The younger brother used liquid chromatography for the first time, and the baseline fluctuated very

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....

Your question is detailed, but you still don't say: do your columns have incubators?

First of all, I suspect that the temperature of the column fluctuates. (Even small temperature changes can cause fluctuations in the baseline.) This typically affects differential index detectors, conductivity detectors, lower sensitivity UV detectors, or other optoelectronic detectors.

Solution: Control the temperature of the column and mobile phase.

Secondly, I suspect it's the mobile phase, which has bubbles. Baseline fluctuations due to changes in mobile phase conditions are greater than fluctuations due to temperature. Solution: Use HPLC-grade solvent mobile phase to degas before use, and degas if possible.

If your pump pressure fluctuates, check the system for leaks, and if it doesn't, you're basically sure there are bubbles.

Other Cause Workarounds.

1. There is air in the mobile phase, detector or pump 1. Degassing of the mobile phase. Flush the system to remove air from the detector or pump.

2. Leakage diagram 2. Check whether the pipeline joint is loose, whether the pump is leaking, whether there is salt precipitation and abnormal noise. Replace the pump seal if necessary.

3. Incomplete mixing of mobile phase 3. Shake by hand to mix evenly or use a low-viscosity solvent.

4. Influence of temperature (column temperature is too high, detector is not heated) 4. Reduce the difference or add a heat exchanger.

5. There are other electronic devices on the same line 5. Disconnect the LC, detector and recorder to check whether the interference is coming from the outside and correct it.

6. Pump vibration 6. Add pulse damper to the system.

The reason for the increase in the baseline may be detector contamination or other ** contamination, or flame anomalies caused by an inappropriate hydrogen-to-air ratio. If the baseline drifts, it is estimated that the damage resistance meter is due to the fact that the column has not aged well or other reasons.

The main reasons for the high noise at the baseline:

First, the column is not aging well.

The second is that the detector is dirty.

3. Check for electromagnetic interference.

In the case of low temperature, the baseline is very flat, and after the temperature rises, the baseline will rise and regret the leakage. The baseline is arc-shaped and upward, which may be due to the aging of the column, or it may be that the temperature is rising too fast.

Column fixed line loss: whether the column box temperature exceeds the maximum tolerance temperature of the column, or the sample contains a large number of strong oxidizing, acidic or alkaline substances, or even a large amount of gaseous water into the water-resistant column, etc., will cause the loss of the stationary phase of the column, and the lost silica gel will show a signal on the detector and form fluctuations.

You have to find the cause before you can solve it.

In general, the causes of baseline fluctuation and baseline drift are as follows:

1. Gas pollution: including the oil pollution of the air pump into the gas pipeline, the filter (silica gel) of the air pump is too wet or polluted, and the gas cylinder gas is impure.

2. Unstable flow: due to leakage of gas pump or cylinder, injection septum, unscrewed inlet, poor sealing of the column sealing port, failure of the gas flow control system of the chromatograph, etc.

3. Chromatographic system pollution: including injection port contamination (including insufficient injection septum purge gas, liner pollution, column head pollution), chromatographic column contamination (try aging), detector contamination (after the detector and nozzle are cooled down, after disassembling the bubble methanol ultrasonic, the purified water is ultrasonic for half an hour).

4. Loss of the fixed line of the chromatographic column: whether the temperature of the column box exceeds the maximum tolerance temperature of the column, or the sample contains a large number of strong oxidizing, acidic or alkaline substances, or even a large amount of gaseous water entering the column that is not resistant to water, etc., will cause the loss of the stationary phase of the column, and the lost silica gel will show a signal on the detector and form a fluctuation.

1. Remove the detector end column, seal the detector end, and empty the sample to see the baseline.

If it's flat, it may be that the liner is contaminated or the column is not properly fitted.

If there is no change from baseline, the detector is contaminated and needs to be cleaned or burned at high temperature (FID).

2. To determine whether it is not a leak of gas, detectors and columns, it is necessary to see whether the purity of the gas is not high. I don't know if the carrier gas used is generator or cylinder gas, and if the air is used, it has not been drained for a long time.

There are many reasons for the instability of the baseline, it may be that there is a lot of slag in the column, and it is good to age it. It is possible that the detector is contaminated, and the detector is burned at high temperatures. It may be that the temperature in the column box is not stable (this may not be large), and the temperature change may cause the column to be lost, so it is recommended to change the machine.

There may be a lot of others, send me a private message.

The main factors that cause baseline drift are:

1. The equilibrium time is not long enough;

2. Problems of the detector (such as the unstable energy of the light source of the ultraviolet detector, etc.);

3. Whether there is leakage in the flow path;

4. Keep the temperature of the disturbance system constant;

5. When the wavelength is at the edge, the reagent used in the mobile phase is unqualified, purified water is used for water, and pure reagent for chromatography is used for reagent;

6. Consider the anti-static system of the system.

The main factors that cause baseline drift are:

1. The equilibrium time is not long enough;

2. Detector questions (such as the unstable energy of the light source of the ultraviolet detector);

3. Whether there is leakage in the flow path;

4. Keep the system temperature constant;

5. When the wavelength is at the edge, the reagent used in the mobile phase is unqualified, purified water is used for water, and pure reagent for chromatography is used for reagent;

6. Consider the anti-static system of the system.

It may be that the water in the mobile phase is not of good quality, try to change it to other ultrapure water.