The difference between liquid chromatography quaternary high pressure, quaternary low pressure and binary high pressure pump

When we use second-hand high-performance liquid chromatographs for analysis, we usually come into contact with multi-element pumps, such as quaternary high-pressure pumps, quaternary low-pressure pumps and binary high-pressure pumps
.

So can you tell the difference between them? Today I will tell you how to distinguish the difference between liquid chromatography quaternary high pressure, quaternary low pressure and binary high pressure pump
.

The so-called multi-element pump refers to the number of flow paths that can be controlled at the same time
.

The multi-component pump is further divided into high-pressure mixing and low-pressure mixing
.

High-pressure mixing is also called post-pump mixing.
The multi-element high-pressure pump is composed of multiple pumps, and there are several pumps if there are several yuan
.

Low-pressure mixing, also known as pre-pump mixing, is actually a pump.
A few yuan is to install several solenoid valves, such as the Agilent 1200 quaternary low-pressure gradient pump
.

As shown in the figure, quaternary high pressure gradient: equipped with four independently working pumps + in-line mixer
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The working mode is that four pumps are connected in parallel, and there can be four mobile phases at the same time, which enter according to the preset ratio, and respectively send liquid to the mixing chamber after the pump, and mix under high pressure.
The mixing ratio is more accurate, and it is not easy to generate air bubbles.
, without repeated cleaning for changing the mobile phase, which not only saves the solvent, but also improves the work efficiency
.

There is no need to increase the vacuum degasser, which reduces the dead volume of mixing (when mixing before the pump, the volume of the mixing tube, the pump head, etc.
, the dead volume in the degasser)
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At the same time, gradient elution can be used: when the components of the sample to be tested are complex, and the components in the sample cannot be completely separated by a fixed mobile phase ratio, gradient elution is required, and the instrument automatically changes the flow during the same analysis process.
Matching ratio, the substances in the sample that cannot be separated in the early stage are eluted, and the effect of separate peaks can be obtained in the same spectrum
.

It helps to improve the accuracy of analysis and avoid the omission or wrong quantification of important substances
.

  However, the quaternary low pressure gradient: the configuration is more complicated: it is composed of a single pump + low pressure mixing proportional valve (solenoid valve) + online degasser + mixer, and its working mode is also very different from the high pressure gradient pump: it can have both The four mobile phases enter the flow path and are mixed according to the preset ratio.
It relies on the switching of the solenoid valve to make the pump deliver different mobile phases in sections.
Because of the mixing under normal pressure, the bubbles are easily precipitated from the solvent, which is relatively easy.
Generates air bubbles, so it should be equipped with an online degasser to eliminate the effect of air bubbles
.

Gradient elution can be done.
After setting on the instrument, in the same sample analysis project, after a period of time, the mobile phase ratio can be changed according to the user's setting to separate the components in the sample
.

  Binary High Pressure Gradient: Configuration: Dual Pump + In-Line Mixer
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How it works: Two pumps are connected in parallel, and two mobile phases can be simultaneously entered according to the preset ratio, and then mixed under high pressure.
The mixing ratio is more accurate, and it is not easy to generate air bubbles, and there is no need to repeatedly clean in order to change the mobile phase.
, improve work efficiency
.

At the same time, gradient elution can be used.
When the components of the sample to be tested are complex and the components in the sample cannot be completely separated with a fixed mobile phase ratio, gradient elution is required.
During the same analysis process, the instrument automatically changes the mobile phase matching.
The effect of elution is to obtain separate peaks in the same spectrum by eluting substances in the sample that could not be separated before
.

It helps to improve the accuracy of analysis and avoid missing detection of important substances
.

The comparison of quaternary high pressure, quaternary low pressure and binary high pressure pump has higher flow control accuracy of binary high pressure gradient.
After the mixing chamber is pumped, the mixing efficiency under high pressure is also much higher, and the gradient composition is accurate; the quaternary low pressure gradient system adopts a single pump Add a gradient proportional valve to achieve this, because the proportional valve is before the pump, and the solvents in each flow path are mixed together in the proportional valve, so it is mixed before the pump and at low pressure
.

Generally, for routine analysis, the quaternary low pressure gradient can also meet the needs; if the analysis sample is complex, requires high reproducibility, or needs to perform gradient analysis at low flow rate, it is better to choose a high pressure gradient
.

Here you can take a look first: Comparison of liquid chromatography binary pump and quaternary pump In terms of performance, quaternary high pressure is definitely better than quaternary low pressure
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The mixing ratio of quaternary high pressure is obtained by changing the flow rate of the pump.
Usually, the flow rate of the pump is very accurate, so the mixing accuracy is also very high
.

The mixing ratio of the quaternary low pressure gradient is controlled by controlling the opening and closing time of the solenoid valves of different flow paths.
In theory, the mixing ratio is also accurate, but in fact, there will be a delay in the opening and closing of the solenoid valve, no matter how much it acts.
Hurry up, it still takes some time
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For example, A road and B road are mixed 50% each, in a unit time, the solenoid valve of A road and B road are each open for 50% of the time.
At this time, the problem is not big, and the delay effect of the solenoid valve can be compensated as much as possible by adjusting the compensation coefficient.

.

But if the case is at the end, A road is 99%, B road is 1%, in this case, the solenoid valve of A road is open 99% of the time per unit time, B road only accounts for 1%, the time is very short, At this time, the delay of the B-way solenoid valve has a great influence, and the delay time may even be longer than the working time
.

This is the case of two pipelines.
If four pipelines work at the same time, the result can be imagined
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High pressure gradients do not have this problem
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In addition, the low pressure should also be cleaned, especially when buffer salt is used, the solenoid valve liquid feeding pipeline is easily blocked
.