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@ARTICLE{Echtermeyer:888871,
      author       = {Echtermeyer, Alexander and Marks, Caroline and Mitsos,
                      Alexander and Viell, Jörn},
      title        = {{I}nline {R}aman {S}pectroscopy and {I}ndirect {H}ard
                      {M}odeling for {C}oncentration {M}onitoring of {D}issociated
                      {A}cid {S}pecies},
      journal      = {Applied spectroscopy},
      volume       = {75},
      number       = {5},
      issn         = {1943-3530},
      address      = {London},
      publisher    = {Sage},
      reportid     = {FZJ-2020-05281},
      pages        = {506–519},
      year         = {2021},
      abstract     = {We propose an approach for monitoring the concentration of
                      dissociated carboxylic acid species in dilute aqueous
                      solution. The dissociated acid species are quantified
                      employing inline Raman spectroscopy in combination with
                      indirect hard modeling (IHM) and multivariate curve
                      resolution (MCR). We introduce two different titration-based
                      hard model (HM) calibration procedures for a single mono- or
                      polyprotic acid in water with well-known (method A) or
                      unknown (method B) acid dissociation constants pKa. In both
                      methods, spectra of only one acid species in water are
                      prepared for each acid species. These spectra are used for
                      the construction of HMs. For method A, the HMs are
                      calibrated with calculated ideal dissociation equilibria.
                      For method B, we estimate pKa values by fitting ideal acid
                      dissociation equilibria to acid peak areas that are obtained
                      from a spectral HM. The HM in turn is constructed on the
                      basis of MCR data. Thus, method B on the basis of IHM is
                      independent of a priori known pKa values, but instead
                      provides them as part of the calibration procedure. As a
                      detailed example, we analyze itaconic acid in aqueous
                      solution. For all acid species and water, we obtain low HM
                      errors of < 2.87 × 10−4mol mol−1 in the cases
                      of both methods A and B. With only four calibration samples,
                      IHM yields more accurate results than partial least squares
                      regression. Furthermore, we apply our approach to formic,
                      acetic, and citric acid in water, thereby verifying its
                      generalizability as a process analytical technology for
                      quantitative monitoring of processes containing carboxylic
                      acids.},
      cin          = {IEK-10},
      ddc          = {610},
      cid          = {I:(DE-Juel1)IEK-10-20170217},
      pnm          = {899 - ohne Topic (POF4-899)},
      pid          = {G:(DE-HGF)POF4-899},
      typ          = {PUB:(DE-HGF)16},
      pubmed       = {33107761},
      UT           = {WOS:000648987200002},
      doi          = {10.1177/0003702820973275},
      url          = {https://juser.fz-juelich.de/record/888871},
}