As an efficient separation and purification method, preparative liquid phase is widely used in the fields of production and R&D. Common injection methods can be divided into Manual Injection, Auto Sampling and Pump Sampling by Pump. But with so many injection methods, how should I choose? Today, I will introduce the respective characteristics of these injection methods.

1.Manual injection

This is a relatively economical and simple injection method in preparative liquid phase, but requires manual operation, which is time-consuming and labor-intensive.

Sampling principle: Generally, a certain amount of sample solution is drawn through a syringe, and then injected into the quantitative loop on the six-way valve. The quantitative loop is connected to the pump and the preparation column by switching the rotor by manually pulling the valve, and the mobile phase transports the sample to the preparation column. inject.

Injection process： Before injection, you need to manually wash the needle and remove the bubbles in the syringe. After injection, you need to clean the injection port. The specific injection volume is determined by the quantitative loop and the amount of liquid sucked.

Features:

● Simple to use and easy to learn;

● The injection volume can be changed by changing the quantitative loop;

● Humans are required to perform sample injection operations, which cannot be automated;

● It is suitable for small-scale preparation, and the maximum injection volume is generally several tens of milliliters.

2.Automatic injection

There are many types of preparative autosamplers on the market, but the core is basically a six-port valve, which is an upgraded version of manual injection.

Sampling principle: The suction device of the automatic sampler is controlled by the software to suck a certain amount of sample solution from the sampling bottle, and then realize the sampling through the six-way valve.

Features:

● It can realize automatic and continuous injection of multiple samples, greatly reducing manual operation;

● The injection is more accurate and stable, and automatic cleaning can be performed to reduce residual pollution;

● It is suitable for small-scale preparation, and the maximum injection volume is generally several tens of milliliters.

3.Pump injection

For large-volume injection in large-scale preparation, if a six-port valve type injector is used, peak tailing and peak broadening will increase due to the excessively large volume of the loop. Therefore, pump injection is generally used for large-volume injection. kind of way.

Sampling principle: The sample solution is sucked at a certain speed by the sampling pump and injected directly into the preparation column.

Sampling process: equilibrate the preparative column before injecting the sample, stop the solvent pump after the equilibration is completed, start the injection pump to extract the sample and transport it to the preparative column, and then start the solvent pump to start the separation of the sample after the injection is completed.

Features

● The injection volume is large, and different injection speeds can be set flexibly;

● The length of the system pipeline will not be increased due to the increase of the injection volume;

● Suitable for large-scale preparation, the injection volume is from milliliter level to upgrade.

Preparative LC Sampler Application Checklist

Injection method	Application scenarios	Injection quantity and volume
Manual injection	Small scale preparation	Single/microliter to milliliter
Automatic injection	Small scale preparation	Multiples/microliter to milliliter
Pump injection	Large scale preparation	Single/ml to liter