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@PHDTHESIS{Schlatter:991097,
author = {Schlatter, Nils},
othercontributors = {Lottermoser, Bernd G. and Banning, Andre Wilhelm},
title = {{Q}uantitative {A}nalyse des anorganischen
{L}ösungsinhalts wässriger {P}roben mittels portabler
laserinduzierter {P}lasmaspekroskopie (p{LIBS}) :
{E}ntwicklung der {M}ethodik, {A}nwendung und {E}valuation},
school = {Rheinisch-Westfälische Technische Hochschule Aachen},
type = {Dissertation},
address = {Aachen},
publisher = {RWTH Aachen University},
reportid = {RWTH-2024-07682},
pages = {1 Online-Ressource : Illustrationen},
year = {2024},
note = {Veröffentlicht auf dem Publikationsserver der RWTH Aachen
University; Dissertation, Rheinisch-Westfälische Technische
Hochschule Aachen, 2024},
abstract = {The inorganic solution content of aqueous samples is
currently still analysed almost exclusively in the
laboratory using conventional laboratory methods such as ion
chromatography (IC) or atomic absorption spectroscopy (AAS).
These methods are costly, time-consuming and not always
practical. Many of the field methods developed to date lack
the ability to quantify a large number of elements
simultaneously in real time. The research objective of this
thesis is therefore to evaluate whether and how aqueous
solutions can be quantitatively analysed on site for
inorganic solution content using portable laser-induced
plasma spectroscopy (pLIBS). Laser-induced plasma
spectroscopy (LIBS) is an atomic spectroscopic method in
which a pulsed laser is focused on a small area of the
surface of a sample. This creates a plasma, the vaporised
sample material is atomised and ionised and the
electromagnetic radiation released is then analysed. The
first application of LIBS to aqueous solutions took place as
early as 1984, albeit with stationary laboratory equipment.
Difficulties in directly analysing the liquid surface with
LIBS subsequently led to different types of sample
preparation. Until now, the analysis of aqueous solutions
has been limited to stationary or large, transportable LIBS
devices. However, with advancing miniaturisation, analysis
is also possible with portable devices. This thesis
documents the method development, application and evaluation
of a portable method. Using the pLIBS Z-300 (SciAps),
liquid-to-solid conversion is used as sample preparation in
order to avoid the physical issues associated with analysing
liquid surfaces and to reduce the detection limits by
concentrating the sample during evaporation. Aluminium foil
is used as a substrate because it is inexpensive, readily
available and has few spectral interferences. To optimise
the distribution of the evaporation residue and prevent the
so-called coffee ring effect, a thin pencil layer is applied
to the metal surface. The calibrations are created with
dilution series from AAS standards. A 3D-printed sample
holder guarantees the focusing and analysis of the
evaporation residue and makes the method reproducible.
Consisting of a base into which the aluminium foil is
inserted and a stencil that is placed on top, the device can
be mounted during the measurement process on the one hand
and automatically focused on the other. For calibration,
dilution series with concentrations between 0.1 and 1000
mg/L are prepared from single-element AAS standard
solutions. A drop of 0.75 µL is added with a pipette
through the stencil onto the surface-enhanced Al-foil and
then evaporated on a hot plate. A square grid of 10 * 10
analysis points per vaporised drop with four individual
analyses per point guarantees the complete detection of the
evaporation residue. In the device-specific software,
several lines of the element of interest with as little
interference and as high intensity as possible are selected
and an intensity ratio is formed with the strongest Al lines
for each concentration. These can be used to create
calibration lines for the elements of interest in a
spreadsheet.When analysing the spectra, which were also used
for calibration, it is shown using the calibration curves
that the three elements Li, Na and K can be quantified in
standard solutions from 0.1 to around 100 mg/L (Li, Na) and
160 mg/L (K). At higher concentrations, the signal is no
longer directly proportional to the concentration. In
addition, the surface enhancement leads to a significantly
improved shape and distribution of the evaporation residue
and consequently to more reproducible results. At 0.006 to
0.011 mg/L, the detection limits for the three alkali metals
are well below the concentration of 0.1 mg/L of the lowest
standard solution used. When applied to mineral waters, with
further calibrations for Ca, Mg, Sr, Cl, NO3 and SO4,
similar results are obtained. In low mineralised waters up
to about 1000 µS/cm, the dissolved ions can be quantified
with the exception of NO3. In addition, self-absorption of
the emitted light occurs in the plasma, which cancels out
the proportionality of concentration and signal intensity.
The effect can be investigated in more detail using mixed
standard solutions. Divalent ions are more susceptible to
self-absorption than monovalent ions.Potentially toxic
elements such as Cr, Ni, Cu, Zn, As, Se, Cd and Pb can also
be quantified in standard solutions using the method.
Although the calculated detection limits for these elements
are below 0.03 mg/L, it is not possible to create
calibration curves below the concentration of 0.1 mg/L for
Zn and As. In addition, when comparing produced and
predicted concentrations, only Cr shows plausible results
for the concentration range below 0.1 mg/L. Only Cu can
currently be reliably quantified in the range of the limit
values for drinking water set by the WHO and the German
Drinking Water Ordinance. The results show that the method
developed cannot compete with laboratory methods such as AAS
or ICP-MS in the field of trace analysis. However, it has a
major advantage when rapid results or cost-effective
preliminary screening are required. The distribution and
shape of the evaporation residue can be optimised in the
future by further developing the application process or the
applied material. Self-absorption prevents the analysis of
higher concentrations and must be mathematically minimised,
which not only enables the analysis of higher concentrations
but also increases reproducibility. The hot plate in
combination with the sample holder can also be further
developed with a metal version to further facilitate the
methodology in the field. The calibration of further
elements opens up a broader field of application in
different sectors and thus leads to a significant market
potential.},
cin = {511110 / 510000},
ddc = {620},
cid = {$I:(DE-82)511110_20151029$ / $I:(DE-82)510000_20140620$},
typ = {PUB:(DE-HGF)11},
doi = {10.18154/RWTH-2024-07682},
url = {https://publications.rwth-aachen.de/record/991097},
}
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