bypass injector

in gas chromatography
https://doi.org/10.1351/goldbook.B00766
A sample injector by means of which the eluent (carrier gas) may be temporarily diverted through a sample chamber so that the sample is carried to the column.
Source:
Orange Book, 2nd ed., p. 99 (http://media.iupac.org/publications/analytical_compendium/)