Sample injection port septum

Figure 4.14 Sample injection ports, (a) Rash-vaporizer, (b) Split injector with septum purge for capillary columns, (c) Direct -cold on-column injection onto a capillary column showing rotating valve and insertion of needle into the base of the column. (Reproduced by permission of Dr Alfred I liithig Verlag from J. High Res. i hromuiogr., Chromalogr. Contniun., 2. 35.X (1979).)...

Samples are injected onto the top of the column, through a sample injection port containing a gas-tight septum. The two common sample injection methods for capillary GC are ... 

Another important factor for reliable capillary column GC is the sample injection method. Various types of sample injection ports are available. The split/splitless sample injection port unit series is designed so that the glass insert is easily replaced and the septum is continuously purged during operation. This type of sample injection unit is quite effective for the analysis of samples containing high boiling point compounds as the major components. 

The injection port septum is an unsolved weak point in GC. It is arguably the most important but often overlooked functional part of the injector. The septum is used to seal the injection port, and withstands the inlet pressure and provides smooth and repeated access for the syringe needle to inject the sample. The syringe needle punches the septum repeatedly in a small area causing only gradual small leaks, which are detectable with an electronic leak detector already before a noticeable analyte response drop occurs. The risk of leaks increases with use, older septa take longer to re-seal than new ones (Hinshaw, 2008). 

The sample enters the GC at the injection port (Fig. 107). You use a microliter syringe to pierce the rubber septum and inject the sample onto the column. Don t stab yourself or anyone else with the needle. Remember, this is not dart night at the pub. Don t throw the syringe at the septum. There is a way to do this. 

Now quickly and smoothly push on the plunger to inject the sample, and pull the syringe needle out of the septum and injection port. 

This is the equivalent of the injection port for the GC technique. With GC you could inject through a rubber septum directly onto the column. With HPLC it s very difficult to inject against a liquid stream moving at possibly 1000 psig. That s why they invented injection port valves for HPLC you put your sample into an injection loop on the valve that is not in the liquid stream, then turn the valve, and voila., your sample is in the stream, headed for the column. 

Fig. 5.18. Reservior inlet of a JEOL JMS-700 sector instrument with the septum injection port opened. The operation valve switches between evacuation, isolation and admission of the sample a needle valve allows regulation of the sample flow. The GC transfer line crosses in the upper background from the GC (left) to the ion source housing (upper right).

Injection generally occurs through a resealable rubber septum. The injector port is held at 150-250° depending on the volatility of the sample and direct injection of 0.1-10 /A of sample is made onto the head of the column. The amount of sample injected onto a packed column is ca 1-2 pg per component. Injection into packed... 

Here is a student procedure to measure nicotine in urine. A 1.00-mL sample of biological fluid was placed in a 12-mL vial containing 0.7 g Na2CO , powder. After 5.00 pig of the internal standard 5-aminoquinoline were injected, the vial was capped with a Teflon-coated silicone rubber septum. The vial was heated to 80°C for 20 min and then a solid-phase microextraction needle was passed through the septum and left in the headspace for 5.00 min. The fiber was retracted and inserted into a gas chromatograph. Volatile substances were desorbed from the fiber at 250°C for 9.5 min in the injection port while the column was at 60°C. The column temperature was then raised to 260°C at 25°C/min and eluate was monitored by electron ionization mass spectrometry with selected ion monitoring at m/z 84 for nicotine and m/z 144 for internal standard. Calibration data from replicate... 

Injection port. Closure column on one side and a septum inlet on the other through which the sample is introduced into system. 

The essential components of a gas chromatography system are shown in Figure 3.4. The mobile phase (called the carrier gas) is inert, usually helium, nitrogen, or argon. The gas is directed past an injection port, the entry point of the sample. The sample, dissolved in a solvent, is injected with a syringe through a rubber septum into the injection port. The column, injection port, and detector are in individual ovens maintained at elevated temperatures so that the sample components remain vaporized throughout their residence time in the system. 

New accessories are continually made available. This unit discusses the basics necessary to conduct SPME analysis for flavor analysis. An automated sampling and injection system is available from Varian. Supelco offers a manual sampling stand setup. Injection liners are available that reduce the injection port volume to presumably produce sharper peaks. Predrilled septa for the GC are available to reduce septum coring. 

A gas chromatograph is an apparatus consisting of an injection port connected to a column that has a detector at its outlet end. The column is contained in an oven that is electrically heated, either isothermally or at a programmed rate. A stream of inert carrier gas, usually helium, is introduced into the injection port and flows through the column and detector. The injection port is a heated region that is sealed from the outside environment by a silicone rubber septum through which the sample is injected using a hypodermic... 

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