Injection port liners

The liner choice need to fit the analytical method setup if split or splitless injections are planned, or the basic injection techniques hot needle with thermo spray or the cold needle with hquid band formation are preferred. Different liner geometries are available to support the individual injection and vaporization process. There is not a single liner that serves all injection modes. So, a few basic rules help identifying the hner of choice for the chosen injection technique. 

---

Programmed-temperature vaporizers are flexible sample-introduction devices offering a variety of modes of operation such as spHt/sphtless, cool-sample introduction, and solvent elimination. Usually the sample is introduced onto a cool injection port liner so that no sample discrimination occurs as in hot injections. After injection, the temperature is increased to vaporize the sample. 

Clean or change injection port liners frequently because nonvolatile materials in extracts from body fluids can accumulate in the injection port and/or head of the GC column and cause separation problems. 

The purge activation time (or the sample transfer time) depends on the sample solvent and carrier gas flow relative to the volume of the injection port liner and the boiling points of the sample components. For most applications, a purge activation time of 50-120 sec is better than 25-50 sec. Early activation results in the loss of sample, while late activation results in peak tailing. A more accurate method of determining purge activation time is to divide the volume of the injector liner by the flow rate (F) of the carrier gas and multiply this value by 1.5 or 2.0. (Do not use a packed liner.)... 

Ranid instrumental techniques were used to elucidate off-flavor problems in raw and processed rice products, raw and roasted peanuts, and corn-soy food blends. Less than a gram of the solid material was secured in a standard or special injection port liner of the gas chromatograph. Then, the volatiles from the sample were steam distilled in situ and identified by combined gas chromatography/mass spectrometry. 

Different injection port liners are designed for split, splitless, and on-column injection and for use with solid-phase microextraction. 

Sometimes thermal decomposition and reaction can be shown by variation of injection port temperature, and possibly column temperature. The only real solution is to operate at as low a temperature as possible and perhaps use "on-column injection. Low-loaded columns sometimes help. Use of glass columns and glass injection port liners often relieve the problem of unwanted thermal degradation and may help in some cases. However, in all cases the precision and accuracy of the quantitative analysis will be affected until a solution is found or until a decision is made to "live with it."... 

Specially designed direct flash injection port liners, called Uniliners, made by Restek Corporation (Port Matilda, PA) can be used for both flash vaporization and wide-bore on-column injections. In the direct flash mode, an injection syringe with up to a 22-gauge needle can be used to seal the vaporization chamber while a 530-um ID column butts to the bottom of the... 

The heat from the injection port liner combined with the GC column flow causes the volatiles contained in the sample to be thermally desorbed directly onto the GC column. This reduces or eliminates interfering components of the sample matrix. An example of this additive specific extraction is shown in Figure 2-2. This technique also can be used to obtain the purity and identity of neat additive standards which are not readily soluble. By altering the injection port temperature, an analyst can extract various types of additives without thermally degrading the sample matrix. There are no limitations on the additive/polymer combinations which can be analyzed. Another advantage of this technique is that it requires only a few milligrams of sample typically 2-5 milligrams per analysis. 

The additive standards for the MS library were dissolved in a suitable solvent and a sample was injected into the GC/MS system, or a sample was transferred into an injection port liner as is done for real world samples. Additive standards were mn at temperature program rates of 10 °C or 15 °C due to the lack of the necessity for multi-component separation. The actual temperature program used is listed on each Total Ion Chromatogram (TIC). 

The injection port liner is used to minimize dead volume when a sample is injected. Several are shown in Figure 20-27. Those shown are 0.8 mm i.d. with an internal volume of 12 pL. The solvent expansion type prevents flashback when injecting large volumes of dilute samples. 

Long-term reproducibility is affected by eveutual deterioration of resistive filaments or sample wires. All components exposed to sample during pyrolysis (GC injection port liners and quartz sample tubes if used) often require acid cleaning, solvent washing, and oven drying. Active pyrolyzer elements (coils and ribbons in filament pyrolyzers) can be heated without sample to ranove contamination (lOOO C for 2 sec is usually adequate). Curie-poiut wires are inexpensive enough to be discarded after use. 

Either split, splitless, or on-column injections can be used in GCMS. Split injections are usually avoided in cases where trace-level components are being analyzed. Splitless or on-column injections are preferred for trace component analysis. Often splitless injections (septum purgeoff) are made with split injection port liners that are packed with a small amount of adsorbent to trap nonvolatile, polar materials that could contaminate the column and/or the mass spectrometer. For the same reasons, a retention gap is recommended for on-column injections, as the initial column section can be replaced with little effect on the chromatogram. When using a retention gap, however, care must be taken to ensure leaktight connections since a small air leak can have greater consequences for the mass spectrometer than for other detectors. 

Gas-liquid chromatography has been the focus of much discussion of GC. It is often the case that development of hardware for GC focuses on removing interactions with solid surfaces because the surfaces are considered to be sources of undesirable adsorption sites that contribute to peak asynunetry, especially those in the injection port liner or the chromatographic colunm. However, interactions between a solid substrate and a gas (mobile) phase are also informative. When a solid without a liquid substrate is solely and deliberately used inside the chromatographic column, the techniqne is called gas-solid chromatography (GSC). 

Thermal Desorption (direct) Direct thermal desorption from sample located within the injection port liner (see discussion below). (15)... 

Figure 2.54 Injection port liner activity dependence from the injection number (Klee, 2013)...

Figure 2.55 Injection port liner types for split and splitless injections.

For the pyrolysis of PVC, a ribbon probe was used. On-line hydrogenation of the pyrolysis products was accomplished using hydrogen as the carrier gas with 1% palladium on Chromasorb-P catalyst inserted in the injection port liner. Maximum... 

---