Let s explain how gas chromatography and HPLC are the same and different

When encountering baseline problems, you should first check whether the instrument conditions have changed, and whether there are new gas cylinders and equipment accessories in the near future. If there is a change or change in conditions, first check to see if the baseline issue is caused by these changes, which are often the cause of the baseline issue. Some people have encountered this situation at work:

The purity of the new carrier gas is not enough, and the baseline gradually rises after the overload gas is replaced (the baseline does not change immediately due to the carrier gas purification pipe). After the next day, the baseline was very high with strong baseline jitter, and all peaks were lost in the noise and could not be detected. After inspection, the problem appeared on the newly replaced carrier gas, and after the replacement of the carrier gas, it immediately returned to normal.

Once the above possible causes of baseline issues have been ruled out, the injection pad should be inspected for deterioration (should....

Haocunha answer: wide range of applications, product destruction, easy to collect and other advantages, three points, barely efficient: the number of general gas phase theoretical plates is 10,000 levels, higher than the liquid phase 1,000 levels, high sensitivity: the general liquid phase is more microgram level, the gas phase is more than nanogram level, and the analysis speed is up to the picogram level:

The difference between gas phase and liquid is short, mainly according to the product, the gas phase is more than 40min, the liquid phase is considered to be too high, the product should run 12 columns, durability: maintenance, use the gas chromatography column for a longer time, liquid chromatography, gas chromatography, the detection range is the same as the advantages, and the comparison is said in general, 3 advantages: 1. The quantitative accuracy is more; 2. More repeatability; 3. The liquid phase change is more flexible and conducive to research and development.

The differences between gas chromatography and high-performance liquid chromatography are that the mobile phase is different, the injector is different, the column length is different, and the analysis types are different. The similarities are the same basic principles.

1. The differences between gas chromatography and high-performance liquid chromatography: different mobile phases, different injectors, different column lengths, and different types of analysis.

1. The mobile phase is different: HPLC is the liquid mobile phase, and GC is the permanent gas as the mobile phase (usually called the carrier gas).

2. The injector is different: the high-performance liquid phase is a flat-headed needle, and the gas chromatography is a pointed needle.

3. The length of the chromatographic column is different

(1) The gas chromatography column is usually a few meters to tens of meters.

Gas chromatography can increase the column length to improve the column efficiency due to the low relative analysis volume of the carrier gas and the large molecular gap, so the viscosity is low, the fluidity is good, and the components flow fast in the gas phase.

(2) Liquid chromatography columns are usually tens to hundreds of millimeters.

4. There are differences in the types of analysis

1) The objects of gas chromatography analysis are mostly (unsuitable absolute): compounds with molecular weight less than 1000, low boiling point, volatile, and good thermal stability.

(2) Liquid chromatography: It is more suitable for the analysis of liquid compounds with high boiling point, difficult to volatilize, poor thermal stability and large molecular mass (1000-2000).

Second, the similarity between gas chromatography and high-performance liquid chromatography: the basic principle is the same.

It is the use of the difference in the partition coefficient of the substance in the mobile phase and the stationary phase, so that the partition between the two phases is repeated many times (1000-1000000 times, or even more), so that the components with a small difference in the original partition coefficient are separated.

First, the mobile phase is different.

The liquid phase is liquid, and the liquid phase has an extra pump to operate. The mobile phase of the gas phase is the carrier gas, which is the gas. In general, the stationary phase in liquid chromatography is mostly solid, and the mobile phase is mostly liquid; The carrier gas in gas chromatography is mostly inert gas (N2, AR, etc.), from the perspective of the scope of application:

Liquid chromatography is the most widely used and can be used for chemical analysis, food analysis, environmental analysis, drug analysis, Chinese herbal medicine spectrum analysis, etc., according to the polarity of the target analyte, the peak time is also different; While the analytes of gas chromatography are mostly gases or volatile substances, liquid chromatography is more widely used from the perspective of analytes.

Second, the scope of application is different.

Gas chromatography: good separation ability, high sensitivity, fast analysis speed, convenient operation, etc. Restricted by technical conditions, substances with too high boiling point or poor thermal stability are difficult to apply gas chromatography for analysis, and derivatization or cracking method can be used for the part of substances below 500 that are not volatile or easy to decompose by heating.

Third, the structure of the instrument is different.

1. The gas chromatograph is composed of a carrier gas source, a sampling part, a chromatographic column, a column heater, a detector and a data processing system. The temperature of the injection section, column, and detector is under control.

2. The high-performance liquid chromatograph mainly consists of: injection system, infusion system, separation system, detection system and data processing system.

The principle of gas chromatography and liquid chromatography is the same, but in fact, the two are quite different. It's hard to explain in a few words. The "Learning and Training" column of "Biochemical Chromatography Network" has a detailed and systematic introduction to chromatography, I will not copy it here, you can see for yourself.

The common denominator: they are all methods of carrying the sample with its own mobile phase, and after column separation, the target sample is detected with a detector.

Differences: Gas chromatography is a gas as a mobile phase, while liquid chromatography is a liquid (the main difference).

In addition, there are different applicable samples, different daily maintenance methods, and so on.

Similarities: all are high-efficiency, high-speed, high-selectivity chromatographic methods, with both separation and analysis functions, and can be detected online.

1. In the analysis of polymers, adsorption chromatography is generally used to separate additives, such as azo dyes, anti-transport oxidants, surfactants, etc., and can also be used for the composition analysis of petroleum hydrocarbons.

2. It is used for the analysis of amino acids and proteins, and is also suitable for the separation and analysis of some inorganic ions (inorganic anions such as NO3-, SO42-, CL-, and inorganic cations such as Na+, Ca2+, Mg2+, K+), etc., which plays a very important role.

3. It is suitable for the system of aqueous solution and the system of organic solvent. When the eluent used is an aqueous solution, it is called gel filtration chromatography, and it has many applications in the biological world.

Principles of liquid chromatography:

The mobile phase in the reservoir is blocked into the system by the high-pressure pump, and the sample solution enters the mobile phase through the injector, and is loaded into the chromatographic column (stationary phase) by the mobile phase.

When passing through the detector, the sample concentration is converted into an electrical signal and sent to the recorder, where the data can be printed out as a spectrum for analysis by researchers.

Answer] :(1) Similarities and differences between high performance liquid chromatography and classical liquid chromatography.

Similarities. It's all liquid chromatography, and the principle is the same.

Differences. a.High efficiency of separating hidden oak;

b.High sensitivity;

c.operational automation;

d.Fast analysis.

2) Similarities and differences between high performance liquid chromatography and gas chromatography.

Similarities. They are all separated by the fact that the substances have different partition coefficients in the two items.

Different foci alongside points.

a.High performance liquid chromatography does not destroy the sample, and can easily prepare pure samples;

b.The separation effect is closely related to the nature of the trapped phase, and there are many types of mobile phases.

c.It is widely used in the separation and analysis of organic compounds, especially those with low volatility, poor thermal stability or high relative mass.

Answer] :(1) Analyze the object aspect. Gas chromatography requires the object to be analyzed to have a certain volatility at column temperature, so it is suitable for the analysis of gases, volatile and thermally stable substances, and volatile and thermally stable derivatives, which can analyze about 20% of organic matter.

Because the mobile phase is liquid, the high performance liquid chromatography can be analyzed as long as the analyzed substance has a certain solubility in the mobile phase, so it is widely used, especially suitable for the analysis of compounds with high boiling point, poor thermal stability, large relative molecular weight and ionic compounds, accounting for about 80% of the analysis of color annihilation spectrum.

2) Change the selective pathway aspect. The mobile phase of gas chromatography is a gas, which has no force on the components, only plays a carrying role, and the separation mainly depends on the force between the component molecules and the stationary phase, so the selectivity of the components is mainly changed by changing the stationary phase. The mobile phase of HPLC not only plays a carrying role, but also has a certain affinity for the relative components, and the realization of the separation process is the result of the interaction between the components, the mobile phase and the stationary phase, mainly by changing the type and composition of the mobile phase to improve the selectivity of the separation.

3) Other aspects. Gas chromatography can use longer capillary columns to achieve overall high efficiency, with less influence from off-column effects. Compared to gas chromatography, HPLC makes it easier to collect the separated components.

However, after the mobile phase change, the equilibration time is longer. In addition, the instrumentation and equipment of the two are also different.

Answer]: Gas chromatography is limited to gases and compounds with low boiling points, which account for only 20% of the total number of organic matter. For those substances with high boiling point, poor thermal stability and large molar mass, which account for nearly 80% of the total organic matter, high performance liquid chromatography is mainly used for separation and analysis.

Gas chromatography uses a mobile phase that is an inert gas, which has no affinity for the components, i.e., does not produce interaction forces, and only plays a carrying role. In high-performance liquid chromatography, the mobile phase can be used to select liquids of different polarities, which can produce a certain affinity for the components and participate in the fierce competition of fixing the relative components. Therefore, the flow relative separation plays a large role, which is equivalent to adding a parameter to control and improve the separation conditions, which provides great convenience for selecting the optimal separation conditions.

Gas chromatography is generally performed at higher temperatures, while HPLC often works at room temperature.

Liquid chromatography** is relatively tolerant and can quantify the isolated components**, which is convenient for identification or preparation of pure substances with auxiliary techniques.