Splitless Injection Total Sample Transfer

With the correct choice of insert, the sample cloud does not reach the septum so that the low purge flow does not have any effect on the injection itself. 

The solvent condensing on the column walls acts temporarily as an auxiliary phase, accelerates the transfer of the sample cloud on to the column by volume contraction due to re-condensation. The solvent phase holds the sample components and focusses them at the beginning of the column with increasing evaporation of solvent into the carrier gas stream (solvent peak). Here the use of GC compatible solvents that are miscible with the stationary phase becomes important. Incompatible solvents do not generate a suitable solvent effect and 

The splitless technique therefore requires working with temperature programs. Because of the almost complete transfer of the sample on to the column, total sample transfer is the method of choice for residue analysis (Grob, 1994, 1995). 

After the sample transfer into the analytical column is completed, the split valve is opened until the end of the analysis to prevent the further entry of sample material or contaminants on to the column. 

Because of the longer residence times in the injector, with the splitless technique, there is an increased risk of thermal or catalytic decomposition of labile components. There are losses through adsorption on the surface of the insert, which can usually be counteracted by suitable deactivation. Much more frequently there is an (often intended) deposit of involatile sample residues in the insert or septum particles get collected at the bottom of the liner. This makes it necessary to regularly check and clean the insert according to a preventive maintenance procedure. 

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The purpose of this injection technique is to introduce the entire injected sample into the column and use it for trace determination. Different techniques can be used, but the most common is the solvent effect technique, which uses the same instrumentation as used for spht injection (Figure 2.4). In splitless injection, the sample is introduced into the heated liner as in split injection and brought into the gas phase. Contrary to the spht injection, the splitter outlet valve is now dosed. Hence, the total sample volume (1-2 ml of gas) is transferred to the column. When splitiess injection is carried out, the column inlet temperature is kept at a temperature that is 20-50 °C lower than the solvent Bp. Hence, when the sample arrives at the column inlet, the solvent condenses as a thick film on the column wall. This film will act as a plug of stationary phase into which the sample components will be dissolved. Following the sample transfer to the column, which will take 2 min when 2 pi is injected and the carrier gas flow rate is 1 ml min , the column oven temperature is increased. The solvent evaporates first from the column entrance and thereafter the analytes, which will subsequently be separated in the column. The sphtter valve is opened when the whole sample has been transferred to the column in order to wipe out remains of the sample before the next injection. This injection technique is used for trace determinations and can only be carried out in combination with temperature programming. 

The transfer can only be partial for concentrated extracts (split mode), or a total transfer of the sample into the column for trace analysis is performed (splitless mode). Both injection methods require a different parameter setting, choice of inlet liners and oven program start temperature to achieve the optimum performance. Also the possible injection volumes need to be considered. The operating procedures of split injection and total sample transfer (splitless) differ according to whether there is partial or complete transfer of the solvent/sample on to the column. 

Organophosphate esters have been analyzed mainly in the indoor air samples. SAE has been relatively popular in the extraction of organophosphates from air samples, which have been collected either on filters or adsorbents. Both static and dynamic extraction can be used. An example of dynamic SAE (DSAE) is the extraction of OPEs from quartz filters by hexane MTBE (7 3). The flow rate was 0.2 ml/min, and the total extraction time was only 3 min, at a temperature of 70°C. The recoveries were compared with static SAE (2 X 20 min) and PEE and the recoveries obtained with DSAE (>95%) were at the same level or better than those obtained with other methods. No further purification or concentration was needed before GC-NPD analysis of organophosphates. The GC column was a 30 m X 0.32 mm i.d. DB% column with a phase thickness of 0.1 /rm. Splitless injection was applied in the sample introduction. The LODs were better than 0.4 ng/m. The system was developed further, and the DSAE was connected online with GC using PTV and large volume injection during the transfer. The most abundant compound found in the air was tri(w-butyl) phosphate. ... 

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