High performance liquid chromatography and gas chromatography comparison - Database & Sql Blog Articles

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HPLC

The retention values ​​and other related terms of chromatographic analysis, as well as the partition coefficient, partition ratio, plate height, resolution, selectivity, etc. are consistent with gas chromatography; the basic theory used in high performance liquid chromatography: plate theory and rate theory also with gas phase The chromatogram is consistent. Because liquid chromatography replaces the gas in the gas chromatograph as a mobile phase, the rate equation is H=A+B/u + Cu where: the influence of the longitudinal diffusion term (molecular diffusion term) B/u on the plate height and gas chromatography Differently, since the diffusion coefficient of the component molecules in the mobile phase in liquid chromatography is only one ten thousandth of that in the gas chromatogram, the influence of the longitudinal diffusion term on the plate height is negligible, and the main factor affecting the liquid chromatography is the transmission. Quality item Cu. When the flow phase velocity u of the gas chromatograph (GC) increases, the plate height H increases significantly (ie, the column efficiency decreases significantly), while the liquid chromatography (LC) flow rate increases. The increase in plate height is not significant (ie, the reduction in column efficiency is not significant). This shows that high performance liquid chromatography also has high separation efficiency. HPLC can separate and analyze various substances of high polarity, high molecular weight and ionic type. The column efficiency is as high as 30,000 or more per meter. Generally, the column is 20 -- 25cm long. Due to the continuous improvement of the stationary phase, the shortest is only 3cm, and the theoretical number of plates can reach 3000-4000, which can meet the needs of general analysis. And it has a high analysis speed, the column is short, the pressure requirement is low, and the high pressure is high. Now, the pursuit of high precision and high stability is generally performed at room temperature. The sample does not need pretreatment and is easy to grasp. Contact: Mr. Hu 158-6999-6255 QQ 122-600-6936

Liquid chromatography is very suitable for large molecular weight, difficult gasification; non-volatile or heat sensitive substances, separation and analysis of ionic compounds and polymers, accounting for about 70-80% of organic matter, mobile phase carrier gas of gas chromatography Chromatographically inert permanent gases do not participate in the equilibrium process of distribution, have no affinity with the sample molecules, and the sample molecules interact only with the stationary phase. The liquid phase in liquid chromatography is a variety of low boiling organic solvents and aqueous solutions. It is also involved in the interaction of sample molecules. Therefore, the liquid phase of liquid chromatography is larger than that of gas chromatography. There are only a few kinds of carrier gas in gas chromatography, and the difference in properties is not large, and the effect on separation is not significant. The liquid phase of liquid chromatography has many kinds of mobile phases, and the difference in properties is also large, which has a significant influence on the separation effect. For LC, the choice of mobile phase is important and adds a factor to increase selectivity. Liquid chromatography can also use two or more liquids in different proportions as the mobile phase to increase the selectivity of separation.

Liquid Chromatography

It can complete the difficult separation work. According to the different separation mechanism, high performance liquid chromatography can complete the difficult separation work. With regard to the separation mechanism, high performance liquid chromatography can complete the difficult separation work. Depending on the separation mechanism, high-performance liquid-liquid chromatography can complete difficult separation work. Depending on the separation mechanism, high-performance liquid-liquid chromatography can complete difficult separation work. High performance liquid chromatography can be divided into liquid-solid adsorption chromatography; liquid-liquid partition chromatography; ion exchange chromatography and gel permeation chromatography. The liquid-solid chromatography column is filled with a solid adsorbent, which has different adsorption capacities due to different components. Therefore, when the mobile phase carries the component to be tested through the column, the components are separated from the liquid phase and the stationary phase of the liquid-liquid chromatography is a liquid. The liquid as the stationary phase is coated on the inert support, the mobile phase is immiscible with the fixed solution, and when the mobile phase with the component to be tested enters the column, the components quickly reach a distribution equilibrium between the two phases, since the components are The two phases have different distribution coefficients and are separated from each other. Liquid-liquid chromatography using a non-polar solution as a mobile phase, a polar substance as a stationary phase is called normal phase chromatography; a polar solution is used as a mobile phase, and a liquid-liquid chromatography using a non-polar substance as a stationary phase is called reversed-phase chromatography. The ion exchange chromatography column is filled with an ion exchange resin, and the separation is achieved by the difference in ion exchange capacity of the sample. Gel chromatography is separated by the size of the molecules in the sample. Among the above four types of chromatography, the most widely used is liquid-liquid chromatography. Liquid chromatography has a large margin of choice for analysis, but gas chromatography does not.