Heating the column

Some attempts, not yet very convincing, have been made to extend the field of application to gas oils by heating the column. 

For samples that decompose easily, an on-column injection may be necessary. In this method the sample is injected on the column without heating. The column temperature is then increased, volatilizing the sample with as low a temperature as is practical. 

Increasing the speed of analysis has always been an important goal for GC separations. All other parameters being equal, the time of GC separations can be decreased in a number of ways (1) shorten the column (2) increase the carrier gas flow rate (3) reduce the column film thickness (4) reduce the carrier gas viscosity (5) increase the column diameter and/or (6) heat the column more quickly. The trade-off for increased speed, however, is reduced sample capacity, higher detection limits, and/or worse separation efficiency. 

The checkers found it necessary to heat the column to obtain the maximum available product. 

Chirica and Remcho first created the outlet frit, packed the column with ODS beads, and then fabricated the inlet frit. The column was filled with aqueous solution of a silicate (Kasil) and the entrapment achieved by heating the column to 160 °C [105,106]. The monolithic column afforded considerably reduced retention times compared to the packed-only counterpart most likely due to a partial blocking of the pores with the silicate solution. This approach was recently extended to the immobilization of silica beads in a porous organic polymer matrix [107]. 

The effect can be counteracted by heating the column walls and nowadays it is commonplace to use jacketed columns. If a jacketed column is not available, the effect can be minimized by either lagging the column or by winding a tube around the column and circulating a heating fluid in the direction of the outlet to the inlet of the column. 

Steam supplied for heating the column (through a coil) has a pressure of 18-20 atm. It is fed through the boiler (3) mid regulating valve (22). A constant level in the boiler is maintained by means of regulator (25). The vapours me partially condensed in the still-head (5), cooled by water flowing from (1). The same water is used to cool the condensers of both columns. The flow of water is regulated by means of valves (29) and (27). 

For the thermal regeneration, firstly, put the fixed bed packed with the polymeric adsorbent on which the saturated amount adsorbed of the VOCs was qn in temperature-maintaining container. Then, heat the column and maintain its temperature at % . After that, use N2 to sweep the VOCs desorbed from the adsorbent out. The regeneration efficiency of the adsorbent can be measured using previously stated method. 

Before any column is used, it must be thermally conditioned by heating the column at various temperatures for different lengths of time. This removes volatile contaminants, including residual monomers, in the polymeric stationary phase. In addition, thermal conditioning of used columns removes accumulated nonvolatile contaminants that cause unstable baselines. To condition a column thermally, it is disconnected from the detector and purged for at... 

The basic concept of a TSA drying process consists of (a) selective adsorption of trace or dilute water from the contaminated fluid mixture by flowing the fluid over a packed column of alumina particles while withdrawing a dry product stream until the water concentration at the column effluent rises to a predetermined value and then (b) thermal desorption of the adsorbed water by heating the column with a relatively dry fluid stream. The adsorbent is repeatedly used in a cyclic manner by carrying out steps (a) and (b). More than one adsorbent column is required for continuous processing of the wet feed fluid stream and production of a dry fluid stream. 

To retain heat, the column should be wrapped with heating tape (Figure 3-24) or covered with a layer of glass wool held in place with tape. Aluminum foil can be wrapped around the column. Insulated nichrome wire connected to a variable transformer also can be wrapped around the column or any object to heat it. 

Because the conditions for the separation of the alkyl nitrates are very similar to those used for the PANs, both groups can be determined in a single analysis. In a typical temperature program for analysis of the C1-C5 alkyl nitrates and the PANs on a nonpolar HPl capillary column, one would hold the column at 30°C for 20 to 35 min to allow the PANs to elute first, then heat the column to 100°C at a rate of 70°C min to allow the alkyl nitrates to be removed and to recondition the column. The BCD must be held at 45°C to prevent thermal loss of the PANs. The detector temperature can be increased periodically to 150°C for reconditioning. 

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