Warsaw, 19.02.2013
Damian Walaszek
University of Warsaw
Faculty of Chemistry
Laboratory of Basic Aspects of Analytical Chemistry
“CALIBRATION STRATEGIES FOR LA-ICPMS DIRECT ELEMENTAL ANALYSIS OF ANCIENT
OBJECTS”
(„METODYKA WZORCOWANIA LA-ICPMS NA PRZYKŁADZIE BEZPOŚREDNIEJ ANALIZY
PIERWIASTKOWEJ WYKOPALISKOWYCH OBIEKTÓW ZABYTKOWYCH”)
Supervisor: Prof. Dr. Hab. Ewa Bulska
In cooperation with: Dr. Andrea Ulrich
Swiss Federal Laboratories for Materials Science and Technology
Dübendorf, Switzerland
The studies of historical objects, because of their unique cultural and material value,
require a specific approach for planning and perform of the investigations. The specificity of
the archaeological samples puts strict requirements with regards to the measurement
techniques used. The requirements for analytical techniques used for the analysis of the
elemental composition of archaeological artifacts are as follows:

No or limited to a minimum damage to the object during the measurement.

Limited to a minimum sample preparation before measurement.

Possibility of simultaneous and rapid multielemental analysis in a wide range of
concentrations and the ability to obtain isotopic information.

Potential opportunity to obtain information about the spatial distribution of
elements on the surface and sub-surface layers of the object.
Laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) is one of
the few analytical techniques meet the above criteria. Unique analytical capabilities make
LA-ICPMS increasingly used in the analysis of a variety of historic objects. It should be noted
however that this technique cannot be used routinely – it requires the development of
analytical procedure, depending on the properties of the object and analytical purpose.
1
The main goal of my study was to develop tailored for the purpose, specific analytical
procedures for the rapid and micro-destructive multielemental analysis of historic objects
(bone materials and copper alloys) by LA-ICPMS. In order to maintain transparency of the
research, I divided the work into several sections, depending on the type of investigated
objects as well as the main aim of the work respectively.
In Section 2, I proposed the use of natural apatite crystal as solid in-house reference
material with the matrix matched to bone tissues as a new tool for the calibration of LAICPMS measurements. In that case I optimized the analytical conditions of LA-ICPMS to
attain the closest agreement between quantitative results obtained for the same apatite
crystals by means of LA-ICPMS and ICPOES/ICPMS after samples digestion. I found that the
homogeneity of elemental distribution in crystals was the key criterion distinguishing natural
apatite candidates for the in-house reference material. Therefore I made subsequently a
careful selection of natural apatite crystals to construct multi-point calibration curves with
the best linearity, which were then used for the quantification of element content in
archeological bones objects. Then I validated the measurement procedure by the
comparison of elemental composition of NIST 1400 and NIST 1486 bone reference materials
(certified values) with those determined by the LA-ICPMS, with the use of either NIST 610 or
chosen natural apatite crystals (considered as in-house reference materials). I also took
under the consideration the data obtained for the archaeological samples. On the basis of
the obtained results I can conclude, that apatite crystals used as reference materials allow
obtaining at least similar or even better coherence of the obtained results in comparison to
NIST 610. Therefore, the natural apatite crystals can be successfully applied as the in-house
reference materials for the analysis of archaeological bone tissues by LA-ICPMS.
Section 3 of my dissertation presents a systematic investigation of market available
copper based alloy reference materials with respect to LA-ICPMS analysis for the most
relevant ancient copper alloy compositions (copper, tin bronzes and leaded tin bronzes). The
choice of the laser parameters, the sampling procedure as well as the calibration of the LAICPMS was optimized based on metallographic characteristics of the selected reference
material as well as the assessment of their heterogeneity on LA-ICPMS results. Based on the
obtained results I prepared the recommended analytical procedure for the elemental
analysis of different copper alloys by LA-ICPMS, having also in mind the requirement of
minimizing damage to the sample.
2
Later on I applied the previously proposed LA-ICPMS analytical procedure to the
analysis of model samples for the validation, the results are presented in Chapter 4. As
model samples I used two copper alloys from an experimental archaeological study on
ancient metal smelting processes and historical casting techniques, complemented by one
modern alloy. As the control samples two sets of reference materials (RMs) were also used.
For most of the determined elements in all the investigated alloys, satisfactory agreement of
LA-ICPMS results vs. bulk ICPMS results was obtained. This confirms the reliability of the
proposed analytical procedure for elemental analysis of various copper alloys LA-ICPMS.
However, for highly heterogeneous samples and heterogeneously distributed elements (Pb,
Bi, Sb, As) I found, that the proposed analytical procedure was still insufficient. To improve
the sampling and in consequence the values of the statistical evaluations of experimental
data, the number of repetitions increase, laser spot size increase or different ablation mode
can be applied. However in such cases the damages of the investigated ancient object are
usually unacceptable.
Part of the results was published in the journal "Spectrochimica Acta Part B". Two
other publications have been sent for review.
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