Improve reproducibility of syringe injections for GC analysis

Reliable quantitative analysis requires high degree of reproducibility of sample volume injections. Auto samplers provide the desired reproducibility of injection volumes and in addition automate the analysis sequence thereby saving your precious time. However, even to this day, syringe manual injections are the most widely used sample injection technique.

Syringe injection requires development of right skill through practice as this alone can help achieve high degree of precision of sample injection volumes. It is possible for an individual to achieve less than 1% RSD precision in manual injections provided required expertise is gained and required precautions are taken before making injection every time.

Useful tips are provided below for improvement of the reproducibility of injection volumes:

• Syringe capacity should be compatible with the required injection volume. For example, if sample injection volume is 2μl a syringe over 10μl capacity should not be used. In such a situation, for example, if syringe with 50μl capacity is used the error in repeat injections is bound to be large.
• Syringe should not be used even if it has a hair line crack or any visible residues inside the barrel as these can obstruct free movement of plunger and contribute to errors. Similarly if the needle is bent or develops kinks it should be replaced or in case of fixed needle syringe it should be replaced.
• Before beginning the injection if the sample is removed from a refrigerator or an oven it should be allowed sufficient time to attain laboratory temperature.
• The barrel and needle should be thoroughly cleaned with a suitable solvent followed by water and acetone before final flushing with the sample solution.
• Hold the syringe by its flange and plunger button so as to avoid any deviation of barrel temperature through body heat.

Precautions while making injections

• Remove parallax errors in reading the volume by holding the syringe in line with your eye level and adjusting the volume reading to the barrel marking.
• Plunger should be moved in a single rapid and firm push. Allow the content to vaporize in the injector block for 3-4 seconds and remove the needle again in a single swift move. When making repeat injections follow the same timing sequence.

Perfection can be achieved only through practice and in order to assist you please see the video below: