Inlet liner

The 0-rings, septums, and glass wool were conditioned at 200 C for 16 hr liefore use.) Inlet liners, 10 X 84 mm, were cut from borosilicate glass tubing. The experimental food blend samples were obtained from the Northern Regional Research Center, Peoria, Ill, The rice samples cane from the USDA rice experiment station in Beaumont, Tex., and the peanuts from the USDA Coastal Plain Experiment Station in Tifton, Ga. 

Physical condition of the fiber coating (cracks, contamination) GC inlet liner type and volume... 

For semi volatile compounds, inlet optimization is very simple. Classical splitless inlet conditions, followed by an initial column temperature cool enough to refocus the analyte peaks following the desorption, work well. Thus, a typical condition would be a temperature of about 250° C, a head pressure sufficient to maintain optimum GC column flow and an initial column temperature at least 100°C below the normal boiling point of the analyte. For semivolatile analytes, a classical splitless inlet liner can be used, as the cool column will refocus these peaks. The desorption time in the inlet must be determined by experimentation, but typically, runs between 1 and 5 minutes. 

Figure 4.12. Effect of inlet liner diameter on SPME injection of hydrocarbons, (a) 4-mm-diameter liner (b) 2-mm-diameter liner (c) 0.75-mm-diameter liner. Analytes 1, octane 2, decane 3, undecane 4, tridecane 5, tetradecane 6, pentadecane. [Reprinted with permission from Ref. 44 (Fig. 3). Copyright Advanstar Communications.]...

Both high resolution and good quantitation result from cold on-column injections. A liquid sample is injected into either a cold inlet liner or a cold column. The cold injector is rapidly heated and the sample vaporized and carried through the column. Minimal sample decomposition is observed. For thermolabile compounds, cold on-column is the best injection tech-... 

Channel closure Feeder coupling Inlet liner tube End fitting body Channel annulus bellows Fueling tubesheet Endshield shielding balls... 

A GC inlet liner of low volume should transfer desorbed analytes to the chromatographic column inlet. The effect of the inlet liner diameter on the broadening of VOCs peaks is reported by Okeyo and Snow [179]. Peak broadening of the most volatile compoimds is avoided using smaller diameter liners. Less volatile compoimds are not broadening and the peaks are not affected by the liner diameter. 

Guides for syringe, septa, ferrule, and inlet liner selection... 

The first chromatogram obtained on a new column may be viewed as the birth certificate of a column and defines column performance at time t = 0 in the laboratory a test mix should also be analyzed periodically to determine any changes in column behavior occurring with age and use. For example, a column may acquire a pronouncedly basic character if it has been employed routinely for amine analyses. /Mother important but often overlooked aspect is that a test mixture serves to monitor the performance of the total chromatographic system, not just the performance of the column. If separations gradually deteriorate over time, the problem may not always be column-related but could be due to extra-column effects, such as a contaminated or activated inlet liner. Commonly used components, their accepted abbreviations, and functions are listed in Table 3.16. 

FIGURE 9.13 Schematic Diagram of PTV Inlet. The inlet liner is packed with deactivated glass wool or other inert packing material to hold the liquid sample during vaporization. 

FIGURE 11.22 Effect of inlet liner diamete on SPME injection of hydrocarbons (a) 4-mm-i.d. liner (b) 2-mni-i.d. liner (c) 0.75-mm-i.d. liner [reprinted with permission from P. Okeyo and N. H. Snow, LC/GC 15, (1997) 1130-1136 (1997), Figure 3 copyright 1997, Advanstar Publications]. 

Routinely inspect and replace dirty inlet liners poor peak shape can also be attributed to a dirty liner in addition to column fatigue, active sites, and other factors. 

Guides to column and stationary-phase selection Guides to selection of inlet liners Guides to column installation Guides to derivatization... 

Another very flexible solution for numerous applications in pyrolysis, outgassing or thermal extraction experiments is the use of a micro-furnace, which can be resistively heated to temperatures above 1000 C (Roussis and Fedora, 1998). The sample is placed in a small, low, thermal mass cup of 50-80 pL volume, which is dropped into the heated pyrolysis furnace consisting of a vertical quartz tube. The furnace tube size is comparable to a GC inlet liner with 4.5 mm inner diameter and 12 mm length and allows programmable temperature profiles with heating rates of up to 200 C/min (Frontier Laboratories Ltd., Japan). 

Due to the necessary frequent exchange of the inlet liner, it is recommended to replace both, the septum and insert liner regularly on a preventive maintenance schedule. 

The transfer time of analytes from injection and evaporation into the analytical column is the residence time of the solvent/analyte cloud in the inlet liner. The residence time depends on the flow conditions within the inlet. The sample vapours are diluted exponentially as they are transferred into the analytical column increasing the residence time for a certain part of the analytes. Labile compounds require a short residence time in the liner for reduced surface contacts. 

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