Splitless injection liner volume

Withdraw 0.5 mL of the gas phase by using 1-mL gaslight syringe, and inject this volume in GC/MS in splitless mode equipped with the specific liner for syringe injections. 

Splitless injector liners are normally straight tubes without any flow-disruption devices. Any flow disruption in the injector usually causes peak broadening. Therefore, it is not recommended to pack a splitless liner with glass wool. Sometimes there is a restriction at the bottom of the liner. This is to keep the column centered in the liner and away from the liner walls. Use of small-volume liners will result in greater inlet efficiency, since the sample will be transferred into the column over a shorter period of time. However, smaller-volume liners are more subject to backflash problems. For small injection volumes (<0.5 pi), the 2-mm-I.D. splitless liner is recommended for larger injection volumes, the 4-mm liner is recommended to minimize backflash problems. 

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. 

Solvent Effect OTQ. An effect noted in splitless injections for concentrating higher boilers at the head of the column so that the peak band will reflect the efficiency of the column and not the volume of the injecUon port liner. For this effect to occur, the oven temperature must be close to the boiling point of the major solvent component in the system so that it condenses at the head of the column and acts as a barrier for the solute. 

Understanding the relationships between inlet liner geometry, carrier gas flow, injection volume and solvent vapour volume is essential for optimizing splitless injections. Especially the expansion volume of the solvent used must be taken into account. The maximum liquid injection volume needs to be adjusted in the hot... 

Cold splitless WCOT thick film Idem Reproducible and accurate sampling Controlled evaporation No discrimination on basis of b.p. Large volume injection Low detection limits Minimisation of solvent entering column Allows polar solvents Automation Small sample size introduction (<2 xL) Thermal degradation possible (long residence times of components in liner)... 

Thermal desorption from the SPE cartridge is a further possibility [77,122]. In this approach, the sample is introduced at a controlled speed into the packed liner of a PTV injector set to a low temperature with the water eliminated via the split vent. Salts and involatile polar material are rinsed from the sorbent with water and the sorbent dried by purging with a high carrier gas flow rate. The trapped analytes are subsequently desorbed in the splitless mode by rapidly heating the PTV to the injection temperature. The most commonly used sorbents are Tenax and Carbofrit. The method is restricted to a narrow range of applications by the low breakthrough volume of polar analytes on the... 

Classical splitless Easy operation Certain protection of analytical column against nonvolatile matrix components Degradation/adsorption of susceptible analytes Matrix-induced response enhancement Small injection volumes Potential discrimination of volatile analytes due to the liner overflow... 

Pulsed splitless Reduction of the residence time in the liner resulting in the decreased analyte degradation/adsorption and reduced matrix-induced response enhancement Larger injection volumes (limited by the liner size and solvent expansion volume) Potential transfer of nonvolatile matrix cx)mponents further into the column... 

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. 

---