorimeter by taking a ratio of the responses seen when an unknown sample and an amorphous standard were exposed to ethanol vapour. It was found that large amounts of the material (up to 75%) became amorphous with protracted micronisation. The XRPD, DSC and isothermal microcalorimetry methods could all be used to characterise the amorphous content for these highly disordered samples. When the drug was milled in a ball mill, considerably less of the sample mass became amorphous (less than 10% even for reasonably long milling times) and for such samples, only isothermal microcalorimetry was a suitable technique for quantifying the degree of disorder as no difference was observed by use of DSC or XRPD for materials with up to 10% amorphous content. Microcalorimetry is a suitable approach for crystallinity studies on hydrophobic powders, giving a lower limit of detection for amorphous content that is in the order of 1% or less, which is well below that seen for XRPD.     

The use of net analyte signal orthogonalization in the separation of multi-component diffraction patterns obtained from X-ray powder diffraction of intact compacts

X-ray powder diffraction (XRPD) analysis of intact multi-component consolidated mixtures has significant potential owing to the ability to non-destructively quantify and discriminate between solid phases in composite bodies with minimal sample preparation. There are, however, limitations to the quantitative power using traditional univariate methods on diffraction data containing features from all components in the system. The ability to separate multi-component diffraction data into patterns representing single constituents allows both composition as well as physical phenomena associated with the individual components of complex systems to be probed. Intact, four-component compacts, consisting of two crystalline and two amorphous constituents were analyzed using XRPD configured in both traditional Bragg–Brentano reflectance geometry and parallel-beam transmission geometry. Two empirical, model-based methods consisting of a multiple step net analyte signal (NAS) orthogonalization are presented as ways to separate multi-component XRPD patterns into single constituent patterns. Multivariate figures of merit (FOM) were calculated for each of the isolated constituents to compare method-specific parameters such as sensitivity, selectivity, and signal-to-noise, enabling quantitative comparisons between the two modes of XRPD analysis.     

Influence of particle size and preparation methods on the physical and chemical stability of amorphous simvastatin

This study investigated the factors influencing the stability of amorphous simvastatin. Quench-cooled amorphous simvastatin in two particle size ranges, 150-180 μm (QC-big) and ?10 μm (QC-small), and cryo-milled amorphous simvastatin (CM) were prepared, and their physical and chemical stability were investigated. Physical stability (crystallization) of amorphous simvastatin stored at two conditions was monitored by X-ray powder diffractometry (XRPD) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Assessment of enthalpy relaxation of amorphous forms was conducted using DSC in order to link the physical and chemical stability with molecular mobility. Chemical stability was studied with high-performance liquid chromatography (HPLC). Results obtained from the current study revealed that the solubility of amorphous forms prepared by both methods was enhanced compared to the crystalline form. The rank of solubility was found to be QC-big = QC-small > CM > crystalline. For the physical stability, the highest crystallization rate was observed for CM, and the slowest rate was detected for QC-big, with an intermediate rate occurring for QC-small. QC exhibited lower molecular mobility and higher chemical degradation than CM. Therefore, the current study demonstrated that QC and CM have obvious differences in both physical and chemical properties. It was concluded that care should be taken when choosing preparation methods for making amorphous materials. Furthermore, particle size, a factor that has often been overlooked when dealing with amorphous materials, was shown to have an influence on physical stability of amorphous simvastatin.     

Polymorphic form of piroxicam influences the performance of amorphous material prepared by ball-milling

The objective of this study was to investigate the influence of the starting solid state form of piroxicam (anhydrate form I: PRXAH I vs form II: PRXAH II) on the properties of the resulting amorphous material. The second objective was to obtain further insight into the impact of critical factors like thermal stress, dissolution medium and storage conditions on the thermal behavior, solid state transformations and physical stability of amorphous materials. For analysis differential scanning calorimetry (DSC), Raman spectroscopy and X-ray powder diffractometry (XRPD) were used. Pair-wise distribution function (PDF) analysis of the XRPD data was performed. PDF analysis indicated that the recrystallization behavior of amorphous samples was influenced by the amount of residual order in the samples. The recrystallization behavior of amorphous samples prepared from PRXAH I showed similarity to the starting material, whereas the recrystallization behavior of amorphous samples prepared from PRXAH II resembled to that of the PRX form III (PRXAH III). Multivariate data analysis (MVDA) helped to identify that the influence of storage time and temperature was more pronounced in the case of amorphous PRX prepared from PRXAH I. Furthermore, the wet slurry experiments with amorphous materials revealed the recrystallization of amorphous material as PRXMH in the biorelevant medium.