Method Statement Metals
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Revised on 12/09/02
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.
The analytical procedure described herein outlines the
determination of metals in soils, waters and filters by Inductively
Coupled Plasma –Optical Emission Spectrophotometry (ICP-OES).
Principle
Soil samples and filters are digested using aqua regia; water
samples are digested on a hot plate using nitric acid. The filtered
extracts are aspirated into the plasma torch. Measurement
of the atomic emission of the element is made by an optical
spectroscopic technique. Acidified samples are nebulised and the
aerosol produced is transported to a plasma torch where excitation
occurs. Characteristic atomic-line emission spectra are produced by a
radio-frequency inductively coupled plasma. The spectra are dispersed
by a grating spectrometer and intensities of the lines are monitored
by photomultplier tubes. The photocurrents from the photomultiplier
tubes are processed and controlled by a computer system. The lower
range of determination may be extended by pre-concentration of the
extract by up to ten fold (for non-volatile metals).
Performance
Characteristics
Substances Determined
Arsenic, Mercury, Selenium, Copper, Lead, Zinc, Cadmium, Chromium,
Nickel, Antimony, Vanadium, Manganese, Molybdenum, Tin, Thallium,
Cobalt and Sulphur (as Sulphate).
Range of Application
Soil samples 1 to 500 mg / kg
(depending upon specific element)
Aqueous samples 0.001 to 10 mg / l (depending upon specific
element)
Filters 1 to 500 ug (depending upon specific element)
Limit of Detection
Soil samples circa 1 mg / kg
(depending upon specific element)
Aqueous samples circa 0.001 mg / l (depending upon specific
element)
Filters circa 1 ug per filter (depending upon specific
element)
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
A Handbook of Inductively Coupled Plasma Spectrometry. M.
Thompson, J.N.. Walsh. 1983. ISBN 0-412-00371-6)
Cadmium, Chromium, Copper, Lead, Nickel and Zinc in Sewage Sludges
By Nitric Acid /AAS. 1981, DOE Methods for the Examination of Waters
and Associated Materials, published by HMSO.
Standard Methods for the Examination of Waters and Wastewaters.
APHA-AWWA-WEF, 1992 18th Edition
National Institute for Occupational Safety and Health, method
7300, trace metals by ICP-OES.
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