Method Statement Preparation of Soil, Sludge and
Sediment
@(#) Uncontrolled Document SoilSludgeSedimentPreparation.html Version 1.2 Last
Revised on 11/21/02
Contents
Introduction
Principle
Performance
Characteristics
Range
of Application
Limit of
Detection
Analytical
Quality Control
References
Introduction
In general, only a small aliquot of the total sample is required
for a chemical analysis. Furthermore, more than one aliquot will be
required if the analyses dictate that the sample be treated in
different ways prior to analysis. Hence, it is imperative that
aliquots taken from a sample are truly representative of the whole.
Soil extracted from trial pits is inherently heterogeneous and
care must be taken to ensure that a representative sample is obtained
from the pit. It is good practice to collect at least four
sub-samples and combine these to give a relatively large (1kg)
composite sample for each monitoring point. Even so, it is likely
that the coefficient of variation (CV) in analytical results for
sampled of nominally the same material would be in the range 50-100%.
Principle
The laboratory assumes that a sample which it is given is
heterogeneous and every effort is made to obtain truly
representative aliquots where they are required. In addition, the
analysts will select methods which are suitable and appropriate to
the needs of the investigation and will ensure that adequate quality
assurance procedures are applied. In many cases, visual assessment
of samples is extremely informative and in some cases will reveal
that a particular analysis is not worthwhile. For example, samples
which are contaminated with substantial quantities by coal tar are
extremely sticky and cohesive which makes analysis more difficult.
The laboratory prepares samples in a manner which reduces the
random error and does not introduce a bias in the analytical result.
Hence, the uncertainty of the analytical measurement on aliquots
taken from a sample received by the laboratory is usually small in
comparison to that introduced by sampling and sub-sampling. Hence, a
result pertaining to a particular location, is often of less
significance than the overall characterisation of a site.
To obtain useful results from site sampling and sub-sampling, the
analytical method must:
be able to measure reliably the parameter of interest
have an appropriate detection limit
have a known response to possible interfering species
be suitable in terms of time and cost
The procedure described herein, on the sample preparation of
soils, sludges and sediments cover the first important aspect towards
providing an accurate and reliable result i.e. the sub-sampling of
the original 'as received' material.
Soil Sludge and Sediment samples
The sample container, usually a bag or jar, is opened and a
suitable amount (at least 100g) is transferred into a shallow
aluminium tray labeled with the unique sample reference. Clods and
or lumps are broken up by hand. Stones, metal artifacts and fibrous
non-crushable materials are excluded. In cases where correction for
'stones and moisture' is required, the weights of material, stones
and residue are recorded before drying. The remainder of the
original sample is retained until disposal is authorised by the
Laboratory Manager.
If the sample requires analysis of volatile determinands a
separate sample in a 40 ml vial should be supplied. In instances
where this has not been supplied a suitable portion of the 'as
received' sample will be utilized.
Performance
Characteristics
Substances Determined
Not Applicable
Range of Application
This procedure is suitable for the ICRCL range of analytes and
many organic parameters.
Limit of Detection
Not Applicable
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
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