Method Statement Cyanide
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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 Total and Free
Cyanides in soils and waters by distillation using appropriate
reagents followed by a colorimetric measurement of a
isonicotinate-barbiturate complex.
Principle
Simple and most complex cyanides are decomposed by steam
distillation using concentrated Phosphoric Acid. The hydrogen cyanide
liberated is trapped in a solution of dilute sodium hydroxide and
measured colorimetrically.
Soil samples
Preliminary extraction with sodium hydroxide. Acid distillation of
the extract with suitable reagents to form HCN gas which is absorbed
in sodium hydroxide solution. Cyanide ion concentration in the
distillate determined spectrophotometrically using chloramine-T and
isonicotinate-barbiturate mixed reagent.
Water samples
As above but omitting the sodium hydroxide extraction stage.
Performance
Characteristics
Substances Determined
Total Cyanide and free (simple) cyanide and cyanide in most of its
complexed forms. However, strongly complexed cyanides (notably the
Cobalt complex) are incompletely recovered by this method. Type of
Sample:
Soils
Sediments
Sewage Sludges
Ground-waters
Leachates
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
Cyanide in Waters, DOE
Methods for the Examination of Waters and Associated Materials,
published by HMSO. 1988.
Cyanide. Part 4500.
Standard Methods for the Examination of Waters and Wastewaters. 18th
Edition 1992. APHA-AWWA-WEF.
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