Question 20 on chromatography, question about chromatography

Differences: First, the mobile phase is different: HPLC is a liquid mobile phase, and GC is a permanent gas as the mobile phase (usually called carrier gas) Second, the injector is different

3. Different column lengths: (1) Gas chromatography columns are usually a few meters to tens of meters (gas chromatography has low viscosity and good fluidity due to the low relative analysis volume of the carrier gas and large molecular gaps, so the components flow fast in the gas phase, so the column length can be increased to improve the column efficiency). 2) Liquid chromatography columns are usually tens to hundreds of millimeters Fourth, there are differences in the types of analysis:

The objects of gas chromatography analysis are mostly (unsuitable absolute): compounds with molecular mass less than 1, low boiling point, volatile, and good thermal stability. Liquid Chromatography:

It is more suitable for the analysis of high boiling point, difficult to volatilize, thermal stability....

Chromatography is used to separate and purify substances with different adsorption to the stationary phase.

In chromatography, a stationary phase (solid or liquid) is called a stationary phase; A moving phase (usually a gas or liquid) is called a mobile phase.

Column chromatography is to fill the glass tube with a stationary phase, infiltrate the mobile phase solvent and pour the solution to be separated above, and then add the mobile phase dropwise, because the adsorption force of the substances to be separated on the stationary phase is different, the adsorption force of the large is fixed or moves slowly, and the small adsorption force is washed down by the mobile phase solvent and flows down with the mobile phase, so as to achieve separation.

Paper chromatography uses the filter strip as the stationary phase, and the sample point of the mixed solution to be separated is dotted on the paper strip, and the lower end of the paper strip is immersed in the mobile phase solvent and suspended, and the solvent rises along the filter paper strip due to capillary action, and the solute in the sample point is separated.

Thin layer chromatography is performed by coating a glass plate with a stationary phase, then spotting, and the lower end is immersed in a solvent, again separated from the bottom up. It is often used to explore column chromatography experimental conditions, solvent and stationary phase selection, etc.

Commonly used stationary phases are gypsum, alumina, sucrose, starch, etc., and commonly used mobile phases are various organic solvents such as water and benzene.

High performance liquid chromatography (HPLC) is a new chromatography technique developed in the early 70s after gas chromatography, which uses liquid as mobile phase.

HPLC was developed on the basis of gas chromatography and classical chromatography. There is no essential difference between modern liquid chromatography and classical liquid chromatography. The only difference is that modern liquid chromatography is more efficient and automated than classical liquid chromatography.

In classical liquid chromatography, the mobile phase is delivered at atmospheric pressure, and the stationary phase used is inefficient and the analysis cycle is long. Modern liquid chromatography refers to the theory of gas chromatography, and the mobile phase is changed to high-pressure delivery (the highest delivery pressure can reach; The column is packed with a small particle size packing material in a special way, resulting in a much higher efficiency than classical liquid chromatography.

Chromatographic analysis refers to the method of separating and analyzing substances according to the difference in partition coefficients between stationary phase and mobile phase. According to the molecular aggregation state of the mobile phase, it can be divided into liquid chromatography, gas chromatography and supercritical fluid chromatography. According to the separation principle, it can be divided into many categories, such as adsorption, partitioning, spatial repulsion, ion exchange, affinity and chiral chromatography.

According to the principle of operation, it can be divided into column chromatography and plate chromatography. Chromatography has become the most widely used and most widely included analytical method in pharmacopoeia. There are two elements to chromatographic analysis – the mobile phase and the stationary phase.

As the mobile phase flows from one end of the stationary phase to the other, the solute added to the start of the stationary phase flows with the mobile phase and is transferred back and forth between the mobile and stationary phases. Different solutes have different affinities for these two phases, and solutes move at different speeds, so they are separated. The stationary phase is generally solid, and it can also be a liquid attached to the solid; The mobile phase is either liquid or gaseous.

Chromatography has many advantages: good separation effect, simple equipment, convenient operation, mild conditions, and various methods, which can adapt to different needs. The main disadvantages are:

The processing capacity is small, the cycle is long, and it cannot be operated continuously; Some chromatography media** are expensive, and sometimes a suitable medium cannot be found.

There are various types of chromatography (chromatography). According to the form of stationary phase, it can be divided into column chromatography, paper chromatography, and thin layer chromatography. According to the way of solute, it can be divided into leading chromatography, displacement chromatography, and elution chromatography.

According to the physical state of the mobile phase, it can be divided into gas chromatography and liquid chromatography, as well as supercritical fluid chromatography. According to the separation mechanism, it can be divided into partition chromatography, adsorption chromatography, ion exchange chromatography, exclusion chromatography, hydrophobic chromatography, ion-pair chromatography, affinity chromatography, and bonded phase chromatography. According to the relative polarity of the stationary phase and the mobile phase, it can be divided into normal-phase chromatography and reversed-phase chromatography.

In layer operation, one-component eluents are often unsatisfactory for the elution of multi-component samples. Either the components that were washed out first were mixed together, or the components that were washed out later took a long time to produce peaks and increased peak widths. In order to improve resolution, change peak shape, or shorten chromatography time, it is sometimes necessary to change the composition of the mobile phase (pH, ionic strength) during chromatography.

The composition of the mobile phase is changed in stages, and the composition of the mobile phase changes in a step-like manner, which is called stage elution. Gradually changing the composition of the mobile phase, which varies in a curve or straight line, is referred to as gradient elution. Gradient elution can be used for mobile phase formation.

In high-performance liquid chromatography, several pumps are commonly used to deliver different solvents, and the composition of the eluent can be controlled by controlling the flow rate of each pump.

Ways to improve chromatography separations include changing the composition or pH of the mobile phase, changing the stationary phase, changing the temperature, etc. In liquid chromatography, it is most important to change the composition of the mobile phase.

The rest of the conditions to pay attention to are: the column should be thin and long; The separation medium should be filled tightly and uniformly, with fine particles and uniform size distribution; The operating temperature remains constant; The sample Li Zi changed the dosage to be small; The flow rate is slow and constant. [

Summary. Gas chromatographs are the detection and analysis of gaseous substances or substances that can be converted into gases at a certain temperature. The range of detection is that the substances contained are relatively wide.

What properties of substances can be analyzed by gas chromatography in chromatography?

Gas chromatographs are the detection and analysis of gaseous substances or substances that can be converted into gases at a certain temperature. The range of detection is that the substances contained are relatively wide.

Gas chromatography is suitable for the separation of volatile compounds. GC can be divided into gas-solid chromatography (GSC) and gas-liquid chromatography (GLC) according to different stationary phases, among which GLC is the most widely used.

I hope I can help you, thank you for your consultation and trust, I am happy to answer for you, you can ask me any questions you have at any time If you are satisfied with me, you can give a thumbs up, give an encouragement Finally, I wish you a happy life!

Categories: Education, Science, >> Science & Technology.

Problem description: What is gas chromatography? What is liquid chromatography? What is temperament? What is liquid?

Analysis: Stationary phase: A phase that is immobilized in a chromatographic separation and retains the sample.

Mobile phase: Another phase that is in equilibrium with the stationary phase and moves the sample forward.

Chromatography: Also known as chromatography or chromatography, it is a physicochemical analysis method, which uses the difference in the forces (partition, adsorption, ion exchange, etc.) between different solutes (samples) and the stationary phase and the mobile phase.

There are many ways to classify chromatography, and the coarsest classification is to divide chromatography into four broad categories based on the state of the mobile phase.

Chromatography is classified by the type of mobile phase.

Chromatographic Type Mobile phase is the main object of analysis.

Gas chromatography Gases Volatile organic compounds.

Liquid chromatography is a liquid of various substances that can be dissolved in water or organic solvents.

Supercritical fluid chromatography Supercritical fluids Various organic compounds.

Electrochromatography buffers solutions, electric field ions, and various organic compounds.

Big brother, I am an expert in this area, the 2nd floor is not strict, a bottle of things can not measure the exact concentration, and it is completely possible to not measure who is who, give you an unknown chromatogram, which peak represents which, who dares to say that he knows? Basically, you have to use standard samples.

The purpose of chromatography is to separate and detect. As a separation, chromatography is the best method in the world, it can divide the mixture into individual components for you, like what is pure in the factory, what is high purity, many of which are made by chromatographic instruments (except for those who sell fakes or do it in other ways).

As a test, chromatography is also convenient and simple, the operation is simple, but it is flawed, and its principle is relative sampling. The ordinate of the chromatogram is not the concentration value, but the voltage value, what is relative? If a concentration is already known, the unknown is not also calculated?

So basically if you want to measure something, or you just want to measure a certain component, such as carbon dioxide in a gas mixture, you need to buy a standard sample similar to your sample, the concentration of the component is known, and it's relatively close to your sample.

If you don't buy a standard sample, you can only calculate a percentage of rough ones, for example, if you want to simply measure the content of oxygen and nitrogen in the air, you just blow a breath, and the percentage is about 20% oxygen and 80% nitrogen. This is relatively coarse, if you require high precision, you use this method to calculate, and you get the result is not as good as you just make up a number.

As for the chromatogram, one peak represents a substance, and each separate peak represents a separate component. I'm an expert in this area, and if you want to finish this instrument, you can Zhao me.

Analyze the chemical composition of organic compound mixtures. For example, if you have a bottle of ethanol, you want to know how much it contains, whether there will be impurities such as methanol and acetone in it, and if so, what is the content. These can then be analyzed by gas chromatography.

For example, if you have a polymer liquid, you can analyze its molecular weight composition by liquid chromatography.

The chromatograph is to analyze the content of organic matter, as long as you have the standard sample you want to analyze the organic matter, all the organic content contained in a mixture can be analyzed, the type mainly depends on your standard sample, such as to test benzene, first there is a standard sample of benzene, and then measure the content, otherwise there is no way to measure. Therefore, the test type is set first and then the standard sample is purchased, and then the content can be analyzed whether the content exceeds the standard. The chromatogram is generally high, but it is related to the column and the detection line.

Contact me if you need more details, I have a buddy who is an expert in this area.

It is used quantitatively, and if there is a standard sample, it can be qualitative.

Chromatography can only analyze the substances with withering, but not all inorganic substances. （）

a.It's not the first to be sure.

b.Mistake. Correct answer: B

The dead time is the time from the beginning of the injection to the occurrence of the air peak, the adjusted retention time is the retention time of the component minus the retention time of the air peak, the retention time is the time when the component appears from the beginning of the injection to the maximum concentration after the column, the peak height is the distance from the peak of the chromatographic peak to the baseline, and the peak width refers to the width from the inflection point on both sides of the peak to make a tangent and intersect the baseline.