Page 86 - Illustrated Pocket Dictionary of Chromatography

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is 10 , and the detection limits are in the parts per billion range.
Because of the very low detection limits of this detector the input
gases to the detector must be hydrocarbon free to keep the back-
ground noise at an acceptable level. The FID has a linear range of
7
approximately 10 .
flashback In GC systems using a vaporization inlet, flashback is the
condition in which the sleeve volume is overloaded because of the
large volume of expansion that occurs as a liquid sample is converted
to a gas. This expansion causes the vapors to move back to the top
of the inlet and recondense, leading to low and irreproducible results.
Florisil A patented magnesium silicate (Mg 2 SiO 3 ) used predomi-
nantly in sample cleanup.

flow restrictor Most commonly used in SCF work and placed
after a column to maintain constant system pressure during a
separation.

flow controller Used in GC systems to produce a constant gas
flow in the system even though the resistance to flow may vary with
time (e.g., as temperature changes during a gradient).

flow injection analysis (FIA) The basic FIA technique is based
on the injection of a sample into a nonsegmented continuous carrier
stream that brings the analyte to the detector. Selectivity is either
based on the purity of the sample (no other component in the system
that the detector responds to) or a selective reaction (e.g., enzymatic
or derivatization) of the analyte of interest. In more complex FIA
systems there can be segmentation between samples. This is often
accomplished through the injection of an air bubble between sample
injections. Carry over and sample adsorption to the tubing can cause
irreproducibility. Quantitation can be done either by peak height or
peak area. Standards must be run along with samples.

flow meter Used to determine the volume (mL/min) flow rate of
gases through the GC system. Two common flow meters are (1) soap
bubble and (2) electrical sensor. The soap bubble flow meter is a
manual operation in which a soap bubble moves up a calibrated
volume tube and the time to move a given volume is recorded and
from that the rate is calculated. The electrical sensor provides an
automatic digital readout of the flow rate. Note that the flow rate is