Page 227 - Vogel's TEXTBOOK OF QUANTITATIVE CHEMICAL ANALYSIS

ION CHROMATOGRAPHV 7.4
- SAMPLE

PUMP
lNJECTlON
e
VALVE

SEPARATOR
R 'HCO; COLUMN
NaHC03
Strong base anion
exchange separator
resin separates
ELUANT
sample anions in
a background of
NaHC03 eluant

R-H+ SUPPRESSOR
1 1 COLUMN
Strong acid suppressor
resin removes NaHC03 l l (Regenerated
eluant and converts periodically to
samule anions to remove unwanied
thei; acids which 1 1
pass unreiarded
through the suppressor
column
r

CONDUCTIVlTY Il :21VlTY
METER AND
RECORDER
Conductivity meter
quantifies anion acids 1
(sample ions) in a
background of diluie
carbonic acid WASTE
Fig. 7.3 Ion chromatography flow scheme (anion analysis).

into species giving low or zero conductance, e.g. where NaHCO, is used as
eluant for anion analysis this is converted into a background of dilute carbonic
acid by using a strong acid suppressor resin.
The low-concentration eluants used to separate the sample ions on the
separator column allow a substantial number of samples (typically about 50)
to be analysed before the suppressor column is completely exhausted. Clearly
an important practical consideration is the need to minimise the frequency of
regeneration of the suppressor column and, for this reason, the specific capacity
of the column is made as large as possible by using resins of moderate to high
cross-linking. Some instruments contain two suppressor columns in parallel,