Method Statement Ammonia
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Revised on 11/20/02
Contents
Introduction
Principle
Performance
Characteristics
Range
of Application
Limit of
Detection
Analytical
Quality Control
References
Introduction
The performance of this method is validated in accordance with
internationally recognised procedures.
This procedure describes the determination of ammonia and ammonium
ions in groundwaters, rivers, effluents and leachates. Ammonia
reacts with hypochlorite and salicylate ions in solution in the
presence of sodium nitroprusside to produce a coloured complex which
is measured spectrophotometrically.
The procedure can also be used for the determination of ammonia
adsorbed onto silica gel by desorption with water and subsequent
spectrophotometric measurement as described above.
Principle
Ammonia reacts with hypochlorite ions, generated in situ by the
alkaline hydrolysis of sodium dichloroisocyanurate, and with sodium
salicylate at about pH 12.6 in the presence of sodium nitroprusside
to form a coloured compound (thought to be related to Indophenol
Blue). The compound is blue, but appears green against the yellow
colour of the reagent blank. The absorbance of the solution is
measured spectrophotometrically and related to the ammonia
concentration in the sample by means of a calibration curve. Sodium
citrate is used to mask possible interfering cations.
Performance
Characteristics
Substances Determined
Ammonia and ammonium ion.
Range of Application
Limit of Detection
Analytical Quality
Control
Analytical quality control is maintained by a number of measures:
Multi-point calibration with
authentic standards (with defined minimum performance
characteristics)
Analysis of control samples within
each analytical batch, such as independent standards, matrix spikes
or reference materials
Analysis of reagent/method blanks
within each analytical batch
Ongoing quality assured by the use
of control charts in conjunction with warning and action limits for
the QC sample data
Participation in external
proficiency testing and interlaboratory schemes such as LGC CONTEST,
HSE WASP, CSL FAPAS
References
Ammonia in Waters 1981, DOE Methods for The Examination of Waters
and Associated Materials, published by HMSO.
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