For enterprises, the quantitative study of drug crystal forms is not only of great significance to the quality control of drugs, but also focuses on the patents of drug crystal forms in intellectual property rights. For example, new crystalline drugs that are bioequivalent to the original crystalline form and even have better curative effect can be used as additional patents to extend the patent protection period of drugs, and the quantitative study of crystalline forms is also an important basis to support the patent protection of crystalline forms.
At present, X-ray diffraction (XRD), Raman spectroscopy (Raman), dynamic water adsorption (DVS), differential scanning calorimetry (DSC) and infrared spectroscopy (IR) are widely used in the quantitative study of crystal forms. This paper mainly introduces these analysis methods.
1
X-ray diffraction (X-ray diffraction)
X-ray diffraction is the main method to study the crystal form of drugs. This method can be used to distinguish crystalline from amorphous, identify crystal varieties, distinguish mixtures and compounds, determine the crystal structure of drugs, and determine cell parameters (such as the distance between atoms, the distance between ring planes, the included angle between two sides, etc.). ) and compare different crystal forms. X-ray diffraction can be divided into powder diffraction and single crystal diffraction. The former is mainly used for the identification and purity inspection of crystal substances, while the latter is mainly used for the determination of molecular weight and crystal structure.
①X-ray powder diffraction method
XPRD is an early developed method for drug crystal analysis, which has been widely used for quantitative analysis of different crystal mixtures and determination of crystallinity. The diffraction intensity and distribution of each crystal measured by this method have special laws, so that information such as crystal form change, crystallinity, crystal structure state and whether there are mixed crystals can be obtained. When applying this method, we should pay attention to the fineness of powder, and pay special attention to whether crystal transformation occurs during grinding and sieving. The research methods mainly include single peak method, multi-peak method and full spectrum method.
② Single crystal X-ray diffraction method
The analysis object of SXRD is single crystal, and the principle is to use the diffraction effect of X-ray on crystal, and its analysis data represents the result of a certain crystal form. SXRD method can reveal the origin of the crystal form of the sample and give various crystallographic quantitative data of the crystal form. SXRD was used to analyze the data, and the PXRD spectrum and data of 100% pure crystalline product were obtained by theoretical calculation, which was used as the standard spectrum of crystalline substances.
In order to reduce the influence of dilution of auxiliary materials, deviation of operation or instrument, inorganic substances in sample preparation and other factors, the quantitative study of crystal form in preparation is usually combined with other methods, the most typical of which is the study of Varasteh et al. The author successfully quantified the content of REJ-333369B crystal form in OROS tablets developed by ALZA Company by combining XPRD with Fourier transform infrared spectroscopy and Raman spectroscopy.
2
Raman spectrum (RM)
Similar to infrared spectroscopy, Raman spectroscopy is a vibration spectroscopy technique. The difference is that the former is related to the change of dipole moment when the molecule vibrates, while Raman effect is the result of the change of molecular polarizability.
Because the Raman shift of the functional group or chemical bond of the compound is consistent with its absorption wave number in infrared spectrum, the analysis of Raman spectrum is similar to that of infrared absorption spectrum. The strong band that usually appears in Raman spectrum becomes weak band or even does not appear in infrared spectrum, and vice versa. Therefore, these two spectroscopic techniques are often complementary.
Raman spectrum peaks are clear and sharp, and the quantitative speed is fast, which is especially suitable for the polymorphic analysis of aqueous slurry (such as suspension). ), the polymorphic forms in pharmaceutical preparations can be directly determined.
The advantages of Raman spectroscopy are fast and accurate, and the sample is usually not damaged during measurement, and the sample preparation is simple or even unnecessary. Spectral band signals are usually in the visible or near infrared range and can be effectively combined with optical fibers; This also means that the band signal can be obtained by encapsulating in any medium transparent to laser (such as glass, chronograph or plastic) or dissolving the sample in water. Modern Raman spectrometer is simple to use, fast in analysis (several seconds to several minutes) and reliable in performance. Therefore, the combination of Raman spectroscopy with other analytical techniques is simpler than other spectral combination techniques in a sense (univariate and multivariate methods and calibration can be used).
Figure: Raman spectra of L- glutamic acid aqueous solution, α crystal suspension and β crystal suspension.
Source: Mo Yuxin. Application of Raman spectroscopy in quantitative analysis of L- glutamic acid polymorphism [J]. Chemical engineer, 20 13(08):3 1-33.
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three
Dynamic water adsorption (DVS)
Dynamic water adsorption (DVS) is a specific gravity testing technique, which is used to test the speed and degree of solvent absorption by samples, such as the water absorption of dry powder. By changing the steam concentration around the sample, and then testing the changed sample quality, the experimental results are obtained. In the process of the transition from amorphous state to crystalline state induced by the gradual increase of humidity, there is generally a process of mass loss.
By detecting the change curve of sample weight with relative humidity and time, we can study the physical and chemical fields such as water adsorption equilibrium, adsorption and desorption, diffusion coefficient and permeability coefficient of the sample. It is suitable for the quantification of a small amount of amorphous impurities in the study of drug crystal forms, and is used for special dosage forms.
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four
Differential scanning calorimetry (DSC)
Because the crystal will produce thermal effect in the process of crystal transformation or melting, the relative content of each crystal form in the sample can be quantitatively analyzed by using the melting enthalpy or crystal transformation enthalpy of different crystal forms in different temperature regions. Differential scanning calorimetry (DSC) has high sensitivity and convenient quantitative study, and can conveniently and accurately quantitatively analyze the contents of different crystalline components in mixtures with large melting points.
Because the damage of DSC to samples is inevitable, it is not suitable for analyzing and testing samples with few samples and expensive samples. At the same time, the particle size, weight, heating rate, uneven sampling and mixing of samples will all affect the final experimental results. Therefore, it is necessary to consider the combination with other analytical techniques when studying the quantification of pharmaceutical crystalline preparations.
Figure: DSC curves of mixtures with different crystal form A contents.
Source: Yuan Zuanru, Zhang Aiming, Fang Jianglin. Study on quantitative determination of adefovir dipivoxil crystal form by differential scanning calorimetry [J]. Analysis and testing technology and instrument, 2008(02): 105- 108.
five
infrared spectrum
In recent years, near infrared spectroscopy has been widely used, especially in the rapid identification and moisture determination of a large number of samples. Near infrared spectroscopy is especially suitable for the determination of hydroxyl and amino groups, such as water in ethanol, hydroxyl groups in the presence of amino groups, ethanol in hydrocarbons and primary and secondary amines in the presence of tertiary amines.
Some compounds will appear polymorphic in solid state, which will lead to the difference of infrared spectra. Usually, subtle differences in structure will make obvious differences in infrared spectra. There are a lot of absorption peaks in infrared spectrum, and sometimes a specific component in a mixture of known components can be quantitatively determined without pre-separation.
When using solid sample technology, the most common problem is polycrystalline phenomenon. The infrared spectra of solid samples with different crystal forms are often different. The crystal form of the components to be tested has changed, and the auxiliary materials have also interfered. In this case, infrared spectrum is generally not suitable for identification. For some drugs with different crystal forms but the same or little difference in infrared spectra, infrared spectra are difficult to distinguish. For example, if the infrared spectra of crystalline form I and crystalline form II of phenylethyl atropine are the same, or the purity of the sample is not enough, it will be difficult to distinguish the infrared spectra.
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In addition to the quantitative methods mentioned above, there are mid-infrared spectroscopy, near-infrared spectroscopy, solid-state nuclear magnetic resonance, terahertz spectroscopy and so on. It is also used in the study of crystal morphology. Generally, several methods can be combined to study the crystal form to make up for their respective shortcomings. The quantification of drug polymorphism is also an indispensable link in drug research and development.
References:
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Zhang Xin, Li, et al. Dynamic water adsorption analysis and its application in drug research [J]. chinese journal of pharmaceutical analysis, China, 2008( 10): 197-200.
Yuan Ru, Ming, Lin. Study on quantitative determination of adefovir dipivoxil crystal form by differential scanning calorimetry [J]. Analysis and testing technology and instrument, 2008(02): 105- 108.
Zhang Xiaonan, Guo Shiling, Chen Yixiu, et al. Application of differential scanning calorimetry in quantitative analysis of drug polymorphism [J]. chinese medicine guides, 20 12000(032):435-436.
Guo Yonghui, Lv Yang, Institute of Pharmacology, Peking Union Medical College, China Academy of Medical Sciences, Beijing, 10007 1. Application of Differential Scanning Calorimetry in the Study of Crystalline Drugs [J]. The 2nd China Symposium on Crystal Drugs, 20 12.
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Shenzhen Xinyang Weikang Technology Co., Ltd. is a new enterprise focusing on crystal screening, dosage form innovation and "nondestructive reverse analysis of original drugs" in consistency evaluation. Xinyang Weikang was founded on 20 15, when the pharmaceutical industry in China was developing rapidly. It has a standardized laboratory of 1, 100 square meters. As a Sino-European joint venture company, we try our best to provide tailor-made technical services for pharmaceutical companies. Our vision is to bring high-end, high-quality drugs to the China market and provide high-quality solid-state technical services for the global pharmaceutical industry.