Syringes are of great importance in the operation of GC systems, since the sample is poured in through them from the sample bottle into the inlet. When using syringes, different sources of error can falsify the result. The reason for this is primarily the large selection of inlets from various manufacturers as well as the variety of autosamplers. The following table helps to counteract this problem by opposing possible needle shapes and their corresponding applications.
Needle tip
Application
Conical tip (Cone)
Most versatile needle when using autosamplers or inlet septa
Minimizes the punching-out of septum particles when used with GC autosamplers
Beveled tip (Bevel)
Standard needle shape for universal fluid transfer
Ideal for easily pricking the septum during GC analysis with manual injection
Reduced septic attrition
Rounded tip with side hole (Side Hole)
The liquid is sucked in and discharged through the side hole
Often used in headspace applications or for large injection volumes
LC tip (LC)
The 90°C bevel prevents damage to the rotor seal and the stator in the injection valves
Can be used with injectors without inlet-septa like MicroSeal
Also suitable for pipetting liquids
Dual gauge tip (Dual Gauge)
Smaller OD (0.47mm) in the front area (20mm) allows on-column injection
Higher OD (0.63mm) in the back enables increased stability in autosampler injection
Connection of the needle tip
In addition to the selection of a suitable needle tip for the respective application, the connection of the needle to the injection body can also be varied. A distinction is made between fixed needles, interchangeable needles and injection needles with a luer connection. The characteristics of the respective needle types can be found in the table below.
Tip connection
Application
Solid needle
Easy to handly
Economical
Disposable needle
A bent needle can be easily replaced, which saves costs
Allows to use a needle with a different outer diameter (OD) or different length/tip
Luer Connection
Luer-Lock connection for secure connection of luer-lock needles, fittings, syringe filters and pump flushing adapters
Luer-Tip connection for luer-lock needles and fittings
Selection guide for syringe plungers
The materials for the production of syringe plungers are divided into metals (stainless steel, titanium/nickel alloys, etc.) and synthetics (PP, PTFE, etc.). Apart from the material, different types of plungers are distinguished as well. The most frequently applied plunger types as well as their application areas are summarized in the following table.
Plunger type
Application
Standard plunger (metal)
Stainless steel plungers are individually ingrained on the glass body
Plungers are not replaceable
Industry standard
Gastight plunger (PTFE tipped)
Plunger with PTFE (Teflon®) tip
Suitable for liquids and gases
Suitable for gas or headspace applications
Plungers are replaceable
Plunger-in-needle (micro volume)
Plunger reaches the tip of the needle
Sample is only inside the needle (no contact with the glass)
Ideal for very small sample quantities
Plunger Protection
Protective sleeve of upper flange helps to prevent the plunger from bending
Guided Plunger
Extended glass body protects the plunger during injection
Suitable for students and rough operating conditions
