📚 Solid Pharmaceutical Analysis: Common Methods and Techniques | 固体药物分析常用方法与技术
Solid pharmaceutical analysis is a cornerstone of quality control and drug development. Tablets, capsules, powders, and other solid dosage forms must be verified for identity, purity, uniformity, and stability before reaching patients. This article reviews the most commonly used analytical methods and techniques for solid drugs, with a focus on A-level chemistry concepts and practical applications.
固体药物分析是质量控制和药物开发的基石。片剂、胶囊、粉末及其他固体剂型在到达患者手中之前，必须经过鉴别、纯度、均匀性和稳定性等方面的验证。本文回顾了用于固体药物最常见的分析方法与技术，重点关注A-level化学概念及其实际应用。
1. Sample Preparation and Dissolution | 样品制备与溶出
Most instrumental analyses require a solid sample to be converted into a solution. For tablets and capsules, this involves grinding, extracting, and diluting with a suitable solvent. The chosen solvent must dissolve the active pharmaceutical ingredient (API) completely without causing degradation. For example, weakly acidic drugs often dissolve better in slightly alkaline buffer solutions.
大多数仪器分析需要将固体样品转化为溶液。对于片剂和胶囊，这涉及研磨、提取并用合适的溶剂稀释。所选溶剂必须完全溶解活性药物成分（API）而不导致降解。例如，弱酸性药物在微碱性缓冲溶液中通常溶解得更好。
Dissolution testing is a special form of preparation used to assess the release rate of a drug from a solid dosage form. A tablet is placed in a stirred vessel containing simulated gastric or intestinal fluid at 37 °C, and samples are withdrawn at timed intervals. The amount of dissolved drug is measured by UV-Vis spectroscopy or HPLC, providing crucial information about bioavailability.
溶出度测试是用于评估药物从固体剂型中释放速率的一种特殊制备方式。将药片置于装有模拟胃液或肠液的搅拌容器中，保持37 °C，并在设定时间间隔取样。通过紫外-可见光谱或HPLC测量已溶解药物的量，从而提供有关生物利用度的关键信息。
2. Melting Point Determination | 熔点测定
Melting point is a fundamental physical constant used for both identification and purity assessment of solid drugs. A pure compound has a sharp, characteristic melting range of about 1 °C. If impurities are present, the melting point broadens and usually decreases, a phenomenon known as melting point depression.
熔点是用以鉴别固体药物并评估其纯度的一项基本物理常数。纯化合物具有尖锐的特征性熔程，通常不超过1 °C。若存在杂质，熔点会变宽并通常降低，这一现象称为熔点降低。
In the laboratory, a capillary tube containing a small amount of finely powdered sample is heated slowly in a melting point apparatus. The temperature range from the first sign of melting to complete fusion is recorded. This simple technique remains the first step in many pharmacopoeial monographs, especially for crystalline APIs.
在实验室中，将装有少量细粉末样品的毛细管置于熔点仪中缓慢加热，记录从开始熔融到完全熔化时的温度范围。这一简单方法仍是许多药典专论的第一步，尤其适用于结晶性原料药。
3. Fourier Transform Infrared Spectroscopy (FTIR) | 傅里叶变换红外光谱法（FTIR）
FTIR spectroscopy provides a molecular fingerprint of a solid drug sample. Functional groups such as O–H, N–H, C=O, and C–O absorb specific infrared frequencies, producing a characteristic spectrum. Since each compound has a unique combination of functional groups, FTIR is excellent for confirming the identity of a solid API.
傅里叶变换红外光谱提供固体药物样品的分子指纹。O–H、N–H、C=O和C–O等官能团吸收特定红外频率，产生特征光谱。由于每种化合物具有独特的官能团组合，FTIR非常适合确证固体原料药的身份。
Two common sampling methods for solids are the KBr pellet technique and attenuated total reflectance (ATR). For a KBr pellet, a small amount of drug is ground with dry KBr and compressed under high pressure to form a transparent disc. Alternatively, ATR allows the solid powder to be analysed directly, with the infrared beam penetrating into the sample at the crystal interface. This requires minimal preparation and is widely used in quality control.
固体样品的两种常用制样方法是KBr压片法和衰减全反射（ATR）法。对于KBr压片，将少量药物与干燥KBr研磨并在高压下压缩成透明薄片。另外，ATR法可直接分析固体粉末，红外光束在晶体界面处穿透样品。此法无需过多制样，广泛应用于质量控制。
4. UV-Visible Spectroscopy | 紫外-可见光谱法
UV-Vis spectroscopy measures the absorption of ultraviolet or visible light by a drug molecule. For solid pharmaceuticals, the sample must first be dissolved in a suitable solvent. The absorbance at a characteristic wavelength is then measured and compared to a standard solution. This is one of the fastest and most economical methods for quantitative analysis of a solid dosage form.
紫外-可见光谱法测量药物分子对紫外光或可见光的吸收。对于固体药物，首先需要将样品溶解在合适的溶剂中，然后在特征波长下测量吸光度，并与标准溶液进行比较。这是对固体剂型进行定量分析最快、最经济的方法之一。
Quantification relies on the Beer-Lambert law, which states that absorbance is directly proportional to concentration and path length:
定量分析依赖于比尔-朗伯定律，该定律指出吸光度与浓度和光程长度成正比：
A = ε × c × l
where A is absorbance, ε is molar absorptivity, c is concentration in mol/dm³, and l is the path length in cm. This equation is essential for calculating drug content in tablets and checking the uniformity of dosage units.
其中A为吸光度，ε为摩尔吸光系数，c为浓度（单位为mol/dm³），l为光程长度（单位为cm）。该方程对于计算片剂中的药物含量以及检查剂量单位的均匀性至关重要。
5. Thin Layer Chromatography (TLC) | 薄层色谱法（TLC）
TLC is a simple and rapid method used for the qualitative identification and purity screening of solid drugs. A small spot of the dissolved sample is applied to a TLC plate coated with silica gel or another stationary phase. The plate is developed in a chamber containing a mobile phase solvent, which moves up the plate by capillary action. Different components travel different distances based on their polarity.
TLC是一种简单快速的方法，用于固体药物的定性鉴别和纯度筛选。将少量溶解后的样品点样于涂有硅胶或其他固定相的薄层板上，在装有流动相的层析缸中进行展开，流动相通过毛细作用向上移动。不同组分依据极性差异迁移不同距离。
The retention factor (Rf) is calculated as the distance travelled by the sample divided by the distance travelled by the solvent front:
比较值（Rf）按样品迁移距离除以溶剂前沿迁移距离计算：
Rf = distance moved by compound / distance moved by solvent front
In pharmaceutical analysis, the Rf value of the sample is compared with that of a reference standard. TLC also helps to detect related substances or degradation products, which appear as additional spots under UV light or after chemical derivatisation.
在药物分析中，将样品的Rf值对照参考标准品进行比较。TLC还能检测有关物质或降解产物，它们在紫外灯下或经化学衍生化后显示为额外斑点。
6. High-Performance Liquid Chromatography (HPLC) | 高效液相色谱法（HPLC）
HPLC is the most powerful and widely used technique for the quantitative analysis of solid pharmaceuticals. It separates individual components based on their interaction with a stationary phase inside a column and a mobile phase pumped at high pressure. For solid dosage forms, the tablet or capsule content is extracted and filtered before injection into the system.
HPLC是固体药物定量分析中最强大且应用最广泛的技术。它依据各组分在柱内固定相与高压泵入流动相之间的相互作用进行分离。对于固体剂型，片剂或胶囊内容物需先经提取和过滤，然后注入系统。
A typical HPLC system consists of a solvent reservoir, pump, injector, analytical column, detector (usually UV or diode-array), and data processor. The peak area or peak height is proportional to the amount of drug, allowing accurate quantification using an external standard or internal standard method. HPLC is indispensable for assay testing, uniformity testing, and stability studies.
典型的HPLC系统由溶剂储存器、泵、进样器、分析柱、检测器（通常为UV或二极管阵列）以及数据处理系统组成。峰面积或峰高与药物含量成正比，可采用外标法或内标法进行准确定量。HPLC在含量测定、均匀度检查和稳定性研究中不可或缺。
7. Thermal Analysis: DSC and TGA | 热分析：DSC与TGA
Differential scanning calorimetry (DSC) measures the heat flow associated with physical and chemical changes in a solid sample as it is heated, cooled, or kept at a constant temperature. For pharmaceutical solids, DSC is used to study melting point, crystallinity, polymorphism, and drug-excipient compatibility. A sharp endothermic peak corresponds to melting, while an exothermic peak may indicate crystallisation or decomposition.
差示扫描量热法（DSC）测量固体样品在加热、冷却或恒温过程中伴随物理和化学变化的热流。对于药用固体，DSC用于研究熔点、结晶度、多晶型以及药物-辅料相容性。尖锐的吸热峰对应熔化，而放热峰则可能表示结晶或分解。
Thermogravimetric analysis (TGA) measures the mass change of a sample as a function of temperature or time. It is particularly useful for detecting residual solvents, moisture, or volatile degradation products in solid drugs. The mass loss percentage can be quantified and compared with acceptable limits. Together, DSC and TGA provide a complete thermal profile of a solid pharmaceutical.
热重分析（TGA）测量样品质量随温度或时间的变化。它特别适用于检测固体药物中的残留溶剂、水分或挥发性降解产物。质量损失百分比可被定量并与允许限度比较。DSC和TGA相结合，为固体药物提供完整的热分析图谱。
8. X-Ray Powder Diffraction (XRPD) | X射线粉末衍射法（XRPD）
XRPD is a powerful technique for studying the crystalline structure of solid drugs. When X-rays strike a powdered sample, they are diffracted at specific angles according to Bragg’s law:
XRPD是研究固体药物晶体结构的有力技术。当X射线照射粉末样品时，根据布拉格定律在特定角度发生衍射：
nλ = 2d sin θ
where n is an integer, λ is the X-ray wavelength, d is the interplanar spacing, and θ is the diffraction angle. Each crystalline form produces a unique diffraction pattern, like a fingerprint. This makes XRPD essential for identifying polymorphs and detecting amorphous content.
其中n为整数，λ为X射线波长，d为晶面间距，θ为衍射角。每一种晶型产生独特的衍射图谱，如同指纹。因此XRPD对鉴别多晶型和检测无定形含量至关重要。
In pharmaceutical development, polymorphs of the same drug often exhibit different solubility and bioavailability. XRPD is therefore used to ensure that the correct crystalline form is present in the final product and remains stable during storage.
在药物开发中，同一药物的不同多晶型往往表现出不同的溶解度和生物利用度。因此使用XRPD确保最终产品中存在正确的晶型，并在储存期间保持稳定。
9. Mass Spectrometry (MS) | 质谱法（MS）
Mass spectrometry provides precise molecular mass and structural information for a solid drug sample. The molecule is ionised, usually by electrospray ionisation (ESI) or atmospheric pressure chemical ionisation (APCI), and then separated according to its mass-to-charge ratio (m/z). The resulting mass spectrum reveals the molecular ion peak and fragment ions, allowing the molecular formula to be deduced.
质谱法为固体药物样品提供精确的分子质量和结构信息。分子首先通过电喷雾电离（ESI）或大气压化学电离（APCI）进行电离，然后根据质荷比（m/z）进行分离。所得质谱显示分子离子峰和碎片离子，从而推导出分子式。
For solid pharmaceuticals, MS is often coupled with liquid chromatography (LC-MS). The HPLC first separates the components in a complex tablet matrix, and the mass spectrometer then identifies each component with high sensitivity. This hyphenated technique is invaluable for detecting trace impurities, degradation products, and metabolites in stability studies.
对于固体药物，MS通常与液相色谱联用（LC-MS）。HPLC首先分离复杂片剂基质中的组分，然后质谱仪以高灵敏度鉴别每种组分。这种联用技术在稳定性研究中检测痕量杂质、降解产物和代谢产物方面具有极高的价值。
10. Titration and Elemental Analysis | 滴定法与元素分析
Although modern instruments are dominant, classical wet-chemical methods still play a role in solid drug analysis. Non-aqueous titration is commonly used for the assay of weak acids and bases in solid forms, such as aspirin tablets or amine salts. The solid is dissolved in a suitable non-aqueous solvent and titrated with a standard solution of perchloric acid or sodium methoxide. The endpoint is detected by potentiometry or using a visual indicator.
尽管现代仪器占主导地位，经典的湿化学方法仍在固体药物分析中发挥作用。非水滴定通常用于固体剂型中弱酸和弱碱药物的含量测定，例如阿司匹林片剂或胺盐。将固体溶解在合适的非水溶剂中，并用高氯酸或甲醇钠标准溶液滴定。终点通过电位法或指示剂进行检测。
Elemental analysis, such as CHN combustion analysis, determines the percentage of carbon, hydrogen, nitrogen, and sometimes sulfur and halogens. For a pure solid API, the experimental percentages should closely match the theoretical values calculated from the molecular formula. This technique provides a rapid and reliable check of identity and purity.
元素分析，如CHN燃烧分析，测定碳、氢、氮以及有时包括硫和卤素的百分比。对于纯固体原料药，实验得到的百分比应与根据分子式计算的理论值高度吻合。该技术提供了一种快速可靠的鉴别和纯度检查手段。
11. Dissolution and Drug Release Testing | 溶出度与药物释放度测试
Dissolution testing deserves separate attention because it links solid dosage form performance to patient response. In a standard test, six tablets are each placed in a dissolution vessel containing 900 mL of a suitable medium at 37 ± 0.5 °C. The paddle or basket rotates at a specified speed, and samples are withdrawn at specific time points, typically 5, 10, 15, 20, 30, and 45 minutes.
溶出度测试值得单独关注，因为它将固体剂型性能与患者反应联系起来。在标准测试中，将六片药片分别置于装有900 mL合适介质的溶出杯中，温度保持在37 ± 0.5 °C。桨叶或篮以规定速度旋转，并在特定时间点取样，通常为5、10、15、20、30和45分钟。
The dissolved amount is plotted against time, generating a dissolution profile. For immediate-release products, at least 85% of the labelled dose should usually dissolve within 30 minutes. For modified-release products, the profile must match the specification at multiple time points, ensuring consistent drug delivery over an extended period.
将溶出量对时间作图，得到溶出曲线。对于速释产品，通常要求30分钟内溶出量不少于标示量的85%。对于缓释产品，溶出曲线必须在多个时间点符合规范，以确保在较长时间内药物释放的一致性。
12. Analytical Method Validation and Quality Control | 分析方法验证与质量控制
Every analytical method used for solid drug testing must be validated according to pharmacopoeial guidelines. Key validation parameters include accuracy, precision, specificity, linearity, range, detection limit, quantitation limit, robustness, and system suitability. These parameters ensure that the method is reliable and suitable for its intended purpose.
用于固体药物测试的每一种分析方法都必须按照药典指南进行验证。关键验证参数包括准确度、精密度、专属性、线性、范围、检测限、定量限、耐用性和系统适用性。这些参数确保方法可靠并适合其预期用途。
Table 1 summarises the main analytical techniques and their typical applications in solid pharmaceutical analysis:
表1总结了主要分析技术及其在固体药物分析中的典型应用：
| Technique | 技术 | Typical Application | 典型应用 |
| FTIR | Identity confirmation | 结构鉴别 |
| UV-Vis | Assay and dissolution | 含量测定与溶出度 |
| TLC | Purity screening | 纯度筛选 |
| HPLC | Assay, impurities, uniformity | 含量测定、杂质、均匀度 |
| DSC/TGA | Polymorphism, stability | 多晶型、稳定性 |
| XRPD | Crystal form analysis | 晶型分析 |
| LC-MS | Trace impurities, structural elucidation | 痕量杂质、结构解析 |
Quality control laboratories regularly apply these techniques to ensure that every batch of solid medication meets the required specifications. A well-designed analytical strategy prevents substandard products from entering the market and safeguards patient health.
质量控制实验室定期应用这些技术，以确保每一批固体药品都符合规定标准。精心设计的分析策略可防止不合格产品进入市场，维护患者健康。
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