Nitrate determination based on direct spectrophotometric
measurements in ultraviolet is usually hindered by the
presence of other absorbing species, mainly organic substances.
Separation of nitrate from the concomitants is thus
required for selective determination. In this sense, several
alternatives were evaluated including the retention of organic
substances with activated charcoal, XAD-2 resin or
C18-bonded silica. Preliminary tests with natural water samples
showed that both, organic substances and nitrate, were
retained by activated charcoal, while quantitative separation
was not achieved in the short residence time (<10 s) for flowing
samples with the other materials. In addition, organic
substances retained in XAD-2 and C18-bonded silica were
difficult to remove from the solid phase, limiting the use for
successive measurements.
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