h1

h2

h3

h4

h5
h6
% IMPORTANT: The following is UTF-8 encoded.  This means that in the presence
% of non-ASCII characters, it will not work with BibTeX 0.99 or older.
% Instead, you should use an up-to-date BibTeX implementation like “bibtex8” or
% “biber”.

@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},
}