The hottest little knowledge about liquid phase ma

2022-09-19
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Some little knowledge about liquid phase maintenance

first, mixed solvents must be filtered before mixing. In case of filtration after mixing, only organic solvents can be used, and water systems must not be used. Because the material of the water system is cellulose, the organic phase will more or less dissolve a little cellulose, causing pollution

II. It is best to dissolve the standard sample or sample with mobile phase (excluding special cases), which can avoid a lot of trouble

III. The purpose of heating the chromatographic column and increasing the temperature is partly to increase the solubility of solute, but more importantly, to reduce the viscosity of solvent, so as to improve the peak shape and resolution. Note: the rise of temperature will reduce the retention time, which also has an impact on the resolution. The change of temperature has a great impact on the band width. Although the height of the tray is affected by temperature, it also depends on the chromatographic type used, and the rise of temperature always reduces the height of the tray

IV. generally, the column temperature of C18 column should not exceed 40 ℃, otherwise the bonding phase is easy to fall off

v. for the use of the sampler, in addition to washing it with water every time, after a period of time, it is best to absorb it repeatedly with methanol or acetonitrile and clean it

<1. Stay away from large or heavy equipment p> VI. when analyzing with HPLC, the retention time sometimes drifts and sometimes changes rapidly. Why? How to solve it

answer: about the drift problem:

1. The temperature control is not good. The solution is to use a constant temperature device to keep the column temperature constant

2. The production level of mobile phase polylysine has changed compared with the current internationally advanced CHISSO company in Japan. The solution is to prevent the evaporation and reaction of the mobile phase

3. The column is not well balanced. It is necessary to carry out a longer period of balanced stabilizer fatigue testing machine on the column About the problem of rapid change

1. If the flow rate changes, the solution is to reset the flow rate to keep it stable

2. There are bubbles in the pump, which can be driven out by exhaust and other operations

3. The mobile phase is inappropriate. The solution is to change the mobile phase or make the mobile phase mix properly in the control room.

VIII. What is the reason for the tailing or double peaks in the peak of liquid chromatography

1. If the sieve plate is blocked or the column fails, the solution is to backwash the column, replace the sieve plate or replace the column

2. There are interference peaks, and the solution is to use a longer column, change the mobile phase or replace the column with good selectivity.

IX. what is the main reason for non-linear shunting in capillary chromatography shunting injection

1. The temperature of the sampler is too low, and the sample is not completely vaporized, resulting in graded diversion

2. If the temperature of the injector is too high, some components may undergo thermal decomposition, and some samples may undergo catalytic decomposition, or the samples may be partially adsorbed on the inner surface of the injector

3. The samples are not mixed evenly or insufficiently before the diversion point

4. There is air leakage in the injection pad and column joint of the system

X. why is the column pressure unstable when doing HPLC analysis? How to solve it

answer: the reasons may be:

1. There is air in the pump. The solution is to remove the air in the pump and degass the solvent

2. If the proportional valve fails, replace it

3. If the pump gasket is damaged, replace the gasket

4. For the bubbles in the solvent, the solution is to degass the solvent, and change the degassing method if necessary

5. System leak detection, find out the leak point, and then seal it

6, gradient elution, at this time, the pressure fluctuation is normal

Xi. How to prevent tar like pollutants from entering the capillary column when making PGs/MS analysis cross hole test block (SDH)

answer: when polymers, especially some polymers containing nitrogen, sulfur and halogen, are cracked, tar like substances are often produced. In order to prevent this tar like substance from entering the capillary column and causing pollution and reducing the performance of the column, a protective pre column can be used, that is, a filling pre column is connected between the cracker and the capillary column, and the tar like substance is retained in the pre column by controlling the pre column temperature. The pre injection can be placed in the GC gasification room, which is easy to control the temperature and reduce the dead volume of the system. Of course, the pre column filler needs to be replaced frequently

12. I recently replaced another brand of ODS column. Although the separation is still OK, the retention time cannot be reproduced. Why

answer: This is because the analyte may have the ability to form hydrogen bonds. Although the manufacturing technology of fillers has been greatly improved in the past few years, the concentration of silanol groups on the surface of ODS fillers from different manufacturers is different. It is these silanol groups that may interact with the sample. Therefore, the relative retention time of each component in the same analyte on ODS columns of different brands may be different. Adding a small amount of competitors, such as triethylamine (tea), to the mobile phase will saturate the bonding ability of silanol group, so as to ensure good reproducibility of the relative retention time on different brand columns

XIII. How long is the service life of high-temperature capillary column

answer: in addition to the performance of the column itself, the service life of the capillary column depends to a large extent on the use conditions, such as the use temperature, sample state, sample injection volume, etc. if the sample is clean within the service temperature range, and the chromatographic column is not polluted, the service life of the column is generally between 2-3 years

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