Septum injectors

Although the problems associated with septum injectors can be eliminated by using stop-flow septumless injection, currently the most widely used devices in commercial chromatographs are the microvolume sampling valves (Fig. 8.3) which enable samples to be introduced reproducibly into pressurised columns without significant interruption of the mobile phase flow. The sample is loaded at atmospheric pressure into an external loop in the valve and introduced into the mobile phase by an appropriate rotation of the valve. The volume of sample introduced, ranging from 2 piL to over 100 /iL, may be varied by changing... 

Figure 8.4 Apparatus for sample preparation using physical separation. A - fractionation tube and trap for assisted distillation (A septum injector, B carrier gas inlet, C Florisil trap for collecting volatile pesticides) B, Shapiro-type freeze concentrator and C, apparatus for solvent sublation.

Figure 2.4—Direct vaporisation injector used for packed columns. Typical septum injector with a microseal option (the Merlin microseal) that can be used for thousands of injections (reproduced by permission of Hewlett-Packard).

VENTED SEPTUM INJECTORS. A more radical injector modification is available. It prevents gas which has had contact with the septum from entering into the column. Figure 6.11 illustrates such a system in which the gas contacting the septum is vented by a bypass pipe. The carrier gas stream is split, the main portion going to the column while a small portion moves past the septum and... 

Figure 6.11. Vented septum injector. Any gas coming in contact with the septum is vented out the septum purge line.

Figures. Analysis of protein concentration with the septum injector (from Stein and Moschera, 1981). Varying volumes (2.5, 5.0, 7.5 and 10 fi ) of bovine serum albumin (10 ng//zl on left and (100 ng/ xl on right) were injected at 2 min intervals. Average peak height versus amount of protein is plotted.

The most common method of introducing a sample solution into a liquid chromatograph is via a valve/loop injector. Conventional septum injectors, as... 

The sample injector The sample injector can be a simple septum injector and a hypodermic syringe that can place the sample directly on to the column or a high-pressure sample valve (that can be manually or mechanically operated) fitted with an appropriate sample loop. 

Sample introduction was by means of a Hamilton 701N syringe in combination with a septum injector (HETP Components, Macclesfield, Great Britain) or alternatively a Rheodyne valve injector with 20 pi sample loop was used (HPLC Technology Ltd., Macclesfield, Great Britain). 

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