Topics - Split Injection
Small bore columns, particularly capillary columns 100 micron or less in internal diameter, often require sample loads of less than a microgram for their effective use. It is extremely difficult (if not impossible) to place samples of a microgram or less directly onto such columns, even with a micro-syringe. Thus, to achieve such small sample loads in practice, a split injection system
is employed. Split injection involves vaporizing the sample in a gas stream using a flash heater and subsequently splitting the gas stream at a ratio of 100 to 1 or more so that only 1 % (or less) of the sample, passes into the capillary column, whereas the remainder passes to waste. By adjusting the flow to waste, using a controllable restriction, split ratios of any desired value can be obtained. Due to the diffusivities of the individual solutes in a mixture being different, samples placed on a capillary column using a split injector may not necessarily be precisely representative of the original sample.