Appendix D: Analytical Methods 



small portion of the column at the injector end. Chemically bonded liquid phases require less 

 maintenance. 



5.4.1.6 Inlet and injection: The inlet/injection system should allow introduction of the 

 sample onto the column with minimum change in composition (discrimination). In the split mode, 

 only a small, preset fraction (typically in the order of 1%) of the total amount injected reaches the 

 column. This is an appropriate method for the analysis of major components of mixtures. The 

 low boiling fraction may be lost; this includes components with boiling points up to C15. 

 However, for the determination of components that are present at trace concentrations, it is 

 essential that the entire amount injected is transferred to the column. This is accomplished in the 

 splitless mode, using essentially the same injector with a few modifications. In the splitless 

 injection technique, 0.5 - 3.0 |il sample is introduced into a glass liner in the injector, where flash 

 vaporization takes place at 200 - 250°C. The glass liner must have been deactivated. Such liners 

 are also available commercially. (The temperature should be high enough to allow rapid 

 evaporation of solvent and solutes but it should be low enough to minimize septum bleed and the 

 destruction of labile compounds such as p,p'-DDT.) The solutes are concentrated on the column 

 as a small band at the inlet, which is kept at a temperature 10 - 30°C below the boiling point of the 

 solvent. This creates an area of increased solvent concentration, focuses the sample and results in 

 increased resolution, known as the "solvent effect". If pentane is the solvent the initial temperature 

 should be lower than 60°C (see 5.4.1.8). 



The movement of solvent and solutes from the injector to the column inlet is carried out 

 under low carrier gas flow rate in order to minimize dilution of solute with carrier gas. For the 

 same reason, injected volumes should not be under 0.5 (J.1. After transfer of essentially the entire 

 amount of solutes to the column (usually 20 - 60 seconds, to be operationally determined for 

 optimum results), the injector is flushed with increased carrier gas flow, which removes the 

 remaining solvent. In this way, tailing of the early eluting compounds is avoided. The loss of 

 components of interest is negligible by this technique. In order to minimize contamination of the 

 column by products derived from septa, the inlet is purged continuously except during injection. 

 The column temperature can then be increased at a rate, selected as a compromise between 

 efficiency and length of time required for a given separation. (Note: the concentration effect at the 

 column inlet can also be affected by a condensation technique which involves keeping the column 

 inlet at a sufficiently low temperature. This technique is effective for compounds with boiling 

 points at least 150°C above the column temperature. Compounds with lower boiling points need a 

 "solvent effect" for concentration at the column inlet). Laboratories equipped with on-column 



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