6. Injector

Injector`s role is to introduce a sample into the high-pressure system with high accuracy. We use in our HPLCs a leading Rheodyne 7725i manual injector connected with a genuine Rheodyne 20uL sample loop. The role of the sample loop is to standardize injected sample volume to ensure the cannabinoids are always measured in the same volume of sample. Even though the sample loops are standardized, according to the manufacturer, a 20 uL sample loop can vary in its volume by up to 10% due to the very small diameter of the internal channel. Therefore, before our HPLCs are shipped, they are tested for accuracy and optimized for these volume effects.

Below is a diagram of the Rheodyne 7725i injector. Of particular interest may be the needle port and needle port tube to understand how the provided 100uL Hamilton syringe enters the injector. The syringe needle must be pushed all the way through the needle seal in order to introduce the sample. The needle seal is very easy to puncture and you should feel almost no resistance.

 

Caution!

It is important to assure that there are no bubbles in the sample inside the syringe, as well as to assure the sample does not leak back around the syringe – this would be the case if the needle didn`t penetrate the needle seal.

It is also important that a minimum of 3 volumes of the sample loop are injected to make sure the sample loop is completely filled with sample. In our case with a 20uL sample loop, you should be injecting at least 60uL of the sample. 20 uLs stay inside the loop and the rest goes to the waste vial attached to the side of the HPLC.  

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Below is an explanation of how the injector works.

1. In the Load position, the flow of the mobile phase bypasses the sample loop and goes directly into the column. In this position, you also fill the sample loop, which is separate from the pressurized system and the mobile phase. 
2. When switching the injector lever into the Inject position, the switching valve allows the mobile phase to go through the sample loop to carry the sample into the column for separation.

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Below is a blown-up version of the Rheodyne 7725i manual injector for better understanding of its design.

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