Maintenance Tips for Liquid Chromatography

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WiSys5000 high performance liquid chromatograph is a liquid chromatograph system with flexible configuration, convenient operation and intelligent compliance launched by Welch Materials. It has won the IF Design Award of Germany and the Red Star Design Award of China.

To get better result out of it, we must have to maintain properly. Since everyone has WiSys5000 in the laboratory, let’s talk about the maintenance.

A well-performing liquid chromatograph is like a healthy person as mentioned below:

  • Pump — heart;
  • Mobile phase — blood
  • Sampler — oral cavity
  • Chromatographic column — digestive system
  •  Detector– eyes
  • Workstation — brain
  • Sample — food

The pump acts like a heart to continuously pump the fluid phase to other parts of the system; The sampler adds the sample to the system like our mouth, and the mobile phase carries the sample into the column, just like food enters the digestive system and is digested and absorbed in the gastrointestinal tract. The detector is like our eyes, and what we eat will react in the brain accordingly.

The body needs exercise to maintain health, and liquid chromatography also needs maintenance.

Pump maintenance

High pressure infusion pump is the core of liquid chromatograph. The sealing ring of the pump is the most easily worn part. The damage of the sealing ring may cause liquid leakage or pressure fluctuation; The normal operation of check valve is very important. If it fails, it will directly affect the stability of flow rate. The high-pressure pump in normal condition is the basis of accurate analysis of liquid chromatography. The high-pressure infusion pump is composed of motor, cam group, plunger rod and pump head.

(WiSys5000 pump head assembly)

(Disassembly diagram of WiSys5000 pump head with 24 parts)

Long-term operation under high pressure will gradually wear the internal structure of the pump head, especially the use of salt-containing or unfiltered chromatographic.

The performance and use of the pump are largely related to the mobile phase. The mobile phase must be filtered and degassed before being put into the machin

All solvents must be filtered through 0.45μm (or 0.22μm) before use to remove impurity particles. When filtering with a membrane, pay special attention to distinguish the organic phase (fat-soluble) membrane and the aqueous phase (water-soluble) membrane. The organic phase filter membrane is generally used to filter organic solvents, and the flow rate is low or the filter does not move when filtering the aqueous solution. The water-phase filter membrane can only be used to filter aqueous solutions, and it is strictly prohibited to use organic solvents, otherwise the filter membrane will be dissolved. For mixed mobile phases, they can be filtered separately before mixing. If you need to filter after mixing, select the appropriate filter membrane. When choosing, you can refer to the filter membrane chemical compatibility table.

Mobile phase degassing

Common degassing methods include vacuum pumping, ultrasound, helium blowing, etc.

Ultrasonic degassing has the advantages of simple operation and low cost. 10-20 minutes of ultrasonic treatment is sufficient for degassing many organic solvents or organic solvent / water mixtures (generally, ultrasonic 20-30 minutes is required for 500 ml solution). This method does not affect the solvent composition. During ultrasonic, pay attention to avoid the contact between the solvent bottle and the bottom or wall of the ultrasonic tank to avoid the breakage of the glass bottle, and the liquid level in the container shall not be too much higher than the water surface. The off-line degassing method cannot maintain the degassing state of the solvent. After you stop degassing, the gas begins to return to the solvent immediately. Within 1-4 hours, the solvent will be saturated by the ambient gas.

The wisys5000 system is equipped with an on-line degasser as standard. It is worth noting that the on-line degasser removes small bubbles, so try to remove large bubbles with ultrasonic degassing before running the machine.

(WiSys5000 degassing box)

Generally the gas in the organic solvent is easy to remove, while the gas in the aqueous solution is more stubborn. Blowing helium in the solution is a very effective degassing method. This continuous degassing method is often used in electrochemical detection. But helium is expensive and difficult to popularize.

Use halogenated organic solvents with caution

Halogenated solvents may contain traces of acidic impurities and can react with stainless steel in THE HPLC system. Mixtures of halogenated solvents and water decompose more easily and should not be stored for long. Halogenated solvent (such as, CCl4, CHCl3, etc.) mixed with a variety of ethers (such as, ether, diisopropyl ether, tetrahydrofuran, etc.), may react to generate some products that are highly corrosive to stainless steel, the mixed flow is not used as far as possible, or fresh preparation. In addition, when halogenated solvents (e.g., CH2Cl2) are mixed with some reactive organic solvents (e.g., acetonitrile) and left standing, crystallization occurs. In short, halogenated solvents are best prepared fresh. If mixed with dry saturated alkanes, similar problems do not arise.

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