Cold injection

Cool on-column Liquid sample is directly and totally passed from syringe into column or its extension. Cold injection followed by temperature program Dilute, thermally labile samples high-boiling components Fair, some focusing required 0.1-1 100... 

The 1,3,6 NTS injected in KL4RD validated the cold injection in-flow in AP02D which resulted to the continuous decline in the salinity of the well. 

Thermal desorption unit, combined with transfer line and cold injection system... 

Figure 2.5 Injectors, (a) Above left, injection chamber. The carrier gas enters the chamber and can leave by three routes (when the injector is in split mode). A proportion of carrier gas (1) flows upward and purges the septum, another (2) exits through the split outlet (a needle valve regulates the split) and finally a proportion passes onto the column, (b) Above right, cold injection onto the column, (c) Below, a typical chromatogram obtained in splitless mode. For solvent peaks which are superimposed upon those of the compounds, a selective detector which does not see the solvent is recommended.

This injector, named PTV programmed temperature vaporizer), is conceptually similar to the split/splitless model. The temperature of the injection chamber can be programmed to effect a gradient, e.g. from 20 up to 300 °C, in a few tens of seconds (Figure 2.6). So, the advantages of the split/splitless injection are combined with those of the cold injection onto the column. 

The three principal modes of operation are named split cold injection, splitless cold injection and injection with elimination of solvent. 

Split cold injection the sample is introduced into the vaporization chamber and immediately the vent valve is opened and the injector is heated. As the sample is not instantaneously vaporized, the solvent and the different compounds penetrate onto the column in the order of their boiling points. In this way the column is never overcharged. 

Splitless cold injection this mode is employed for trace analysis. The vent valve is closed during the injection. The injection chamber is then heated in order to transfer the sample to the column, which is maintained cold. 

The actual sampling procedure, whether manual or automated, is as follows (1) The fiber sheath pierces the septum of the sample vial. (2) The fiber is extended from the sheath into either liquid sample or the headspace above liquid, solid, or semisolid samples. (3) Equilibration of analytes between the fiber and liquid or headspace occurs over a period of time. (4) The fiber is withdrawn into its sheath. (5) The sheath is withdrawn from the vial and inserted into a hot or cold injection port of a gas chromatograph. (6) The sample desorbs into the carrier gas stream." Store opened, but unused, cartridges in a plastic bag in a desiccator. 

Although the concentrations of permethrine were quite low (10-30 ng/m ) identification by retention time and quantification was possible with GC-FID because the chamber air was very clean and the PUF blank did not interfere with the peaks of the two permethrine isomers. A cold injection system (Gerstel, Miihlheim) did improve the detection limit by better transfer and allowing the injection of 2-10 pi of the extract. 

Thiomethylation only gives derivatives of arsenic-(III) whereas pentavalent arsenic compounds are reduced by the thiol with formation of the disulfide (SGM)2. The yields for the TGM-derivatization depend on the number of introduced thiomethyl groups. The determined yields and recovery rates are in accordance with the publication of Schoene (Schoene et al., 1995). The derivatization is subjected to sometimes strong matrix influence which can be corrected by determination of the yield of proper reference compounds. Multiple derivatized compounds show often thermal instability, thus the use of cold on-column injection or temperature programmed cold injection systems is required. 

Mass spectrometry is today the method used most frequently for identification and structure elucidation of unknown compounds. GC/MS investigations have been used in the combination with thermal desorption as extraction procedure, for the analysis of the dichloromethane extract and for the derivatization products (Thurow et al., 1997). Investigations have been carried out with an HP 5973 MSD (Hewlett Packard Inc.) in combination with an cold injection system CIS 3 (Gerstel GmbH, Germany). 

Modifications to improve available NPSH at pump suction were carried out viz. balancing leak off line which was earlier heating the suction was routed to the deaerator, continuous cold injection was ensured at pump suction to improve transient performance, additional recirculation line was added to avoid pump operation at low flows. Operating procedures were modified and feed water heating by package boiler steam was strictly adhered to. This resulted in a delay of 8 months to put the SG in service. 

Stress high in part] [mold too cold] /[melt too cold] /injection pressure too high/ faulty post-mold conditioning/faulty mold design. 

In fixed beds, cooling and partial recycling of the exit stream of the reactor is possible but this affects the residence time distribution. To overcome this difficulty and obtain a very high conversion level, a second reactor in series could be required. Cold injections of gas or liquid in a multibed reactor are another technique but it is thermodynamically very inefficient (Figures 1 and 2). 

Because of the variety of columns and samples that can be analyzed by GC, several injection techniques have been developed. The packed inlet system is designed mainly for packed and wide-bore columns. However, an adapter can be used to enable capillary columns to be used. When injection is carried out in the on-column mode, glass wool can be used for packing the injector. For capillary GC, spht technique is most common, which is used for high concentration samples. This technique allows injection of samples virtually independent of the selection of solvent, at any column temperature, with httle risk of band broadening or disturbing solvent effects. The sphtless technique, on the other hand, is used for trace level analysis. The so-called cold injection techniques (on-column, temperature programed vaporization, cooled needle split) have also been recently developed. " " ... 

However this kind of action will decrease the final conversion. The problem is what part of the total stream of inlet gas should be directed as an cold injection and where it should be placed when a limit of maximum temperature is imposed. 

The sampling and elution of such high-molecular-J weight materials requires careful attention in order to avoid quantitative sample losses during the sample in- troduction step. In general, cold injection tech- niques are required for accurate nondiscriminative... 

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