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LC/MS daily maintenance and common failures

2021-03-24
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1. Clean the ion source

Cleaning the ion source is the basic operation of the daily maintenance of LC/MS. Usually, when common problems in ion current chromatograms are encountered, such as peak splitting, unstable baseline, impurity peaks, etc., the first consideration is to clean the ion source. Generally speaking, the frequency of ion source cleaning is at least once a week. The basic steps for cleaning the ion source are as follows:

Step 1: Put on gloves, carefully remove the ion source and various parts according to the instructions, place them on a clean cloth, pay attention to static electricity, and wipe with a dust-free paper dipped in solvent (methanol, isopropanol or acetone);

Step 2: Put the dismantled parts in a large beaker, and sonicate them with methanol, isopropanol or acetone for 30-60 minutes (non-metallic parts cannot be sonicated with acetone). The ultrasonic time can be determined according to the degree of contamination;

Step 3: If the pollution is serious, after performing operation 2, dry it at low temperature or dry it with cold air, and polish the dirt and oxides on the surface of the part with sandpaper. Be careful not to wear parts excessively;

Step 4: Repeat 2 steps of ultrasonic cleaning;

Step 5: Dry at low temperature or dry with cold air, and put back the parts as they are;

*You can take a photo in one step during the process to avoid omissions during installation.

Step 6: Tuning and calibration.

*In the case of personal maintenance of the LC/MS, it is generally recommended to only disassemble and assemble the ion source part. For the disassembly and assembly of Q components, ion optical system and other components, it is recommended to consult the official after-sales service of the mass spectrometer manufacturer.

2. Daily maintenance of mechanical pumps

1. Mechanical pump cleaning

Mechanical pump cleaning is usually achieved through exhaust. When the mechanical pump is working, as the working time increases, gas will accumulate in the pump, so it needs to be discharged regularly.

The exhaust frequencies under ESI and APCI ion sources are as follows:

2. Mechanical pump oil change

The frequency of mechanical pump oil change is 4-6 months and needs to be changed once. Be sure to confirm with the mechanical pump manufacturer whether the replacement pump oil model is suitable for the pump.

3. No ion current appears in the sample

▪ Is the PG value too low? The PG value is generally 100-200. If the PG value is too low, it will seriously affect the detection sensitivity. If the PG value is lower than 70, it is recommended to replace the DL tube;

▪ If the PG value is normal, the capillary of the ion source may be blocked, and it can be flushed with acetonitrile: water (90:10);

▪ If the above flushing is invalid, replace the capillary;

▪ If the ion current intensity is too low, the flow rate, column temperature, or ion source temperature can be increased.

4. The peak shape becomes worse after the instrument is cleaned

▪ Is the connection well connected? Failure to connect will cause the dead volume to increase;

▪ If it is not the problem of the instrument itself, it may be a loss of data acquisition. You can increase the scanning speed appropriately or adjust the detection voltage.

5. The reproducibility of the detector is worse than before

▪ Check the stability of the method itself, or whether the method parameter settings are correct;

▪Check if there is any problem with the LC part, and troubleshoot the pump, sampler, pipeline, chromatographic column, etc.;

▪ If the LC part is normal, check whether the spray chamber, spray needle, and corona needle are contaminated and need to be cleaned;

▪Clean the ion source parts;

▪Exhaust the mechanical pump and replace the pump oil.

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