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Colorimetric Determination of Nitrate Plus Nitrite in Water by Enzymatic Reduction, Automated Discrete Analyzer Methods (Paperback)
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Colorimetric Determination of Nitrate Plus Nitrite in Water by Enzymatic Reduction, Automated Discrete Analyzer Methods (Paperback)
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List price R419
Loot Price R339
Discovery Miles 3 390
You Save R80 (19%)
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This report documents work at the U.S. Geological Survey (USGS)
National Water Quality Laboratory (NWQL) to validate enzymatic
reduction, colorimetric determinative methods for nitrate + nitrite
in filtered water by automated discrete analysis. In these
standard- and low-level methods (USGS I-2547-11 and I-2548-11),
nitrate is reduced to nitrite with nontoxic, soluble nitrate
reductase rather than toxic, granular, copperized cadmium used in
the longstanding USGS automated continuous-flow analyzer methods
I-2545-90 (NWQL laboratory code 1975) and I-2546-91 (NWQL
laboratory code 1979). Colorimetric reagents used to determine
resulting nitrite in aforementioned enzymatic- and
cadmium-reduction methods are identical. The enzyme used in these
discrete analyzer methods, designated AtNaR2 by its manufacturer,
is produced by recombinant expression of the nitrate reductase gene
from wall cress (Arabidopsis thaliana) in the yeast Pichia
pastoris. Unlike other commercially available nitrate reductases we
evaluated, AtNaR2 maintains high activity at 37 C and is not
inhibited by high-phenolic-content humic acids at reaction
temperatures in the range of 20 C to 37 C. These previously
unrecognized AtNaR2 characteristics are essential for successful
performance of discrete analyzer nitrate + nitrite assays
(henceforth, DA-AtNaR2) described here. Method detection levels (or
limits; MDL) estimated for standard- and low-level DA-AtNaR2
nitrate + nitrite methods were 0.02 milligrams nitrogen per liter
(mg-N/L) and 0.002 mg-N/L, respectively, which are comparable to
2010 NWQL long-term MDLs of the continuous-flow analyzer,
cadmium-reduction methods (henceforth, CFA-CdR) they replace.
Typically, reagent-water blanks for standard- and low-level
DAAtNaR2 nitrate + nitrite methods are one half MDL or less.
Nitrate + nitrite concentration differences for between-day
replicates were 3 percent or less at or above 5 times the MDL and
were as great as 35 percent near the MDL. Typically, nitrate
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