Column trapping techniques

The GC was operated in accordance with the whole column trapping technique using a standard medium bore capillary column with a 1 pm stationary phase and liquid CO2 as coolant. 

The gas chromatograph was equipped with a flame ionization detector. A 50-foot length of 0.020 inch i.d. stainless steel open tubular capillary column coated with Carbowax 1540 served as the main column. A freeze out trapping technique was used to concentrate the a-pinene before entering the main column. The pre-column trap consisted of an in-line capillary column, identical to the main one, inserted between the injector and inlet of the main column. The trap was located outside the oven and cooled with a dry ice-ethanol bath before injection of a 5 cc sample. A 80°C hot water bath was used to release the a-pinene. The operating conditions of the gas chromatograph were as follows ... 

Specially designed injection port inlet sleeves have been available on the market for direct and hot on-column injection.In the direct injection mode, 2 -mm-lD inlet sleeves are commonly used, which permit a sufficient space for sample evaporation however, the on-column mode is usually performed by inserting a 26-gauge needle inside a 0.53-mm-lD column. Direct injection is more favorable because it is less problematic than the hot on-column mode. Because the liner can trap nonvolatile residues before entering the column, this technique is suitable for dirty samples. Compared to the splitless mode, the direct injection is advantageous, involving less adsorption of the solutes and better sensitivity. However, with this technique, the adsorption of the sample may occur on the inlet sleeve during the evaporation process.In this case, the hot on-coIumn mode offers more benefits. 

Propyn-l-ol is analyzed by GC-FID using a suitable column for alcohol. It can be analyzed in all types of samples, such as ground-water or soils, sediments, and sludges by GC/MS using a purge and trap technique or by direct injection (U.S. ERA 1986, Method 8240, SW-846). A column containing 1% SP-1000 on Carbopack-B is suitable. The primary ion is 55 and the secondary ions are 39, 38, and 53 (electron-impact ionization). 

In the dynamic headspace method, the sample is put in a thermal desorption unit in order to desorb the RS a continuous flow of a carrier gas pushes the RS into a trapping system which is refrigerated and where they are accumulated prior to analysis. Then the RS are rapidly desorbed by rapid heating and carried onto the column via the carrier gas. There are different ways to apply this technique. The arrangement when purge gas passes through the sample is often called the purge and trap technique (some other equipment uses the acronym DCI (desorption, concentration, injection)). This method is particularly useful for very low concentrations of RS as the total amount of a substance is extracted and can be applied directly to powders without need to dissolve them. The main drawback is that the dynamic headspace methods are not readily automated. ... 

Solid-phase micro extraction is a useful technique in which volatiles are partitioned from the sample onto fibers coated with polar or nonpolar bonded phases. The fiber is then placed directly into the heated injection port of the GC where compounds are volatilized and carried onto the capillary column. The technique is less sensitive than the techniques described above as it is an equifibrium process. However, modern ion trap mass spectrometers have increased in sensitivity and the technique is becoming widely used. 

Flash temperature programming is a new technique for rapidly heating capillary GC columns. The technique utilizes resistive heating of a smallbore metal sheath that contains the GC column. This technology is based on the flash GC system, an innovative chromatographic system that accomplishes in 1-2 min what takes a conventional GC from 30 min to a 1 h or more. The flash GC can be over 20 times faster than conventional GC (Fig. 11) and is also more sensitive and far more versatile. Additionally, the flash GC can be used to concentrate samples as part of its purge-and-trap capabilities. On-column cryotrapping procedures can be accomplished within the system and incorporated as part of the very fast analysis procedure. 

Column-switching techniques for the determination of dmgs in biological fluids usually involve on-line solid-phase extraction on reversed-phase columns coated with albumin or modified with peptides and enzymes. To determine a-tocopherol and retinol in serum, Japanese investigators developed a unique sample preparation involving treatment of the serum with SDS and ethanol, deproteinization and trapping of the analytes on a BSA-80TS precolumn, followed by stepwise... 

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