Injection Technique

The most reproducible injections with least discrimination are given by the 'hot needle' (1.5-2 |L) and 'solvent flush' techniques. Needle-in-plunger syringes cannot be used because samples start to evaporate as soon as the syringe enters the injector, leading to fractionation and discrimination. Injector temperature should be near the boiling point of the sample's least volatile components or discrimination might arise even from a well-designed splitter, especially at low (<100: 1) split ratios. If it is essential to use a low split ratio, e.g. in trace analysis, then a high temperature must be used. For unstable compounds a low injector temperature and high split ratio are desirable.

If the column temperature is below the solvent boiling point and the solvent vapour pressure is sufficiently high (depending on injection size and split ratio), sample can condense in the column. The resulting sudden drop in pressure leads to suction of material from the injector and the split ratio will vary. Similar effects might lead to condensation in gas lines control valves, etc., leading to ghost peaks later in the analysis as the material diffuses back into the injector.

The column should be mounted with its inlet at, or near, the injector base to minimize the volume from which back-diffusion might occur. For the largest signal, needle length should be such that sample is released at the column inlet (10 mm gap). The effect of needle length on response should be checked experimentally.

It is worth varying the split ratio over a wide range - a high split ratio might result in such rapid flow through the injector that the sample passes the column inlet while still in the form of a concentrated plug. The vapour cloud concentration can be optimized to prevent back-diffusion by use of an injector liner compatible with injection. For low split ratios (10:1-50:1) and 8 cm liner typical values are: a 1.5 mm i.d. liner for 0.4 |L injection, a 2.0 mm i.d. liner for 0.6 |L injection, and a 3.5 mm i.d. liner for 2.0 | L injection.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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