IAEA Reference Materials
Reference
Sheets
IAEA-336
TRACE AND MINOR ELEMENTS IN LICHEN
Intended
Use
This
sample is intended to be used as a reference material for the measurement
of trace and minor elements in lichens. It can also be used as a quality control
material for the assessment of a laboratory's analytical work, for the validation
of analytical methods and for quality assurance within a laboratory.
Origin
and preparation of the material
The
epiphytic lichen Evernia prunastri (L.) Ach. was selected and collected
by hand. The lichen was collected from areas in Portugal remote from pollution
sources. These areas included Gavião (center of Portugal), Ourique
and Serra do Cladeirão (south of Portugal). The lichen was harvested
from both the Cistus ladanifer and Quercus species of tree. About 25 kilograms
were collected, separated from debris and other epiphytic lichen species by
visual inspection, then washed in deionized water and oven-dried at 40°C
for 24 hours. The lichen was ground using a Teflon "Mikro-dismembrator" mill.
The final material was passed through a 125 µm sieve and mixed in a
rotating plastic drum. Sufficient material was obtained to produce 800 units
of 20 g. The material was radiation-sterilized to a total dose of 12 kGy using
a 60Co source.
Date of Release:
October 1994
|
Unit Price:
130 €
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Unit Size:
20 g
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| Producer:
Chemistry Unit Agency's Laboratories, Seibersdorf A-2444 Seibersdorf, Austria |
Supplier:
Analytical Quality Control Services Agency's Laboratories, Seibersdorf A-2444 Seibersdorf, Austria |
|
Reference Sheet:  IAEA-336(.pdf) |
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| * | It should be noted
that the confidence interval was calculated from the combination of
the standard deviation of the mean value and an additional 5% to account
for any variation due to sample inhomogeneity. |
| ** | Number
of accepted laboratory results which were used to calculate the recommended
or information values and their respective confidence intervals about
the mean value. |
| (R/I) | Classification assigned to the property value for Analyte (Recommended/Information) |
The
values listed above were established on the basis of statistically valid results
submitted by laboratories which had participated in an international intercomparison
exercise organized during 1992/1994. The details concerning the criteria for
qualification as a recommended or an information value can be found in the
report NAHRES-33 (IAEA/AL/79) "Intercomparison run for the determination of
trace and minor elements in lichen material IAEA-336" [1]. This report is
available free of charge upon request.
Homogeneity
Homogeneity
tests were performed on two 100 mg sub-samples taken from each of 20 bottles.
The homogeneity was evaluated based on the variation in the concentration
of the elements As, Br, Fe, K, La, Mn, and Sm which were determined by instrumental
neutron activation analysis using the k0 method [2]. The results of a one
way ANOVA test showed no significant difference between the within-bottle
variance and the between-bottle variance. The relative standard deviation
of these results varied from 3 to 11 %. Taking into account the measurement
uncertainty, the relative uncertainty due to inhomogeneity was estimated to
be between 3 and 6%. Additional measurements for Br, Ca, Fe, Sr, and Zn using
X-ray fluorescence [3] supported these results. For these latter measurements
the additional uncertainty due to inhomogeneity was estimated to be between
1 and 5 %. Although the degree of inhomogeneity was not the same for all the
elements, an additional component of uncertainty (5%) was added in quadrature
to expand the confidence interval of each analyte. The final confidence interval
includes this additional uncertainty.
Dry
weight determination
All
recommended and information values are expressed on a dry weight basis. Therefore
the dry weight must be determined at the time of analysis, using separate
sub-samples of 500 mg dried to constant weight in a drying oven set to 100
°C. Subsequent weighings should differ by less than 5 mg.
Instructions
for use
The
recommended minimum sample size for analysis is 100 mg. Analysts are reminded
to take appropriate precautions in order to avoid contaminating the remaining
material in the bottle. It is recommended that the material be stored in a
dark place, below 20°C (refrigeration is advised).
References:
| [1] | |
| [2] | Freitas
M. C., Catarino F. M., Branquinho C. and Maguas C., Preparation of a
Lichen Reference Material. J. Radioanal. Nucl. Chem. 169 (1993) 47-55. |
| [3] | Stone
S. F., Freitas M. C., Parr R. M. and Zeisler, R., Elemental Characterization
of a Candidate Lichen Research Material IAEA-336. Fresenius J. Anal.
Chem. 352 (1995) 227-231. |
Last updated 30 March 2004
