What are the types of high-performance liquid chromatographs?

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https://mmbiz.qpic.cn/mmbiz_png/WpHergcCLC45rwoicFJTrtIQuPPcCbXhLD12k08xseSoOdsYdfZRfttxU9u3lGOwjiau0I3Ljq0p8GJ4Yqd6boFw/640#imgIndex=2 I. Classification by separation mechanism https://mmbiz.qpic.cn/mmbiz_png/48tJhhc85r9TReM6qzmkFnSCFFLP3APZI6vJdIh7hptszwfXH0WPRMfMHFiaBjlCYJLMt0xfAQZx8phTcd036vg/640#imgIndex=3 1. Liquid-liquid distribution chromatography Normal-phase chromatography (NP-HPLC): The polarity of the stationary phase is higher than that of the mobile phase (such as silica bonded with amino or cyano groups); it is suitable for the separation of polar compounds (such as fat-soluble vitamins). Reversed-phase chromatography (RP-HPLC): The polarity of the stationary phase is lower than that of the mobile phase (such as C18/C8 bonded silica gel); it is the most widely used method (accounting for 70%-80%) and is suitable for non-polar or weakly polar substances (such as drugs, amino acids). Chemically bonded phase chromatography: The stationary phase is bonded to the surface of the carrier through a chemical reaction, which prevents the loss of the stationary phase and enhances stability. 2. The stationary phase in liquid-solid adsorption chromatography is an adsorbent (such as silica gel or alumina); separation is based on the differences in the adsorption capacity of various substances, and this method is commonly used for geometric isomers or medium-molecular-weight non-ionic substances. 3. Ion exchange chromatography utilizes the interaction between ion exchange resins and the charges of the substances to be analyzed; it is suitable for ionic compounds (such as inorganic salts, organic acids/bases) as well as biological macromolecules (proteins, nucleic acids). 4. Size-exclusion chromatography (gel chromatography) separates substances based on differences in molecular size; the stationary phase is a porous gel (such as agarose), and it is suitable for the purification and analysis of high-molecular-weight substances (such as proteins and polysaccharides). 5. Affinity chromatography is based on biospecific interactions (such as antigen-antibody, enzyme-substrate) and is used for the highly selective separation of bioactive substances (such as antibodies, enzymes). https://mmbiz.qpic.cn/mmbiz_png/WpHergcCLC45rwoicFJTrtIQuPPcCbXhLD12k08xseSoOdsYdfZRfttxU9u3lGOwjiau0I3Ljq0p8GJ4Yqd6boFw/640#imgIndex=4 II. Classification by technical upgrade https://mmbiz.qpic.cn/mmbiz_png/48tJhhc85r9TReM6qzmkFnSCFFLP3APZI6vJdIh7hptszwfXH0WPRMfMHFiaBjlCYJLMt0xfAQZx8phTcd036vg/640#imgIndex=5 1. Classical liquid chromatography: This is an early form of liquid chromatography, in which the mobile phase is forced to pass through the stationary phase by gravity. It is simple to operate, but its separation efficiency is low and the analysis speed is slow. It is often used for the preliminary separation of substances that are relatively simple and do not require high levels of separation precision, such as for the initial separation of components in crude extracts of natural products in earlier times. 2. High-pressure aspect of high-performance liquid chromatography (HPLC): High-pressure pumps are used to enable the mobile phase to flow rapidly at high pressure through the chromatography column filled with very fine stationary phase particles, thereby greatly improving separation efficiency and reducing analysis time. In terms of efficiency: the particle size of the stationary phase is smaller and its uniformity is better, resulting in a significant increase in column efficiency. This enables precise separation of complex mixtures; it is widely used in applications such as the analysis of drug impurities and the detection of various components in food. High-sensitivity detection: Equipped with various high-sensitivity detectors, such as UV detectors and fluorescence detectors, it can detect substances in very low concentrations. 3. Ultra-high performance liquid chromatography (UPLC) features higher pressure and flow rates: Compared to HPLC, it can withstand higher pressures, allowing the mobile phase to flow at faster speeds through columns filled with particles that are smaller in size. This further accelerates the analysis process, with some analysis times being reduced to a fraction of those required by HPLC. Ultra-high separation efficiency: Thanks to its advanced packing technology and the ability to operate at high pressure and high speed, it enables narrower chromatographic peak widths and better resolution. It is particularly effective in separating substances with complex compositions and similar properties, and is widely used in fields such as the detailed analysis of biological macromolecules and complex natural products. https://mmbiz.qpic.cn/mmbiz_png/WpHergcCLC45rwoicFJTrtIQuPPcCbXhLD12k08xseSoOdsYdfZRfttxU9u3lGOwjiau0I3Ljq0p8GJ4Yqd6boFw/640#imgIndex=6 III. Classification by application scenario https://mmbiz.qpic.cn/mmbiz_png/48tJhhc85r9TReM6qzmkFnSCFFLP3APZI6vJdIh7hptszwfXH0WPRMfMHFiaBjlCYJLMt0xfAQZx8phTcd036vg/640#imgIndex=7 1. Prepary HPLC is used for the large-scale purification of compounds such as drug intermediates and natural products; it features a large column capacity and high separation efficiency. 2. Analytical HPLC is focused on qualitative and quantitative analysis, featuring high sensitivity (with a UV detection limit as low as 10⁻¹¹ g/mL), making it suitable for trace analysis. https://mmbiz.qpic.cn/mmbiz_png/WpHergcCLC45rwoicFJTrtIQuPPcCbXhLD12k08xseSoOdsYdfZRfttxU9u3lGOwjiau0I3Ljq0p8GJ4Yqd6boFw/640#imgIndex=8 IV. Types of special functions https://mmbiz.qpic.cn/mmbiz_png/48tJhhc85r9TReM6qzmkFnSCFFLP3APZI6vJdIh7hptszwfXH0WPRMfMHFiaBjlCYJLMt0xfAQZx8phTcd036vg/640#imgIndex=9 1. Ion-pair chromatography: Ion-pairing reagents are added to the mobile phase to enable the separation of highly polar substances (such as organic acids/bases). 2. Chiral chromatography uses chiral stationary phases to separate enantiomers, and it is particularly important in drug quality control. The primary classification criterion for HPLC is the separation principle; in practical applications, various techniques are often combined (such as LC-MS in conjunction with mass spectrometry) to enhance its functionality. We can select the appropriate type based on the properties of the sample (polarity, molecular weight, charge); for example, reverse-phase chromatography is suitable for most organic compounds, ion-exchange chromatography is suitable for charged substances, and gel chromatography is suitable for the separation of macromolecules.