Chemistry Reference
In-Depth Information
Lens
f:60mm, 25mmØ
Photomultiplier
R 787
Hamamatsu TV Co Ltd
Power supply picoammeter
part of ICAP-500
Nippon Jarrell-Ash Co Ltd
Chart recorder
B-181H
Rigakudenki Co Ltd
Source: Reproduced with permission from the American Chemical Society [451]
2.62.6
Atomic absorption spectrometry
Cresser [450] showed that nitrate can be rapidly reduced to ammonia by the action of
titanium(III) sulphate at room temperature. Subsequent displacement of the ammonia by
a current of air enables the gas-phase molecular absorbance the ammonia to be measured
using an atomic absorption spectrophotometer and thus provides a sensitive and selective
method for the determination of nitrate. Ions which affect the reduction of nitrate by
titanium salts, such as cobalt, copper, iron and zinc, interfere with this method and must
be removed if present in large amounts.
2.62.7
Helium microwave induced emission spectrometry
Ultratrace amounts (µg L
−1
) of nitrate, nitrite (and ammonium) have been determined in
pond waters by atmospheric pressure helium microwave induced emission spectrometry
utilising a gas generation technique [451]. The instrument components are summarised in
Table 2.28. The instrumental set-up consists primarily of the plasma system, the optical
measurement system and the gas generation system.
Ammonium ion is oxidised to nitrogen gas by sodium hypochlorite in an alkaline
medium and nitrite ion by sulphamic acid in an acidic medium. Nitrate ion is reduced to
nitrite in a cadmium/copper column and then determined as above. The nitrogen
produced by the chemical reduction is introduced into the helium flow via a three-way
valve system connecting the reaction vessel. Plasma is generated by a microwave
generator and the emission signals are measured at 391.4nm. Experimental procedures
are summarised in Table 2.9.
Four wave-lengths listed in Table 2.30 were used for the determination of nitrogen.
These peaks of nitrogen-containing species provided different
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