Autosamplers may be classified by their capacity, such as autosamplers as opposed to auto-injectors; the latter instrument is capable of running more than one sample at once. Robotic instruments offer another classification of autosampler, with rotating/SCARA robots being among the most widely used.
In gas-liquid chromatography, the column inlet (or injector) provides for the introduction of samples into a continuous flow of carrier gas. Common inlet types are the split/splitless injectors, on-column inlets, PTV injectors, the gas source inlet (also called a gas switching valve), purge and trap systems and SPME (solid phase micro extraction) systems. In the split/splitless injector, the sample is introduced to a heated chamber using a syringe.
With an on-column inlet, the sample is introduced in its entirety without the use of heat. PTV injectors introduce the sample through a heated liner at a controlled rate. In the gas source inlet method, the sample is inserted into the gas stream from collection bottles, a method which allows samples to be introduced without interrupting the carrier gas flow.
Purge and trap autosampler systems involve bubbling an inert gas through aqueous samples, purging insoluble volatile compounds from the matrix. These volatile compounds are then trapped in an absorbent column which is then heated – the volatiles are directed into the carrier stream. Solid phase micro extraction (SPME)is a more economical alternative to purge and trap systems which provides greater ease of use and a lower cost.
The type of automatic sampling system used depends largely on the specific application; in gas chromatography alone, there are two different types of columns used – with the different types of autosampler being more appropriate for one or the other. There are packed columns (usually made of glass or stainless steel and containing an inert, solid and highly granular material which is coated with a liquid or solid stationary phase).
The other type are capillary columns; these columns feature a very small internal diameter, with the inside of the column being coated with the phase. Other capillary columns are made with a semi-solid construction and parallel micropores; this style allows for great flexibility, so a long column can be wound into a tight coil which takes up far less room.
While it is gas and liquid chromatography which often first come to mind when discussing different types of autosampler, there are samplers used in many different applications from the life sciences to geological surveys, the pharmaceutical industry, water quality testing and nearly every other application in the materials and life sciences as well as quality control testing of all types. These instruments allow laboratories to handle higher sample throughputs while increasing reproducibility and efficiency.