Gas chromatography principle?

If one day someone asks the principle of gas chromatography. What is gas chromatography used for? If you tell him, the gas chromatograph can be used to separate mixtures and determine the amount of substances. Its main function is to separate and test different components in samples. You are sure to receive the second question. Why can the gas chromatograph separate the mixture and determine the content of the substance? ..... answer it again, and it will become the "why" of the life version. How can these problems about gas chromatography be simply described? Why don't you give him this document?

Original? Richard:

Chromatographic analysis is a tool for separating and analyzing multicomponent mixtures.

Mainly use the physical properties of substances to separate the mixture and determine the composition of the mixture. The components in the mixture were analyzed quantitatively and qualitatively.

Gas chromatograph uses gas as mobile phase (carrier gas). When the sample is sent to the sampler, it is carried into the chromatographic column by the carrier gas. Because the distribution or adsorption coefficient of mobile phase (gas phase) and stationary phase (liquid phase or solid phase) in chromatographic column is different. Under the washing of carrier gas, the components are repeatedly distributed between the two phases, so that the components are separated in the chromatographic column, and then the components are detected in turn by a detector connected to the chromatographic column according to their physical and chemical characteristics. ?

What is 1 gas chromatography? How many categories does it fall into?

All chromatographic techniques using gas phase as mobile phase are collectively called gas chromatography. Generally can be classified according to the following aspects:

1, classified according to stationary phase aggregation:

(1) gas-solid chromatography: the stationary phase is a solid adsorbent,

(2) Gas-liquid chromatography: the stationary phase is liquid coated on the surface of the carrier.

2, according to the principle of process physical and chemical classification:

(1) adsorption chromatography: separation chromatography is realized by using the differences of physical adsorption properties of different components on solid adsorption surfaces.

(2) partition chromatography: Different components have different partition coefficients in two phases, thus realizing separation chromatography.

(3) Others: ion exchange chromatography based on ion exchange principle: electrochromatography based on colloid electrokinetic effect; Thermal chromatography developed by using temperature changes and so on.

3, according to the type of stationary phase classification:

(1) column chromatography: stationary phase is installed in the chromatographic column, including packed column, hollow column and capillary column.

(2) paper chromatography: using filter paper as a carrier,

(3) Thin film chromatography: the stationary phase is thin desert pressed by powder.

4. According to the principle of dynamic process, it can be divided into flushing method, displacement method and head-on method.

What is the separation principle of gas chromatography?

Gas chromatography is a physical separation method. Using the tiny difference of distribution coefficient (solubility) between two different phases of the tested substances, when the two phases move relatively, these substances are distributed repeatedly between the two phases, which makes the original tiny difference in properties have a great effect and separates the different components.

Explanation of some common terms and basic concepts of gas chromatography?

1, phase, stationary phase and mobile phase:

The unified part of the system is called phase; In the process of chromatographic separation, the stationary phase is called stationary phase; A fluid flowing through or along a stationary phase is called a mobile phase.

2. Chromatographic peak:

After the substance enters the discriminator through the chromatographic column, the curve appearing on the recorder is called chromatographic peak.

3. Baseline:

Under chromatographic operation conditions, when no detected component passes through the discriminator, the graph of detector noise changing with time recorded by the recorder is called baseline.

4. Peak height and half-peak width:

The height from the maximum concentration point of the chromatographic peak to the intersection point between the vertical line and the baseline of the time coordinate index is called the peak height, which is generally expressed by H, and the width of the chromatographic peak at half height is half peak width, which is generally expressed by x 1/2.

5. Peak area: The area formed by the outflow curve (chromatographic peak) and the baseline is called the peak area, which is denoted by A. ..

6. Dead time and retention time:

The time from injection to the peak of inert gas is called dead time, which is expressed by td. The time from injection to peak appearance is called retention time, which is expressed by tr.

7. Dead volume and reserved volume:

The product of dead time and average flow velocity of carrier gas is called dead volume, which is expressed by Vd, and the average flow velocity of carrier gas is expressed by Fc, and Vd=tdxFc. The product of retention time and average flow rate of carrier gas is called retention volume, which is expressed by Vr, and Vr=trxFc.

8. Reserved value and relative reserved value:

Retention value is a numerical value indicating the retention time of each component in the sample in the chromatographic column, which is usually expressed by time or the volume of carrier gas required to take out the component from the chromatographic column. Taking a substance as a standard, the ratio of the retention value of other substances to this standard is called relative retention value.

9. Instrument noise: The instability of baseline is called noise.

10. basic flow: hydrogen flame chromatography, the initial current (underflow) existing in the instrument itself when there is no sample injection, which is called basic flow for short.

4 What is the basis for general selection of carrier gas? What are the carrier gases commonly used in gas chromatography?

As a carrier gas for gas chromatography, it is required to have good chemical stability;

High purity;

Cheap and easy to get;

Can be adapted to the detector used.

Commonly used carrier gases are hydrogen, nitrogen, argon, helium, carbon dioxide and so on.

5 Why purify the carrier gas? How to purify?

The so-called purification is to remove some impurities such as organic matter, trace oxygen and moisture from the carrier gas and improve the purity of the carrier gas. Impure gas as carrier gas will lead to column failure and sample change, hydrogen flame chromatography will lead to the increase of underflow noise, and thermal conductivity chromatography will lead to the linear deterioration of discriminator, so the carrier gas must be purified.

Generally, oxygen is removed by chemical treatment, such as oxygen removal with active copper; Use adsorbents such as molecular sieve and activated carbon to remove organic impurities; Adsorbents such as silica gel and molecular sieve are used to remove water.

What are the sampling methods of samples?

Chromatographic separation requires injecting a certain amount of samples in the form of "plug" in the shortest time. Sampling methods can be divided into:

1. Gas sample: There are four common injection methods:

(1) syringe injection

(2) Sampling by measuring tube

(3) Constant volume injection

(4) Automatic gas sampling.

Commonly used are syringe sampling and gas automatic sampling. The advantages of syringe injection are flexible use and simple method, but the repeatability of injection quantity is poor. Automatic gas injection is quantitative valve injection with good repeatability and automatic operation.

2. Liquid samples:

Generally, it is simple and quick to inject with a micro syringe. Quantitative automatic sampling can also be used, with good repeatability.

3. Solid samples:

Usually, the sample is dissolved in a solvent and then injected in the same way as liquid injection. There is also a solid sampler for sampling.

7 briefly describe the influence of various operating conditions on the test results in gas chromatography analysis?

Operating conditions have great influence on chromatographic separation.

1, column length, column inner diameter:

Generally speaking, the column tube length can improve the separation ability, and the short column tube fractionation speed is faster;

The separation effect of small column diameter is good, and the flux of large column diameter is large, but the column diameter is too large, which will lead to uneven distribution of supports in the chromatographic column.

2. Chromatographic column temperature:

It is an important operating variable, which directly affects the separation efficiency and analysis speed. The selection of column temperature is based on the boiling point range of the mixture, the ratio of stationary liquid and the sensitivity of the discriminator. Increasing the column temperature can shorten the analysis time;

Lowering the column temperature can increase the selectivity of the column, which is beneficial to the separation of components, the stability of the column and the life of the column.

Generally speaking, it is more appropriate to use column temperature equal to or higher than the average boiling point of the sample, low column temperature for volatile samples and high column temperature for non-volatile samples.

3. Carrier gas flow rate:

The flow rate of carrier gas is one of the important reasons for chromatographic separation. Generally speaking, when the flow rate is high, the chromatographic peak is narrow, and when the flow rate is too high or too low, the chromatographic peak is wide, which has an adverse effect on separation.

4. Stationary phase:

The stationary phase consists of a solid adsorbent or a carrier coated with a stationary liquid.

When columns with the same length are used, the separation efficiency of fine particles is better than that of coarse particles.

The content of stationary liquid has a great influence on the separation efficiency, and its weight ratio to carrier is generally 15%-25%. Too large a ratio is not conducive to separation, and too small a ratio will tail the chromatographic peak.

5. Sample injection:

Generally speaking, the injection speed is fast, the injection volume is small, and the separation effect is good when the injection temperature is high. For the incoming liquid, the speed should be fast, and the vaporization temperature should be higher than the boiling point of the high-boiling components in the sample. Once vaporized, the chromatographic peak shape will not widen, and the column efficiency is high. When the sample volume is within a certain range, the half-peak width of the chromatographic peak remains unchanged. If too many samples are injected, the chromatographic column will be overloaded.

Generally speaking, if the column length is increased by four times, the allowable amount of samples will be doubled.

8 What is a load? What are the requirements for the load?

Carrier is a porous chemically inert solid used to support stationary liquid in gas chromatography. There are the following requirements for the carrier:

1. Large surface area;

2. Chemical inertness and thermal stability;

3. It has certain mechanical strength, so that the coating and filling process will not cause crushing;

4. Appropriate pore structure is beneficial to rapid mass transfer between two phases;

5. It can be made into uniform spherical particles, which is beneficial to gas phase infiltration and has good filling uniformity;

6. It has good wettability and is convenient for the uniform distribution of stationary liquid.

It is difficult to fully meet the above requirements, and people can only find better carriers in practice.

9 How many kinds of carriers are there? What are its characteristics?

It is usually divided into diatomaceous earth and non-diatomaceous earth, and each category has various subclasses.

1, diatomite type:

(1) white: small surface area, loose and fragile, low adsorption performance and strong polar components, which can be analyzed after proper treatment;

(2) Red: large surface area, good mechanical strength, but large adsorption capacity.

2. Non-diatomite type:

(1) Fluorocarbon: The surface is inert, which can be used to analyze strongly polar and corrosive substances, but it is not easy to pack columns and the column efficiency is low.

(2) Glass microspheres: small surface area, which can greatly reduce the column temperature and separate completely and quickly. However, smear is difficult and column efficiency is low.

(3) Porous polymer beads: high mechanical strength, good thermal stability, low adsorption, corrosion resistance and high separation efficiency, which is a new chromatographic stationary phase with excellent performance.

(4) Carbon molecular sieve: neutral, large surface area, high strength and long removal life, which has incomparable advantages in microanalysis.

(5) Activated carbon: It can be used as stationary phase alone.

(6) Sand: mainly used for separating metals.

10 How to choose the common load?

All kinds of bearers, all kinds of names Among that commonly use diatomite carriers:

Red carriers (such as 620 1 and 20 1) can be used to separate nonpolar or weakly polar substances.

White brackets (such as 10 1) can be used for polar substances or alkaline substances.

Glaze red carrier (such as 30 1) can be used for medium polar substances.

Silanized white carrier can be used to determine strongly polar hydrogen bonding substances, such as wastewater.

To separate acidic substances, such as phenols, acid-washed supports should be used.

In order to separate alkaline substances, such as ethanolamine, the treated carrier should be washed with alkali.

In some special cases, it is necessary to use special carriers, such as fluorine carriers, to separate isocyanates.

But in ordinary constant analysis, you don't need to pay too much attention to the load, even refractory brick powder, glass bead sand and sea sand can be used.

What is 1 1 solid stationary phase? Can be roughly divided into several categories?

Refers to the active porous solid material directly packed into chromatographic column as stationary phase. Solid stationary phases can be roughly divided into three categories:

The first category is adsorbent. Such as molecular sieve, silica gel, activated carbon, alumina, etc.

The second category is polymers. For example, GDX porous polymer microspheres in China and Porapak series abroad.

The third category is chemically bonded stationary phase. In gas chromatography, stationary liquid is usually coated on the surface of carrier.

Symmetrical peaks can usually be obtained by using chemically bonded stationary phases to analyze polar or nonpolar substances. This method has high column efficiency and improves the thermal stability of stationary phases.

12 what is a stationary liquid? What are the requirements for stationary liquid?

Generally, it is a liquid membrane of high boiling point organic matter, and the components are separated in the chromatographic column through the interaction between different molecules of different components. Gas chromatographic stationary liquid generally has the following requirements:

1. At the working temperature, the steam pressure is low, the thermal stability is good, and there is no irreversible reaction with the analyzed physical or carrier gas;

2. It is liquid at working temperature, and the lower the viscosity, the better. The mass transfer rate of substances in high viscosity stationary liquid is slow, which reduces the column efficiency. This determines the minimum use temperature of fixed liquid;

3. It can be firmly attached to the carrier and form a uniform and structurally stable thin layer;

4. The separated substance must have a certain solubility in it, otherwise it will be quickly taken away by the carrier gas and cannot be distributed between the two phases;

5. It has the ability to separate substances with similar boiling points but different types, that is, the ability to retain one type of compound is greater than the other. This separation ability is the selectivity of stationary liquid.

What is the selection principle of 13 stationary liquid?

According to the interaction between the separated components and the molecules of the stationary liquid, the selection of the stationary liquid is generally based on the so-called "similarity principle", that is, some properties of the stationary liquid and the separated components are similar, such as functional groups, chemical bonds, polarity, certain chemical properties, etc. When the properties are similar, the interaction between the two molecules is strong, and the solubility of the separated components in the fixed solution is large and the distribution coefficient is large, so the retention time is long; On the contrary, the solubility is small, the distribution coefficient is small, and it can flow out of the chromatographic column quickly.

The following is a discussion of different situations:

A, separating polar compounds and adopting polar stationary liquid. At this time, the forces between the components of the sample and the static liquid molecules are mainly directional force and induced force, and the peak order of each component is polar order, with the smaller polarity appearing first and the larger polarity appearing slower;

B, separating the nonpolar compound, adding nonpolar stationary liquid, wherein the intermolecular force between each component of the sample and the stationary liquid is dispersive force, and has no special selectivity; At this time, the components peak in the order of boiling point, and the ones with low boiling point peak first. For the separation of isomers with similar boiling points, the efficiency is very low;

C, when separating the mixture of nonpolar and polar compounds, polar stationary liquid can be used, and then the nonpolar components are distilled first. The stronger the polarity of the stationary liquid, the easier it is for the nonpolar components to flow out;

D, for samples that can form hydrogen bonds. For example, for the separation of alcohol, phenol, amine and water, polar or hydrogen-bonded stationary liquid is generally selected, and the separation is carried out according to the hydrogen bonding ability between the components and the molecules of the stationary liquid.

"Similarity compatibility principle" is a general principle for selecting stationary liquid. Sometimes, when the existing stationary liquid can not achieve satisfactory separation effect, "mixed stationary liquid" is often used to mix two or more stationary liquids with different properties in a proper proportion, so that the separation has satisfactory selectivity without prolonging the analysis time.

How does 14 column behave after failure? What is the reason for its failure?

The main failure of chromatographic column is poor chromatographic separation and the retention time of components is obviously shortened. The main reasons of chromatographic column failure are: for gas-solid chromatography, the activity or adsorption performance of stationary phase decreases; For gas-liquid chromatography, it is caused by the gradual loss of stationary liquid during use.

Aging operation of 15 capillary column

Purpose of aging: The stationary phase of gas chromatography column is usually distributed in the form of coating on the inside of tube wall (capillary column) or on the surface of carrier (packed column). For a new gas chromatography column, the combination of external stationary phase and carrier is often weak, and it will slowly lose when used at high temperature, resulting in baseline fluctuation and increased noise. In order to avoid this phenomenon, it can be heated at a higher temperature (generally the tolerance temperature of the chromatographic column) for a period of time in advance. In addition, for gas chromatographic columns that have been used for a long time, aging treatment can be carried out to remove residual pollutants in the chromatographic column.

The temperature of the chromatographic column rises to a constant temperature, which is usually the upper limit of its temperature. Under special circumstances, it can be heated to about 10-20℃ higher than the operating temperature, but it must not exceed the upper temperature limit of the chromatographic column, which is easy to damage the chromatographic column. In addition, don't adjust the programmed temperature too slowly.

When the aging temperature is reached, record and observe the baseline. Enlarge the baseline for observation. At the initial stage, the baseline will continue to rise, and it will begin to decline at 5- 10 minutes after reaching the aging temperature, lasting for 30-90 minutes. When a fixed value is reached, the baseline will stabilize. If the baseline is still unstable after 2-3 hours or there is no obvious downward trend after 15-20 minutes, it may be that the system equipment is leaking or polluted.

In this case, the column temperature should be immediately reduced to below 40℃, and the system should be checked as soon as possible to solve related problems. If aging continues, it will not only damage the chromatographic column, but also fail to obtain a normal and stable baseline. In addition, the aging time should not be too long, otherwise the service life of the chromatographic column will be reduced.

Generally speaking, columns coated with polar stationary phase and thick coating have a long aging time, while columns coated with weak polar stationary phase and thin coating have a short aging time. PLOT columns have different aging methods. Please refer to the operating instructions for specific steps.

If the column is aged without a detector connected, the end of the column may have been damaged after aging. The 10-20cm section at the end of the column should be cut off first, and then the chromatographic column should be connected to the detector. Temperature limit refers to the application temperature range where the chromatographic column can be used normally. If the operating temperature is below the lower temperature limit of the chromatographic column, the separation effect and peak shape will not be ideal. But there is no harm to the chromatographic column itself.

The upper temperature limit usually has two values. The lower value is the constant temperature limit. At this temperature, the chromatographic column can be used normally, and there is no specific duration limit. The higher value is the heating limit of programmed heating. The duration of this temperature usually does not exceed ten minutes. Operation above the upper temperature limit will shorten the service life of the chromatographic column.

16 Troubleshooting of Baseline Drift

Baseline drift often occurs when programmed temperature rise is used in GC. This phenomenon is usually caused by the following reasons: loss of chromatographic column, loss of injection pad, pollution of injector or detector, and change of gas flow rate. If a highly sensitive detector is used, even a slight column loss or system pollution may bring significant baseline drift. In order to improve the reliability of qualitative and quantitative analysis, baseline drift should be reduced or eliminated as much as possible.

17 how to reduce the baseline drift caused by samples and injectors?

If there are polymer nonvolatile substances left on the chromatographic column, it is easy to cause baseline drift when the temperature is programmed, because these substances are strongly retained and move slowly in the column, and this strongly retained component can be driven out of the column through re-aging, but this method increases the possibility of oxidation of stationary liquid;

In addition, you can also clean the chromatographic column with solvent (please read the precautions for the use of chromatographic column before cleaning, so as to select the appropriate solvent);

Protective columns can also be installed to prevent problems. If the baseline drift is caused by injector pollution, it can be solved by replacing the injection pad, liner and sealing ring. At the same time, clean the syringe with solvent. After maintenance, use fused quartz tube to connect the sampler and detector, and inject an empty sample to confirm that the sampler is clean.

18 how to reduce the baseline drift caused by the detector?

The baseline drift caused by the detector is usually caused by a small amount of hydrocarbons in the compensation gas or fuel gas, which can be reduced by using a high-purity gas purifier to treat the compensation gas or fuel gas. The baseline stability of FID can be improved by using high purity gas generator; Proper detector maintenance, including regular cleaning, can reduce this drift.

19 how to reduce the baseline drift caused by column loss?

Before using a new column, aging can reduce the column loss by the following methods: aging at 20℃ higher than the experimental operating temperature or the operating temperature of the column (whichever is lower). Compared with short-term high-temperature aging, long-term low-temperature aging is beneficial to reduce column loss. If the carrier gas contains a small amount of oxygen or moisture or the gas pipeline leaks, the stationary liquid is easily oxidized at high temperature, resulting in column loss and baseline drift.

Once the stationary liquid is oxidized, it must be aged with high-purity carrier gas for several hours before the baseline becomes horizontal. This damage to the still liquid is irreparable. Therefore, if oxygen continuously passes through the chromatographic column, the baseline cannot be lowered to this level even after aging. Therefore, during the experiment, high-quality oxygen/moisture filter should be used in the gas pipeline, and high-quality electronic leak detector should be used to strictly detect the leakage.

20 no peak

1.FID detector flame goes out;

2. The gasification degree of the sampler is too low to gasify the sample;

3. The column temperature is too low to condense the sample in the chromatographic column;

4. Air leakage at the injection port;

5. The chromatographic column inlet leaks or is blocked;

6. The problem with injection needles is that they can't take samples.

The peaks of 2 1 all components are smaller or smaller.

Possible causes and suggested measures:

1. The injection needle is defective, so use a new needle;

2. Leak after injection, and judge the leakage point;

3. The shunt ratio is too large;

4. If the molecular weight of the analyte is too large, increase the temperature of the sample inlet;

5.NPD is covered by pollutants (silicon dioxide) to replace rubidium beads;

6. If 6. If the NPD temperature is too high (use or ambient temperature) and the gas is impure, replace rubidium beads: avoid high-temperature use;

7. The detector does not match the sample.

22 Qian Yanfeng

1. peak extension tongue is mostly due to the overload of chromatographic column, reducing sample volume and using large capacity column;

2. Increase the temperature of oven and INJ;

3. Increase the flow rate of carrier gas;

4. Master sampling skills;

5. The previous sample condensed in the chromatographic column and failed to be exhausted in time;

6. The sample reacts with the stationary phase carrier.

23 peak height and peak area are not repeated.

1. Sample injection is not repeated, with large deviation;

2. Peak dislocation caused by other peak type changes;

3. Interference of baseline;

4. Changes in instrument system parameter setting, standardization and normalization of parameters;

5. The performance of chromatographic column has changed.

The sensitivity and repeatability of continuous sampling are poor.

Under the condition of continuous injection, the peak area is large or small, and the determination accuracy is not high. The reason for this is the following：

1. poor injection technology;

2. The carrier gas leaks or the flow rate is unstable;

3. The detector is polluted;

4. If the chromatographic column and liner are polluted, clean the liner, and clean the chromatographic column with solvent (excellent pure methanol): replace (if necessary);

5. The syringe is leaking;

6. The sample volume exceeds the linear range of the detector, which leads to the overload of the detector.

25-peak tailing

1. If the liner and chromatographic column are contaminated or improperly installed, dead volume will occur. Inject methane. If the peak is trailing, reinstall;

2. The temperature of the sampler is too high;

3. Cut the uneven stigma with emery;

4. If the polarity index of the stationary phase does not match the sample, replace it with a matched chromatographic column;

5. There are cold wells in the sample circulation route to eliminate the low temperature zone in the route;

6. If there are chips accumulated in the liner or chromatographic column, clean and replace the liner to remove the stigma10 cm; ;

7. The sampling time is too long;

8. The split ratio is low and the split ratio is increased (at least greater than 20/1);

9. If the injection amount is too high, please reduce the injection amount or dilute the sample.

26 Reduce the resolution

1. Column is contaminated;

2. The stationary phase is destroyed (loss of chromatographic column);

3. If the sample injection fails, check for leakage;

4. Check the adaptability of temperature and check the inner container;

5. If the sample concentration is too high, dilute it, reduce the sample volume and use a high split ratio.

27 solvent peak broadening

The installation of 1. column failed;

2. Injection leakage;

3. The larger the sample volume, the higher the evaporation temperature;

4. The shunt ratio is low, and the shunt ratio is improved;

5. Low column temperature;

6. When split injection, the initial oven is too high to reduce the initial column temperature, so high boiling point solvent is used;

7. If the purging time is too long (regardless of the sample flow), define a short purging procedure.

28 baseline drift downward

1. For the newly installed chromatographic column, the baseline drifts for several minutes and continues to age;

2. The detector does not reach the balance, and the balance time of the detector is prolonged;

3. The detector or other components of the gas chromatography system will dry and clean the deposits.

29 Baseline Drift Up

1. The stationary phase of the chromatographic column was destroyed;

2. The carrier gas flow rate decreases and the carrier gas pressure is adjusted.

30 noise

1. The capillary column is inserted into the detector too deeply, so reinstall the chromatographic column;

2. Check and maintain the gas path by using baseline noise caused by ECD and TCD air leakage;

3.FID, NPD, FPD gas flow or gas selection is improper, high purity gas, adjust the flow;

4. Clean the entrance when it is polluted, replace the shelf and replace the glass fiber in the liner;

5. When the capillary column is polluted, cut off the first end of 10cm, clean the column with solvent and replace it;

6. The detector is out of order.

Several methods to improve the resolution of 3 1

1. Increasing the column length can improve the resolution;

2. Reduce the sample volume (increase the solvent volume of the solid sample);

3. Improve the injection process to prevent secondary injection;

4. Reduce the flow rate of carrier gas;

5. Reduce the temperature of chromatographic column;

6. Increase the temperature of the vaporization chamber;

7. Reduce the dead volume of the system, for example, the chromatographic column connection should be inserted in place, and the vaporization chamber should adopt a no-shunt structure without shunt;

8. To split the capillary column, choose the appropriate resolution ratio.

To sum up, we need to explore in the experiment according to the specific situation. For example, reducing the carrier gas flow rate and column temperature will widen the chromatographic peak, so the conditions should be changed according to the chromatographic peak type. The ultimate goal is to achieve good separation and fast peak time.

How to determine whether column aging is complete?

FID detector is most suitable for detecting aging baseline of chromatographic column. At the end of the heating process, the baseline will rise, and then the baseline decline will gradually stabilize. At this point, it can be considered that the aging of the chromatographic column has been completed.

When the chromatographic column is at high temperature, the life of the chromatographic column decreases sharply. If the column is still damaged after aging for more than 2 hours, cool the column to room temperature, and find out the sources of column loss such as oxygen permeation, gasket leakage, and instrument itself residue.

Column loss: Do column loss experiment after the aging of the chromatographic column, do programmed heating without sampling, and start heating from 50℃ to the highest working temperature of the chromatographic column, and keep it at the highest temperature 10min. The chromatogram is column loss diagram. Compare this picture with the blank space in the future.

If there are many peaks in the blank operation, the performance of the chromatographic column will change, which may be due to oxygen or sample residue in the carrier gas. If there is GC-MS, the typical mass-to-charge ratio m/z of low polarity chromatographic columns (such as DB/HP- 1 or 5) will be 207, 73, 28 1, 355, etc. And most of them are cyclosiloxanes.

It is generally believed that column loss will lead to noise and baseline instability. True column loss usually has a positive drift similar to noise. See if the baseline drifts upward and there is an outflow peak in the blank.

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