Anions in non saline waters - Determination of Anions in Natural and Treated Waters - page 279

2.90.6 High performance liquid chromatography
High performance ion exchange chromatography has been used [679] to separate selenite
and selenate which were determined by post column derivatisation using 2, 3-
diaminonaphthalene. Peak broadening was minimised by an air-segmented continuous
flow autoanalyser. 2, 3-diaminonaphthalene reacted with selenium(IV) but not with
selenium(VI). Selenium(VI) was determined after on-line reduction with hydrogen
bromide (1.8N) at 100°C Selenium(IV) was detected in potable water at 0.17µg L −1 .
Injection of larger volumes improved the detection limits. Samples of river or lake water
were concentrated by column head techniques.
Cartoni and Coccioli [680] characterised mineral waters using high performance liquid
chromatography. Filtered mineral water was pumped through a column packed with
LiChrosorb RP-18. Traces of organic material dissolved in the water were adsorbed on to
the first part of the column and were then desorbed using an acetonitrile gradient. The
eluate was monitored with an ultraviolet variable wavelength detector.
2.90.7 Gas chromatography
Uchida et al. [673] have described a method for determination of selenium in rivers and
sea water by gas chromatography with electron-capture detection. The specific reaction
of 1, 2-diamino-3, 5-dibromobenzene with selenium(IV) is used, the product (4, 6-
dibromopiazselenol) being extracted into toluene and determined from its peak height in
the gas chromatogram. Selenium (-II, 0) is oxidised to selenium(IV) by bromine solution
and selenium(VI) is reduced to the same state by bromine/ bromide redox buffer solution
and determined as the piazselenol as above.
The gas chromatograph used in this study was equipped with 63Ni electron capture
detector and the column comprised 15% of SE-30 on 60-80 mesh Chromosorb W. The
column and detector temperatures were maintained at 200 and 280°C respectively. The
nitrogen flow rate was 28ml min −1 .
Procedure 1
In this method concentrated hydrochloric acid is added to the sample immediately after
sampling (1ml L −1 ). The solution is filtered by a membrane filter (pore size 0.45µm) to
remove suspended matter.
Se(IV) determination (procedure 1) is carried out as follows; to a 500ml separating
funnel is added 500ml of the pretreated sample water and 20ml of concentrated
hydrochloric acid. The solution is shaken vigorously with 25ml of toluene to saturate
with toluene and to remove toluene soluble matter. The aqueous phase is transferred into
another 500ml separating funnel after phase separation. To the solution is added 0.12% 1,
2-diamino-3, 5-dibromobenzene solution (10ml), and the solution left to stand for 2h, 1ml
of toluene is added and the solution shaken vigorously for 5min and the 4, 6-
dibromopiazselenol extracted. The extract is washed twice with 3ml of perchloric acid
(2+1), and 2µL of the extract injected into the gas chromatograph and the peak height of
4, 6-dibromopiazselenol measured.